Magnetic property measuring device and magnetic property measuring method

Abstract

The present application provides a kind of magnetic property measuring device and magnetic property measuring method, which can evaluate the effective magnetic property of the magnetic layer constituting heat-assisted magnetic recording medium. The magnetic property measuring device for measuring the magnetic property of the magnetic recording medium comprises: a rotating mechanism for rotating the magnetic recording medium; a heating and cooling mechanism for heating or cooling the magnetic recording medium; a temperature measuring mechanism for measuring the temperature of the magnetic recording medium; a laser heating mechanism arranged opposite to the measurement site of the magnetic recording medium, for heating the measurement site in a non-contact manner; a magnetic writing part arranged opposite to the measurement site, for magnetizing the measurement site in a non-contact manner; and a magnetic reading part arranged opposite to the measurement site, for reading the magnetic leakage field of the measurement site in a non-contact manner.

Description

TECHNICAL FIELD

[0001] The present application relates to a magnetic property measuring apparatus and a magnetic property measuring method. BACKGROUND

[0002] In order to further increase the recording capacity of a hard disk drive (HDD), development of high-density magnetic recording media is being conducted. In particular, research and development of a magnetic recording medium (or heat-assisted magnetic recording medium) that records information using a heat-assisted magnetic recording method, which is expected as the next-generation HDD, is being actively conducted.

[0003] The heat-assisted magnetic recording method is a method in which a surface of a magnetic recording medium is locally heated by irradiating near-field light to the magnetic recording medium with laser light generated by a laser generating portion mounted on a magnetic head, thereby reducing the coercive force of the magnetic recording medium and recording information.

[0004] The heat-assisted magnetic recording medium includes a magnetic layer, a heat dissipation layer composed of a high thermal conductivity material in order to improve the thermal gradient and heat dissipation, a heat resistance layer provided under the magnetic layer in order to efficiently heat the magnetic layer, and a reflection control layer in order to suppress heat reflection from the magnetic recording medium.

[0005] As a method for measuring the magnetic properties of a heat-assisted magnetic recording medium, for example, in Non-Patent Literature 1, a method for evaluating the magnetic properties of a heat-assisted magnetic recording medium by changing the output of laser light irradiated to the heat-assisted magnetic recording medium is disclosed.

[0006] <Related Art>

[0007] <Non-Patent Literature>

[0008] Non-Patent Literature 1: Douglas A. Saunders et al., “Magnetic Field Strength Measurements in Heat-Assisted Magnetic Recording”, IEEE TRANSACTIONS ON MAGNETICS, VOL. 55, NO. 12, DECEMBER 2019 SUMMARY

[0009] <Problems to be Solved by the Invention>

[0010] Here, the layer stack structure of the layers that constitute the heat-assisted magnetic recording medium is designed in a manner to control the heating temperature based on laser light, the diffusion of heat, and the like. When designing the layer stack structure of the heat-assisted magnetic recording medium, it is important to grasp the Curie temperature of the magnetic layer and the variance of the Curie temperature.

[0011] The Curie temperature is a transition temperature at which a ferromagnet changes to a paramagnet. In a heat-assisted magnetic recording system, a surface of a magnetic recording medium is locally heated by laser light from a laser light generating section provided in a magnetic head, and a reversal magnetic field of a magnetic layer is reduced to record information.

[0012] The Curie temperature of a magnetic material included in the magnetic layer is generally measured by a vibrating sample magnetometer (VSM) provided in a heating mechanism. However, there is a problem in that even if the obtained Curie temperature is used to design a heat-assisted magnetic recording medium, there are cases in which the heat-assisted magnetic recording medium does not exhibit predicted magnetic characteristics. That is, because a heat dissipation layer, a heat resistance layer, a reflection control layer, or the like is provided on the substrate side of the magnetic layer of the heat-assisted magnetic recording medium in most cases, the flow of heat within the stacked structure of the heat-assisted magnetic recording medium is complex. In addition, because the magnetic layer has a columnar magnetic particle and a non-magnetic grain boundary phase, and has thermal conductivity anisotropy, the flow of heat within the stacked structure of the heat-assisted magnetic recording medium is further complex. Therefore, there are cases in which the heat-assisted magnetic recording medium does not exhibit magnetic characteristics as predicted.

[0013] One embodiment of the present application was made in view of the above-described circumstances, and an object thereof is to provide a magnetic characteristic measurement device and a magnetic characteristic measurement method capable of measuring effective magnetic characteristics of a magnetic layer constituting a heat-assisted magnetic recording medium.

[0014] <Method for solving the problem>

[0015] The magnetic characteristic measurement device of one embodiment of the present application is a device for measuring magnetic characteristics of a magnetic recording medium, and includes a rotation mechanism for rotating the magnetic recording medium, a heating and cooling mechanism for heating or cooling the magnetic recording medium, a temperature measurement mechanism for measuring a temperature of the magnetic recording medium, a laser heating mechanism disposed opposite a measurement site of the magnetic recording medium, for heating the measurement site in a noncontact manner, a magnetic writing section disposed opposite the measurement site, for magnetizing the measurement site in a noncontact manner, and a magnetic reading section disposed opposite the measurement site, for reading a leakage magnetic field of the measurement site in a noncontact manner.

