JP2015206641A - Ferromagnetic resonance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of measuring ferromagnetic resonance occurring on an extremely small magnetic material sample of a micron-to-nano-level size with a low S/N ratio.SOLUTION: A ferromagnetic resonance measuring device comprises: a microwave oscillator (1); branch unit (2) for branching a microwave into a first microwave and a second microwave; a first path where the first microwave is transmitted; a second path where the second microwave is transmitted; a waveguide (6) provided in the first path; a phase shifter (7) and an amplitude adjuster (8) which are provided in the second path; a coupler (9) for coupling the first microwave and the second microwave which are completely transmitted through the first path and the second path, respectively; external DC magnetic fields H(5a,5b); amplifier (10); and microwave detector (11). By placing a sample (S) in the middle of the waveguide (6) to which means of applying a low-frequency modulation magnetic field Hand means (15) of extracting only modulation frequency components of the low-frequency modulation magnetic field Hfrom an output signal of the detector are added, by applying a high-frequency modulation magnetic field Hinduced by the first microwave to the sample (S), and by sweeping the intensity of the external DC magnetic fields H(5a,5b), ferromagnetic resonance of a predetermined intensity His caused to occur on the sample (S).

Description

  In the present invention, for example, a magnetic material having an extremely small micron to nano-size level (for example, permalloy (NiFe alloy), CoFeB alloy) such as a diameter φ = 3 μm, a thickness 100 nm, and a diameter φ = 200 nm, a thickness 5 nm. ) Ferromagnetic Resonance (FMR).

Measuring the ferromagnetic resonance of a magnetic material (sample) is an effective means of knowing the properties of the magnetic material. In the case of a thin film having the most general sample shape, the conditions under which ferromagnetic resonance occurs are as follows: Kittel's equation 2πf = γ {(H _B + H _K ) (H _B + H _K + 4πM _S )} ^1/2 (1)
It is represented by In the above formula (1),
F is the ferromagnetic resonance frequency, γ is the gyromagnetic constant, H _B is the strength of the external DC magnetic field, M _S is the saturation magnetization of the magnetic material, and H _K is the strength of the internal anisotropic magnetic field.

Therefore, the measurement of the ferromagnetic resonance is, for example, in the conventional hard disk (HDD) or the magnetic recording technology (MAMR) that actively uses the ferromagnetic resonance of the magnetic material for the magnetic medium or the magnetic head. This is an important method for development.
Conventionally, as a device for measuring ferromagnetic resonance, a device as shown in FIG. 6 (see FIG. 1 and FIG. 3 of Non-Patent Document 1) has been used. The FIG. 1 apparatus is the oldest type of ferromagnetic resonance measuring apparatus.
This apparatus (see FIG. 6) is basically a microwave oscillator (1), a waveguide through which microwaves output from the oscillator pass, and a microwave is placed by placing a sample (S) therein. A waveguide (6) in which a high frequency magnetic field (H _RF ) induced by the magnetic field is applied to the sample, a magnet (5a + 5b) for applying an external DC magnetic field to the sample (S), and a microwave output from the waveguide (6) It comprises a detector (11) for detecting. The sample (S) is placed in the waveguide (6), and the ferromagnetic resonance of the sample (S) is measured by sweeping the intensity of the external DC magnetic field (H _B ) from low to high.

The ratio (P2 / P1) between the output P1 of the microwave oscillator (1) and the output P2 of the detector (11) is called a transmission coefficient “S ₂₁ ”. The case where the microwave propagates to the detector without being attenuated is defined as “1”, and S ₂₁ when the microwave transmission path (M) is interrupted is defined as “0”. The state of a change in S ₂₁ in the ferromagnetic resonance measurement shows the vertical axis in S _21, FIG. 7 as a graph (ferromagnetic resonance curve) for the horizontal axis and the intensity of the external DC magnetic field (H _B). When ferromagnetic resonance occurs, microwaves transmitted through the waveguide (6) is absorbed by the sample (S), microwave amplitude detected by the detector (11), thus S ₂₁ is reduced. This creates a dip in the graph. Thus by monitoring the change in S _21, it is possible to measure the ferromagnetic resonance. The intensity of the external DC magnetic field (H _B ) at the point where S ₂₁ is the lowest in the dip is called “ferromagnetic resonance magnetic field (H _R )”.

