A magnetic nanowire thermal pulse excitation device and measurement method

Abstract

The application discloses a magnetic nano-wire thermal pulse excitation device and a measuring method. The device utilizes the property of the magnetic material itself, i.e. the characteristic that the magnetic material can absorb and release heat during the process of applying a magnetic field, to generate a temperature gradient and a pulse. The scheme does not generate secondary effects and does not need complex and expensive equipment. In addition, the application also utilizes the Seebeck effect to measure the size of the thermal pulse, and the operation is simple.

Description

Technical Field

[0001] This invention relates to a thermal pulse excitation device and measurement method on magnetic nanowires, belonging to the field of measurement and sensing technology. Background Technology

[0002] The combination of spintronics and thermoelectricity in magnetic nanostructures can be used to develop future spin-based devices and apply them to sensing and magnetic data storage. Currently, the main methods for obtaining large temperature gradients or heat flows are resistance heating and laser heating. Resistance heating requires an electric current and generates a magnetic field, which affects the magnetic moment of the magnetic thin film and thus the measurement results. Laser heating is another method, as it can generate large thermal pulses, and related patents have been filed. However, lasers are hot and require expensive equipment, posing a certain threat. Therefore, this application proposes a method that utilizes the inherent properties of the material itself, specifically the ability of magnetocaloric materials to absorb and release heat during the application of a magnetic field, to generate temperature gradients and pulses. This approach avoids secondary effects and does not require complex or expensive methods. Furthermore, this application also utilizes the Seebeck effect to measure the magnitude of the thermal pulse. Summary of the Invention

[0003] The purpose of this invention is to provide a thermal pulse excitation device and measurement method for magnetic nanowires. The excitation device comprises the following components: magnetic nanowires made of [FM / Cu / FM]. n The device consists of a multilayer film with positive and negative electrodes at both ends. The positive electrode is coated with either a normal or anomalous magnetocaloric material, while the corresponding negative electrode is coated with either an anomalous or normal magnetocaloric material. In other words, the positive electrode has a normal magnetocaloric material, and the negative electrode has an anomalous magnetocaloric material, while the positive electrode has an anomalous magnetocaloric material, and the negative electrode has a normal magnetocaloric material. Both the magnetic nanowires and the electrodes are located on a Si substrate. The measurement principle and method are as follows: A pulsed magnetic field is applied to the magnetic nanowires. Due to the magnetocaloric effect, the normal magnetocaloric material releases heat, and the anomalous magnetocaloric material absorbs heat, thus forming a thermal pulse along the nanowire direction. Due to the Seebeck effect, a thermal voltage is generated at the positive and negative electrodes. The magnitude of the thermal pulse, ΔT, is calculated using the formula ΔT = ΔV / S, where S is the Seebeck coefficient of the magnetic nanowire and ΔV is the thermal voltage.

[0004] Specifically, in step (1), the magnetic nanowire [FM / Cu / FM]n, FM is one or more of Co, CoFeB, CoFe and CoNi ferromagnetic films, n is greater than or equal to 2, the width of the magnetic nanowire is 50nm~1000nm, the length is 1μm~10μm, the material of the positive and negative electrodes is one or more of Pt, Cu, CuN and Au, the normal magnetocaloric material and the anomalous magnetocaloric material have a large magnetocaloric effect, the magnetocaloric material is one or more of LaFeSi system, perovskite manganese oxide or multi-element alloy, the normal magnetocaloric material and the anomalous magnetocaloric material have the same operating temperature, and the thickness is 10 μm-2 mm.

[0005] Specifically, the magnetic field magnitude in step (1) is 0.1 T-5 T, the pulse width is 0.1 s-2 s, the interval is 0.5 s-2 s, the direction of the applied magnetic field is perpendicular to the direction of the nanowire, and the voltage measuring instrument is a nanovoltage meter.

[0006] Compared with current methods that use resistance and laser to generate thermal pulses, this invention proposes to utilize the inherent properties of materials, namely the ability of magnetocaloric materials to absorb and release heat during the application of a magnetic field, to generate temperature gradients and pulses. This approach does not produce secondary effects, does not require complex and expensive methods, and the method for measuring thermal pulses is also relatively simple. Attached Figure Description

[0007] Figure 1 A schematic diagram of the device for measuring thermal pulse excitation on magnetic nanowires. Detailed Implementation

