High-precision multifunctional open type ferromagnetic resonance test platform

Abstract

The invention discloses development of a coplanar waveguide ferromagnetic resonance measurement and multifunctional magnetoelectric measurement platform based on coil modulation microwaves of a phase-locked amplifier, and mainly relates to the technical field of ferromagnetic resonance testing. The measurement precision of ferromagnetic resonance is improved through a series of settings, the sample table and the connecting column are made of high-heat-conductivity red copper and have good heat conduction, high-precision temperature control is provided through the compressor, the heating resistor and the temperature sensor, the precision can reach 0.005 K, and noise caused by unstable temperature is reduced; the high vacuum environment prevents the sample from being oxidized, provides a stable test environment, and provides a basis for low-temperature measurement. The coplanar waveguide designed by the invention has good impedance matching, so that a sample can be fully acted by a microwave alternating magnetic field.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of ferromagnetic resonance testing, and in particular to development of a platform for coplanar waveguide ferromagnetic resonance measurement and multifunctional magnetoelectric measurement based on a phase-locked amplifier coil modulated microwave. BACKGROUND

[0002] Ferromagnetic resonance refers to the phenomenon that when an iron magnetic substance is subjected to a certain external constant magnetic field and a certain frequency microwave magnetic field bias, strong absorption resonance is generated when a resonance condition is met. Under the external magnetic field, the magnetic moment of the iron magnetic substance is gradually flipped to the external magnetic field, and the flipping process is described by the LLG (Landau-Lifshitz-Gilbert) equation, that is, the magnetization vector precesses around the external field. However, due to the existence of damping, the precession consumes energy, so that the magnetization gradually approaches the direction of the external magnetic field. The precession frequency at a certain temperature is related to the direction of the external field, and if an alternating magnetic field of the same frequency is applied in the damping direction, the magnetic moment will precess ceaselessly, which is the ferromagnetic resonance. And the alternating magnetic field can be provided by the microwave in a specific direction.

[0003] The essence of ferromagnetic resonance testing is to detect the loss of microwave energy when the iron magnetic material resonates under the external magnetic field and the microwave magnetic field. By detecting the loss of microwave power in the form of fixed field sweeping or fixed frequency sweeping, the resonance peak, damping factor, and effective field of vertical anisotropy can be obtained. Based on the propagation principle of the microwave, the ferromagnetic resonance measurement is divided into closed and open types. The closed type is generally carried out in a resonant cavity with several fixed frequency microwave fields, and cannot be used for wideband ferromagnetic resonance measurement. The open type takes the coplanar waveguide as an example, which can realize wideband ferromagnetic resonance. The coplanar waveguide used in the laboratory is generally prepared by a photolithography and sputtering system, and the preparation cost is too high, and the preparation process is inefficient and difficult to mass-produce. The ferromagnetic resonance testing equipment purchased on the market usually has only single function and can only be used for ferromagnetic resonance testing. Under this background, whether it is the laboratory ferromagnetic resonance testing platform preparation or the direct purchase of ferromagnetic resonance testing equipment on the market, the cost is too high. SUMMARY

[0004] The purpose of the present application is to overcome the above problems, and provide a coplanar waveguide structure design which can be prepared at low cost by a conventional printed circuit board manufacturer on the market, and high-precision ferromagnetic resonance testing is realized through a self-designed sample table and a coil.

[0005] The coplanar waveguide ferromagnetic resonance testing platform comprises a coplanar waveguide plate, a sample table, a circuit board, a coil and an insulating sleeve.

[0006] The coplanar waveguide plate is made of Rogers high-frequency plate material.

[0007] The circuit board substrate is FR4, and the internal embedded copper wire is electrically connected.

[0008] The sample table and the connecting column are made of high-thermal-conductivity material for conducting the cooling capacity of the compressor and precisely controlling the temperature.

[0009] The circuit board comprises a sample table front panel and a sample table back panel.

[0010] The sample table has a three-section structure, which is a rectangular structure, a disc structure and a cylindrical structure.

[0011] The coplanar waveguide board substrate is made of Rogers high-frequency board material, and the surface is covered with copper to form a coplanar waveguide structure; 20 gold electrodes are arranged on the edge for sample electric transport measurement, and the gold electrodes are fixed on the front surface of the rectangular structure of the sample table through screws, and the center of the gold electrodes corresponds to the center of the magnet.