[0016] The magnetic property measurement method of one embodiment of the present application is a magnetic property measurement method for measuring magnetic properties of a magnetic recording medium, including: Step A, rotating the magnetic recording medium by a rotation mechanism; Step B, causing a laser heating mechanism, a magnetic writing portion, and a magnetic reading portion to float from the surface of the magnetic recording medium and scan; Step C, keeping the magnetic recording medium at a temperature X lower than the Curie temperature by a heating and cooling mechanism and a temperature measurement mechanism; Step D, magnetizing a measurement site of the magnetic recording medium to a saturated state by the laser heating mechanism and the magnetic writing portion; Step E, demagnetizing the measurement site magnetized to the saturated state in Step D by heating the measurement site with the laser heating mechanism and reading the leakage magnetic field of the demagnetized site with the magnetic reading portion; Step F, repeating Steps D and E while changing the amount of laser heating in Step E, and thus obtaining a relationship between the amount of laser heating in Step E and the leakage magnetic field; Step G, keeping the magnetic recording medium at a temperature Y lower than the Curie temperature and different from the temperature X by the heating and cooling mechanism and the temperature measurement mechanism; Step H, magnetizing a measurement site of the magnetic recording medium to a saturated state by the laser heating mechanism and the magnetic writing portion; Step I, demagnetizing the measurement site magnetized to the saturated state in Step H by heating the measurement site with the laser heating mechanism and reading the leakage magnetic field of the demagnetized site with the magnetic reading portion; Step J, repeating Steps H and I while changing the amount of laser heating in Step I, and thus obtaining a relationship between the amount of laser heating in Step I and the leakage magnetic field; and Step K, calculating the magnetic properties of the magnetic recording medium based on the relationships between the amount of laser heating and the leakage magnetic field obtained in Steps F and J.

[0017] <Effects of the Invention>

[0018] According to one embodiment of the present application, the effective magnetic properties of a magnetic layer constituting a heat-assisted magnetic recording medium can be measured. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG. 1 is a perspective view schematically showing one example of the configuration of a magnetic property measurement apparatus according to an embodiment of the present application.

[0020] Figure 2 FIG. 6 is a graph showing one example of the relationship between the amount of laser heating and the leakage magnetic field / saturation magnetization.

[0021] Figure 3 FIG. 7 is a graph showing one example of the relationship between the input current value and the leakage magnetic field / saturation magnetization.

[0022] Figure 4is a graph showing a relationship of a plot of measured data based on a leakage magnetic field / saturation magnetization amount with respect to an input current value and a cumulative distribution function of regression.

[0023] Figure 5 is a cross-sectional view showing one example of a heat-assisted magnetic recording medium.

[0024] Explanation of Reference Numerals

[0025] 1 Magnetic property measuring device

[0026] 2 Heat-assisted magnetic recording medium (measuring sample)

[0027] 10 Rotation mechanism

[0028] 20 Heating and cooling mechanism

[0029] 30 Temperature measuring mechanism

[0030] 40 Laser heating mechanism

[0031] 50 Magnetic head

[0032] 51 Magnetic write section

[0033] 52 Magnetic read section

[0034] 60 Magnetic head driving mechanism

[0035] 70 Hanger DETAILED DESCRIPTION

[0036] Hereinafter, an embodiment of the present application will be described in detail. Note that the present embodiment is not limited to the examples shown below, and the number, the configuration, the position, the material, and the like can be changed unless particularly limited. Also, in order to make the description easy to understand, the same reference numerals are given to the same constituent elements in each drawing, and repeated description is omitted. Also, the scale of each component in the drawings is different from the actual scale, and the scale is different between the drawings. Unless particularly described, "〜" indicating a numerical range in the present specification indicates a numerical value recited before and after the lower limit value and the upper limit value.

[0037] [Magnetic property measuring device]

[0038] The magnetic property measuring device of the present embodiment will be described. Note that in the present embodiment, a case where the magnetic property measuring device uses a heat-assisted recording method to magnetically record information (hereinafter, also referred to as "write information") will be described. The magnetic playback of information from the magnetic recording medium is also referred to as "reading information" from the magnetic recording medium. In the present specification, the magnetic recording medium that uses the heat-assisted recording method to magnetically write information will be referred to as a heat-assisted magnetic recording medium.

[0039] Figure 1 is a perspective view schematically showing one example of the configuration of a magnetic property measuring apparatus of the present embodiment. As shown in the figure, the magnetic property measuring apparatus 1 includes a rotating mechanism 10, a heating / cooling mechanism 20, a temperature measuring mechanism 30, a laser heating mechanism 40, and a magnetic head 50. The magnetic property measuring apparatus 1 is used to measure the magnetic properties of a heat-assisted magnetic recording medium (or a measurement sample) 2 used for an HDD. The magnetic property measuring apparatus 1 can include a magnetic head driving mechanism 60 in addition to the above-described elements. Figure 1

[0040] The rotating mechanism 10 rotates the heat-assisted magnetic recording medium 2. Since the heat-assisted magnetic recording medium 2 is generally in a disc shape having an opening in the center, in the example shown in the figure, the rotating mechanism 10 has a spindle that holds the heat-assisted magnetic recording medium 2 through the opening in the center of the heat-assisted magnetic recording medium 2. It is preferable that the rotating mechanism 10 rotate the heat-assisted magnetic recording medium 2 in a range of, for example, 5000 rpm to 10000 rpm. Figure 1

[0041] The heating / cooling mechanism 20 is used to heat or cool the heat-assisted magnetic recording medium 2. It is preferable that the temperature range of heating or cooling be set to 0°C (273 K) from the lower limit of the temperature of use of the HDD to less than the Curie temperature of the magnetic material used in the heat-assisted magnetic recording medium 2.

[0042] As the heating / cooling mechanism 20, a general apparatus such as a ceramic heater, a Peltier element, or the like can be used, and the heating / cooling mechanism 20 can heat or cool the heat-assisted magnetic recording medium 2 in either a contact or a non-contact manner. It is preferable that the heating / cooling mechanism 20 heat or cool the heat-assisted magnetic recording medium 2 by heat conduction in the case of contact, and heat or cool the heat-assisted magnetic recording medium 2 by heat radiation in the case of non-contact.

