Tri-state single pass recording in a hamr device with dual recording layers

Abstract

This application discloses tri-state single-pass recording in a HAMR device with dual recording layers. A heat-assisted magnetic recording (HAMR) device is configured to write neutral-polarity zones on a magnetic medium during a same pass of a recording head, with other zones being written to positive and negative polarities. Various disclosed write techniques can facilitate creating "zero-state" (substantially net-zero polarity) transition areas between each pair of data bits of opposite polarity and / or can help encode three different logical states (e.g., 1, 0, and -1) on the medium.

Description

Background Technology

[0001] Conventional magnetic media encodes magnetic bits with positive and negative polarities to store data corresponding to two different binary states (1 and 0). However, other types of media, such as flash memory, can utilize multi-level cells to encode more than two logical states. For example, a two-level multi-level flash memory cell can be programmed to store four different logical states corresponding to the programmed value pairs [1,0], [0,0], [1,1], and [0,1], fundamentally increasing storage density compared to a single-level cell that only stores 1 or 0. In magnetic storage devices, theoretically, if the magnetic medium can be used to store three different logical states (e.g., -1, 1, and 0), the areal density capacity (ADC) can be increased by up to 58%.

[0002] While several methods for three-state magnetic recording have been proposed previously, existing solutions have significant drawbacks. One existing method utilizes a single-layer recording medium and encodes the zero-polarity state by performing a so-called AC erase. According to this method, 1 and -1 are encoded by magnetizing bits with positive and negative polarities, while the zero state is created by rapidly pulse-modulating the write current between the positive and negative polarities within a single bit, such that approximately half of the magnetic grains in that bit are positively magnetized and approximately half are negatively magnetized, resulting in a net bit magnetization close to zero. The current implementation of this method suffers from very high noise levels, preventing the achievement of net ADC gain.

[0003] Another existing three-state magnetic recording method utilizes dual-pass write processing to encode data on a dual-layer recording medium in a heat-assisted magnetic recording (HAMR) device. According to this method, each layer is designed to have a significantly different Curie temperature to achieve the goal of writing demagnetization in two different layers of the storage medium by varying the recording temperature during different head passes, thus writing one layer at a time. However, since the different stacked layers of the recording medium are written during different head passes, two full revolutions of the disk are required to encode a single data bit. Therefore, this method significantly increases write time and is also plagued by many other problems, such as increased noise (due to head misalignment during the second pass) and unintentional adjacent track overwriting. Summary of the Invention

[0004] According to one embodiment, the HAMR recording device is configured to perform a single-pass recording process that facilitates the recording of data bits in three logical states during a single pass of the writing element over the underlying data track. These three logical states include a "zero state," characterized by stacked layers of opposite polarities such that the number of individual dies forming the zero-state data bit is substantially zero.

[0005] According to another embodiment, the HAMR device is configured to create a neutral polarity region at the boundary between each pair of adjacent data bits having opposite polarities. The neutral polarity region is created in the same pass of the read / write head as the pass of writing data to the adjacent data bits. The neutral polarity region is created by changing the polarity of the corresponding magnetic grain in the other of the two stacked recording layers after fixing the polarity of the magnetic grain in one of the two stacked recording layers.

[0006] The present invention is provided to introduce, in a simplified form, some concepts further described below in the detailed description. The present invention is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.

[0007] This article also describes and narrates other implementation schemes. Attached Figure Description

[0008] Figure 1 A data storage device is shown that includes a read / write head assembly for writing data on a magnetic storage medium.

[0009] Figure 2 An example magnetic medium is shown that facilitates writing zero-state polarity into a localized region on a magnetic medium in a HAMR device.

[0010] Figure 3 This illustrates various aspects of an example HAMR device that writes regions of zero-state polarity by utilizing the different thermomagnetic properties of the upper and lower recording layers.

[0011] Figure 4 This shows what is suitable for implementing the above reference. Figure 3 Another example of the technology discussed is the properties of magnetic media.

[0012] Figure 5A A cross-sectional view of the dielectric layer is shown during a first example recording operation in a HAMR device for writing a neutral polarity region into a magnetic medium.

[0013] Figure 5B Shown during the second example recording operation Figure 5A A cross-sectional view of the dielectric layer.

[0014] Figure 5C This is shown during the third example recording operation. Figure 5A and Figure 5B A cross-sectional view of the dielectric layer.

[0015] Figure 5D This is shown during the fourth example recording operation. Figures 5A-5C A cross-sectional view of the dielectric layer.

[0016] Figure 6A Another example magnetic medium suitable for writing neutral polarity regions on a magnetic medium is shown.

[0017] Figure 6B The display shows information including about Figure 6A Example diagrams illustrating the thermal characteristics of a HAMR device with a magnetic medium.

[0018] Figure 6C Show Figure 6A More details about the recording medium.

[0019] Figure 7 A cross-sectional portion of another example magnetic medium suitable for implementing HAMR writing techniques to create neutral polarity regions is shown.

[0020] Figure 8 A cross-sectional portion of another example magnetic medium suitable for implementing HAMR writing technology to create neutral polarity regions is shown.

[0021] Figure 9 A cross-sectional portion of another example magnetic medium suitable for implementing HAMR writing technology to create neutral polarity regions is shown.

[0022] Figure 10 A cross-sectional portion of another example magnetic medium suitable for implementing HAMR writing technology to create neutral polarity regions is shown.

[0023] Figure 11 A cross-sectional portion of another example magnetic medium suitable for implementing HAMR writing technology to create neutral polarity regions is shown.

[0024] Figure 12 This shows another example section of a magnetic medium that has been encoded with a neutral polarity region.

[0025] Figure 13 A top view is shown of an example magnetic grain on a magnetic medium flying under the read / write head in a HAMR device, the example magnetic grain comprising some neutral polarity grains. Detailed Implementation

[0026] According to one embodiment, the techniques disclosed herein facilitate the single-pass writing of three distinct logic states to various data bits along the data tracks of a magnetic medium. The magnetic medium has two stacked magnetic recording layers with a discontinuity layer between them, exhibiting different characteristics in the various embodiments disclosed herein. Each data bit includes magnetic grains vertically stacked in a lower and upper recording layer. A first logic state (e.g., 1) is encoded by magnetizing the stacked grains in the upper and lower recording layers of the data bit to present a positive polarity. A second logic state (e.g., -1) is encoded by magnetizing the stacked grains in the upper and lower recording layers of the data bit to present a negative polarity. A third logic state, referred to herein as a “zero state,” is encoded by magnetizing the individual grains in the upper recording layer of the data bit to have a polarity opposite to that of the corresponding stacked grains in the lower recording layer of the data bit. As used herein, the terms “zero state” and “neutral polarity” are used to refer to a localized region of the magnetic grains that, when read back from the medium, is interpreted as having a net polarity of zero or substantially zero. When the readback signal from the HAMR device is within + / -10% of zero, the region can be understood as having a polarity that is “essentially zero”.

[0027] According to another embodiment, the writing technique disclosed herein is used to create neutral polarity transition regions at the boundaries between directly adjacent data bits of opposite polarities. For example, between each 1 and -1 data bit, there exists a narrow region with a magnetic grain having substantially zero polarity. Because the width of these regions is much smaller than the size of the data bit, they do not function as data bits and are referred to herein as neutral polarity transition regions rather than zero-state data bits. These regions help to provide a clear, easily distinguishable boundary between positive and negative polarity regions, thus significantly improving the signal-to-noise ratio (SNR) when included in conventional magnetic (e.g., 2-state) recording systems and the proposed 3-state recording system disclosed herein.

[0028] Figure 1 A data storage device 100 is shown, including a read / write head assembly 120 for writing data on a magnetic storage medium 108. The magnetic storage medium 108 is a magnetic storage disk on which data bits can be recorded and read using read and write elements on the read / write head assembly 120. As shown in view A, the magnetic medium 108 includes an inner diameter 104 and an outer diameter 107, between which are a plurality of concentric data tracks (e.g., data tracks 110), along which data can be written and read at corresponding bit positions as the magnetic medium 108 rotates about its axis center or disk rotation axis 112.

