A temperature sensor based on the random flipping of ferromagnetic materials

Abstract

The present invention provides a temperature sensor based on the random flipping of a ferromagnetic body. The temperature sensor includes a ferromagnetic body having perpendicular magnetic anisotropy. When a perpendicular magnetic field is applied to the ferromagnetic body and the current is withdrawn after the current is applied to the ferromagnetic body, the magnetic moment of the ferromagnetic body is affected by the Zeeman energy. The energy levels of the magnetic moment in the two states of magnetization upward and magnetization downward are not equal, and the probabilities of the magnetic moment returning from the metastable state to the two states are also not equal. The magnetic moment flipping probability of the ferromagnetic body under the current drive is obtained by measuring multiple times the random flipping of the ferromagnetic body, and the ambient temperature is obtained by substituting the magnetic moment flipping probability into the curve of the magnetic moment flipping probability varying with the ambient temperature of the ferromagnetic body. The temperature sensor based on the random flipping of a ferromagnetic body designed by the present invention has the advantages of high precision, high spatial resolution, miniaturization, and little influence from the environment, and has a moderate measurement range.

Description

Technical Field

[0001] The present invention relates to the field of spintronics technology, and in particular, to a temperature sensor based on the random flipping of a ferromagnet. Background Art

[0002] Currently, there are three common methods for industrial temperature measurement on the market: thermistors, thermocouples, and infrared temperature measurement.

[0003] Among them, a thermistor is a special resistor whose resistance value can change with the ambient temperature. It is not suitable for measuring temperature changes over a wide range and has a slow response time.

[0004] A thermocouple basically consists of two wires made of different metals, which are connected together at one end and separated at the other end. A temperature change at the connected end causes a small voltage at the separated end, and its value is proportional to the temperature difference between the two junctions. The temperature is measured by the temperature difference value. The temperature measurement range of a thermocouple is very wide, but the generated signal strength is very low, and advanced signal conditioning is required to enhance the signal-to-noise ratio. The signal conditioning is complex and the accuracy is not high, generally within ±1 - 2K.

[0005] The working principle of infrared temperature measurement is based on the fact that every object emits thermal radiation, and according to the Stefan - Boltzmann law, the measured temperature can be obtained non - contactlessly, with a maximum accuracy of up to ±0.3K. However, it has a high cost, and the measurement accuracy and accuracy are greatly affected by the environment, and the measurement range is narrow. Summary of the Invention

[0006] Aiming at the above problems, the present invention provides a temperature sensor based on the random flipping of a ferromagnet, which has the advantages of high precision, high spatial resolution, miniaturization, and little influence from the environment, and has a moderate measurement range.

[0007] The present invention provides a temperature sensor based on the random flipping of a ferromagnet, including:

[0008] A ferromagnet with perpendicular magnetic anisotropy;

[0009] A perpendicular magnetic field is applied to the ferromagnet. When the current is applied to the ferromagnet and then withdrawn, the magnetic moment of the ferromagnet is affected by the Zeeman energy. The energy levels of the magnetic moment in the two states of magnetization upward and magnetization downward are not equal, and the probabilities of the magnetic moment returning from the metastable state to the two states are also not equal. The magnetic moment flipping probability of the ferromagnet under the current drive is obtained by measuring multiple times, and the ambient temperature is obtained by substituting the magnetic moment flipping probability into the curve of the magnetic moment flipping probability changing with the ambient temperature of the ferromagnet.

[0010] According to a temperature sensor based on the random flipping of a ferromagnet provided by the present invention, the Zeeman energy E received by the magnetic momentz The calculation formula is as follows:

[0011] E z = -μ0VM s (T)H z,eff

[0012] Wherein, V is the volume of a single magnetic domain or crystal grain, M s is the saturation magnetization intensity, which varies with the ambient temperature T, μ0 is the vacuum permeability, and T is the ambient temperature.