[0043] The temperature measuring mechanism 30 is used to measure the temperature of the heat-assisted magnetic recording medium 2. The temperature measuring mechanism 30 is used to keep the temperature of the heat-assisted magnetic recording medium 2 constant. As the temperature measuring mechanism 30, a known apparatus can be used as long as it can measure the temperature of the heat-assisted magnetic recording medium 2. As the temperature measuring mechanism 30, for example, a thermocouple can be used in the case of contact, and a radiation thermometer can be used in the case of non-contact. Since the magnetic property measuring apparatus 1 heats and cools the heat-assisted magnetic recording medium 2 from the back, the measurement is performed on the surface of the heat-assisted magnetic recording medium 2, and thus it is considered that a temperature difference will occur between the front and the back of the heat-assisted magnetic recording medium 2. Therefore, it is preferable that the temperature measuring mechanism 30 be disposed at a position opposite to the heat-assisted magnetic recording medium 2 to measure the surface of the heat-assisted magnetic recording medium 2 in a non-contact manner. ​​

[0044] The laser heating mechanism 40 locally heats the measurement site of the heat-assisted magnetic recording medium 2 in a noncontact manner. The laser heating mechanism 40 is disposed at a position opposite the heat-assisted magnetic recording medium 2 in order to heat the measurement site of the heat-assisted magnetic recording medium 2 from the surface side. That is, as shown in FIG. 1, the laser heating mechanism 40 is mounted to the magnetic head 50 and scans the surface of the heat-assisted magnetic recording medium 2 by the magnetic head driving mechanism 60. The laser heating mechanism 40 is suspended from the surface of the heat-assisted magnetic recording medium 2 by air vortexes generated between the heat-assisted magnetic recording medium 2 that is rotationally driven and scans. Figure 1

[0045] Since the magnetic property measurement apparatus 1 aims to measure the effective magnetic properties of the heat-assisted magnetic recording medium 2, it is preferable that the laser heating mechanism 40 have the same or as similar a configuration as the laser heating mechanism used in the magnetic head of the heat-assisted magnetic recording type HDD. That is, as the laser heating mechanism 40, it is preferable to use a semiconductor laser that emits laser light in a range of 780 nm to 980 nm as a light source. It is preferable that the beam diameter of the laser light be equal to or greater than the track width of the HDD, and specifically equal to or greater than 40 nmφ. In this example, the site of the heat-assisted magnetic recording medium 2 irradiated by the laser light is the measurement site. In addition, the laser heating mechanism 40 can use a near-field transducer (NFT) and an optical waveguide as in the magnetic head of the heat-assisted magnetic recording type HDD.

[0046] The magnetic head 50 has a magnetic write section 51 and a magnetic read section 52.

[0047] The magnetic write section 51 is disposed at a position opposite the measurement site of the heat-assisted magnetic recording medium 2 and magnetizes the measurement site of the heat-assisted magnetic recording medium 2. The magnetic write section 51 is disposed at a position opposite the heat-assisted magnetic recording medium 2 in order to magnetize the measurement site of the heat-assisted magnetic recording medium 2. That is, as shown in FIG. 1, the magnetic write section 51 is mounted to the hanger 70 and scans the surface of the heat-assisted magnetic recording medium 2 by the magnetic head driving mechanism 60. The magnetic write section 51 is suspended from the surface of the heat-assisted magnetic recording medium 2 by air vortexes generated between the heat-assisted magnetic recording medium 2 that is rotationally driven by the rotation mechanism 10 and scans. Figure 1

[0048] Since the magnetic property measurement apparatus 1 aims to measure the effective magnetic properties of the heat-assisted magnetic recording medium 2, it is preferable that the magnetic write section 51 have as similar a configuration as the magnetic write section used in the magnetic head of the heat-assisted magnetic recording type HDD. That is, the magnetic write section 51 is an electromagnet that combines a coil and a magnetic body, and in order to miniaturize the write region, it is preferable to use a thin-film magnetic head that generates a coil on the surface of the magnetic body by etching.

[0049] ​​The magnetic write region is preferably set to about the track width of the HDD, and specifically, is preferably set to about 40 nm.

[0050] The magnetic read section 52 is disposed at a position opposite the measurement site of the heat-assisted magnetic recording medium 2, and is used to read the leakage magnetic field of the measurement site of the heat-assisted magnetic recording medium 2. The magnetic read section 52 is disposed at a position opposite the heat-assisted magnetic recording medium 2 in order to read the leakage magnetic field of the measurement site of the heat-assisted magnetic recording medium 2. That is, as shown in FIG. 6, the magnetic read section 52 is mounted to the hanger 70, and scans the surface of the heat-assisted magnetic recording medium 2 by the head driving mechanism 60. The magnetic read section 52 is suspended from the surface of the heat-assisted magnetic recording medium 2 by air vortex generated between the heat-assisted magnetic recording medium 2 that is rotationally driven by the rotation mechanism 10. Figure 1

[0051] Since the magnetic read section 52 is used for the purpose of measuring the effective magnetic characteristics of the heat-assisted magnetic recording medium 2, it is preferable that it have the same or as similar a configuration as the magnetic read section used in the magnetic head of the HDD of the heat-assisted magnetic recording type. That is, as the magnetic read section 52, it is preferable to use an MR (Magneto Resistive) magnetic head that has high sensitivity by use of the magnetoresistance effect, a GMR (Giant Magneto Resistive) magnetic head that uses the giant magnetoresistance effect, and a TMR (Tunnel Magneto Resistive) magnetic head that uses the tunnel magnetoresistance effect, and the like.