This apparatus includes means for applying a low frequency modulation magnetic field (H _LF ) together with an external DC magnetic field (H _B ) to a sample and a detector (11) in order to remove noise and drift from each part of the apparatus. A lock-in amplifier is provided as means (15) for extracting only the modulation frequency component of the low-frequency modulation magnetic field (H _LF ) from the output signal. Thereby, the differential of S ₂₁ is detected (differential detection method), and a graph as shown in FIG. 8 is output. The intensity of the external DC magnetic field (H _B ) when this graph crosses the “0” position on the vertical axis is “ferromagnetic resonance magnetic field (H _R )”.
Recently, internalized and detector (11) the microwave oscillator (1), a value obtained by calculation including phase not only the amplitude ratio of P1 and P2, in other words, a vector network capable of measuring S ₂₁ complex・ Analyzer (Vector Network Analyzer, abbreviated VNA) is often used. VNA is also used in FIG. 3 of Non-Patent Document 1. In this apparatus (FIG. 3), since the electromagnet is an air-core Helmholtz coil and not an electromagnet using an iron core, the intensity of the external DC magnetic field (H _B ) is considerably weak. Since there is no modulation coil and it is not a differential method, S ₂₁ is directly measured by VNA to obtain a graph as shown in FIG.

  Sample sizes are becoming smaller and the sample sizes that are of particular interest in today's research and development are on the micro to nano size level. For example, in magnetic recording, as the magnetic domain (corresponding to a bit) representing an information unit is reduced, the recording density is improved and the recording capacity is increased. A magnetic head for writing / reading such a small magnetic domain must also be reduced in accordance with the domain size. The size of the magnetic material embedded in such a magnetic head is extremely small.

However, in such a small sample, since the change in S ₂₁ is proportional to the volume of the sample, the signal to be detected becomes extremely small. On the other hand, the strength of the microwaves for causing ferromagnetic resonance of it, (i) desires to see there are relatively very large background compared to the change of the signal S _21, the noise accompanying the fluctuations (trace noise) There occurs, an attempt to amplify a signal S ₂₁ wants to see (ii), the background to be superimposed even will be amplified together, because the amplifier is saturated and can not amplify the signal, for reasons like, The conventional apparatus (FIG. 6) has a low signal-to-noise ratio (S / N ratio), and it is not possible to measure a very small sample from the micron to the nano size level. For example, in the configuration of the measuring apparatus shown in Non-Patent Document 1, since the S / N ratio is low for the above-described reason, a signal having a strength necessary for measurement is obtained by increasing the size of the sample. The sample of Non-Patent Document 1 is an alloy of Ni 80% Fe 20%, and the size is 1 cm in length × 1 cm in width × 50 nm or 100 nm in thickness (see the middle column on page 093909-2 of Non-Patent Document 1).

  Then, the present inventors paid attention to the ferromagnetic resonance measuring apparatus disclosed in Non-Patent Document 2. This apparatus is characterized in that it has a structure (interferometer) that divides the input microwave into two paths and makes them destructively interfere.

Sangita S. Kalarickal, et al ,, JOURNAL OF APPLIED PHYSICS 99, 093909 (2006) Hanqiao Zhang, et al., REVIEW OF SCIENTIFIC INSTRUMENTS 82, 054704 (2011)

However, although the ferromagnetic resonance measuring apparatus disclosed in Non-Patent Document 2 uses an interferometer, according to the study by the present inventors, it has been found that there are the following problems.
(1) A reference channel (see FIG. 1 in Non-Patent Document 2, Non-Patent Document 2, second path in the present invention) is provided to cause interference, but the means for shifting the phase of the path by a half wavelength is made of a gold thin film. This is the length of the Reference channel. However, since there is an error in creating the reference channel, it is difficult to accurately shift the phase by half a wavelength at the frequency originally designed as the measurement condition.
(2) Since there is no means for adjusting the amplitude in the reference channel, the extinction ratio of the interferometer is small. In general, the performance of an interferometer is the extinction ratio defined as the ratio of the maximum output when two signals are constructively interfered to the minimum output when they are destructively interfered. The larger the value, the better the performance as an interferometer. The extinction ratio of the interferometer of Non-Patent Document 2 can be read as a maximum value of −30 dB and a minimum value as −77 dB from the graph of FIG. 3 on the right column of page 05744-2, and the difference is 47 dB. This has poor performance as an interferometer.
(3) The signal output from the interferometer is directly measured by the VNA without being amplified. Therefore, the detection sensitivity of VNA is low.
(4) As a comprehensive result of the problems listed in (1) to (3) above, the S / N ratio in the ferromagnetic resonance measurement is still low. Since samples tend to become smaller and smaller, higher S / N ratios are required.