[0008] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0009] Example 1: Thermal pulse excitation device and measurement method for magnetic nanowires [Co / Cu / Co] 80 Taking the thermal pulse as an example, the magnetic nanowire has a width of 200 nm and a length of 1.5 μm, located on a Si substrate. The positive and negative electrodes are Au electrodes directly connected to the magnetic nanowire. A 10 μm thick layer of normal magnetocaloric material LaFeSi is deposited on top of the positive electrode, with a magnetic entropy change of -4.1 J∙ / kg∙K (2T) and a Curie temperature of 300.5 K. A 10 μm thick layer of anomalous magnetocaloric material Pr is deposited on the negative electrode. 0.6 Sr 0.4 MnO3 has a magnetic entropy change of +2.8 J∙ / kg∙K (2T) and a Curie temperature of 301.3 K. Both materials exhibit large magnetic entropy changes. Specific devices are shown below. Figure 1As shown; at 301 K, the magnetic nanowire device was placed in a magnetic field, and a pulsed magnetic field with a magnitude of 0.5 T and a duration of 0.5 s was applied, perpendicular to the nanowire direction. The instantaneous voltage change was measured using a nanovoltmeter, and the maximum voltage value was ΔV = 18.2 uV. From the literature, we know that [Co / Cu / Co]... n The Seebeck coefficient S = 15.5 uV / K, so the magnetic field excited a temperature gradient of up to ΔT = 1.17 K on the nanowire, i.e., a thermal pulse. Further increasing the magnetic field, when the magnetic field strength is 2T, a thermal pulse of ΔV = 36.3 uV and ΔT = 2.3 K is generated. When the magnetic field is increased to 5T, the thermal voltage is ΔV = 45.7 uV and the temperature gradient is ΔT = 2.95 K. As the magnetic field increases, the temperature gradient does not increase nonlinearly. This is because the magnetic entropy change of the magnetocaloric material is also nonlinear with the magnetic field, and it is also related to the rate at which the magnetic field is applied.

[0010] Example 2: Excitation and Measurement of Magnetic Nanowires [CoFe / Cu / CoFe] 60 Taking the thermal pulse as an example, the magnetic nanowire has a width of 300 nm and a length of 2.5 μm, located on a Si substrate. The positive and negative electrodes are Pt electrodes directly connected to the magnetic nanowire. A layer of normal magnetocaloric material LaFeSi with a thickness of 5 μm is deposited on top of the positive electrode, with a magnetic entropy change of -4.1 J∙ / kg∙K(2T) and a Curie temperature of 300.5 K. A layer of anomalous magnetocaloric material Pr is deposited on the negative electrode. 0.6 Sr 0.4 MnO3 has a magnetic entropy change of +2.8 J∙ / kg∙K (2T) and a Curie temperature of 301.3 K. Both materials exhibit large magnetic entropy changes. At 301 K, a magnetic nanowire device was placed in a magnetic field, and a pulsed magnetic field with a magnitude of 0.5 T and a duration of 0.5 s was applied perpendicular to the nanowire direction. The instantaneous voltage change was measured using a nanovoltmeter, with a maximum voltage value of ΔV = 15.2 uV. Based on the literature, [CoFe / Cu / CoFe]... n The Seebeck coefficient S = 14.0 uV / K, so the magnetic field excited a temperature gradient of up to ΔT = 1.08 K on the nanowire, i.e., a thermal pulse. Further increasing the magnetic field, when the magnetic field strength is 2 T, a thermal pulse of ΔV = 33.5 uV and ΔT = 2.4 K is generated. When the magnetic field is increased to 5 T, the thermal voltage is ΔV = 43.6 uV and the temperature gradient is ΔT = 3.11 K.

Claims

1. A thermal pulse excitation device on magnetic nanowires, characterized in that... The excitation device consists of the following components: a magnetic nanowire composed of a [FM / Cu / FM]n multilayer film, positive and negative electrodes at both ends, a layer of normal or anomalous magnetocaloric material on the positive electrode, and a layer of anomalous or normal magnetocaloric material on the corresponding negative electrode. That is, the positive electrode is coated with normal magnetocaloric material and the negative electrode with anomalous magnetocaloric material, while the positive electrode is coated with anomalous magnetocaloric material and the negative electrode with normal magnetocaloric material. Both the magnetic nanowire and the electrodes are located on a Si substrate. The measurement principle and method are as follows: a pulsed magnetic field is applied to the magnetic nanowire. Due to the magnetocaloric effect, the normal magnetocaloric material releases heat and the anomalous magnetocaloric material absorbs heat, thereby forming a thermal pulse along the direction of the nanowire. Due to the Seebeck effect, a thermal voltage is generated at the positive and negative electrodes. According to the formula ΔT=ΔV / S, where S is the Seebeck coefficient of the magnetic nanowire and ΔV is the thermal voltage, the magnitude of the thermal pulse ΔT is calculated. In the aforementioned magnetic nanowire [FM / Cu / FM]n, FM is one or more of Co, CoFeB, CoFe, and CoNi ferromagnetic films, and n is greater than or equal to 2. The width of the magnetic nanowire is 50nm~1000nm, and the length is 1μm~10μm. The positive and negative electrodes are made of one or more of Pt, Cu, CuN, and Au. The normal magnetocaloric material and the anomalous magnetocaloric material have a large magnetocaloric effect. The magnetocaloric material is one or more of 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. The magnetic field strength is 0.1T-5T, the pulse width is 0.1s-2s, the interval is 0.5s-2s, the applied magnetic field direction is perpendicular to the nanowire direction, and the voltage measuring instrument is a nanovoltmeter.

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