[0052] The magnetic read region is preferably set to about the track width of the HDD, and specifically, is preferably set to about 40 nm.

[0053] Thus, the magnetic characteristics measurement device 1 of the present embodiment includes the rotation mechanism 10, the heating and cooling mechanism 20, the temperature measurement mechanism 30, the laser heating mechanism 40, and the magnetic head 50. In addition, the laser heating mechanism 40 and the magnetic head 50 can be configured to have the same or as similar a configuration as the laser heating mechanism and the magnetic head (magnetic write section and magnetic read section) used in the magnetic head of the HDD of the heat-assisted magnetic recording type. Thus, the magnetic characteristics measurement device 1 can measure the effective magnetic characteristics of the heat-assisted magnetic recording medium 2. Therefore, the magnetic characteristics measurement device 1 can make it possible to more efficiently perform design of the layered structure of the heat-assisted magnetic recording medium 2.

[0054] ​The magnetic property measuring device 1 allows the temperature measuring mechanism 30 to be arranged opposite the heat-assisted magnetic recording medium 2, and is capable of measuring the temperature of the heat-assisted magnetic recording medium 2 in a non-contact manner. Since the heat-assisted magnetic recording medium 2 is heated or cooled from the back side thereof by the heating and cooling mechanism 20, and is measured on the surface side thereof, it is possible that a temperature difference occurs between the front and back of the heat-assisted magnetic recording medium 2. The magnetic property measuring device 1 is capable of suppressing the temperature difference occurring between the front and back of the heat-assisted magnetic recording medium 2 by causing the temperature measuring mechanism 30 to measure the temperature of the heat-assisted magnetic recording medium 2 in a non-contact manner, and is thus capable of measuring the temperature of the heat-assisted magnetic recording medium 2 with higher precision.

[0055] [Method of measuring magnetic property]

[0056] A case in which the method of measuring magnetic property of the present embodiment is used for a heat-assisted magnetic recording medium will be described as an example. The method of measuring magnetic property of the present embodiment uses the magnetic property measuring device of the present embodiment.

[0057] In the method of measuring magnetic property of the present embodiment, the heat-assisted magnetic recording medium 2 is placed on the spindle that constitutes the rotating mechanism 10, and is caused to rotate (Step A).

[0058] Next, the magnetic head 50 including the laser heating mechanism 40, the magnetic writing section 51, and the magnetic reading section 52 is caused to hover from the surface of the heat-assisted magnetic recording medium 2 and scan (Step B).

[0059] Next, the heat-assisted magnetic recording medium 2 is maintained at a temperature X that is less than the Curie temperature by the heating and cooling mechanism 20 provided directly below the back surface of the heat-assisted magnetic recording medium 2, and the temperature measuring mechanism 30 that is arranged opposite the surface of the heat-assisted magnetic recording medium 2 in a non-contact manner (Step C). Note that the temperature X can be the temperature of the substrate of the heat-assisted magnetic recording medium 2.

[0060] Next, the measurement site of the heat-assisted magnetic recording medium 2 is magnetized to a saturated state by the laser heating mechanism 40 and the magnetic writing section 51 provided in the magnetic head 50 (Step D).

[0061] That is, since the coercive force of the magnetic material used for the heat-assisted magnetic recording medium 2 is high, the surface of the heat-assisted magnetic recording medium 2 is locally heated by the laser heating mechanism 40, and the reversal magnetic field of the magnetic material is reduced to perform writing.

[0062] Next, the measurement site that is magnetized to a saturated state is heated by the laser heating mechanism 40, and the magnetic material of the measurement site of the heat-assisted magnetic recording medium 2 that is heated is demagnetized, and the leakage magnetic field of the demagnetized site is read by the magnetic reading section 52 provided in the magnetic head 50 (Step E).

[0063] Next, while the heat-assisted magnetic recording medium 2 of Step C is maintained at a prescribed temperature (temperature X), the laser heating amount in Step E is changed, and Steps D and E are repeated to obtain the relationship between the laser heating amount and the leakage magnetic field in Step E (Step F).

[0064] Here, in Step F, it is important to repeat Steps D and E. It is also possible to consider that Step D is set to only once, and Step E is repeated while gradually increasing the laser heating amount thereafter. However, in the case where such a method is set, an error of a main cause of a slight variation in the flying height of the magnetic head 50 and the like is added in each Step E. Therefore, the error of the Curie temperature and the variance of the Curie temperature of the heat-assisted magnetic recording medium 2 finally obtained also becomes large.

[0065] The ratio of the leakage magnetic field is the ratio of the leakage magnetic field to the saturation magnetization amount of the measurement site "(leakage magnetic field / saturation magnetization amount)". As described later Figure 2 As shown in the graph of FIG. 6, if the temperature of the magnetic layer reaches the vicinity of the Curie temperature by heating by the laser heating mechanism 40, the magnetic layer in the saturation magnetization state is gradually demagnetized. Figure 2 In the magnetic characteristics of the heat-assisted magnetic recording medium 2 shown in the graph of FIG. 6, it is important that the point at which the ratio of the leakage magnetic field starts to decrease from 1, the point at which the ratio of the leakage magnetic field becomes 0.5, and the point at which it becomes zero, and particularly important is the point at which the ratio of the leakage magnetic field becomes 0.5.