As a result of earnest research, the present inventors have solved the above-mentioned problems by combining an improved interferometer and a differential detection method, and invented a ferromagnetic resonance measuring apparatus that exhibits superior performance.
That is, the present invention relates to a microwave oscillator, a branching device that divides the microwave output from the oscillator into a first microwave and a second microwave, a first path that transmits the first microwave, and a second microwave that is transmitted A second path, a waveguide provided in the middle of the first path, a magnet for applying an external DC magnetic field H _B to the sample, an “n + 0.5” wavelength provided in the first path or the second path, or both, Where n is an integer, a phase shifter to be shifted, an amplitude adjuster provided in the first path or the second path or both, a first microwave transmitted through the first path, and a second microwave transmitted through the second path , A device for amplifying the microwave output from the coupler, and a detector for detecting the microwave output from the amplifier, the sample S being disposed in the middle of the waveguide In addition, 1 high frequency magnetic field H _RF induced by microwaves are applied, the ferromagnetic resonance measurement device which causes the ferromagnetic resonance in the sample S at a predetermined intensity by sweeping the intensity of the external DC magnetic field H _B, the sample S low frequency means for applying a modulated magnetic field H _LF, and is characterized in that the addition means for extracting only the modulation frequency component of the low frequency modulation magnetic field H _LF from the output signal of the detector.
Further, the present invention provides the above-described ferromagnetic resonance measuring apparatus, wherein a reference signal source and a phase-locked loop circuit are added to the microwave oscillator to oscillate a microwave with reduced phase noise, and the microwave is It is characterized by being input to a branching device.
In the ferromagnetic resonance measuring apparatus according to the present invention, the waveguide is a “coplanar waveguide including a plurality of strip-shaped conductor foils”, and the sample is placed on a central strip-shaped conductor foil.
Further, the present invention is characterized in that the ferromagnetic resonance measuring apparatus has an extinction ratio of 60 dB or more.

  According to the present invention, even when the sample size is small, the above problems are solved, and a higher S / N ratio is realized.

It is a conceptual diagram which shows one Example (Example 1) of the ferromagnetic resonance measuring apparatus of this invention. It is a block diagram of a PLL circuit and the like. FIG. 7 is a conceptual diagram showing another embodiment (embodiment 2) of the ferromagnetic resonance measuring apparatus of the present invention, in which the PLL circuit of FIG. 2 is added to the embodiment of FIG. It is explanatory drawing which expands and shows the waveguide (3) used for the apparatus of FIG. It is a conceptual diagram explaining the waveguide (3) of FIG. 3, (a) is the top view, (b) is when the waveguide (6) is cut | disconnected in the position of AA 'in a top view (a). FIG. It is a conceptual diagram which shows the structure of the conventional ferromagnetic resonance measuring apparatus. The state of a change in S _21, the vertical axis S _21, is a diagram for explaining a ferromagnetic resonance magnetic field H _R graphically showing the horizontal axis as the intensity of the external DC magnetic field H _B (ferromagnetic resonance curve). Ferromagnetic resonance based on a graph (ferromagnetic resonance curve) showing the change of the derivative of S ₂₁ (dS ₂₁ / dH _B ) with the vertical axis representing dS ₂₁ / dH _B and the horizontal axis representing the intensity of the external DC magnetic field H _B is a diagram for explaining a magnetic field H _R (differential detection method). It is a graph of the measurement result by a differential detection method, (a) is a graph of the measurement result by the Example of this invention, (b) is a graph of the measurement result by the conventional apparatus shown in FIG. It is a graph of the measurement result by the Example of this invention, Comprising: It is the graph which showed the sensitivity improvement.

<Example 1>
The present invention provides a ferromagnetic resonance measuring apparatus that exhibits excellent detection sensitivity and a high S / N ratio by combining an interferometer and a differential detection method.
An embodiment of the ferromagnetic resonance measuring apparatus of the present invention is shown in FIG. This apparatus includes a microwave oscillator (1), a branching unit (2) for dividing a microwave M output from the oscillator into a first microwave and a second microwave, and a first path (3) for transmitting the first microwave. ), A second path (4) for transmitting the second microwave, a waveguide (6) provided in the middle of the first path (3), and a magnet for applying an external DC magnetic field (H _B ) to the sample (S) (5a + 5b), a half-wavelength phase shifter (7) provided in the second path (4), an amplitude adjuster (8) provided in the second path (4), and the first path (3) transmitted through the first path (3) A coupler (9) for combining one microwave and a second microwave transmitted through the second path (4), an amplifier (10) for amplifying the microwave output from the coupler (9), and an output from the amplifier or microwave detector for detecting (11), means for applying a low frequency modulation magnetic field (H _LF) to the sample (S), and an output signal of the detector (11) Wherein comprising means (15) for extracting only the modulation frequency component of the low frequency modulation magnetic field (H _LF).
When the sample (S) is arranged in the middle of the waveguide (6), the high frequency magnetic field (H _RF ) induced by the first microwave is applied to the sample, and at this time, the intensity of the external DC magnetic field (H _B ) is increased. By sweeping, ferromagnetic resonance can be caused in the sample (S) with a predetermined intensity.
Note that the interferometer portion of this apparatus (see FIG. 1) follows the teaching of Non-Patent Document 2.