[0029] The read / write head assembly 120 is mounted on the actuator assembly 109 at one end distal to the actuator rotation axis 114. The read / write head assembly 120 flies over the surface of the magnetic medium 108 immediately adjacent to it during disk rotation. During seek operations, the actuator assembly 109 rotates about the actuator rotation axis 112, which positions the read / write head assembly 120 over the target data track for read and write operations.

[0030] The read / write head assembly 120 is a heat-assisted magnetic recording (HAMR) head, which includes a heat source applied to the bit positions on the magnetic medium 108 during recording. By temporarily heating the magnetic medium 108 during the recording process, the magnetic coercivity of the magnetic grains in the storage medium 108 can be selectively reduced below the applied magnetic write field in a tightly focused region of the magnetic medium 108 that substantially corresponds to an individual data bit. The heated region is then encoded using the recorded data bit, depending on the polarity of the applied magnetic write field. After cooling, the magnetic coercivity substantially returns to its preheated level, thereby stabilizing the magnetization of the data bit. After being recorded, such a data bit can be read out using a magnetoresistive read head.

[0031] Referring to view B, among other features, the read / write head assembly 120 includes a heat source 132 (e.g., a laser) coupled to a sub-substrate assembly 134. Light from the heat source 132 is directed into a waveguide 138 mounted to a slider 143. Light exiting the waveguide is focused via a near-field transducer (NFT) 144 and applied to a bit position on the magnetic medium 108, which is simultaneously affected by a magnetic field generated by the write element 130. As the air-supported surface 146 of the read / write head assembly 120 “flies” across the surface of the magnetic medium 108, the write element 130 selectively magnetizes the underlying magnetic grains of the magnetic medium 108.

[0032] Controller 106 generates control signals to control the power supply to writing element 130 and to control the polarity of the magnetic field generated by writing element 130. In one embodiment, controller 106 controls writing element 130 to encode data bits of three logic states as writing element 130 passes through a data track on the magnetic medium once. That is, writing element encodes data bits with positive magnetic polarity (1), data bits with negative magnetic polarity (-1), and data bits with approximately zero net magnetization. Referring to view C, magnetic medium 108 is shown to include at least two magnetic recording layers, an upper recording layer 150 and a lower recording layer 152, both of which contain a magnetic material, such as FePt or an alloy thereof. Interface layer 154 separates upper recording layer 150 and lower recording layer 152 and may have different properties in different embodiments, examples of which are discussed in detail here.

[0033] In one embodiment, the upper recording layer 150 and the lower recording layer 152 comprise granular magnetic material (e.g., a material having magnetic grains separated from each other by non-magnetic material). During manufacturing, individual grains in the upper recording layer 150 are grown on top of corresponding individual grains in the lower recording layer 152. In at least one embodiment, the magnetic grains in the upper layer are each aligned in a 1:1 configuration with their corresponding individual grains in the lower layer. The sizes of the magnetic grains in both layers may be substantially the same (e.g., within + / - 10% of each other), such that the boundaries between the magnetic grains in the lower recording layer 152 are substantially aligned with the boundaries between the grains in the upper recording layer 150 (e.g., the grain centers are aligned within + / - 10%).

[0034] View C illustrates four data bits that have been sequentially written during a single pass of the read / write head assembly 120 over the medium. Each data bit is represented by a pair of vertically stacked arrows, which further represent multiple magnetic grains in a tightly focused region. From left to right, View C shows the sequence of data bits in corresponding states 1, 1, 0, and -1. The '1' state data bits each have a positive polarity, meaning that substantially all grains in the upper recording layer 150 and lower recording layer 152 are fixed to have a positive polarity. The '-1' state data bits each have a negative polarity, meaning that substantially all grains in the upper recording layer 150 and lower recording layer 152 are fixed to have a negative polarity. Because each grain in the upper recording layer 150 is fixed to have a polarity opposite to that of the corresponding (stacked) magnetic grains in the lower recording layer 152, the '0' state data bits (e.g., in region 140) have a substantially zero polarity. In view C, the '0' state data bit shown has negative polarity in the upper recording layer 150 and positive polarity in the lower recording layer 152. While it is possible that all grains in the upper layer of the data bit have negative polarity and all grains in the lower layer of the data bit have positive polarity, it should be understood that this is merely one example of a magnetic grain orientation that results in a net polarity of essentially zero within region 140. Other examples are discussed herein.

[0035] The term "substantially zero polarity" is used here to refer to regions where each grain has a truly substantially zero net polarity (e.g., each grain has an upper portion whose polarity is opposite in size and sign to that of the corresponding lower portion). However, "substantially zero polarity" is also intended to include situations where the magnetic and / or physical properties of the two recording layers are tuned such that when the true net polarity of a given region is slightly greater than or less than substantially zero, the read element on the read / write head assembly 120 detects substantially zero polarity in that region. Because the upper recording layer 150 is closer to the read / write head assembly 120 than the lower recording layer 152, the lower recording layer 152 may contribute less to the readback signal than the upper recording layer 150. Therefore, real-world situations exist where the net polarity of a region can actually be zero, but the read element still detects a non-zero signal. To mitigate this effect, some embodiments of the disclosed technology may provide that the lower recording layer 152 is adjusted to have a Mrt (magnetic saturation multiplied by layer thickness) greater than that of the upper recording layer 150, ensuring that the readout element detects a net polarity that is substantially zero in the zero-state region. In these cases, the “zero-state” region on the medium may have a true polarity biased towards the polarity of the lower recording layer 152 (due to its larger Mrt), but with an effective polarity that is detected as zero or substantially zero by the readout element. This adjustment of Mrt can be performed relative to any embodiment disclosed herein.

[0036] According to the various embodiments disclosed herein, the three logic states shown in view C can all be written in their entirety during a single pass of the read / write head over the rotating magnetic medium 108. The techniques used to achieve this will be discussed with reference to the following figures.

[0037] The "zero-state" writing technique disclosed herein can also be used in conventional recording processes (e.g., recording processes that perform binary state recording) or in recording processes using the 3-state recording technique disclosed herein, to insert small regions of neutral polarity between positive and negative data bits. By inserting small regions of zero net polarity along the boundaries between data bits, the signal-to-noise ratio can be significantly improved.

[0038] Figure 2An example magnetic medium 200 is shown that facilitates the writing of zero-state polarity into a localized region of magnetic grains in a HAMR device. The magnetic medium 200 includes at least a lower recording layer 204, an upper recording layer 202, and an antiferromagnetic coupling (AFC) layer 206. In this embodiment, both the lower recording layer 204 and the upper recording layer 202 contain a recording material (e.g., FePt or an alloy thereof) and may have the same or different magnetic properties (e.g., Curie temperature Hk, same anisotropy). The AFC layer 206 is a thin metal intercalation layer that promotes weak antiferromagnetic coupling between the upper recording layer 202 and the lower recording layer 204. In the absence of an applied magnetic field, the antiferromagnetic coupling causes the magnetic grains in the upper recording layer 202 to align with opposite polarities along the interface of the AFC layer 206, as shown in region 208.

[0039] exist Figure 2 In the diagram, time steps t0, t1, and t2 indicate the states of the heat source and the write field applied by the write element, which are valid for writing the corresponding logic states 1, -1, and 0 (from left to right) on the data bits of the magnetic medium 200. At time t0, the heat source is in the "on" state, and the applied write field has a positive polarity. As the magnetic medium 200 cools in the presence of the applied positive magnetic field, the magnetization in the upper recording layer 202 and the lower recording layer 204 aligns in the same direction as the applied magnetic field upon cooling, and remains positive due to the high anisotropy of the FePt grains within each layer.

[0040] At time t1, the heat source is in the "on" state, and the applied write field is switched to negative polarity. When the magnetic medium 200 cools in the presence of the applied negative polarity magnetic field, the magnetization in the upper recording layer 202 and the lower recording layer 204 aligns with the same direction as the applied magnetic field as they cool, and remains negative polarity due to the high anisotropy of the FePt grains within each layer.

