Magnetic measurement system and apparatus utilizing X-ray to measure comparatively thick magnetic materials

Abstract

A magnetic measurement system includes an X-ray source, a monochromator that converts right- and left-polarization X-ray into right- and left-monochromatic X-ray, an aperture slit that allows the right- and left-monochromatic X-ray to pass through, an analytical section, and piezoelectric scanning devices. The analytical section has a Fresnel zone plate that receives and focuses the right- and left-monochromatic X-ray on a single point being 10 nm or less wide of a magnetic sample, an order-sorting aperture that allows the focused X-ray to selectively pass through, a sample-stage that sets a comparatively thick magnetic sample that is more than 150 nm thick and less than or equal to 1000 nm thick to be irradiated with the X-ray, and an X-ray-detector that detects transmittance of transmission X-ray passing through the comparatively thick sample and that generates X-ray magnetic circular dichroism (XMCD) data by directly measuring the detected transmittance of the transmission X-ray.

Claims

1. A magnetic measurement system, comprising: an X-ray source; a monochromator that converts right- and left-polarization X-ray of the X-ray source into right- and left-monochromatic X-ray; an aperture slit that allows the right- and left-monochromatic X-ray converted by the monochromator to pass through; an analytical section having a combination of a Fresnel zone plate (FZP) that receives and focuses the right- and left-monochromatic X-ray on a single point being 10 nm or less wide of a magnetic sample, an order-sorting aperture (OSA) that allows the X-ray focused by the FZP to selectively pass through, a sample-stage that sets the comparatively thick magnetic sample that is more than 150 nm thick and less than or equal to 1000 nm thick to be irradiated with the X-ray, and an X-ray-detector that detects transmittance of transmission X-ray passing through the comparatively thick sample set by the sample-stage and that generates X-ray magnetic circular dichroism (XMCD) data by directly measuring the detected transmittance of the transmission X-ray; piezoelectric scanning devices that accurately control X-, Y- and Z-stages of the analytical section with an accuracy in nanometers which includes the sample-stage of the analytical section; wherein, the system accurately generates XMCD data by directly measuring transmittance of transmission X-ray passing through the comparatively thick magnetic sample even within an external magnet field.

2. A magnetic measurement apparatus, comprising: an analytical section having a combination of a Fresnel zone plate (FZP) that focuses right- and left-polarization X-ray on a single point being 10 nm or less wide of a polycrystalline magnetic sample, an order-sorting aperture (OSA) that allows the X-ray focused by the FZP to selectively path through, a sample-stage that is configured to set the polycrystalline magnetic sample that is more than 150 nm thick and less than or equal to 1000 nm thick to be irradiated with the X-ray passing the OSA, an X-ray-detector that, using an Avalanche photodiode, detects transmittance of transmission X-ray passing through the polycrystalline magnetic sample, and that generates two-dimensional X-ray magnetic circular dichroism (XMCD) data based on the detected transmittance of the transmission X-ray; piezoelectric devices that control X-, Y- and Z-stages of the analytical section with an accuracy in nanometers which includes the sample-stage of the analytical section; wherein, the apparatus accurately generates two-dimensional XMCD data of each single crystalline-grain contained in the polycrystalline sample by directly measuring transmittance of transmission X-ray passing through the polycrystalline sample even within an external magnet field.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-eye view showing the sample before etching.

(2) FIG. 2 is a cross-eye view showing the sample after etching.

(3) FIG. 3 is a cross-eye view showing the observation process.

(4) FIG. 4 is a schematic view illustrating the principle of X-ray magnetic circular dichroism (XMCD).

(5) FIG. 5 is a configuration of the present apparatus equipping a scanning transmission electron microscope to carry out the present method.

(6) FIG. 6 is a configuration of the present apparatus to carry out the present method.

(7) FIG. 7 shows a relationship between X-ray transmittance and thickness of the sample.

(8) FIG. 8 is a transmission electron microscope (TEM) image of the sample plane.

(9) FIG. 9 is a cross-eye view showing a sample geometry after processing.

(10) FIG. 10 shows thickness-distribution obtained from intensity of the transmission X-ray.

(11) FIG. 11 shows an observed XMCD interval distribution.