In the first path (3) and the second path (4), two microwaves passing through the respective paths are coupled by a coupler (9) to cause "interference". It is called an “interferometer”. The extinction ratio of the interferometer of Non-Patent Document 2 is 47 dB as described above. In contrast, the apparatus of the present invention (see FIG. 1) has a phase shifter (7) and an amplitude adjuster (8) unlike the non-patent document 2 in the configuration of the interferometer. Therefore, since phase adjustment and amplitude adjustment can be performed with higher accuracy, the extinction ratio is as high as 60 dB or more.
The roles of means for applying a low frequency modulation magnetic field (H _LF ) and means (15) for extracting only the modulation frequency component of H _LF from the output signal of the detector (11) are the same as those described in Non-Patent Document 1. Role) is different. In the device of FIG. 1 (FIG. 1), the drift is not so great, but the trace noise accompanying the fluctuation of the signal level of the microwave oscillator is very large. In order to solve this problem, the apparatus (FIG. 1) employs a differential method that extracts only the modulation frequency component.
On the other hand, in the present invention (see FIG. 1), the first microwave and the second microwave cancel each other due to destructive interference and do not reach the detector (11). The problem due to the provision, that is, the drift due to the misalignment of the interferometer becomes relatively very large.
In order to solve this problem, the present invention (see FIG. 1) employs a differential method that extracts only the modulation frequency component.

<Example 2>
Since the sample size tends to become smaller and smaller, a higher S / N ratio is required. Therefore, it is preferable to add a reference signal source and a phase-locked loop (PLL) circuit (1a) to the microwave oscillator (1) (see FIG. 2). As a result, a microwave with reduced phase noise is oscillated and this microwave is input to the branching device (2), thereby realizing a higher S / N ratio.
FIG. 3 shows an apparatus obtained by adding the PLL circuit shown in FIG. 2 to the ferromagnetic resonance measuring apparatus (Example 1) shown in FIG. The ferromagnetic resonance measuring apparatus (Example 2) shown in FIG. 3 is as follows.
A microwave oscillator (1), a branching device (2) for dividing the microwave output from the oscillator into a first microwave and a second microwave, a first path (3) for transmitting the first microwave, a second microwave A second path (4) for transmitting a wave, a waveguide (6) provided in the middle of the first path (3), and an external direct current magnetic field (S) placed in the middle of the waveguide (6) ( H _B ) magnet (5a + 5b), phase shifter (7) for shifting “n + 0.5” wavelength (n is an integer) provided in the first path (3), the second path (4) or both, The amplitude adjuster (8) provided in the first path (3) or the second path (4) or both, the first microwave transmitted through the first path (3), and the second path (4) were transmitted. A coupler (9) for coupling with the second microwave, an amplifier (10) for amplifying the microwave output from the coupler (9), and the microwave output from the amplifier Detector output (11), means for applying a low frequency modulation magnetic field (H _LF) to the sample (S), and the modulation frequency of the low frequency modulation magnetic field (H _LF) from the output signal of the detector (11) An apparatus having means (15) for extracting only the component, and when the sample (S) is arranged in the middle of the waveguide (6), the high frequency magnetic field (H _RF ) induced by the first microwave is generated. In the ferromagnetic resonance measuring apparatus that can be applied to the sample (S), and at this time, the ferromagnetic resonance can be caused in the sample (S) at a predetermined intensity by sweeping the intensity of the external DC magnetic field (H _B ). By adding a reference signal source and a PLL circuit (1a) to the microwave oscillator (1), the microwave M with reduced phase noise is oscillated, and the microwave is input to the branching device (2). As a result, an even higher S / N ratio is realized.