[0013] For a temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, the calculation formula for the saturation magnetization intensity varying with the ambient temperature is as follows:

[0014]

[0015] Wherein, M s (0) is the saturation magnetization intensity at T = 0K, T c is the Curie temperature of the ferromagnetic material of the ferromagnetic body, and x is a preset constant.

[0016] For a temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, the curve of the magnetic moment flipping probability varying with the ambient temperature of the ferromagnetic body is obtained through the following steps:

[0017] According to the Boltzmann statistics or the Arrhenius-Néel theorem, determine the probability calculation formula for the magnetic moment to return from the metastable state to the magnetization-up and magnetization-down states;

[0018] According to the probability calculation formula for the magnetic moment to return to the magnetization-up and magnetization-down states, obtain the curve of the magnetic moment flipping-up probability or the magnetic moment flipping-down probability varying with the ambient temperature.

[0019] For a temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, the probability P of the magnetic moment returning from the metastable state to the magnetization-up state up The calculation formula is as follows:

[0020]

[0021] Wherein, E b is the barrier height, E z is the Zeeman energy received by the magnetic moment, k B is the Boltzmann constant, and T is the ambient temperature.

[0022] For a temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, the probability P of the magnetic moment returning from the metastable state to the magnetization-down state down The calculation formula is as follows:

[0023]

[0024] A temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, the calculation formula for the probability of the magnetic moment flipping upward is as follows:

[0025]

[0026] A temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, the ferromagnetic material includes a plurality of array units, and each array unit is a vertical film cross structure.

[0027] A temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, each array unit includes a heavy metal layer, a ferromagnetic layer, an MgO layer, and a metal protection layer arranged in sequence from bottom to top.

[0028] A temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, the heavy metal layer is Ta, the ferromagnetic layer is CoFeB, the MgO layer is MgO, and the metal protection layer is Ta.

[0029] The temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention, by applying a perpendicular magnetic field to a ferromagnetic material with perpendicular magnetic anisotropy, the magnetic moment is affected by the Zeeman energy, and the energy levels in the two states of magnetization upward and magnetization downward are no longer equal. The probabilities of the magnetic moment returning from the metastable state to the two states are also not equal. The dynamic process of the random magnetization flipping of a single-domain ferromagnetic material induced by current is studied and analyzed, and a curve of the magnetization flipping probability varying with temperature is established. By measuring the magnetic moment flipping probability at different ambient temperatures multiple times, the ambient temperature is inversely calculated according to this curve, which has high precision and high spatial resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0031] Figure 1 is a schematic structural diagram of the temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention;

[0032] Figure 2 is a schematic diagram of the curve of the magnetization flipping upward probability of the ferromagnetic material (array unit) in the temperature sensor based on the random flipping of ferromagnetic materials provided by the present invention varying with temperature;

[0033] Figure 3It is a schematic three-dimensional structure diagram of an array unit in a temperature sensor based on ferromagnetic random flipping provided by the present invention. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0035] The following combines Figure 1 to describe a temperature sensor based on ferromagnetic random flipping of the present invention, including:

[0036] A ferromagnetic body with perpendicular magnetic anisotropy;

[0037] When a large current is applied to the ferromagnetic body with perpendicular magnetic anisotropy, the magnetic moment will deflect under the action of spin orbit torque (SOT), and the direction of the magnetic moment will be pulled to the in-plane direction and be in a metastable state; when the current is removed, the magnetic moment will randomly jump back to the vertically upward or vertically downward state. Since the energy levels of the two states are equal at this time, the probabilities of returning to the two states are equal.

[0038] After applying a perpendicular magnetic field (external magnetic field or equivalent field) H z,eff to the ferromagnetic body, the magnetic moment is affected by the Zeeman energy (E z ), and the energy levels of the magnetic moment in the two states of magnetization upward and magnetization downward are no longer equal, and the probabilities of the magnetic moment returning from the metastable state to the two states are also not equal.