[0066] The point at which the ratio of the leakage magnetic field becomes 0.5 indicates that half of the magnetic particles constituting the magnetic layer are demagnetized by heating by the laser heating mechanism 40, and it indicates the Curie temperature Tc (for example, the average value) of the heat-assisted magnetic recording medium 2. Note that the point at which the ratio of the leakage magnetic field becomes zero indicates the point at which all of the magnetic particles constituting the magnetic layer are demagnetized, and it indicates the maximum Curie temperature of the heat-assisted magnetic recording medium 2. Note that since there is a case where a measurement error occurs when the relationship between the laser heating amount and the leakage magnetic field is obtained by Step F, it is preferable that the measurement of the laser heating amount and the leakage magnetic field is repeated several times (for example, 3 times), and the average value of the measurement results is used.

[0067] Next, the temperature of the heat-assisted magnetic recording medium 2 is maintained to be less than the Curie temperature and different from the temperature X to a substrate temperature Y by the heating and cooling mechanism 20 and the temperature measurement mechanism 30 (Step G). Note that, like the temperature X, the temperature Y can be the temperature of the substrate of the heat-assisted magnetic recording medium 2.

[0068] Next, the relationship between the laser heating amount and the leakage magnetic field is obtained by the same method as in the case of the temperature X.

[0069] That is, as in the previous processes D to F, the measurement site of the heat-assisted magnetic recording medium 2 is magnetized to a saturated state by the laser heating mechanism 40 and the magnetic write section 51 provided in the magnetic head 50 (process H).

[0070] Next, the measurement site magnetized to the saturated state is demagnetized by heating with the laser heating mechanism 40, and the leakage magnetic field of the demagnetized site is read by the magnetic read section 52 provided in the magnetic head 50 (process I).

[0071] Next, while the heat-assisted magnetic recording medium 2 of the process G is maintained at a prescribed temperature (temperature Y), the laser heating amount in the process I is changed, and the processes H and I are repeated to obtain the relationship between the laser heating amount and the leakage magnetic field in the process I (process J).

[0072] In the process J, the repetition of the processes H and I is important, as described above.

[0073] Figure 2 and Figure 3 is a graph for illustrating one example of the relationship between the laser heating amount and the leakage magnetic field / saturated magnetization amount in the substrate temperature Y obtained by the process J. Figure 2 One example of the relationship between the laser heating amount and the leakage magnetic field / saturated magnetization amount is shown, and the vertical axis shows the leakage magnetic field / saturated magnetization amount, and the horizontal axis shows the laser heating amount in arbitrary units. Figure 3 One example of the relationship between the input current value applied to the laser heating mechanism 40 and the leakage magnetic field / saturated magnetization amount is shown, and the vertical axis shows the leakage magnetic field / saturated magnetization amount, and the horizontal axis shows the input current value (mA). As shown in Figure 2 and Figure 3 The two curves are curves that are displaced horizontally with respect to the horizontal axis in parallel, and the displacement amount represents the difference between the temperature X (K) and the temperature Y (K).

[0074] Since the measurement time of the leakage magnetic field is very short, the heat diffused from the measurement site in the measurement of the leakage magnetic field can be ignored. Therefore, it can be considered that there is a proportional relationship between the input current value to the laser heating mechanism 40 and the temperature rise amount of the measurement site. That is, if T0 (K) represents the substrate temperature, L P (mA) represents the input current value to the laser heating mechanism 40, and T L (K) represents the temperature of the measurement site, the following equation (1) holds.

[0075] T L = C E × L P + T0... (1)

[0076] In equation (1), C E (K / mA) represents the proportionality constant with respect to the input current value LP The heating efficiency is equivalent to the temperature rise that occurs when the current increases by 1 mA. Heating efficiency C E (K / mA) is a constant determined by the conditions of the heat-assisted magnetic recording medium 2, the magnetic property measuring device 1, etc., and it can be obtained in the following way.

[0077] Specifically, the temperature at which the leakage magnetic field / saturation magnetization = 0.5 is a constant value determined by the heat-assisted magnetic recording medium 2. Therefore, if L P1 (mA) represents the input current value to the laser heating mechanism 40 when the substrate temperature is X and the leakage magnetic field / saturation magnetization is 0.5 after laser irradiation from the laser heating mechanism 40, denoted by L. P2 (mA) represents the input current value (L) to the laser heating mechanism 40 when the substrate temperature Y is such that the leakage magnetic field / saturation magnetization is 0.5 after laser irradiation from the laser heating mechanism 40. P2 (mA), using T 0.5 (K) represents the temperature (effective Curie temperature) of the heat-assisted magnetic recording medium 2 with leakage magnetic field / saturation magnetization = 0.5, then the following equations (2) and (3) hold true.

[0078] T 0.5 =C E ×L P1 +X…(2)

[0079] T 0.5 =C E ×L P2 +Y…(3)

[0080] In equations (2) and (3) above, X, Y, L P1 L P2 All are known values. Since the unknown value is C... E And T 0.5 Therefore, the heating efficiency C can be calculated using equations (2) and (3). E and temperature T 0.5 .

[0081] For example, in Figure 3 In the example shown, temperature X is 348 (K) and temperature Y is 298 (K). The substrate temperature X is further reduced to temperature T. 0.5 The input current to the laser heating mechanism 40 when the leakage magnetic field / saturation magnetization = 0.5 is 16 mA, and the substrate temperature Y becomes temperature T. 0.5 When the input current to the laser heating mechanism 40 is 14 mA, the heating efficiency C of the laser heating mechanism 40 can be calculated according to equations (2) and (3) above. E Given 25 (K / mA), calculate the temperature T. 0.5698 (K).

[0082] If the input current value to the laser heating mechanism 40 and the temperature of the measurement site are found, the relationship can be converted to a relationship of the laser heating amount (input current value) of the heat-assisted magnetic recording medium 2 based on the laser heating mechanism 40 and the temperature of the measurement site.

