A device for exciting and measuring thermomagnetic voltage

Abstract

This invention discloses a magnetocaloric voltage excitation device and measurement method, comprising the following steps: In order to obtain a large temperature gradient, a magnetocaloric material with an anomalous magnetocaloric effect is deposited on the lower surface of a spin valve, and a magnetocaloric material with a normal magnetocaloric effect is deposited on the upper surface. By applying a pulsed magnetic field, positive and negative temperature gradients are formed on the upper and lower surfaces of the spin valve, thereby generating an AC thermoelectric voltage pulse. This technology is the first to combine magnetocaloric material with spintronic devices. The sample structure is simple and the measurement is convenient, which is conducive to promoting the application of spintronic devices and the development of spin thermoelectronics.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials and measurement methods, specifically to a magnetocaloric voltage excitation device and measurement method. Background Technology

[0002] Recent discoveries in nanodevices have shown that pure spin currents can be generated through thermal gradients, advancing the emerging field of spin thermoelectronics. However, a deep understanding of thermoelectric voltage signals in nanoscale magnetic structures is still needed.

[0003] Currently, thermal voltage can be generated by heating a resistive thin film or by laser heating to create a temperature gradient. For resistive heating, a heating film needs to be deposited and a heating current needs to be applied to generate a temperature gradient, but the heating process will bring an additional magnetic field, which will affect the measurement results. Laser heating will generate thermionic electrons, which will affect the magnetic moment of the magnetic film and reduce the accuracy of thermal voltage measurement. At the same time, laser equipment is not easy to move, which will cause inconvenience to measurement and calibration.

[0004] This invention provides a novel method for generating the thermal voltage of magnetic multilayer spin valves. At the same time, this temperature gradient excitation technique can be used for thermally assisted magnetic reversal, which has an important role in promoting fundamental research such as spin thermoelectronics. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a magnetothermal voltage excitation device and measurement method.

[0006] The specific preparation includes the following steps:

[0007] A magnetocaloric voltage excitation device and method are disclosed. The excitation device comprises, from bottom to top, a substrate, an anomalous magnetocaloric material thin film, a negative electrode, a nanomagnetic multilayer film spin valve, a positive electrode, and a normal magnetocaloric material thin film. The measurement principle and steps are as follows: the excitation device is placed in a two-dimensional magnetic field, the magnetoresistance curve is measured, the required magnetic field strength is determined based on the magnetoresistance curve, a current pulse is generated through a current source, and a pulsed magnetic field is excited in the two-dimensional magnetic field. Therefore, when there is a magnetic field pulse, due to the magnetocaloric effect, the normal magnetocaloric material in the device releases heat, and the anomalous magnetocaloric material absorbs heat, thereby forming a positive temperature gradient on the upper and lower surfaces of the device. At the same time, due to the Seebeck effect, a positive thermal voltage is generated across the spin valve. When there is no magnetic field, the normal magnetocaloric material absorbs heat, and the anomalous magnetocaloric material releases heat, thereby forming a reverse temperature gradient on the upper and lower surfaces of the spin valve, and a negative voltage is generated across the spin valve. The thermal voltage pulse is measured using a high-frequency sampling oscilloscope.

[0008] Specifically, the nanomagnetic multilayer spin valve described in step (1) is composed of a magnetic (FM) / non-magnetic (NFM) multilayer film and a connecting layer. The multilayer film [FM / NFM]n is characterized by n being 6~80, and the GMR of the spin valve being 5%-60%. The positive and negative electrodes are one or more of Pt, Au, Cu, and CuN. The normal magnetocaloric material and the anomalous magnetocaloric material have a large magnetocaloric effect. The magnetocaloric material is one or more of the LaFeSi system, perovskite manganese oxide, or multi-element alloy. The normal magnetocaloric material and the anomalous magnetocaloric material have the same operating temperature and a thickness of 10um-2mm.

[0009] Specifically, the magnetic field in step (1) is 0.1 T-2 T, the pulse width is 0.1 s-1 s, the interval is 0.5 s-2 s, and the direction of the applied magnetic field is the direction of the easy magnetization axis of the magnetic multilayer film junction, so that the magnetic moments of the magnetic layer are arranged in antiparallel, that is, in a high resistance state.

[0010] Compared with the prior art, the implementation effects of the present invention are as follows:

[0011] This invention utilizes the magnetocaloric effect principle of magnetocaloric materials to create a temperature gradient across a nano-magnetic multilayer spin valve by applying a magnetic field pulse. Because it uses both normal and anomalous magnetocaloric materials, it can generate a large temperature gradient and AC voltage. This technology results in a simple sample structure and avoids the influence of other factors that occur with resistance heating and laser heating. Attached Figure Description

[0012] Figure 1 A schematic diagram of the device for pulsed thermal voltage excitation in a nanomagnetic multilayer film spin valve.