[0041] At time t2, the heat source remains "on," but the write field is off. In this case, the magnetic grains in the underlying region are heated but not subjected to a magnetic field. As the grains in this region cool, a small number of AFC configurations (e.g., grains of opposite polarity) begin to form near the interface of the AFC layer 206. As cooling continues, the opposite polarities within these grains are frozen due to the high anisotropy of the FePt grains. This effect drives the net magnetization of the individual grains within the corresponding data bits to approach zero.

[0042] In one embodiment, the AFC layer 206 is an extremely thin (subnanometer) paramagnetic layer having an upper and lower interface to facilitate grain formation within the upper recording layer 202. This provides spatial continuity with the underlying grains in the lower recording layer 204, such that the upper and lower grains are stacked at a 1:1 ratio with substantially aligned grain boundaries. Furthermore, the AFC layer 206 is heat-resistant in that it can withstand the high-temperature deposition process of the upper recording layer 202 without being susceptible to interlayer diffusion.

[0043] although Figure 2 The implementation method utilizes a weak AFC coupling field to create a net zero polarity region (e.g., region 208). Figure 3-13 Alternative implementations are shown that rely on the difference in magnetic properties between two stacked magnetic recording layers to generate a zero-state polarity region. Among other features, these implementations provide a lower Curie temperature in one of the recording layers than the other layers. In the examples disclosed herein, the upper recording layer is the layer with the lower Curie temperature. However, it will be understood that the same effect disclosed herein (e.g., magnetic grain reversal isolated to a single layer) can be achieved using a medium in which the lower layer has a lower Curie temperature. Therefore, although the terms “upper layer” and “lower layer” are used consistently herein, there are other implementations of the disclosed techniques in which the magnetic properties of the two layers are opposite.

[0044] The Curie temperatures and anisotropy of the two layers result in (1) a first higher temperature range that promotes demagnetization in both layers and (2) a second lower temperature range that promotes demagnetization in the upper recording layer but not in the lower recording layer.

[0045] In the embodiments described below, zero-state polarity is achieved by selectively utilizing the grain polarity reversal that occurs when the medium is heated by different portions of α generated by the recording head of the HAMR device. When the high-temperature region passes through the data bit, demagnetization can be achieved in both magnetic layers. However, when a subsequent lower-temperature region passes through the data bit, further demagnetization can be achieved in the upper recording layer, while the magnetic grains in the lower recording layer maintain a fixed polarity. Therefore, the grains in the upper recording layer can be magnetically aligned in the opposite direction to the corresponding grains in the lower recording layer. This effect will be discussed with reference to the following figures.

[0046] Figure 3 This illustrates various aspects of an example HAMR device 300 that selectively isolates certain demagnetizations from the upper recording layer while allowing other demagnetizations to occur simultaneously in both layers by utilizing the different thermomagnetic properties of the upper and lower recording layers, thereby writing into a zero-state polarity region. Figure 3 In this process, the lower recording layer has a higher Curie temperature than the upper recording layer (e.g., the layer closest to the write element). Therefore, the lower recording layer is referred to as the high-Tc layer 302, and the upper recording layer is referred to as the low-Tc layer 304.

[0047] As the write element 306 flies over the rotating underlying magnetic medium 308, the laser 311 heats a tightly localized underlying region of the magnetic medium 308. The laser 311 generates a heat distribution 312 that moves along the data track as data is being recorded. The heat distribution 312 varies according to a thermal gradient that has the highest temperature below the NFT 320 and decreases with distance from the NFT 320. As the heat distribution 312 moves along the plane of the magnetic medium 308, a higher temperature region 314 exists near the center of the heat distribution 312 (e.g., at least partially below the NFT 320), while a lower temperature region 316 follows the higher temperature region 314.

[0048] The magnetic medium 308 has the property that the higher temperature region 314 is within a temperature range sufficient to promote demagnetization in both the low-Tc layer 304 and the high-Tc layer 302 in the presence of an applied magnetic field. In contrast, in the presence of the applied magnetic field, the lower temperature region 316 is within a temperature range sufficient to promote demagnetization in the low-Tc layer 304 and... no Within the demagnetization temperature range of the high-Tc layer 302. For this reason, the magnetic grains in the low-Tc layer 304 can be recorded over a longer period of time (e.g., when passing under the NFT 320) compared to their corresponding (stacked) magnetic grains in the high-Tc layer 302. That is, the magnetic grains in the low-Tc layer 304 can be recorded when passing through both the higher temperature region 314 and the lower temperature region 316, while only the magnetic grains in the high-Tc layer 302 can be written when passing through the higher temperature region 314.

[0049] As an example, and not a limitation, the grains in region 324 can initially be recorded in a positive polarity state when they pass through the higher temperature region 314 (which simultaneously induces demagnetization in the underlying region 326). Once region 324 moves into the lower temperature region 316, the grains within region 324 can still be recorded without affecting the polarity of the grains in the underlying region 326. For example, if the polarity of the magnetic field is switched when region 324 moves from the higher temperature region 314 to the lower temperature region 316, then region 324 can have data bits fixed in a magnetic state opposite to the magnetic state of the underlying grains in region 326.

[0050] exist Figure 3 In this structure, the low-Tc layer 304 and the high-Tc layer 302 are separated from each other by a discontinuity layer 310. In one embodiment, the discontinuity layer 310 is a non-magnetic layer with a thickness sufficient to completely decouple the low-Tc layer 304 from the high-Tc layer 302 at room temperature. For example, the discontinuity layer 310 may comprise a dielectric material, ruthenium, pure platinum, chromium, or cobalt-chromium.

[0051] Regarding Figure 2Similar to the described AFC coupling layer, ideally, the discontinuity layer 310 is a material that provides upper and lower interface properties to promote L10-level lattice growth within the top layer (low Tc layer 304). In one embodiment, the decoupling layer is also a material that provides spatial continuity with the underlying and overlying magnetic grains, such that the upper and lower grains are stacked in a 1:1 ratio, with the grain boundaries approximately aligned. Furthermore, the discontinuity layer 310 may contain a material with high thermal stability, allowing it to withstand the high-temperature deposition process of the low Tc layer 304 without tending towards interlayer diffusion.

[0052] Figure 4 The diagram shows what is suitable for achieving the above regarding Figure 3 The discussed techniques include graphs 400 and 410 showing the characteristics of the medium in the HAMR device. The HAMR device includes components with... Figure 3 A magnetic medium (not shown) with a structure identical or similar to the one described includes a dual recording layer, wherein the lower recording layer, farther from the writing element, has a higher Curie temperature than the upper recording layer, closer to the writing element. The lower and upper recording layers are separated by a discontinuity layer, which may have the same characteristics as described above. Figure 3 The same or similar characteristics discussed.

[0053] Graph 400 illustrates example thermal properties of the dielectric layer and the recording temperatures used in HAMR devices. Here, horizontal line 420 shows the magnitude of the write field (Ha) applied as the dielectric layer undergoes changes in magnetic anisotropy and temperature. First line 422 shows trends in these properties for high-Tc layers, and second line 424 shows trends for these properties for low-Tc layers. Points labeled "Tc_high" indicate the Curie temperature of high-Tc layers (lower layers), while points labeled "Tc_low" indicate the Curie temperature of low-Tc layers (upper layers).

[0054] For each of the high-Tc layer (lower layer) and the low-Tc layer (upper layer), there exist different temperature ranges within which magnetization reversal can occur in the presence of an applied magnetic field (Ha). Between Tr_high and Tc_high, demagnetization can occur for the high-Tc layer (lower recording layer). Between Tr_low and Tc_low, demagnetization can occur for the low-Tc layer (upper recording layer).

[0055] These temperature ranges depend on the anisotropy (Hk) of the material in each layer and the Curie temperature. Generally, demagnetization of individual grains cannot occur above the Curie temperature of a layer. As the material cools below the Curie temperature, the magnetic moment of the material gradually increases, while simultaneously, the magnetic field required to reverse the direction of the magnetic moment from its current orientation increases. Therefore, if a layer is placed in a magnetic field when its temperature drops below its Curie temperature, the layer will be magnetized in the direction of the applied field, and the magnetic moment of the layer will increase as the layer cools (locked in magnetization). If the direction of the applied field is then reversed while the same layer continues to cool, the resulting magnetic moment then switches to the direction of the newly applied field, provided that the anisotropy (Hk) of the layer has not increased beyond the strength of the applied field.