In the first and second embodiments, the waveguide (6) is “a coplanar waveguide including a plurality of strip-shaped conductor foils”, and it is preferable that the sample is placed on the central strip-shaped conductor foil.
The extinction ratio is 60 dB or more (preferably 70 dB or more, particularly 80 dB or more).

<Description of operation of measuring apparatus and measuring method>
The microwave oscillator (1) outputs a microwave of, for example, 1 to 110 GHz. A higher output strength P1 is advantageous for the S / N ratio as long as the sample and the waveguide are not affected by heat. In general, an intensity of about −20 dBm to +20 dBm is used. When ferromagnetic resonance does not occur in the sample, the output of the microwave output from the coupler (9) is adjusted to be minimized by the phase shifter (7) and the amplitude adjuster (8). Thereby, the extinction ratio of the interferometer can be set to 60 dB or more.
As the branching device (2), for example, a resistance type power divider or a Wilkinson type power divider is used.

As the waveguide (6), for example, a coplanar waveguide (coplanar waveguide) as shown in FIG. 4 is used. This coplanar waveguide is composed of an input-side high-frequency probe (6a), three strip-shaped conductor foils (6b, 6c, 6d) and an output-side high-frequency probe (6e). In addition, a waveguide such as a microstrip line is also used.
As the magnet (5a + 5b) for applying the external DC magnetic field (H _B ), for example, a permanent magnet or an electromagnet is used. For example, the strength is suitably about 100 to 30 kOe. The width for sweeping H _B is, for example, about ± 10 to ± 30 kOe, although it depends on the sample.
As the phase shifter (7), for example, a mechanical phase shifter, an electronically controlled phase shifter, or the like is used.
As the amplitude adjuster (8), for example, a mechanical variable attenuator or an electronically controlled variable attenuator is used.
As the coupler (9), for example, a resistive power divider, a Wilkinson power divider, or the like is reversely connected and used as a power combiner.
For example, a low noise amplifier is used as the amplifier (8).
As the detector (9), for example, a semiconductor diode or a high-frequency mixer is used.
For example, a 50 ohm coaxial cable is used as the microwave transmission path (M).

Next, the operation of this apparatus will be described.
A microwave (high frequency excitation signal) having an intensity P1 is output from the microwave oscillator (1), reaches the branching device (2) through the microwave transmission path (M), and the first path (2) by the branching device (2). It is divided into a first microwave of 3) and a second microwave of the second path (4).
In the first path (3), the first microwave passes through the waveguide (6) and reaches the coupler (9) as in the conventional ferromagnetic resonance measuring apparatus.
On the other hand, in the second path (4), the second microwave reaches the coupler (9) through the phase shifter (7) and then the amplitude adjuster (8). In some cases, the phase shifter (7) and / or the amplitude adjuster (8) may be provided in the first path (3) or both.

The coupler (9) outputs the sum of the microwaves input from these two paths. At this time, the phase of the second microwave propagating through the second path is changed by the phase shifter (7) with respect to the first microwave propagating through the first path in the state where no ferromagnetic resonance occurs in the sample (S). Shift "n + 0.5" wavelength (n is an integer). As a result, the phase of the second microwave is just 180 degrees reversed with respect to the first microwave. Further, the amplitude adjuster (8) performs adjustment so that the first microwave and the second microwave have the same amplitude. As a result, in the state where no ferromagnetic resonance occurs in the sample (S), the first microwave and the second microwave that have reached the coupler (9) cause destructive interference, and the coupler (9) outputs. The output of microwave is minimized.
When the intensity of the external DC magnetic field (H _B ) is swept from small to large in this state, the resonance condition is satisfied at a predetermined intensity, that is, “ferromagnetic resonance magnetic field (H _R )”. Then, ferromagnetic resonance occurs in the sample (S), so that the first microwave propagating through the first path (3) is absorbed by the sample (S). As a result, the balance between the first microwave and the second microwave is lost, and the change in the first microwave due to ferromagnetic resonance appears in the output signal of the coupler (9).

This output signal is amplified by the amplifier (10) and sent to the microwave detector (11). Then, the microwave intensity P2 is output by the microwave detector (11).
The transmission coefficient S21 is obtained from the ratio (P2 / P1) between the input P1 and the output P2. In the preferred embodiment, a microwave oscillator stabilized by a PLL circuit is added to the VNA, a microwave (high frequency excitation signal) is output from the port 1 of the VNA, enters the branching device (2), and the amplifier (10). The microwave amplified in step 2 enters port 2. Then, the transmission coefficient S ₂₁ is obtained in this VNA.
Thereby, in a state where ferromagnetic resonance has not yet occurred, the microwave (high frequency excitation signal) is canceled by itself, and the background becomes theoretically zero. That is, even if the intensity of the microwave (high-frequency excitation signal) fluctuates due to the situation of the oscillator (1), the trace noise associated with the fluctuation (background fluctuation) disappears in principle.

