A Method for Exciting and Measuring Alternating Current Thermal Voltage in a Magnetic Tunnel Junction

Abstract

The present invention discloses a method for exciting and measuring the alternating current thermal voltage in a magnetic tunnel junction, comprising the following steps: In order to obtain a large temperature gradient, a magnetic thermal material with an anomalous magnetocaloric effect is plated on the lower surface of the tunnel junction, and a magnetic thermal material with a normal magnetocaloric effect is plated 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 magnetic tunnel junction, thereby generating an alternating current thermal voltage pulse; This technology combines magnetic thermal materials with spintronic devices for the first time. The sample structure is simple, and at the same time, it does not bring the influence of other factors like resistance heating and laser heating.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials and measurement methods, and specifically relates to a method for exciting and measuring alternating current thermal voltage in a magnetic tunnel junction. Background Art

[0002] In recent years, due to the rapid development of spintronics, the voltage generated by heat flow has received attention. As important sensor devices and storage devices, magnetic tunnel junctions provide new ideas for thermoelectric conversion due to the discovery of the spin Seebeck effect. Currently, heat flow is usually generated by resistive thin film heating or laser heating. For resistive heating, since a heating thin film needs to be deposited and a heating current needs to be applied to generate a temperature gradient, however, the heating process will bring an additional magnetic field, affecting the measurement accuracy. And through laser heating, hot electrons will be generated, and the generated hot electrons will also affect the magnetic moment of the magnetic thin film, reducing the measurement accuracy of the thermal voltage. At the same time, laser equipment is not easy to move, bringing inconvenience to measurement and calibration.

[0003] This application proposes to utilize the magnetothermal effects of two types of magnetic thermal materials, normal and anomalous, to generate a large temperature gradient. Since only one magnetic field is required, and measuring the magnetoresistance of a magnetic tunnel junction itself requires a magnetic field, the entire process will not be interfered by other effects, and the measurement process becomes simpler. The present invention provides a brand-new method for generating the thermal voltage of a magnetic tunnel junction; in addition, since the magnetic thermal material can release and absorb heat during the application and removal of the magnetic field, thus generating temperature gradients in both positive and negative directions, and thus obtaining positive and negative voltages, it is more convenient to study the spin Seebeck effect. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for exciting and measuring alternating current thermal voltage in a magnetic tunnel junction.

[0005] The specific preparation includes the following steps:

[0006] A method for exciting and measuring alternating current thermal voltage in a magnetic tunnel junction includes the following steps. In order to obtain a large temperature gradient, a magnetic thermal material with an anomalous magnetothermal effect is deposited on the lower surface of the tunnel junction, and a magnetic thermal material with a normal magnetothermal effect is deposited on the upper surface. By applying a pulsed magnetic field, due to the magnetothermal effect, the normal magnetic thermal material releases heat, and the anomalous magnetic thermal material absorbs heat, thereby forming a positive temperature gradient on the upper and lower surfaces of the magnetic tunnel junction. At the same time, due to the Seebeck effect, a positive thermal voltage is generated at both ends of the magnetic tunnel junction. When the magnetic field is removed, the normal magnetic thermal material absorbs heat, and the anomalous magnetic thermal material absorbs heat, thereby forming a reverse temperature gradient on the upper and lower surfaces of the magnetic tunnel junction, and a negative voltage is generated at both ends of the magnetic tunnel junction. Therefore, by applying and removing magnetic field pulses to the magnetic tunnel junction, an alternating current thermal voltage pulse can be generated at both ends of the magnetic tunnel junction.

[0007] Specifically, the main magnetic sandwich structure of the magnetic tunnel junction in step (1) and other magnetic auxiliary layers. The magnetic sandwich structure includes two ferromagnetic layers and an insulating layer. The insulating layer is one of MgAl2O4, MgO or Al2O3. The other magnetic auxiliary layers include an artificial antiferromagnetic layer and a metal electrode layer. The size of the magnetic tunnel junction is 100 nm to 1 μm.

[0008] Specifically, the magnetic field in step (1) has a magnitude of 0.01 T - 0.2 T, a pulse width of 5 ms - 1 s, an interval of 0.05 s - 1 s, and the applied magnetic field direction is along the easy magnetization axis direction of the magnetic tunnel junction, so that the magnetic moments of the two magnetic layers are arranged in an antiparallel manner.

[0009] Compared with the prior art, the implementation effects of the present invention are as follows:

[0010] The present invention utilizes the magnetocaloric effect principle of magnetocaloric materials to form a temperature gradient at both ends of the magnetic tunnel junction by applying a magnetic field pulse. Since both normal and anomalous magnetocaloric materials are used, a large temperature gradient and an alternating voltage can be generated. The structure of this technology sample is simple and easy to measure, and at the same time, it does not bring the influence of other factors like resistance heating and laser heating. Description of the Drawings

[0011] Figure 1 Schematic diagram of the device for exciting pulsed alternating thermal voltage in the magnetic tunnel junction.