[0012] The sample table front panel is fixed on the front surface of the rectangular structure of the sample table through screws, and 14 rectangular electrodes are arranged on the sample table front panel for electrical contact with the waveguide board.

[0013] The sample table back panel is fixed on the back surface of the rectangular structure of the sample table through screws, and two pairs of solder pads are arranged on the sample table back panel for connecting temperature sensors and heating resistors, one pair of rectangular electrodes is arranged for welding spring needles to supply power to the coil, and the rectangular structure of the sample table is electrically connected to the front panel through the rectangular through hole in the middle of the rectangular structure.

[0014] The coil is fixed in the alumina shell, and the coil is fixed in the groove of the rectangular structure of the sample table and fixed through the screw holes at both ends of the alumina shell.

[0015] The disc structure of the sample table is provided with a rectangular through slot for supplying power to the sample table back panel.

[0016] The cylindrical structure of the sample table is used for increasing the thermal contact with the connecting column.

[0017] The connecting column is used for heat conduction of the compressor, and is provided with a cylindrical groove for butt joint with the cylindrical structure of the sample table.

[0018] After the above components are assembled, the connecting column through hole is connected with the compressor, the entire assembly is placed in a vacuum cavity, and the vacuum cavity is sealed by butt joint with the compressor vacuum cavity through an aluminum shell, and the vacuum cavity is vacuum pumped by a mechanical pump; the high-frequency line is connected between the inner and outer packaging plates through a high-frequency connector for microwave conduction; and the sample table back panel is connected through a 26-core wire connector for electrical conduction.

[0019] The high-temperature in-situ magnetic property testing device further comprises a matching external electromagnet, a microwave source, a lock-in amplifier, a high-frequency diode and the like.

[0020] The application also comprises a test method for the ferromagnetic resonance spin pumping electrical test. The sample is electrically connected with the waveguide plate, the waveguide plate is electrically connected with the sample stage, and finally connected to the nanovolt table to measure the spin pumping voltage.

[0021] The wave source is connected to the packaging plate and the coplanar waveguide for microwave input, the output end is connected to a high-frequency diode to convert the microwave power signal into a voltage signal output to the lock-in amplifier, and then the output end of the lock-in amplifier provides an oscillation voltage to the coil, and the program controls the electromagnet to scan the field; when the ferromagnetic resonance starts, the sample resonant absorption is carried out with the oscillation voltage of the same frequency, and the signal is detected by the lock-in amplifier.

[0022] The beneficial technical effects of the present application include: The present application is a kind of high measurement accuracy ferromagnetic resonance test platform for coplanar waveguide ferromagnetic resonance measurement system. The specially designed coil and the related structure provide stable and adjustable perturbation magnetic field, and can provide an oscillating magnetic field of minimum 1 oersted. Since the signal of coplanar waveguide ferromagnetic resonance is the differential of microwave absorption to magnetic field, the size of oscillating magnetic field is equivalent to dH of dP / dH, and smaller dH means higher test accuracy. Combined with lock-in amplifier measurement, high signal-to-noise ratio ferromagnetic resonance measurement is realized, and more detailed signals can be measured to prevent signal loss.

[0023] Under the above settings, the present application improves the measurement accuracy of ferromagnetic resonance through a series of settings. The sample stage and the connecting column are made of high thermal conductivity red copper, which has good heat conduction. High-precision temperature control is provided by the compressor, heating resistor and temperature sensor, and the precision can reach 0.005 K to reduce the noise caused by temperature instability. High vacuum environment prevents sample oxidation and provides a stable test environment and a basis for low temperature measurement.

[0024] The coplanar waveguide designed in the present application has good impedance matching. The 3 GHz microwave in the center section of the waveguide has only 0.25 dB attenuation, and the waveguide core width is 0.96 mm, which can make the sample fully affected by the microwave alternating magnetic field. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the structure diagram of the sample stage, coplanar waveguide, circuit board, coil and coil shell for coplanar waveguide ferromagnetic resonance provided by the embodiment of the present application.

[0026] Figure 2 is a cross-sectional view of the coplanar waveguide provided by the embodiment of the present application.

[0027] Figure 3 is a top view of the coplanar waveguide provided by the embodiment of the present application.