Also, only when the ferromagnetic resonance occurs, the amplitude of the first microwave decreases due to the intensity absorption accompanying the resonance, thereby causing a difference in amplitude between the second microwave and the difference signal. Output from the coupler (9). Since no background is superimposed on this output signal, it can be amplified by the amplifier (10) without being saturated.
Amplification is equivalent to an increase in VNA detection sensitivity, and the S / N ratio is improved by these effects.

This apparatus (FIG. 3) includes an improved interferometer as a first feature, and as a second feature, a low frequency modulation magnetic field (H) is applied to a sample (S) to solve the problem of the improved interferometer. _LF ) and means (15) for extracting only the modulation frequency component of the low-frequency modulation magnetic field (H _LF ) from the output signal of the detector (11). Specifically, a modulation coil (12) is used as the former means (means for applying a low-frequency modulation magnetic field (H _LF )), and a lock-in amplifier is added as the latter means (15). , or by performing numerical processing S ₂₁ measured on the computer VNA.
A low-frequency (for example, 10 to 10 kHz) AC signal is generated by the signal source (14), and is sent to the current source (13). H _LF ) is superimposed on the external DC magnetic field (H _B ) and applied to the sample (S). This modulation magnetic field (H _LF ) causes the transmission coefficient S ₂₁ to oscillate at the modulation frequency. The S ₂₁ to the vibration, by sending to the lock-in amplifier which adds the detector output to the outside, taking out only the modulated frequency component. In the case of using the VNA, taken by only the Fourier transform modulation frequency component of S ₂₁ obtained in VNA. By this signal processing, the derivative of the S ₂₁ curve shown in FIG. 7 is obtained (see FIG. 8). Significant signals reflecting ferromagnetic resonance are concentrated only in the modulation frequency component, while interferometer drift and other noise spread to frequency components other than the modulation frequency. Therefore, by amplifying only the modulation frequency component with the lock-in amplifier, it is possible to effectively remove the signal due to interferometer drift and other noises, and to extract only the ferromagnetic resonance signal of interest. The ratio is dramatically improved.

In the apparatus of FIG. 1, the first microwave passing through the first path (3) and the second microwave passing through the second path (4) interfere with each other in a destructive manner, and as a result, output from the coupler (9). The signal to be transmitted becomes large with an extinction ratio of 60 dB or more. However, the interferometer is tuned to cause destructive interference for certain frequencies of microwaves. On the other hand, in the microwave transmitter (1), the oscillation frequency is not constant and fluctuates with time (this frequency fluctuation is quantified as phase noise). Therefore, even if the first path (3) and the second path (4) are adjusted in order to ideally cause destructive interference, a finite background signal is actually caused by the frequency fluctuation of the microwave transmitter (1). Leaks and superimposes with a signal reflecting the ferromagnetic resonance. When the leakage of the background signal due to the frequency fluctuation of the microwave transmitter (1), that is, the fluctuation of the extinction ratio is the same as the frequency of the low frequency modulation magnetic field, the microwave emitted from the interferometer is converted into the microwave source. It is not possible to distinguish whether it is due to the frequency fluctuation of the sample or due to the ferromagnetic resonance of the sample.
In order to solve this problem, as a third feature, the present embodiment stabilizes the oscillation frequency by adding a reference signal source and a PLL circuit (1a) to the microwave oscillator (1) as shown in FIG. . Thereby, a microwave with reduced phase noise is oscillated, and the microwave is input to the branching device (2). Therefore, the extinction ratio does not fluctuate with time, and the S / N ratio is further improved.

<Measurement result 1>
The measurement result measured using the apparatus of Example 2 of FIG. 3 is demonstrated.
Here, a microwave signal generator Model 605 manufactured by Gigatronics (USA) was used as the microwave oscillator (1), and a microwave (frequency excitation signal) having a frequency of 7.04 GHz and an output of 6 dBm was generated. At this time, the microwave generator was not used as it was, and a 10 MHz reference signal source and an external PLL circuit (see FIG. 2) were added. This external PLL circuit has an Integrer-N type configuration including an ECL phase comparator, a low-pass filter with a cut-off frequency of 200 Hz, and a 1 / N counter set to N = 704. -There are N types.)
A signal reflecting the phase difference generated by the PLL circuit was sent to the above-mentioned microwave signal generator to finely adjust the frequency, thereby stabilizing the frequency accurately at 704 times 10 MHz and suppressing the frequency fluctuation. As a result, the phase noise was reduced to about 1/5 compared with the case of using it as it is.
As a reference signal source, OCXO501-10295 manufactured by Wenzel (USA) was used.