[0013] Figure 2 The magnetic field pulse and the two ends of the spin valve generate an alternating thermal voltage. Detailed Implementation

[0014] Example 1

[0015] A magnetocaloric voltage excitation device and measurement method, comprising the following steps:

[0016] 1. First, a 100 μm thick magnetic material film with anomalous magnetocaloric effect is magnetron sputtered on a Si substrate. Magnetic spin valves and positive and negative electrodes Pt(20) / [Co(10) / Cu(4)] are then fabricated on the anomalous magnetocaloric material by magnetron sputtering and photolithography. 20Co(10)Pt(20), where the numbers in parentheses represent the thickness (nm). Pt serves as the positive and negative electrodes. Finally, a magnetocaloric material with normal magnetocaloric effect is prepared on top of the positive electrode by magnetron sputtering, with a thickness of 200 μm. Here, the normal magnetocaloric material is LaFeSi magnetocaloric material, and the anomalous magnetocaloric material is perovskite manganese oxide La. 1 / 3 Ca 2 / 3 MnO3 magnetocaloric materials, both of which operate at temperatures around 294 K, have the following specific structures: Figure 1 As shown;

[0017] 2. Place the device in a two-dimensional magnetic field and measure the magnetoresistance curve (MR) of the spin valve at 294 K. Based on the measured MR curve, determine the magnitude and direction of the magnetic field required when the magnetic moments of the two magnetic layers are arranged in antiparallel order.

[0018] 3. At 294K, a continuous pulsed current is generated using a current source, thereby producing a pulsed magnetic field with a magnitude of 1 T, directed along the easy magnetization axis, a pulse width of 5 ms, and a pulse interval of 50 ms.

[0019] 4. The AC thermal voltage pulse generated across the spin valve was measured using a sampling oscilloscope; the pulse size was 5.1 uV. Figure 2 As shown.

[0020] Example 2

[0021] A magnetocaloric voltage excitation device and measurement method, comprising the following steps:

[0022] 1. First, a 500 μm thick magnetic material film with anomalous magnetocaloric effect is magnetron sputtered on a Si substrate. Magnetic spin valves and positive and negative electrodes CuN(15) / [Ni] are then fabricated on the anomalous magnetocaloric material by magnetron sputtering and photolithography. 80 Fe 20 (4) / Cu(2)]7Ni 80 Fe 20 (2) CuN(15), where the numbers represent the thickness (nm). CuN is used as the positive and negative electrodes. Finally, a magnetocaloric material with normal magnetocaloric effect is prepared on top of the positive electrode by magnetron sputtering, with a thickness of 500 μm. Here, the normal magnetocaloric material is a binary alloy magnetocaloric material, and the anomalous magnetocaloric material is perovskite manganese oxide La. 1 / 3 Ca 2 / 3 MnO3 magnetocaloric material, both of which operate at temperatures around 305 K, specific structure;

[0023] 2. Place the device in a two-dimensional magnetic field and measure the magnetoresistance curve (MR) of the spin valve at 305 K. Based on the measured MR curve, determine the magnitude and direction of the magnetic field required when the magnetic moments of the two magnetic layers are arranged in antiparallel order.

[0024] 3. At 305K, a continuous pulsed current is generated using a current source to produce a pulsed magnetic field in a two-dimensional magnetic field. The magnitude of the pulsed magnetic field is 0.7 T, the direction is along the easy magnetization axis, the pulse width is 15 ms, and the pulse interval is 100 ms.

[0025] 4. The AC thermal voltage pulse generated across the spin valve was measured using a sampling oscilloscope, and the magnitude was 3.4 uV.

Claims

1. A method for measuring thermoelectric voltage based on a magnetocaloric voltage excitation device, characterized in that, The excitation device consists of, from bottom to top, a substrate, an anomalous magnetocaloric material thin film, a negative electrode, a nanomagnetic multilayer film spin valve, a positive electrode, and a normal magnetocaloric material thin film; The measurement principle and steps are as follows: the excitation device is placed in a two-dimensional magnetic field, the magnetoresistive curve is measured, the required magnetic field size is determined based on the magnetoresistive curve, a current pulse is generated through a current source, and a pulsed magnetic field is excited in the two-dimensional magnetic field. Therefore, when there is a magnetic field pulse, due to the magnetocaloric effect, the normal magnetocaloric material in the device releases heat, and the anomalous magnetocaloric material absorbs heat, thereby forming a positive temperature gradient on the upper and lower surfaces of the device. At the same time, due to the Seebeck effect, a positive thermal voltage is generated across the spin valve. When the magnetic field is removed, the normal magnetocaloric material absorbs heat, and the anomalous magnetocaloric material releases heat, thereby forming a reverse temperature gradient on the upper and lower surfaces of the spin valve, and a negative voltage is generated across the spin valve. The thermal voltage pulse is measured by a high-frequency sampling oscilloscope.

2. The method according to claim 1, characterized in that, The nanomagnetic multilayer spin valve is composed of a magnetic (FM) / non-magnetic (NFM) multilayer film [FM / NFM]n and a connecting layer. The multilayer film [FM / NFM]n is characterized in that n is 6~80; the positive and negative electrodes are one or more of Pt, Au, Cu and CuN; the normal magnetocaloric material and the anomalous magnetocaloric material have a magnetocaloric effect, the normal magnetocaloric material is a LaFeSi system magnetocaloric material, and the anomalous magnetocaloric material is perovskite manganese oxide. The normal magnetocaloric material and the anomalous magnetocaloric material have the same operating temperature and a thickness of 10um-2mm.

3. The method according to claim 1, characterized in that, The magnetic field strength is 0.1T-2T, the pulse width is 0.1s-1s, the interval is 0.5s-2s, and the direction of the applied magnetic field is the easy magnetization axis of the magnetic multilayer film junction, so that the magnetic moments of the magnetic layer are arranged in antiparallel, that is, in a high resistance state.

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