[0056] If one of the given layers has been cooled sufficiently so that the Hk of that layer is greater than the field applied when the field is reversed, the magnetic moment will not be switched and the previous magnetization direction will be "frozen". However, if the temperature is still high enough that the Hk of the material is still less than the applied field, it will switch to the new applied field direction regardless of when it was formed.

[0057] It is assumed that for any magnetic material, the corresponding temperature range for possible magnetization reversal can be easily determined, and the material of the magnetic recording layer can be selected that allows these temperature ranges to “match” the temperature regions within the thermal distribution created by the recording head in the HAMR device, in order to realize the 3-state recording technology disclosed herein.

[0058] For example, the top-down thermal distribution 410 created by the HAMR write element includes a higher temperature region 412 defined by a contour line at temperature Tr_high and a lower temperature region 414 defined by a contour line at temperature Tr_low. When the magnetic grain is heated to the Tr_high temperature, demagnetization can be achieved in both the high-Tc and low-Tc layers. When the magnetic grain is heated to the Tr_low temperature, demagnetization can be achieved in the low-Tc layer but not in the high-Tc layer. Therefore, when data bits pass through thermal distribution 412, both recording layers can be written to Tr_high. However, when data bits reach Tr_low, the magnetization of the high-Tc layer is "locked in," while the magnetization of the low-Tc layer continues to change.

[0059] Figures 5A-5D Showing a diagram of a structure with information about Figure 3 and 4 The HAMR device describes the operation performed by the characteristics described. Specifically, the HAMR device includes a magnetic medium with dual recording layers, comprising a low-Tc layer 502 and a high-Tc layer 504 separated by a decoupling layer 510. The HAMR device includes a recording medium that generates a thermal distribution 512 having a relationship with... Figure 4The description describes temperature regions that are the same or similar, and which may be reversed in each of the two layers. The thermal distribution 512 includes a higher temperature region 514 and a lower temperature region 506. The outer edge of the higher temperature region 514 corresponds to a recording temperature Tr_high, while the outer edge of the higher temperature region 506 corresponds to a recording temperature Tr_low, where Tr_low and Tr_high can be... Figure 4 definition.

[0060] Figure 5A This diagram shows a cross-sectional view of the dielectric layer during a first example recording operation 500 for writing zero-state data bits in a HAMR device. Here, the first localized region "A" passes through a higher temperature region 514 of the dielectric and is cooled to temperature Tr_high when a positive polarity magnetic field is applied. Due to temperature Tr_high (e.g., as... Figure 4 As shown, this is sufficient to promote demagnetization in the low-Tc and high-Tc layers of region “A”, so that the magnetic grains are positively polarized in both layers.

[0061] Figure 5B It is a diagram. Figure 5A The second example recording operation 501 follows. Here, the medium has been slightly rotated, causing the read / write element to shift relative to the magnetic medium in the downtrack track position, and the heating element is now positioned above another localized region "B". Since the positive write field is still applied, the magnetic moments of the grains within the low-Tc and high-Tc layers of region B are again rotated to align with the positive write field. At this same time point, previously... Figure 5A The localized region "A" written by the operation shown is now located within the lower temperature region 506 of the thermal distribution 512. The temperature of region "A" cools towards temperature Tr_low, which is sufficient to promote demagnetization in the low Tc layer 502 but insufficient to promote demagnetization in the high Tc layer 504. Therefore, at Tr_low, the grains in the upper layer of region "A" have the potential to be overwritten (e.g., flipped and locked). However, since the field orientation does not actually change, the region retains its positive polarity.

[0062] Figure 5C It is a diagram. Figure 5B The third example recording operation 503 follows. Here, the medium is rotated slightly again, causing the read / write head to shift in the downward track direction of the magnetic medium, and the heating element is now positioned above another localized region "C". At this point, the direction of the applied write field is switched to negative polarity. Region C, passing through the higher temperature region 514, is magnetized (at Tr_high), causing the grains in the upper and lower layers to rotate to match the direction of the currently negatively applied write field.

[0063] At the same point in time, previously according to Figure 5BThe localized region "B" written in the illustrated operation now passes through the lower temperature region 506 of the thermal distribution 512. The temperature of region "B" is close to Tr_low, which is sufficient to promote demagnetization in the low Tc layer 502, but insufficient to promote demagnetization in the high Tc layer 504. Therefore, at Tr_low, the grains in the upper layer of region "B" have the potential to be overwritten. Since the direction of the applied field has changed, the grains in the upper layer of region B are flipped from the positive direction to the negative direction (as shown) without affecting the polarity of the grains in the high Tc layer 504. At this point in time, region A has a positive polarity (e.g., a 1-bit value), region B has a net zero polarity (e.g., a 0-bit value), and region C has a negative polarity (e.g., a -1-bit value).

[0064] Figure 5D Explanation Figure 5C The fourth example recording operation 505 follows. Here, the medium is rotated slightly again, causing the read / write head to shift in the downward track direction of the magnetic medium, and the heating element is now positioned above another localization region "D". At this point, the direction of the applied write field switches from negative to positive. Region D has just passed through the higher temperature region 514 and is approaching temperature Tr_high. Here, the grains in both the upper and lower layers rotate to match the direction of the magnetic field now being applied.

[0065] At the same time point, previously passed Figure 5C The localized region "C" written in the operation shown has passed through the lower temperature region 506 and is approaching temperature Tr_low, which is sufficient to promote demagnetization in the low Tc layer 502 rather than the high Tc layer 504. Therefore, at this point in time, the grains in the layer above region "C" have the potential to be masked. This is because the direction of the applied field is relative to... Figure 5C The applied field is changed again, so the grains in the upper layer of region C flip from the negative direction to the positive direction (as shown in the figure) without affecting the polarity of the underlying grains in the high-Tc layer 504. At this point in time, region A has position polarity (e.g., 1 position value), regions B and C have zero polarity (e.g., 0 position value), and region D has positive polarity.

[0066] Figure 6A Showing what is suitable for achieving regarding Figure 4 and Figures 5A-5D Another example of the HAMR writing technology discussed is a magnetic medium 600. Magnetic medium 600 includes an upper recording layer 602 and a lower recording layer 604, each containing a soft magnetic material, such as FePt or an alloy thereof. The upper recording layer 602 has a lower Curie temperature than the lower recording layer 604. The upper recording layer 602 is separated from the lower recording layer 604 by a recording temperature discontinuity 606. During magnetic recording, the recording temperature discontinuity 606 functions similarly to... Figure 3The discontinuity layer 310 described herein is used to decouple the upper recording layer 602 from the lower recording layer 604 during the recording process.

[0067] However, Figure 3 Fault 310 and Figure 6A The recorded temperature discontinuity 606 differs in composition and magnetic properties. Although Figure 3 The interruption layer 310 provides a decoupled non-magnetic layer at room temperature and recording temperature of the HAMR device, but the recording temperature interruption layer 606 is a magnetic layer, wherein when heated to a high temperature during recording, the upper recording layer 602 is decoupled from the lower recording layer 604.

[0068] In one embodiment, the recording temperature interruption layer 606 has a Curie temperature lower than either the upper recording layer 602 or the lower recording layer 604. Because the high-temperature HAMR recording process heats the magnetic medium 600 to a temperature higher than the Curie temperature of the recording temperature interruption layer 606, this layer has no magnetic moment during magnetic recording. Therefore, no demagnetization occurs within the recording temperature interruption layer 606 during recording, and the recording temperature interruption layer 606 serves to completely decouple the upper recording layer 602 from the lower recording layer 604 when data is written to the magnetic medium.

[0069] However, with Figure 3 Unlike the interruption layer 310, the recording temperature interruption layer 606 provides some degree of coupling between adjacent recording layers when the medium cools to room temperature. As cooling occurs, the anisotropy within the recording temperature interruption layer 606 increases, causing it to couple to one of the adjacent recording layers. Therefore, the recording temperature interruption layer 606 has a magnetic moment aligned with one of the adjacent layers at room temperature.