[0083] Although the above-described method is a method directly found based on the plot of the measurement data, in a case where a measurement error is locally generated at an input current value close to the temperature T 0.5 , the error of the found temperature T 0.5 becomes large.

[0084] Therefore, according to a method of regressing from the measurement data to a function, as described below, the temperature T 0.5 (effective Curie temperature) can be more correctly found, and the standard deviation σ of the distribution of the Curie temperature Tc possessed by the particles of the magnetic layer can be found.

[0085] It is considered that the leakage magnetic field of the heat-assisted magnetic recording medium 2 measured corresponds to the sum of the magnetic fields generated by the respective particles of the magnetic layer. Also, if the magnetic field generated by each of the magnetized particles of the magnetic layer is assumed to be equal to M, the temperature of the measurement site is assumed to be T L , and the ratio of the particles of the magnetic layer that have not reached the Curie temperature Tc (i.e., particles for which Tc > T L ) is assumed to be PI, and the ratio of the particles of the magnetic layer that have reached the Curie temperature Tc (i.e., particles for which Tc ≦ T L ) is assumed to be P2 (PI + P2 = 1), the leakage magnetic field / saturation magnetization amount of the heat-assisted magnetic recording medium 2 can be represented by PI.

[0086] The ratio P2 of the particles of the magnetic layer of the measurement site that have reached the Curie temperature Tc is the sum of the ratios of the particles of the magnetic layer having the Curie temperature Tc below the temperature of the measurement site. That is, the leakage magnetic field / saturation magnetization amount of the heat-assisted magnetic recording medium 2 at the temperature T L of the measurement site is the value (1 - P2) of the cumulative value of 0 (K) to the temperature T L of the measurement site under the distribution of the Curie temperature of the particles of the magnetic layer, from 1.

[0087] If the curve shape indicating the change of the leakage magnetic field / saturation magnetization amount with respect to the input current value (mA) in FIG. Figure 3 is observed, it can be inferred that the function (1 - Φ) following from 1.0 minus the cumulative distribution function Φ of the normal distribution is followed.

[0088] As described above, the input current value to the laser heating mechanism 40 is in a proportional relationship with the temperature of the measurement site. If the relationship f(LP) of the laser heating amount LP and the magnetic flux leakage / saturation magnetization amount follows the function (1-Φ), the ratio P(TL) (=P2=1-P1=1-f(LP)) of the particles reaching the Curie temperature at the temperature TL of the laser irradiation portion also follows the cumulative distribution function Φ of the normal distribution. Therefore, it is possible to infer that the function P(Tc) representing the ratio of the particles of the magnetic layer having the Curie temperature Tc also follows the normal distribution.

[0089] Figure 4 is a graph showing the relationship of the plot based on the measurement data of the magnetic flux leakage / saturation magnetization amount with respect to the input current value (mA) and the regression function in the substrate temperature X (=298 K). The regression function is [1-Φ{(x-μ1) / σ1}], Φ{(x-μ1) / σ1} represents the cumulative distribution function of the normal distribution, x represents the value of the laser heating amount L P , μ1 represents the central value of the normal distribution, and σ1 represents the standard deviation of the normal distribution. Figure 4 The plot shown corresponds to the measurement data at the substrate temperature X in Figure 3 . In Figure 4 , the vertical axis represents the magnetic flux leakage / saturation magnetization amount, and the horizontal axis represents the input current value (mA). The regression of the cumulative distribution function from the measurement data is performed by the least squares method. If the cumulative distribution function of the normal distribution is determined by regressing the measurement data, the central value μ1 (mA) and the standard deviation σ1 can be found. Here, the found central value μ1 (mA) is the input current value L 0.5 (mA) when the measurement site becomes the temperature T P1 in the substrate temperature X (i.e., μ1=L P1 ).

[0090] In the substrate temperature Y (348 K), [1-Φ{(x-μ2) / σ2}] can also be regressed by the same method, and the central value μ2 (mA) and the standard deviation σ2 (mA) can be found. The central value μ2 is the input current value L 0.5 (mA) when the measurement site becomes T P2 in the substrate temperature Y (i.e., μ2=L P2 ).

[0091] By the above-described method, the found L P1 is substituted into the above-described equation (2), the found L P2 is substituted into the above-described equation (3), and the heating efficiency C E and the effective Curie temperature T 0.5 are found by solving the simultaneous equations. According to the data shown in Figure 3 , the input current value LP1 =16.0mA and input current value L P2 =14.0mA. Additionally, based on this input current value L... P1 L P2 The heating efficiency C can be calculated. E =25.0K / mA and effective Curie temperature T 0.5 =698K.

[0092] As an evaluation metric for the magnetic layer, the distribution of Curie temperatures of the particles constituting the magnetic layer is used to convert the standard deviation obtained by the above method into a temperature value σ. T Specifically, using C E ×σ1 and C E Any one of ×σ² or both. More specifically, although it is C E ×σ1 and C E The arithmetic mean of ×σ² (σ T =(C E ×σ1+C E ×σ2) / 2), but the value σ T Not limited to this.

[0093] It should be noted that, in the above explanation, although the heating efficiency C is calculated based on two measured data points, substrate temperature X and substrate temperature Y... E and effective Curie temperature T 0.5 However, the heating efficiency C can also be calculated based on the temperature measurements of three or more substrates. E and effective Curie temperature T 0.5 In this case, for example, at each substrate temperature, the temperature is measured relative to the Curie temperature T. 0.5 The corresponding input current L to the laser heating mechanism 40 P1 L P2 ... L Pk (k is a natural number greater than 3), for the substrate temperature and Curie temperature T 0.5 The relationship between the input current values ​​to the laser heating mechanism 40 is plotted, and a linear regression is performed using methods such as least squares. The value of the heating efficiency C is the sum of the slope of the regression line and a negative (e.g., a negative coefficient). E The more plots drawn, the more accurately the heating efficiency C can be calculated. E .