A high-frequency mixer included in E8361C (PNA series vector network analyzer) manufactured by Agilent Technologies (USA) was used as the detector (11). The VNA also plays a role of generating a signal (trigger signal) for controlling the entire measuring apparatus and sending the acquired _S21 data to a computer.
A 50 ohm coaxial cable was used as the microwave transmission line (M). The coaxial cable connects the components from the microwave oscillator (1) to the detector (11).
As the branching device (2), a resistor type power divider ZFRSC-183 + manufactured by Mini-Circuits (USA) was used.

The waveguide (6) and the sample (S) were integrally formed as shown in FIG. First, a glass substrate (6 g) is prepared, and a permalloy (Ni 80% Fe 20% alloy) layer having a thickness of 100 nm is formed thereon as a sample (S) by a sputtering method, and then a diameter φ = 3 μm by photolithography & etching. Processed into a shape. As a result, a permalloy sample (S) was formed. Thereafter, an alumina (Al ₂ O ₃ ) layer having a thickness of 540 nm was formed by a sputtering method, and a copper layer having a thickness of 750 nm was further formed thereon by a sputtering method. Finally, the copper layer was processed into three strips (6b, 6c, 6d) by photolithography and etching. The width of the band 6b is 6 μm, the width of the band 6c at the center is 3 μm, and the width of the band 6d is 6 μm. The outer bands (6b, 6d) are ground (minus).
In actual measurement, high frequency probes (6a) and (6e) were brought into contact with both ends of the band, and 7.04 GHz microwaves were passed through the waveguide (6) from one high frequency probe (6a). The intensity of the microwave at this time is 0 dBm, which corresponds to applying a high frequency magnetic field (H _RF ) of about 19 Oe to the sample (S). This high frequency magnetic field causes precession of the magnetic moment of the sample (S).

The magnet (5a + 5b) for applying an external DC magnetic field (H _B ) to the sample (S) is an electromagnet, and its strength can be swept between 0 and 1.3 kOe.
This electromagnet also serves as a modulation coil (12), and a low frequency modulation magnetic field (H _LF ) having a frequency of 28 Hz can be applied to the sample (S). This Experiment was conducted setting the intensity of H _LF to 0.25Oe.
As the phase shifter (7), a mechanical phase shifter Model 9426A manufactured by ARRA (USA) was used. Thereby, the phase of the second microwave can be shifted by a half wavelength.
As the coupler (9), Markkin (USA) Wilkinson power divider PD-0140 was used in reverse connection.
As an amplitude adjuster (8) that makes the amplitude of the first microwave equal to the amplitude of the second microwave by reducing the amplitude of the second microwave before inputting to the coupler (9), Advanced Technical Materials Inc. A mechanical variable attenuator AV065-10 (USA) was used.
When the extinction ratio of the microwave output from the coupler (9) was examined, it showed a high value of 80 dB or more.

A low noise amplifier BZ-00101600 manufactured by B & Z Technologies (USA) was used as an amplifier (10) for amplifying the microwave output from the coupler (9).
The apparatus of the present invention, to solve the problem of the interferometer, the sample and the means for applying the low frequency modulation magnetic field (H _LF) to (S), the low frequency modulation magnetic field from an output signal of the detector (11) (H _LF) Means (15) for extracting only the modulation frequency component.
As a signal source (14) for generating a modulation frequency, a signal generator WF1974 manufactured by "NF Circuit Design Block Co., Ltd." is used, and a 28 Hz signal generated thereby is sent to a self-made current source (13). A current of 28 Hz is passed through the modulation coil (12) to generate a modulation magnetic field.
In FIG. 3, a part “15” is drawn as a means for extracting, and it looks as if there is any real part. However, in this embodiment, a function equivalent to that of the lock-in amplifier (component) is realized by the numerical calculation processing of the computer, so there is no lock-in amplifier.
The ferromagnetic resonance of the sample (S) was measured under the above conditions (measurement time 10 minutes). The result is shown in the graph of FIG.
The vertical axis represents the derivative of S ₂₁ (× 10 ⁻⁴ ), and the horizontal axis represents the intensity (unit: Oersted Oe) of the external DC magnetic field (H _B ). According to this, the ferromagnetic resonance magnetic field (H _R ) is 525 Oe.
For comparison, the second path (second microwave) was cut off, and the amplifier (10) was removed, and ferromagnetic resonance was measured under the same conditions with a configuration corresponding to the conventional apparatus (FIG. 6). The result is shown in FIG.