[0070] In some embodiments, the upper recording layer 602 and the lower recording layer 604 have the same Mrt (magnetic saturation multiplied by layer thickness). In other embodiments, the lower recording layer 604 is adjusted to have a slightly higher Mrt than the upper layer to offset the reduction in readback signal contribution from that layer due to its larger spacing from the readout element. Each of the upper recording layer 602 and the lower recording layer 604 comprises a hard magnetic material (e.g., FePt) and may also include a certain amount of non-magnetic metal to selectively adjust the Curie temperature of the layer to a selected range. Notably, the addition of non-magnetic metal (e.g., copper, nickel) is used to lower the Curie temperature of the layer. In this embodiment, the recording temperature interruption layer 606 also comprises a soft magnetic material (e.g., FePt), but has a larger amount of non-magnetic metal than the two recording layers, such that the recording temperature interruption layer 606 has the lowest Curie temperature of the three layers.

[0071] Figure 6A The implementation provides superior performance. Figure 3Several advantages of this implementation are apparent. Since the recording temperature discontinuity layer 606 can comprise the same underlying magnetic material as both recording layers, it serves as a good template (e.g., FePt) for the growth of the upper recording layer grains and can be granular like the upper and lower recording layers, so that it grows on the magnetic grains of the lower layer in a 1:1 ratio, thereby aligning the boundaries between them substantially with the boundaries between the grains in the lower recording layer 604. Therefore, the upper recording layer can then be grown such that its magnetic grain boundaries are aligned between the upper and lower layers (e.g., because the magnetic grains naturally align with the underlying magnetic grains, and because of the similarity in material composition, the grains can have the same size). These desirable properties are easier to satisfy than with non-magnetic materials when considering magnetic materials (FePt). For this purpose, Figure 6A The implementation method (with the magnetic layer between the recording layers) is better than Figure 3 The implementation method (with non-magnetic layers between recording layers) has significant manufacturing advantages.

[0072] Figure 6B Example graph 601 and heat distribution 636 are shown, illustrating the presence of heat distribution with respect to... Figure 6A The thermal characteristics of the magnetic medium in the HAMR device are described.

[0073] Referring first to graph 601, horizontal line 620 shows the magnitude of the write field (Ha) applied by the HAMR write element as the dielectric layer undergoes changes in magnetic anisotropy and temperature. First line 622 shows the trend of anisotropy (Hk) versus temperature for the lower recording layer 604, which has the highest Curie temperature. This layer has a Curie temperature labeled "Tc_high". Second line 624 shows the trend of Hk versus temperature for the upper recording layer 602. This layer has a Curie temperature labeled "Tc_low", which is lower than the Curie temperature of the lower recording layer 604. Another line 626 shows the trend of Hk versus temperature for the recording temperature discontinuity layer 606. This layer has a Curie temperature labeled "RTBL_Tc", which is lower than the Curie temperature of any adjacent recording layer.

[0074] For each of the upper recording layer (line 622) and the lower recording layer (line 624), there exists a narrow temperature range within which demagnetization can occur in the presence of an applied magnetic field (Ha). In the example shown, demagnetization can occur between Tc_high and Tr_high for the lower recording layer (high Tc layer), and between Tr_low and Tc_low for the upper recording layer (lower Tc layer). The Curie temperature (Tc_RTBL) of the recording temperature discontinuity layer 606 is lower than Tr_low, and therefore falls outside the temperature range where demagnetization can occur in either recording layer. Therefore, demagnetization does not occur in the recording temperature discontinuity layer 606 during recording.

[0075] Figure 6C Show Figure 6A The recording medium 600 also includes an enlarged view (View B) showing a 1:1:1 grain arrangement within three different magnetic layers. The lower recording layer 604 includes individual magnetic grains (e.g., grain 634) aligned with grains in the recording temperature discontinuity layer 606, which are further aligned with grains in the upper recording layer 602. Non-magnetic separators 630 separate each pair of adjacent magnetic grains from each other in the downward and cross-track directions of the magnetic medium. Notably, the grains in the recording temperature discontinuity layer 606 are not as tall as those in the two adjacent layers because this layer is thinner. In one embodiment, the thickness of the recording temperature discontinuity layer 606 is approximately 25% or less of the thickness of the upper recording layer 602 and the lower recording layer 604. According to one embodiment, the upper recording layer 602, the lower recording layer 604, and the recording temperature discontinuity layer 606 have Mrt values ​​(magnetic saturation multiplied by layer thickness), which, when combined, are detected by the readout element as an amplitude substantially zero.

[0076] Figure 7 A cross-sectional portion of another example magnetic medium 700 suitable for implementing HAMR writing technology to create a zero-state polarity region is shown. Medium 700 includes a lower recording layer 704, an upper recording layer 702, and a recording temperature discontinuity layer (RTBL) 706 between the two layers.

[0077] Figure 710 shows the magnetic anisotropy (Hk) and temperature trends of each layer of the magnetic medium 700. The Curie temperature (Tc_high) of the lower recording layer is higher than the Curie temperature (Tc_low) of the upper recording layer 702. The Curie temperature (RTBL_Tc) of the recording temperature discontinuity layer 706 is lower than the Curie temperature of either recording layer 702 or 704, and lower than the recording temperature Tr_low of the low Tc layer. Other characteristics of the upper recording layer 702, the lower recording layer 704, or the recording temperature discontinuity layer 706 can be found in the above reference. Figures 6A-6C The corresponding layers described are the same or similar. Figure 7 The implementation and Figures 6A-6C The difference in implementation is that the magnetic medium 700 also includes a CGC overlay layer 714 on top of the upper recording layer 702.

[0078] The temperature response of the upper layer Hk shown in 710 is a combined response of layers 702 and 714. Typically, the role of the CGC overlay layer 714 is to reduce the coercivity of the upper recording layer complex. One result of this reduced coercivity is that the difference in Curie temperatures between recording layers 702 and 704 can be reduced, while maintaining relative to... Figures 6A-6C The HAMR system described uses the recording temperature for writing to two recording layers. Figure 6BThe same difference exists between Tr_low and Tr_high in the Curie temperature range. From a processing point of view, this is advantageous because a smaller change in Curie temperature leads to better FePt alloy growth.

[0079] Figure 8 A cross-sectional portion of another example magnetic medium 800 suitable for implementing HAMR writing technology to create zero-state polarity regions is shown. Medium 800 includes... Figure 6A The upper recording layer 802 shares some characteristics with the magnetic medium 600, including having a lower Curie temperature than the lower recording layer 804. The upper recording layer 802 is separated from the lower recording layer 804 by a recording temperature discontinuity 806, which can be understood as having a Curie temperature lower than the reference layer 804. Figures 6A-6C The recorded temperature discontinuity layers described have the same or substantially the same properties. Depending on the thermal properties of the selected materials included in the recorded temperature discontinuity layer 806, this layer may readily mix with the magnetic material (FePt) in the adjacent recording during the high-temperature deposition step of the media forming process. This "mixing" of materials in adjacent layers is called interlayer diffusion. Depending on the severity of this effect, the recorded temperature discontinuity layer 806 may lose some of its magnetic properties, primarily its ability to completely decouple the upper recording layer 802 from the lower recording layer 804 during the high-temperature recording process. Furthermore, if the RTBL thickness widens due to interlayer diffusion, the magnetization break location cannot be well defined. To help mitigate interlayer diffusion, the magnetic medium 800 includes a diffusion barrier layer 808 between the recorded temperature discontinuity layer 806 and the lower recording layer 804.

[0080] In one embodiment, the diffusion barrier layer 808 has a base material with low solubility in the FePT and / or L10 lattice constant to promote L10 grain growth in subsequent layers. For example, the diffusion barrier layer 808 may be a metallic grain material comprising a metallic alloy (e.g., Ru or other metallic alloys, such as RuPt, or metallic alloys with segregating materials, such as any combination or mixture of oxides, nitrides, carbon, or silicon).