[0094] It should be noted that there are cases where the plotted autoregressive line deviates. In such cases, for example, the heating efficiency C might be misaligned. E The Curie temperature T obtained by substituting into equation (2) above 0.5 The value of heating efficiency C E The Curie temperature T obtained by substituting into equation (3) above0.5 In cases where the value of C is different, for example, the heating efficiency C can be used. E The value T obtained by substituting into equations (2) and (3) above corresponding to the temperatures X and Y of each substrate 0.5(1) T 0.5(2) ... T 0.5(k) The arithmetic mean can be plotted, but the method of plotting is not limited to this.

[0095] Thus, based on the relationship between laser heating and leakage magnetic field obtained in process F and process I, the Curie temperature and the variance of the Curie temperature (process K) of the heat-assisted magnetic recording medium 2 can be calculated as magnetic properties.

[0096] It should be noted that, in Figure 5 An example of a heat-assisted magnetic recording medium (or measurement sample) 2 measured using the magnetic property measurement method of this embodiment is shown. Figure 5 As shown, the heat-assisted magnetic recording medium 2 has an adhesion layer 202 and an alignment control layer 203 formed on the substrate 201. Furthermore, a first heat dissipation layer 204, a first barrier layer 205, a second heat dissipation layer 206, and a second barrier layer 207 are sequentially stacked on the alignment control layer 203. Here, the first barrier layer 205 is primarily composed of oxides, nitrides, or carbides. Moreover, on the second barrier layer 207, the heat-assisted magnetic recording medium 2 sequentially stacks a magnetic layer 208, a protective layer 209, and a lubricant layer 210, primarily composed of an alloy having an L10 structure.

[0097] By having the above-described configuration, the heat-assisted magnetic recording medium 2 can maintain the signal-to-noise ratio (SNR) while reducing the laser power emitted from the magnetic head 50. Therefore, the heat-assisted magnetic recording medium 2 can increase the recording density and extend the lifespan of the magnetic head 50.

[0098] This effect is achieved because the first barrier layer 205 is sandwiched between a first heat dissipation layer 204 and a second heat dissipation layer 206, which have higher thermal conductivity than the first barrier layer 205, thereby efficiently utilizing the heat from the laser irradiated by the magnetic head 50. Preferably, the thinner first barrier layer 205 is sandwiched between the thicker first heat dissipation layer 204 and the second heat dissipation layer 206. This suppresses the impairment of the heat dissipation layer's (first heat dissipation layer 204 and second heat dissipation layer 206) effect and creates an interface with a large difference in thermal conductivity between the first barrier layer 205, the first heat dissipation layer 204, and the second heat dissipation layer 206. It is believed that a larger thermal gradient is generated within the first heat dissipation layer 204 and the second heat dissipation layer 206 through these two interfaces, which further increases the amount of heat moving in the direction perpendicular to the recording surface of the heat-assisted magnetic recording medium 2.

[0099] Thus, the magnetic property measurement method of the present embodiment can measure the effective magnetic properties of the heat-assisted magnetic recording medium 2 by including the above-described respective processes. Therefore, if the magnetic property measurement method of the present embodiment is used, the design of the heat dissipation layer (the first heat dissipation layer 204 and the second heat dissipation layer 206), the barrier layer (the first barrier layer 205 and the second barrier layer 207), the magnetic layer 208, and the protective layer 209 of the heat-assisted magnetic recording medium 2 can be performed more efficiently.

[0100] The magnetic property measurement method of the present embodiment can calculate the Curie temperature of the heat-assisted magnetic recording medium 2 and the variance of the Curie temperature as the magnetic properties. Thus, if the magnetic property measurement method of the present embodiment is used, the design of the stacked structure of the heat-assisted magnetic recording medium 2 can be performed more accurately.

[0101] Note that in the present embodiment, the temperature Y can be set to a plurality of different temperatures (e.g., temperatures Y1, Y2, Y3, and the like), and the processes G to K can be performed for each of the different temperatures Y. Thus, the heating efficiency of the laser heating mechanism 40 can be more accurately found.

[0102] As described above, although the embodiments have been described, the above-described embodiments are suggested as examples, and the present application is not limited to the above-described embodiments. The above-described embodiments can be implemented in other various ways, and various combinations, omissions, substitutions, modifications, and the like can be made within a range not departing from the gist of the present application. These embodiments and modifications thereof are included in the scope and gist of the present application, and are included in the present application and the equivalent range thereof recited in the claims.

Claims

1. A magnetic property measuring device for measuring the magnetic properties of a magnetic recording medium, the magnetic property measuring device comprising: A rotating mechanism for rotating the aforementioned magnetic recording medium; A heating and cooling mechanism for heating or cooling the magnetic recording medium described above; A temperature measuring mechanism, used to measure the temperature of the aforementioned magnetic recording medium; A laser heating mechanism is configured opposite to the measurement area of ​​the magnetic recording medium and is used to heat the measurement area in a non-contact manner. A magnetic writing section is disposed opposite to the aforementioned measuring region and is used to magnetize the aforementioned measuring region in a non-contact manner. as well as A magnetic reading unit, configured opposite to the aforementioned measuring area, is used to read the leakage magnetic field of the measuring area in a non-contact manner. The aforementioned magnetic property measuring device is configured such that, during measurement, it repeatedly performs the steps of magnetizing the measuring area of ​​the magnetic recording medium to a saturated state using the aforementioned laser heating mechanism and the aforementioned magnetic writing unit, and then demagnetizing the measured area that has been magnetized to a saturated state using the aforementioned laser heating mechanism. By doing so, it determines the relationship between the laser heating amount and the leakage magnetic field during the demagnetizing process, and calculates the magnetic properties of the magnetic recording medium based on this relationship. The aforementioned magnetic properties include the effective Curie temperature of the aforementioned magnetic recording medium, which is the temperature of the aforementioned magnetic recording medium when the leakage magnetic field / saturation magnetization = 0.