Thus, as is apparent, the data in Example (a), relative to indicate S ₂₁ is clear ferromagnetic resonance signal, the conventional apparatus corresponding data (b) is strong because of noise in the same conditions No magnetic resonance signal is visible.
Comparing these experimental results quantitatively, in this embodiment, compared to the conventional apparatus (FIG. 6), the signal intensity of the ferromagnetic resonance is about 20 times and the noise level is about 1/20. An improvement (improvement) in the S / N ratio of 400 times was observed. In addition, the S / N ratio was improved by about 4 times as compared with the device without the PLL circuit (1a) or the like (corresponding to FIG. 1).

<Measurement result 2>
A smaller sample was measured with the apparatus of Example 2 in FIG. The sample has a diameter φ = 200 nm and a thickness of 5 nm. The preparation method of the sample and others is the same as the above measurement result 1. Measurement conditions were such that the microwave frequency 6.4 GHz, was 13Oe the intensity of the modulated magnetic field H _LF. Other measurement conditions are the same as those of the measurement result 1.
The results measured for this sample are shown in the graph of FIG. A clear ferromagnetic resonance signal can be observed from such a very small sample. This is a volume of about 1/500 of the sample size (0.24 × 5 × 0.07 μm) used in Non-Patent Document 2. From this result, the present invention has improved its sensitivity in the measurement of ferromagnetic resonance. It shows a significant improvement.

  The apparatus of the present invention is suitable for evaluation of magnetic properties such as saturation magnetization and anisotropy magnetic field of a very small magnetic material of micro to nano size level.

DESCRIPTION OF SYMBOLS 1 ... Microwave oscillator 1a ... Reference signal source and phase locked loop (PLL) circuit 2 ... Branch device 3 ... First path 4 ... Second path 5a + 5b ...・ External DC magnetic field (H _B )
6 ... Waveguide 7 ... Phase shifter 8 ... Amplitude adjuster 9 ... Coupler 10 ... Amplifier 11 ... Detector 12 ... Modulation coil 13 ... Current source 14 ··· Low-frequency AC signal source 15 ··· Means for extracting only the modulation frequency component of the low-frequency modulation magnetic field (H _LF ) M · · · Microwave transmission line S ···

Claims (4)

A microwave oscillator, a branching device that divides the microwave output from the oscillator into a first microwave and a second microwave, a first path for transmitting the first microwave, a second path for transmitting the second microwave, Waveguide provided in the middle of one path, magnet for applying an external DC magnetic field H _B to the sample, “n + 0.5” wavelength provided in the first path or the second path, or both, where n is an integer, shift A phase shifter, an amplitude adjuster provided in the first path or the second path or both, a coupler for coupling the first microwave transmitted through the first path and the second microwave transmitted through the second path, An apparatus having an amplifier for amplifying the microwave output from the coupler, and a detector for detecting the microwave output from the amplifier,
A high frequency magnetic field H _RF induced by the first microwave is applied to the sample S arranged in the middle of the waveguide, and the sample S is made ferromagnetic to the sample S with a predetermined intensity by sweeping the intensity of the external DC magnetic field H _B. In a ferromagnetic resonance measuring apparatus that causes resonance,
Means for applying a low-frequency modulation field H _LF to the sample S, and ferromagnetic resonance, characterized in that the addition means for extracting only the modulation frequency component of the low frequency modulation magnetic field H _LF from the output signal of the detector measuring device. The ferromagnetic resonance measuring apparatus according to claim 1.
A ferromagnetic resonance measurement characterized by adding a reference signal source and a phase-locked loop circuit to the microwave oscillator to oscillate a microwave with reduced phase noise and inputting the microwave to the branching device. apparatus. The ferromagnetic resonance measuring apparatus according to claim 1 or 2,
2. The ferromagnetic resonance measuring apparatus according to claim 1, wherein the waveguide is a “coplanar waveguide having a plurality of strip-shaped conductor foils”, and a sample is placed on a central strip-shaped conductor foil. In the ferromagnetic resonance measuring apparatus of Claim 1 or 2 or 3,
A ferromagnetic resonance measuring apparatus having an extinction ratio of 60 dB or more.

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