[0039] Through derivation, it can be known that the probability of magnetization flipping upward or the probability of magnetization flipping downward shows a sigmoid function curve with temperature variation, as Figure 2 shown. If the flipping probability of the magnetic moment at different ambient temperatures can be accurately measured, the ambient temperature can be inversely calculated according to this curve.

[0040] By measuring the random flipping of the ferromagnetic body under the current drive multiple times to obtain the experimental probability of the magnetic moment of the ferromagnetic body flipping upward or the magnetic moment flipping downward, and using the experimental probability to represent the classical probability, the ambient temperature can be obtained through data processing. The specific process is as Figure 1 shown.

[0041] In this embodiment, a perpendicular magnetic field is applied to a ferromagnetic material with perpendicular magnetic anisotropy. Under the action of the Zeeman energy, the energy levels of the magnetic moment in the upward magnetization state and the downward magnetization state are no longer equal, and the probabilities of the magnetic moment returning from the metastable state to the two states are also not equal. The kinetic process of the stochastic magnetization reversal of a single-domain ferromagnetic material induced by current is studied and analyzed, and a curve of the magnetization reversal probability varying with temperature is established. By measuring the magnetic moment reversal probability at different ambient temperatures multiple times, the ambient temperature is inversely calculated according to this curve, with high precision and high spatial resolution.

[0042] Based on the above embodiment, in this embodiment, the Zeeman energy E z received by the magnetic moment is calculated as follows:

[0043] E z = -μ0VM s (T)H z,eff (1)

[0044] where V is the volume of a single domain or grain, M s is the saturation magnetization, which varies with the ambient temperature T, μ0 is the vacuum permeability, and T is the ambient temperature.

[0045] Based on the above embodiment, in this embodiment, the calculation formula for the variation of the saturation magnetization with the ambient temperature is as follows:

[0046]

[0047] where M s (0) is the saturation magnetization at T = 0K, T c is the Curie temperature of the ferromagnetic material of the ferromagnetic body, and x is a preset constant, approximately equal to 1.5, which may vary slightly for different materials.

[0048] Based on the above embodiment, in this embodiment, the curve of the magnetic moment reversal probability varying with the ambient temperature of the ferromagnetic body is obtained through the following steps:

[0049] According to the Boltzmann statistics or the Arrhenius-Néel theorem, determine the probability calculation formulas for the magnetic moment returning from the metastable state to the upward magnetization state and the downward magnetization state;

[0050] According to the probability calculation formulas for the magnetic moment returning to the upward magnetization state and the downward magnetization state, obtain the curves of the upward magnetic moment reversal probability or the downward magnetic moment reversal probability varying with the ambient temperature.

[0051] Based on the above embodiment, in this embodiment, the probability P up of the magnetic moment returning from the metastable state to the upward magnetization state is calculated as follows:

[0052]

[0053] Among them, E b is the barrier height, and E z is the Zeeman energy received by the magnetic moment. k B is the Boltzmann constant, and T is the ambient temperature mentioned above.

[0054] Based on the above-mentioned embodiments, in this embodiment, the probability P that the magnetic moment returns from the metastable state to the magnetization-down state down is calculated as follows:

[0055]

[0056] Based on the above-mentioned embodiments, the calculation formula for the probability that the magnetic moment flips upward in this embodiment is:

[0057]

[0058] Based on the above-mentioned embodiments, as Figure 1 shown, in this embodiment, the ferromagnetic body includes a plurality of array units, and each array unit is a vertical film cross structure.

[0059] The size of each array unit can be 20nm × 20nm (the size can be reduced to less than 10nm). The array size can be adjusted according to actual needs, generally 1000 × 1000, and the entire temperature-sensitive part is on the micron scale. Figure 1 What is shown in

[0060] Based on the above-mentioned embodiments, as Figure 3 shown, in this embodiment, each array unit includes a heavy metal layer, a ferromagnetic layer, an MgO layer, and a metal protection layer arranged in sequence from bottom to top.