[0081] Figure 9 Another example magnetic medium 900 suitable for implementing HAMR writing techniques for creating zero-state polarity regions is shown. Figure 8 Similarly, the magnetic medium 900 includes an upper recording layer 902 separated from the lower recording layer 904 by a recording temperature discontinuity layer 906. In this embodiment, two diffusion barrier layers 908 and 910 are present on opposite sides of the recording temperature discontinuity layer 906. The diffusion discontinuity layers 908 and 910 may have the same characteristics as described above. Figure 8The same or similar properties are described. The use of dual-diffusion discontinuity layers 908, 910 to further ensure complete decoupling of the recording temperature discontinuity layer 906 provides consistent decoupling between the upper recording layer 902 and the lower recording layer 904, and ensures that the discontinuity position is precisely within the limits of the RTBL thickness 906.

[0082] Figure 10 A cross-sectional portion of another example magnetic medium 1000 suitable for implementing HAMR writing technology for creating a zero-state polarity region is shown. The temperature characteristics of the magnetic medium 1000 are shown in graph 1010. The medium 1000 includes a lower recording layer 1004 having a first Curie temperature Tc_high, which is higher than the Curie temperature Tc_low of the upper recording layer 1002. The upper recording layer 1002 is separated from the lower recording layer 1004 by a recording temperature discontinuity layer 1006 having a Curie temperature RTBL_Tc lower than that of either the upper recording layer 1002 or the lower recording layer 1004.

[0083] exist Figure 10 In this process, the recording temperature discontinuity 1006 is, for example, a metal (e.g., Cu, Ni, Ru) or a metal burr with segregation, which diffuses into the upper recording layer 1002 and the lower recording layer 1004 during the high-temperature deposition of the upper recording layer 1002. Due to this diffusion, as shown in graph 1010, the Tc values ​​of the upper recording layer 1002 and the lower recording layer 1004 decrease near the interface with the recording temperature discontinuity 1006.

[0084] As long as at least a portion of the recording temperature discontinuity layer 1006 remains below the Curie temperature RTBL_Tc of the recording temperature Tr_low, 1006 is still used to decouple the upper recording layer 1002 from the lower recording layer 1004 during the recording process.

[0085] This implementation leverages diffusion rather than attempting to prevent it (e.g.) Figure 7-8 (as shown), therefore, a diffusion barrier layer that would hinder the growth of the upper recording layer in some cases is not required.

[0086] According to one embodiment, the recording temperature discontinuity layer 1006 is a very thin flash metal layer (e.g., less than 1 nm), thin enough to diffuse into the upper and lower layers and not hinder L10 growth and consistent grain orientation in the upper recording layer.

[0087] Figure 11A cross-sectional portion of another example magnetic medium 1100 suitable for implementing HAMR writing technology for creating a zero-state polarity region is shown. The temperature characteristics of the magnetic medium 1100 are shown in graph 1110. The medium 1100 includes a lower recording layer 1104 having a first Curie temperature Tc_high, which is higher than a second Curie temperature Tc_low of an upper recording layer 1102. In this embodiment, the interface region 1106 between the lower recording layer 1104 and the upper recording layer 1102 has the same substrate material as the recording layers (e.g., FePt), but with an increased amount of nonmagnetic segregates.

[0088] As shown in graph 1112, the segregation added to the interface region 1106 weakens the exchange coupling between recording layers 1102 and 1104, allowing the upper recording layer 1102 to undergo magnetic transitions independently of the lower recording layer 1104, as described elsewhere in this document, for example, referring to... Figures 6A-6C The advantage of this implementation is that the interface region 1106 is easy to implement and does not require modification of the material of the interface region 1106 to provide a significant change in its Curie temperature relative to the Curie temperatures of the recording layers 1102 and 1104.

[0089] Figure 12 It has been shown that the above has been followed. Figure 3-11 Another example of a magnetic medium encoded with a neutral polarity region, from any of the techniques discussed herein. Figure 12 In this medium, the zones labeled A, B, C, D, E, F, and G are each of approximately similar size and correspond to individual data bits. Zones A, C, and F have positive polarity and correspond to logic bits in the '1' state; zones B, C, and E have negative polarity and correspond to logic bits in the '-1' state; and zone D has zero-state (neutral) polarity and corresponds to logic bits in the '0' state.

[0090] It is worth noting that the zero state shown in zone D is achieved by switching the polarity of the write field between positive and negative when the heating element is turned on (a technique called AC erase), and the upper and lower layers switch in response to the changing field, as shown in the reference. Figures 5A-5D General description.

[0091] An interesting effect of the dual-magnetic-layer single-pass write in the three logic states described above is that this technique creates neutral polarity boundary regions (e.g., neutral polarity switching regions 1202) between each pair of data bits with different polarities. This is because each change in the magnetic orientation of the write field causes the most recently recorded region in the upper layer to be overwritten to match the new orientation of the write field. This effect occurs even when no zero-state data bits are written. For example, when writing data bit A, the write field is in the positive direction until time t1, when the write element is about to start writing data bit B. At t1, the write field switches from positive to negative, so the previously written magnetic region 1210 is overwritten and switches from the previously written positive state to match the now negative write field. A similar effect occurs when the write element switches the write field polarity between writing negative polarity data bit B and positive polarity data bit C.

[0092] It is worth noting that each neutral polarity switching region has a substantially identical size, smaller in width than the width of each data bit. The size of the neutral polarity switching region depends on the characteristics of the heat distribution created by the heating elements of the recording head. For example, the width of each neutral polarity switching region may depend on the characteristics of the NFT written to the head, the thermal gradient at the switching region, and the recording temperature difference between the two recording layers. In one embodiment, the neutral polarity switching region has a cross-section in the downtrack direction, which is approximately half the average grain size, or between approximately half the average grain size and the entire grain size.

[0093] It is worth noting that the neutral polarity transition region can be formed between the +1 and -1 data bit boundaries, regardless of whether the HAMR device actually writes any data bits (e.g., such as data bit D) in a zero state. Therefore, in some implementations, the above is relative to... Figures 5A-5D The media and HAMR equipment discussed, along with their corresponding characteristics, can be used to facilitate standard (e.g., 2-state) routine recording with a neutral polarity switching region. It has been shown that including a neutral polarity switching region in HAMR equipment significantly improves the signal-to-noise ratio, for example, by up to 3 dB in media SNR.

[0094] To further illustrate the structural details of the neutral polarity conversion region 1202, Figure 13 For example, it can correspond to Figure 12 A top view of a portion of the medium in zone 1220.

[0095] Specifically, Figure 13 This is a top view showing an example magnetic grain forming the magnetic medium 1300. The magnetic medium 1300 is a bilayer recording material with different Curie temperatures and magnetic properties, which facilitates some demagnetization in both recording layers simultaneously, while isolating other demagnetizations to a single layer within the recording layer, for example, as per [reference to...]. Figures 3 to 12 The discussion is conducted on any of the options.

[0096] For each magnetic grain, the shading indicates the net polarity of the upper and lower grains. White represents a net -1 polarity grain, and dark gray represents a net +1 polarity grain. Medium gray represents a net zero polarity grain.

[0097] The dashed line 1304 corresponds to the ideal transition position between the negative 1 bit and the positive +1 bit. In an ideal (noise-free) recording device using conventional HAMR technology, the transition center 1310 would provide a clear boundary between the positive and negative grain positions. However, due to the grain properties and random positions of the grains forming the recording medium, the transition center 1310 is not a clear division, but rather forms a transition between discrete grain boundaries. Some positively polarized grains "bleed" through the transition center 1310 to the positive polarity side, and some negatively polarized grains bleed through the transition center 1310 to the negative polarity side. This bleeding effect causes a deviation from the ideal transition, known as "transition jitter." The effect of transition jitter is significantly reduced in the case shown where some grains have already been shifted to the neutral polarity in the transition region 1304. It is worth noting that the grains shifted to the neutral polarity (e.g., 1312, 1314) are grains whose centroid positions are close to the transition. Since grain edges contribute to the transformation position, they contribute the most to the jitter if these centers are close to neutral grains in the transformation and their polarity is not neutral.