5. The effective Curie temperature is calculated using the following two formulas: T 0.5 =C E ×L P1 +X, T 0.5 =C E ×L P2 +Y, Among them, L P1 L represents the current input to the laser heating mechanism when the leakage magnetic field / saturation magnetization = 0.5 after laser irradiation of the magnetic recording medium at temperature X. P2 C represents the current value input to the laser heating mechanism when the leakage magnetic field / saturation magnetization = 0.5 after laser irradiation in the magnetic recording medium at temperature Y. E This represents the heating efficiency, and T 0.5 The effective Curie temperature is represented by the above formula, and the current value input to the laser heating mechanism in the above two formulas corresponds to the laser heating amount. The temperature X mentioned above is different from the temperature Y mentioned above. Both the aforementioned temperatures X and Y are lower than the Curie temperature, and are maintained by a heating and cooling mechanism and a temperature measuring mechanism.

2. The magnetic property measuring device according to claim 1, wherein, The temperature measuring mechanism described above is configured opposite to the magnetic recording medium, and is used to measure the temperature of the magnetic recording medium in a non-contact manner. The aforementioned magnetic properties include the variance of the effective Curie temperature of the aforementioned magnetic recording medium. The above L P1 L P2 The method can be obtained by either directly calculating the relationship between the measured data and the leakage magnetic field based on the above-mentioned measurement data, or by regressing the measured data into a function.

3. The magnetic property measuring device according to claim 1 or 2, wherein, This magnetic property measuring device also has: Hanger; A magnetic head, comprising the aforementioned magnetic writing section and the aforementioned magnetic reading section, and mounted on the aforementioned hanger; and The magnetic head drive mechanism drives the magnetic head via the aforementioned hanger. The aforementioned laser heating mechanism is mounted on the aforementioned magnetic head.

4. A method for measuring magnetic properties, used to measure the magnetic properties of a magnetic recording medium, the method comprising: Step A involves rotating the magnetic recording medium via a rotating mechanism. Step B involves suspending the laser heating mechanism, magnetic writing unit, and magnetic reading unit above the surface of the magnetic recording medium for scanning. Step C, which uses a heating and cooling mechanism and a temperature measuring mechanism to maintain the magnetic recording medium at a temperature X lower than the Curie temperature; Step D involves magnetizing the measurement area of ​​the magnetic recording medium to a saturated state using the aforementioned laser heating mechanism and the aforementioned magnetic writing unit. In step E, the measuring portion that was magnetized to the saturation state in step D is demagnetized by heating it with the laser heating mechanism, and the leakage magnetic field of the demagnetized portion is read by the magnetic reading unit. Step F involves changing the laser heating amount in step E and repeating steps D and E to determine the relationship between the laser heating amount in step E and the leakage magnetic field. In process G, the magnetic recording medium is maintained at a temperature Y that is lower than the Curie temperature and different from the temperature X by means of the heating and cooling mechanism and the temperature measuring mechanism. In step H, the measurement area of ​​the magnetic recording medium is magnetized to a saturated state by means of the laser heating mechanism and the magnetic writing unit. In step I, the measuring portion that was magnetized to the saturation state in step H is heated by the laser heating mechanism to demagnetize it, and the leakage magnetic field of the demagnetized portion is read by the magnetic reading unit. Step J involves repeating steps H and I by changing the laser heating amount in step I, thereby determining the relationship between the laser heating amount and the leakage magnetic field in step I; and Step K calculates the magnetic properties of the magnetic recording medium based on the relationship between laser heating and leakage magnetic field obtained in steps F and J above. The aforementioned magnetic properties include the effective Curie temperature of the aforementioned magnetic recording medium, which is the temperature of the aforementioned magnetic recording medium when the leakage magnetic field / saturation magnetization = 0.

5. The effective Curie temperature is calculated using the following two formulas: T 0.5 =C E ×L P1 +X, T 0.5 =C E ×L P2 +Y, Among them, L P1 L represents the current value input to the laser heating mechanism when the magnetic recording medium is irradiated with laser at the aforementioned temperature X, resulting in a leakage magnetic field / saturation magnetization ratio of 0.

5. P2 C represents the current value input to the laser heating mechanism when the magnetic recording medium is irradiated with laser at the aforementioned temperature Y, resulting in a leakage magnetic field / saturation magnetization ratio of 0.

5. E This represents the heating efficiency, and T 0.5 The effective Curie temperature is represented by the above formula, and the current value input to the laser heating mechanism in the above two formulas corresponds to the laser heating amount.

5. The method for measuring magnetic properties according to claim 4, wherein, The aforementioned magnetic properties include the variance of the effective Curie temperature of the aforementioned magnetic recording medium. The above L P1 L P2 The method can be obtained by either directly calculating the relationship between the laser heating amount and the leakage magnetic field based on the plot of the measurement data related to the relationship between the laser heating amount and the leakage magnetic field, or by regressing the measurement data from the above measurement data to a function.

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