[0028] wherein: 1-sample stage; 2-coplanar waveguide substrate; 3-coplanar waveguide core; 4-coplanar waveguide ground; 5-coplanar waveguide solder region; 6-smp; 7-coplanar waveguide electrode; 8-electrode circuit board; 9-sample stage back circuit board; 10-coil and coil housing. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to specific embodiments and drawings. However, those skilled in the art should know that the present application is not limited to the drawings and the following embodiments.

[0030] In the description of the application, it should be noted that, for the orientation words such as the terms "length", "width", "up", "down", "far", "near", "front", "back", "left", "right" and the like, the orientation or position relationship indicated thereby is based on the orientation or position relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and cannot be understood as limiting the specific protection scope of the present application. In addition, the terms "first", "second" are only for the purpose of description, to distinguish technical features, and do not have substantial meaning, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features.

[0031] The present application is a small test platform for coplanar waveguide ferromagnetic resonance testing based on ferromagnetic resonance effect.

[0032] Figure 1 is a structural schematic diagram of a small device for ferromagnetic resonance spin pumping test provided by an embodiment of the present application.

[0033] The ferromagnetic resonance spin pumping test device provided by the embodiment of the present application comprises a sample stage 1, a coplanar waveguide substrate 2, a coplanar waveguide core 3, a coplanar waveguide ground 4, a coplanar waveguide solder region 5, an smp 6, a coplanar waveguide electrode 7, an electrode circuit board 8, a sample stage back circuit board 9, and a coil and coil housing 10.

[0034] The sample stage 1 is made of red copper material with gold plating. In one embodiment of the application, the sample stage 1 is made of red copper material and plated with gold, which has good thermal conductivity at room temperature and low temperature. The function of the sample stage is to provide the sample with a position in the magnetic field and good thermal conduction between the sample and the compressor for refrigeration. The front plane of the sample stage 1 is 0.5 mm away from the center of the magnetic field, which ensures that the sample is in the center of the magnetic field. The cylindrical structure on the upper part of the sample stage provides space for electrical connection and has more contact area with the upper connecting column, achieving the purpose of high-efficiency refrigeration. The sample stage is provided with 32 threaded holes on both sides, each threaded hole having a longitudinal spacing of 3 mm, for fixing the circuit board. The center of the sample stage is provided with an annular groove with an inner diameter of 22 mm, an outer diameter of 27.4 mm and a depth of 2 mm for fixing the coil.

[0035] The coplanar waveguide substrate 2 is made of Rogers high-frequency board with high dielectric constant. The parameters such as the size of the center core wire cross section, the ground distance and the high-frequency board thickness are designed to achieve an impedance of 50 ohms, which matches the 50 ohm impedance of the microwave channel to reduce microwave reflection. Through the test of the vector network analyzer, the waveguide has good impedance matching below 10 GHz, which can provide a microwave magnetic field for the ferromagnetic resonance experiment. The coplanar waveguide core wire 3 is a rectangular copper strip with a width of 0.96 mm, a length of 13.5 mm and a thickness of 35 μm. The transition trapezoidal structure between the core wire 3 and the welding area is 1 mm to 0.5 mm. The coplanar waveguide ground 4 is a metal copper covering most of the front area, with a thickness of 35 μm. The distance between the coplanar waveguide core wire 3 and the coplanar waveguide ground 4 is 0.255 mm. The cross section design makes the waveguide impedance 50 ohms, which is connected to the back ground through the through hole. The coplanar waveguide welding area 5 is the metal area around the square groove at both ends of the coplanar waveguide substrate. The groove is a rectangular groove with a length of 5.1 mm and a width of 4.2 mm. The copper area above and below the groove has a width of 1.6 mm, which is used for the grounding welding of smp6. The transition area at both ends of the coplanar waveguide core wire 3 is a trapezoidal structure with a length of 2 mm, a left side length of 0.5 mm and a right side length of 0.96 mm, which is used for the core wire welding of smp6.

[0036] The coplanar waveguide electrode 7 is 20 gold-plated electrodes on the coplanar waveguide ground 4, each electrode is a square electrode with a side length of 1.5 mm, and each upper and lower electrode is connected by a copper wire with a length of 0.28 mm and a width of 0.3 mm, which can complete the electrical connection required by the experiment. The gold wire adhered to the sample is connected to the indium electrode plate, and the same treatment is performed on the electrode circuit board 8, so as to achieve electrical contact between the sample and the circuit board. The entire microwave circuit is connected through the external smp high-frequency connector male head to complete the connection of the microwave circuit, that is, the vector network analyzer-smp high-frequency connector male head-smp6-coplanar waveguide sheet-smp high-frequency connector female head6-smp high-frequency connector male head-high-frequency diode-lock-in amplifier. The high-frequency diode converts the microwave power signal into a voltage signal, so that the lock-in amplifier receives the signal.