[0061] Based on the above-mentioned embodiments, in this embodiment, the heavy metal layer is Ta, the ferromagnetic layer is CoFeB, the MgO layer is MgO, and the metal protection layer is Ta.

[0062] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A temperature sensor based on random reversal of ferromagnetic material, characterized in that: include: Ferromagnets with perpendicular magnetic anisotropy; A vertical magnetic field is applied to the ferromagnet. When the current is applied to the ferromagnet and then withdrawn, the magnetic moment of the ferromagnet is affected by Zeeman energy, and the energy levels of the magnetic moment in the two states of magnetization upward and magnetization downward are not equal, and the probability of the magnetic moment returning to the two states from the metastable state is also not equal. The magnetic moment reversal probability of the ferromagnet is obtained by repeatedly measuring the random reversal of the ferromagnet driven by the current, and the magnetic moment reversal probability is substituted into a curve of the magnetic moment reversal probability changing with the ambient temperature of the ferromagnet to obtain the ambient temperature.

2. The temperature sensor based on random reversal of ferromagnetic material according to claim 1, characterized in that: The magnetic moment is subject to the Zeeman energy E z The calculation formula is as follows: E z =-μ0VM s (T)H z,eff Where V is the volume of a single magnetic domain or grain, M s is the saturation magnetization, which varies with the ambient temperature T, μ0 is the vacuum permeability, T is the ambient temperature, H z,eff is the vertical magnetic field.

3. The temperature sensor based on random reversal of ferromagnetic material according to claim 2, characterized in that: The calculation formula of the saturation magnetization intensity changing with the ambient temperature is as follows: Among them, M s (0) is the saturation magnetization when T = 0K, T c is the Curie temperature of the ferromagnetic material of the ferromagnet, and x is a preset constant.

4. The temperature sensor based on random reversal of ferromagnetic material according to claim 1, characterized in that: The curve of the magnetic moment reversal probability changing with the ambient temperature of the ferromagnetic body is obtained by the following steps: According to Boltzmann statistics or Arrhenius-Néel theorem, a probability calculation formula of the magnetic moment returning from the metastable state to the magnetization-up state and the magnetization-down state is determined; According to the probability calculation formula of the magnetic moment returning to the magnetization upward state and the magnetization downward state, a curve of the probability of the magnetic moment flipping upward or the probability of the magnetic moment flipping downward changing with the ambient temperature is obtained.

5. The temperature sensor based on random reversal of ferromagnetic material according to claim 4, characterized in that: The probability P of the magnetic moment returning from the metastable state to the magnetized upward state is up The calculation formula is as follows: Among them, E b is the barrier height, E z is the Zeeman energy on the magnetic moment, k B is the Boltzmann constant, and T is the ambient temperature.

6. The temperature sensor based on random reversal of ferromagnetic material according to claim 5, characterized in that: The probability P of the magnetic moment returning from the metastable state to the magnetized downward state is down The calculation formula is as follows:

7. The temperature sensor based on random reversal of ferromagnetic material according to claim 6, characterized in that: The calculation formula for the probability of the magnetic moment flipping upward is:

8. The temperature sensor based on random reversal of ferromagnetic material according to any one of claims 1 to 7, characterized in that: The ferromagnetic body includes a plurality of array units, and each array unit is a vertical film cross structure.

9. The temperature sensor based on random reversal of ferromagnetic material according to claim 8, characterized in that: Each array unit includes a heavy metal layer, a ferromagnetic layer, a MgO layer and a metal protection layer arranged in sequence from bottom to top.

10. The temperature sensor based on random reversal of ferromagnetic material according to claim 9, characterized in that: The heavy metal layer is Ta, the ferromagnetic layer is CoFeB, the MgO layer is MgO, and the metal protection layer is Ta.

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