[0012] Figure 2 Magnetic field pulse and alternating thermal voltage excited at both ends of the magnetic tunnel junction. Detailed Embodiments

[0013] Example 1

[0014] A method for exciting and measuring alternating thermal voltage in a magnetic tunnel junction includes the following steps:

[0015] 1. First, magnetron sputter a magnetic material thin film with an anomalous magnetocaloric effect and a thickness of 0.5 mm on a substrate Si. Prepare a magnetic tunnel junction on the anomalous magnetocaloric material through magnetron sputtering and photolithography, with a size of 200 nm × 500 nm. Finally, magnetron sputter a magnetocaloric material with a normal magnetocaloric effect above the magnetic tunnel junction, with a thickness of 1 mm. 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 material. The working temperatures of both are around 300 K. The specific structure is as Figure 1 shown;

[0016] 2. Place the magnetic tunnel junction in a two-dimensional magnetic field. Determine the direction of the easy magnetization axis of the magnetic tunnel junction according to the magnetoresistance curve (MR) measured at 300 K of the magnetic tunnel junction. Determine the magnitude and direction of the magnetic field required for the antiparallel alignment of the magnetic moments of the two magnetic layers according to the measured MR curve.

[0017] 3. Use a current source to generate a continuous pulsed current to generate a pulsed magnetic field in the two-dimensional magnetic field. The magnitude is 0.1 T and the direction is the direction of the easy magnetization axis. The magnetic field pulse width is 5 ms and the pulse interval is 50 ms.

[0018] 4. Use a sampling oscilloscope to measure and obtain an AC thermal voltage pulse generated at both ends of the magnetic tunnel junction, with a magnitude of 212 uV, as Figure 2 shown.

[0019] Example 2

[0020] 1. First, magnetron sputter a magnetic material thin film with an anomalous magnetocaloric effect and a thickness of 1 mm on a substrate Si. Prepare a magnetic tunnel junction on the anomalous magnetocaloric material through magnetron sputtering and photolithography, with a size of 500 nm × 1000 nm. Finally, magnetron sputter a magnetocaloric material with a normal magnetocaloric effect above the magnetic tunnel junction, with a thickness of 0.5 mm. Here, the normal magnetocaloric material is LaFeSi magnetocaloric material, and the anomalous magnetocaloric material is a perovskite manganese oxide binary alloy magnetocaloric material. The working temperatures of both are around 290 K.

[0021] 2. Place the magnetic tunnel junction in a two-dimensional magnetic field. Obtain the direction of the easy magnetization axis of the magnetic tunnel junction according to the magnetoresistance curve (MR) measured at 290 K of the magnetic tunnel junction. Determine the magnitude and direction of the magnetic field required for the antiparallel alignment of the magnetic moments of the two magnetic layers according to the measured MR curve.

[0022] 3. Use a current source to generate a continuous pulsed current to generate a pulsed magnetic field in the two-dimensional magnetic field. The magnitude is 0.12 T and the direction is the direction of the easy magnetization axis. The magnetic field pulse width is 7 ms and the pulse interval is 100 ms.

[0023] 4. Use a sampling oscilloscope to measure and obtain an AC thermal voltage pulse generated at both ends of the magnetic tunnel junction, with a magnitude of 250 uV.

Claims

1. A method for exciting and measuring the alternating current thermal voltage in a magnetic tunnel junction, characterized in that The steps are as follows: First, a magnetic material thin film with an anomalous magnetocaloric effect is magnetron sputtered on a substrate Si. A magnetic tunnel junction is fabricated on the anomalous magnetocaloric material through magnetron sputtering and photolithography. The magnetic tunnel junction includes a magnetic sandwich structure and a magnetic auxiliary layer. The magnetic sandwich structure contains two ferromagnetic layers and an insulating layer. Finally, a magnetocaloric material with a normal magnetocaloric effect is magnetron sputtered above the magnetic tunnel junction. The normal magnetocaloric material is a LaFeSi magnetocaloric material, and the anomalous magnetocaloric material is La 1 / 3 Ca 2 / 3 MnO3 magnetocaloric material; The magnetic tunnel junction is placed in a two-dimensional magnetic field. According to the measured magnetoresistance curve of the magnetic tunnel junction at the working temperature, the direction of the easy magnetization axis of the magnetic tunnel junction is determined. According to the measured magnetoresistance curve, the magnitude and direction of the magnetic field required for the antiparallel alignment of the magnetic moments of the two ferromagnetic layers are determined; A continuous pulsed current is generated by a current source to generate a pulsed magnetic field in the two-dimensional magnetic field, and the direction is the direction of the easy magnetization axis; By applying the pulsed magnetic field, the normal magnetocaloric material releases heat, and the anomalous magnetocaloric material absorbs heat, forming a positive temperature gradient on the upper and lower surfaces of the magnetic tunnel junction, and a positive thermal voltage is generated at both ends of the magnetic tunnel junction. When the magnetic field is removed, the normal magnetocaloric material absorbs heat, and the anomalous magnetocaloric material releases heat, forming a reverse temperature gradient on the upper and lower surfaces of the magnetic tunnel junction, and a negative voltage is generated at both ends of the magnetic tunnel junction. By applying and removing the magnetic field pulse to the magnetic tunnel junction, an alternating thermal voltage pulse generated at both ends of the magnetic tunnel junction is measured using a sampling oscilloscope.

2. The method according to claim 1, wherein The insulating layer is one of MgAl2O4, MgO or Al2O3. The magnetic auxiliary layer includes an artificial antiferromagnetic layer and a metal electrode layer. The size of the magnetic tunnel junction is 100 nm to 1 μm.

3. The method according to claim 1, wherein The normal magnetocaloric material and the inverse magnetocaloric material have a large magnetocaloric effect. The normal magnetocaloric material and the inverse magnetocaloric material have the same working temperature and a thickness of 1 μm to 1 mm.

4. The method according to claim 1, wherein The magnitude of the pulsed magnetic field is 0.01 T to 0.2 T, the pulse width is 5 ms to 1 s, and the interval is 0.05 s to 1 s.

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