[0037] The back circuit board 9 of the sample stage provides further electrical contact for the electrode circuit board 8, and is finally connected to the nanovolt meter 34420 at the terminal for measuring the spin pumping signal generated when ferromagnetic resonance occurs. The circuit board structure is attached to the surface of the sample stage, which will not be described here. A pair of spring needles are welded on the back circuit board 4 of the sample stage, The coil is a copper coil with an inner diameter of 22 mm, an outer diameter of 26.4 mm, a thickness of 2 mm, a coil wire diameter of 0.1 mm, a single coil resistance of 52 Ω, and a central magnetic field of the double coil under a voltage of 2.75 V is 10 Oe The back circuit board 9 of the sample stage is also welded with a 50-ohm heating resistor and a temperature sensor Pt100, which cooperates with the compressor to regulate and monitor the temperature of the sample stage.

Claims

1. A high-precision, multi-functional open ferromagnetic resonance testing platform, characterized in that: The coplanar waveguide ferromagnetic resonance testing platform includes a coplanar waveguide plate, a sample stage, a circuit board, coils, and an insulating jacket; the coplanar waveguide plate is made of Rogers high-frequency board material; the circuit board substrate is FR4, with copper wires embedded inside for electrical connection; the circuit board includes a sample stage front panel and a sample stage back panel; the sample stage and connecting pillars are made of high thermal conductivity material; the sample stage has a three-section structure, namely a rectangular structure, a disk structure, and a cylindrical structure.

2. The coplanar waveguide ferromagnetic resonance testing platform according to claim 1, characterized in that: The surface of the coplanar waveguide plate is covered with copper to form a coplanar waveguide structure; 20 immersion gold electrodes are provided on the edge for sample electrical transport measurement, and they are fixed to the front of the rectangular structure of the sample stage by screws, with their center corresponding to the center of the magnet.

3. The coplanar waveguide ferromagnetic resonance testing platform according to claim 1, characterized in that: The sample stage disc structure has a rectangular through slot for supplying power to the sample stage back panel; the sample stage cylindrical structure is used to increase thermal contact with the connecting column; the connecting column is used for heat conduction from the compressor; and a cylindrical groove is provided for docking with the sample stage cylinder.

4. The high-precision, multi-functional open ferromagnetic resonance testing platform according to claim 1, characterized in that: The coil is fixed inside the alumina shell, by being snapped into the rectangular groove of the sample stage, and fixed at both ends of the alumina shell by screw holes.

5. The high-precision, multi-functional open ferromagnetic resonance testing platform according to claim 3, characterized in that: The front panel of the sample stage is fixed to the front of the rectangular structure of the sample stage with screws, and is covered with 14 rectangular electrodes for electrical contact with the waveguide plate; the back panel of the sample stage is fixed to the back of the rectangular structure of the sample stage with screws, and has two pairs of pads for connecting the temperature sensor and the heating resistor, and one pair of rectangular electrodes for welding spring pins to power the coil; the sample stage is connected to the front panel through a rectangular through hole in the middle of the rectangular structure of the sample stage.

6. The test method for ferromagnetic resonance spin-pumped electrical testing according to claim 1, characterized in that: The sample is electrically connected to the waveguide plate, the waveguide plate is electrically connected to the sample stage, and finally connected to a nanovoltmeter for spin pump voltage measurement.

7. The test method for ferromagnetic resonance spin-pumped electrical testing according to claim 6, characterized in that: The wave source is connected to the packaged board and coplanar waveguide for microwave input. The output terminal is connected to a high-frequency diode to convert the microwave power signal into a voltage signal and output it to the lock-in amplifier. The output terminal of the lock-in amplifier provides an oscillation voltage to the coil. The electromagnet is controlled by the program to sweep the field. At the beginning of ferromagnetic resonance, the sample resonates and absorbs due to the oscillating magnetic field provided by the coil, and oscillates at the same frequency as the oscillation voltage, so that the signal is detected by the lock-in amplifier.

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