[0098] Any grain whose centroid is located within the width of the transition region 1304 will result in neutral polarity. This region is referred to herein as the "zero-state insertion width". This zero-state insertion width depends on the difference in recording temperatures between the two layers (e.g., as shown in the figure). Figure 6B The curves show the difference between Tr_high and Tr_low, and the thermal gradient in the transition region. Mathematically, the zero-state insertion width is given by dividing the temperature difference between Tr_high and Tr_low by the thermal gradient in the transition region. According to one implementation that provides excellent dithering reduction performance (maximizing SNR in the transition region), the zero-state transition width is between approximately 0.5 and 1 times the average grain size or the center-to-center spacing of adjacent grains.

[0099] The embodiments described herein are implemented as logical steps in one or more computer systems. Logical operations can be implemented as (1) a series of processor-implemented steps executed in one or more computer systems, and as (2) interconnected machines or circuit modules within one or more computer systems. The implementation is a matter of choice, depending on the performance requirements of the computer system utilized. Therefore, the logical operations constituting the embodiments described herein are referred to differently as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations can be performed in any order unless otherwise expressly claimed or the language of the claims inherently requires a specific order.

[0100] While the invention has been shown and described in detail in the accompanying drawings and the foregoing description, such descriptions should be considered exemplary rather than limiting. For example, some embodiments described above may be combined with other described embodiments and / or arranged in other ways (e.g., process elements may be performed in other sequences). Therefore, it should be understood that only preferred embodiments and variations thereof have been shown and described, and protection is intended for all changes and modifications within the spirit and scope of the invention.

[0101] Further examples:

[0102] Example 1. A method for encoding three different logic states in a magnetic storage medium having a dual recording layer including an upper recording layer and a lower recording layer, the method comprising: encoding a first logic state on the magnetic storage medium by fixing a first localization region of the upper recording layer and magnetic grains in the lower recording layer to present a first polarity; encoding a second logic state on the magnetic storage medium by fixing a second localization region of the upper recording layer and magnetic grains in the lower recording layer to present a second polarity opposite to the first polarity; and encoding a third logic state by fixing each of a plurality of magnetic grains in the upper recording layer of a third localization region to have a polarity opposite to that of a corresponding underlying grain in the lower recording layer of the third localization region.

[0103] Example 2. According to the method of Example 1, wherein the upper recording layer and the lower recording layer are separated by a weak antiferromagnetic coupling layer, and wherein encoding the third logic state further includes: turning off the write field and heating the third localization region when the laser is turned on.

[0104] Example 3. The method according to Example 1, wherein the upper recording layer has a lower Curie temperature than the lower recording layer.

[0105] Example 4. The method according to Example 3, wherein the heat generated by the NFT on the recording head is characterized by a heat distribution moving relative to the magnetic medium in the downtrack direction as data is being written, the heat distribution having: a higher temperature region located at least partially below the NFT, the higher temperature region heating the magnetic medium to a temperature that promotes demagnetization in both the upper and lower recording layers; and a lower temperature region offset from the higher temperature region in the downtrack direction, the lower temperature region of the heat distribution heating the medium to a temperature too low to promote demagnetization in the lower recording layer but within a range sufficient to promote demagnetization in the upper recording layer.

[0106] Example 5. The method according to Example 4, wherein encoding the third logic state in the third localization region further comprises at least: applying a magnetic field of a first polarity when a portion of the third localization region is in the higher temperature region; and subsequently applying a magnetic field of a second opposite polarity when the NFT has moved along the downlink track of the third localization region and when a portion of the third localization region is in the lower temperature region of the thermal distribution.

[0107] Example 6. The method according to Example 5, wherein applying the magnetic field of the first polarity and the magnetic field of the second opposite polarity further includes: rapidly changing the polarity of the magnetic field multiple times as the heat distribution moves over the third localization region.

[0108] Example 7. The method according to Example 3, wherein the first recording layer and the second recording layer are separated by a non-magnetic discontinuity layer.

[0109] Example 8. According to the method of Example 4, wherein the first recording layer and the second recording layer are separated by a discontinuity layer, the discontinuity layer being weakly ferromagnetic and having a Curie temperature layer with a temperature range lower than both the higher and lower temperature regions, such that the thermal distribution of the NFT does not promote demagnetization in the discontinuity layer.

[0110] Example 9. The method according to Example 8, wherein the discontinuity layer, when heated during writing to the magnetic medium, completely decouples the first recording layer from the second recording layer.

[0111] Example 10. A storage device comprising: a magnetic storage medium including an upper recording layer and a lower recording layer, the storage medium encoding a plurality of data bits, each data bit including a magnetic grain stacked in the lower recording layer and the upper recording layer; a controller configured to control a read / write head and a heating element to encode three distinct logic states on the magnetic medium during a single pass of the read / write head, the controller being configured to: encode a first logic state in a first localized bit by fixing the magnetic grains in the upper and lower recording layers of a first localized region to present a first polarity; encode a second logic state in a second localized region by fixing the magnetic grains in the upper and lower recording layers of a second localized region to present a second polarity opposite to the first polarity; and encode a third logic state in a third localized region by fixing each of the plurality of magnetic grains in the upper layer of the data bits to have a polarity opposite to that of a corresponding underlying grain in the lower recording layer of the third localized region.

[0112] Example 11. The storage device according to Example 10, wherein the upper recording layer and the lower recording layer are separated by a weakly AFC coupling layer, and wherein the controller encodes the third logic state by turning off the write field and heating the third data bit when the laser is turned on.

[0113] Example 12. The storage device according to Example 10, wherein the upper recording layer has a lower Curie temperature than the lower recording layer, and wherein the upper recording layer and the lower recording layer are separated by a discontinuity layer that magnetically decouples the upper recording layer from the lower recording layer during data being written to the magnetic storage medium.

[0114] Example 13. A storage device according to Example 10, wherein the read / write head includes an NFT that generates a thermal distribution that moves along a data track as data is being written, the thermal distribution having: a higher temperature region located at least partially below the NFT, the higher temperature region heating the magnetic storage medium to a temperature that promotes demagnetization in both the upper and lower recording layers; and a lower temperature region offset from the higher temperature region in the downward track direction, the lower temperature region of the thermal distribution heating the medium to a temperature too low to promote demagnetization in the lower recording layer but within a range sufficient to promote demagnetization in the upper recording layer.

[0115] Example 14. The storage device according to Example 13, wherein the controller is configured to encode the third logical state in the third localization region through a series of operations, the series of operations including: applying a magnetic field of the first polarity when a portion of the third localization region is in the higher temperature region; and subsequently applying a magnetic field of the second opposite polarity when the NFT has moved along a downlink track of the third localization region and when a portion of the third localization region is in the lower temperature region of the thermal distribution.

[0116] Example 15. The storage device according to Example 14, wherein applying the magnetic field of the first polarity and the magnetic field of the second opposite polarity further includes: rapidly changing the polarity of the magnetic field multiple times as the heat distribution moves over the third localization region.

[0117] Example 16. The storage device according to Example 13, wherein the first recording layer and the second recording layer are separated by a non-magnetic discontinuity layer.

[0118] Example 17. The storage device according to Example 13, wherein the recording layer and the second recording layer are separated by a discontinuity layer, the discontinuity layer being weakly ferromagnetic and having a Curie temperature layer with a temperature range lower than both the higher and lower temperature regions, such that the thermal distribution of the NFT does not promote demagnetization in the discontinuity layer.

[0119] Example 18. One or more non-transitory computer-readable storage media having processor-executable instructions for encoding three distinct logic states in the magnetic storage medium during a single pass of a read / write head, the processor-executable instructions being capable of: encoding a first logic state on the magnetic storage medium by fixing a first localization region of the upper recording layer and magnetic grains in the lower recording layer to present a first polarity; encoding a second logic state on the magnetic storage medium by fixing a second localization region of the upper recording layer and magnetic grains in the lower recording layer to present a second polarity opposite to the first polarity; and encoding a third logic state by fixing each of a plurality of magnetic grains in the upper recording layer of the third localization region to have a polarity opposite to that of the corresponding underlying grain in the lower recording layer of the third localization region.

[0120] Example 19. One or more non-transitory computer-readable storage media according to Example 18, wherein the upper recording layer and the lower recording layer are separated by a weakly AFC coupling layer, and wherein the controller encodes the third logic state by turning off the write field and heating the third localization region when the laser is turned on.

[0121] Example 20. One or more non-transitory computer-readable storage media according to Example 18, wherein the heat generated by the NFT on the read / write head is characterized by a heat distribution moving along the data track of the magnetic storage medium as data is being written, the heat distribution having: a higher temperature region located at least partially below the NFT, the higher temperature region heating the magnetic storage medium to a temperature that promotes demagnetization in both the upper and lower recording layers, the upper recording layer having a lower Curie temperature than the lower recording layer; and a lower temperature region offset from the higher temperature region in the downward track direction, the lower temperature region of the heat distribution heating the medium to a temperature too low to promote demagnetization in the lower recording layer but within a range sufficient to promote demagnetization in the upper recording layer.

Claims

1. A method for encoding three different logic states in a magnetic storage medium having two recording layers, including an upper recording layer and a lower recording layer, during a single pass of a recording head, the method comprising: A first logic state is encoded on the magnetic storage medium by fixing a first localized region in the upper recording layer and magnetic grains in the lower recording layer to present a first polarity; A second logic state is encoded on the magnetic storage medium by fixing the second localization region of the upper recording layer and the magnetic grains in the lower recording layer to present a second polarity opposite to the first polarity; The third logic state is encoded by fixing each of the plurality of magnetic grains in the upper recording layer of the third localization region to have a polarity opposite to that of the corresponding lower grain in the lower recording layer of the third localization region. The upper recording layer has a lower Curie temperature than the lower recording layer; and the heat generated by the NFT on the recording head is characterized by the heat distribution that moves relative to the magnetic storage medium in the downward track direction as data is being written.

2. The method of claim 1, wherein the upper recording layer and the lower recording layer are separated by a weak antiferromagnetic coupling layer, and wherein encoding the third logic state further comprises: When the laser is turned on, the write field is turned off and the third localization region is heated.

3. The method according to claim 1, wherein the heat distribution has: A higher temperature region, at least partially located below the NFT, heats the magnetic storage medium to a temperature that promotes demagnetization in both the upper and lower recording layers; In the lower temperature region that deviates from the higher temperature region in the downward magnetic track direction, the lower temperature region of the thermal distribution heats the magnetic storage medium to a temperature that is too low to promote demagnetization in the lower recording layer but is within a range sufficient to promote demagnetization in the upper recording layer.

4. The method according to claim 3, wherein encoding the third logical state in the third localization region further comprises at least: A magnetic field of the first polarity is applied when a portion of the third localization region is within the higher temperature region; as well as Subsequently, when the NFT has moved along the descending magnetic track of the third localization region and when a portion of the third localization region is in the lower temperature region of the thermal distribution, a second magnetic field of opposite polarity is applied.

5. The method of claim 4, wherein applying the magnetic field of the first polarity and the magnetic field of the second opposite polarity further comprises: As the heat distribution moves across the third localized region, the polarity of the magnetic field changes rapidly multiple times.

6. The method of claim 1, wherein the upper recording layer and the lower recording layer are separated by a non-magnetic discontinuity layer.

7. The method of claim 3, wherein the upper recording layer and the lower recording layer are separated by a discontinuity layer, the discontinuity layer being weakly ferromagnetic and having a Curie temperature range lower than both the higher and lower temperature regions, such that the thermal distribution of the NFT does not promote demagnetization in the discontinuity layer.

8. The method of claim 7, wherein the discontinuity layer completely decouples the upper recording layer from the lower recording layer when heated during writing to the magnetic storage medium.

9. A storage device comprising: A magnetic storage medium including an upper recording layer and a lower recording layer, the magnetic storage medium encoding a plurality of data bits, each data bit including a magnetic grain stacked in the lower recording layer and the upper recording layer; A controller configured to control a read / write head and a heating element to encode three distinct logic states on the magnetic storage medium during a single pass of the read / write head, the controller being configured to: A first logic state is encoded in the first localization region by fixing the magnetic grains in the upper and lower recording layers of the first localization region to present a first polarity; By fixing the magnetic grains in the upper and lower recording layers of the second localization region to present a second polarity opposite to the first polarity, a second logic state is encoded in the second localization region; as well as A third logic state is encoded in the third localization region by fixing each of the plurality of magnetic grains in the upper layer of the data bits to have a polarity opposite to that of the corresponding lower record grain in the lower recording layer of the third localization region. The upper recording layer has a lower Curie temperature than the lower recording layer, and the read / write head includes an NFT that generates a heat distribution that moves along the data track as data is being written.

10. The storage device of claim 9, wherein the upper recording layer and the lower recording layer are separated by a weakly AFC coupling layer, and wherein the controller encodes the third logic state by turning off the write field and heating the third data bit when the laser is turned on.

11. The storage device of claim 9, wherein the upper recording layer and the lower recording layer are separated by a discontinuity layer that magnetically decouples the upper recording layer from the lower recording layer while data is being written to the magnetic storage medium.

12. The storage device of claim 9, wherein the heat distribution has: A higher temperature region, at least partially located below the NFT, heats the magnetic storage medium to a temperature that promotes demagnetization in both the upper and lower recording layers; In the lower temperature region that deviates from the higher temperature region in the downward magnetic track direction, the lower temperature region of the thermal distribution heats the magnetic storage medium to a temperature that is too low to promote demagnetization in the lower recording layer but is within a range sufficient to promote demagnetization in the upper recording layer.

13. The storage device of claim 12, wherein the controller is configured to encode the third logical state in the third localization region through a series of operations, the series of operations including: When a portion of the third localization region is within the higher temperature region, a magnetic field of the first polarity is applied. as well as Subsequently, when the NFT has moved along the descending magnetic track of the third localization region and when a portion of the third localization region is in the lower temperature region of the thermal distribution, a second magnetic field of opposite polarity is applied.

14. The storage device of claim 13, wherein applying the magnetic field of the first polarity and the magnetic field of the second opposite polarity further comprises: As the heat distribution moves across the third localized region, the polarity of the magnetic field changes rapidly multiple times.

15. The storage device of claim 12, wherein the upper recording layer and the lower recording layer are separated by a non-magnetic discontinuity layer.

16. The storage device of claim 12, wherein the upper recording layer and the lower recording layer are separated by a discontinuity layer, the discontinuity layer being weakly ferromagnetic and having a Curie temperature range lower than both the higher and lower temperature regions, such that the thermal distribution of the NFT does not promote demagnetization in the discontinuity layer.

17. One or more non-transitory computer-readable storage media, wherein processor-executable instructions are encoded to encode three distinct logical states in the magnetic storage medium during a single pass of a read / write head, the processor-executable instructions being capable of: A first logic state is encoded on the magnetic storage medium by fixing a first localized region in the upper recording layer and magnetic grains in the lower recording layer to present a first polarity; A second logic state is encoded on the magnetic storage medium by fixing the second localization region of the upper recording layer and the magnetic grains in the lower recording layer to present a second polarity opposite to the first polarity; The third logic state is encoded by fixing each of the plurality of magnetic grains in the upper recording layer of the third localization region to have a polarity opposite to that of the corresponding lower grain in the lower recording layer of the third localization region. The upper recording layer has a lower Curie temperature than the lower recording layer, and the heat generated by the NFT on the read / write head is characterized by the heat distribution as data moves along the data track of the magnetic storage medium while data is being written.

18. One or more non-transitory computer-readable storage media according to claim 17, wherein the upper recording layer and the lower recording layer are separated by a weakly AFC coupling layer, and wherein the controller encodes the third logic state by turning off the write field and heating the third localization region when the laser is turned on.

19. One or more non-transitory computer-readable storage media according to claim 17, wherein the thermal distribution has: A higher temperature region, at least partially located below the NFT, heats the magnetic storage medium to a temperature that promotes demagnetization in both the upper and lower recording layers, the upper recording layer having a lower Curie temperature than the lower recording layer. In the lower temperature region that deviates from the higher temperature region in the downward magnetic track direction, the lower temperature region of the thermal distribution heats the magnetic storage medium to a temperature that is too low to promote demagnetization in the lower recording layer but is within a range sufficient to promote demagnetization in the upper recording layer.

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