(12) FIG. 12 shows a result of magnetic characteristic measurement.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

(13) First the sample to be measured is cut into a microtome section of 50 nm1000 nm in thickness. Preferable thickness of microtome section can be determined mainly by sample material, kinetic energy of used x-ray and transmittance of X-ray. For the present invention, a use of X-ray transmittance of 1% or more is sufficient for the measurement of micro-crystal grains. The thickness of microtome section is preferably 1000 nm or less, more preferably 150 nm1000 nm. The preparation of the microtome section of 150 nm1000 nm in thickness makes it possible to measure magnetic characteristic of micro-crystal grains and imaging with resolution of 10 nm or less, accordingly makes it possible to study local magnetic sensitivity induced by an applied magnetic field.

(14) For the preparation of microtome section, various methods can be used. For the preparation of microtome section of 1000 nm or less, the etching using focused ion beams is preferable. For example, the sample 1 as shown in FIG. 1 is etched using the focused ion beam 2 followed by obtaining a microtome section 1000 nm or less thick as shown in FIG. 2.

(15) As the sample, various materials, for example, soft magnetic materials, hard magnetic materials, magnetic materials with plural magnetic phases, can be applied. As an apparatus to generate the focused ion beam 2, a usual focused ion beam machine comprising an ion beam gun and optic system to generate Ga-ion beam and scanning system to scan ion beams on the sample surfaces can be utilized.

(16) After etching the sample using the focused ion beam 2, an observation place is irradiated with the X-ray 3, followed by detection the transmission X-ray to measure magnetic characteristic of the sample.

(17) X-ray to be applied the sample is preferably circular polarization X-ray focused into 10 nm in beam size. In practice, the X-ray 3 generated by an X-ray generator which is capable of generating right-circular polarization X-ray and left-circular polarization X-ray enters a measurement place of the sample 1, successively the transmission X-ray is detected by a detector. The intensity IR of the transmission X-ray corresponding to right-circular polarization X-ray and the intensity IL of the transmission X-ray corresponding to left-circular polarization X-ray are alternately measured, successively the difference between them, that is, XMCD, can be detected. This measurement is corresponding to the magnetization in the inside of the X-ray incident position. Successively, the same measurement is carried out while two-dimensional (2-D)-scanning the sample, thus a 2-D-data is obtained. As another method, the X-ray absorption parallel to the magnetic field direction of the sample and that in the anti-parallel direction are measured using either right-circular polarization X-ray or left-polarization X-ray, the difference between them, that is, XMCD, can be also measured.

(18) Further explaining in detail, magnetic information can be obtained using the principle of XMCD as shown in FIG. 4. The method has the element-selectivity, that is, the method is capable of measuring the direction of magnetic moment for a specific element by adjusting X-ray energy with an excitation energy gap between specific electron orbital.

(19) As shown in FIG. 4, an absorption spectrum changes in accordance with the direction of angular momentum of circular polarization light and the direction of angular momentum of atom. The basic magnetic properties such as orbital angular momentum, spin angular momentum and magnetic momentum can be measured from (1) the measurement of angular momentum of circular polarization X-ray and that of atom in the case both momentums are parallel; (2) the measurement of angular momentums of circular polarization X-ray and that of atom in the case both momentums are anti-parallel; (3) the difference between them, that is, XMCD.

(20) As shown in FIG. 5, the present measurement system comprises a radiation source, a monochromator to disperse white radiation into monochromatic X-ray, an aperture slit to enter X-ray of the radiation source into an analytical section, the analytical section equipping a combination of Fresnel zone plate and order-sorting aperture to focus X-ray flux passing the aperture slit, a sample-stage to set a sample to be irradiated with X-ray and an X-ray-detector to detect transmission X-ray passing the sample; which is characterized by the measurement of X-ray magnetic circular dichroism of X-ray passing the sample within magnetic field or nonmagnetic field. The XMCD at each sample place can be measured through precisely scanning the sample stage and using focused radiation light.

(21) As shown in FIG. 6, the present measurement apparatus comprises the analytical section equipping a combination of Fresnel zone plate (FZP) and order-sorting aperture (OSA) to focus X-ray flux passing the aperture slit, the sample stage to set a sample to be irradiated with X-ray and the X-ray-detector equipping the Avalanche photodiode to detect transmittance of transmission X-ray passing the sample. The FZP, OSA, sample-stage and X-ray-detector are equipping piezoelectric devices, therefore their X-, Y- and Z-stages can be controlled to an accuracy of nanometers. For the efficient X-ray detection under a vacuum and magnetic field, the Avalanche photodiode (APD) having dynamic ranges and optical fibers which is used within external magnetic field is preferable. Also, the exclusion of large-generating parts such as motors and laser prevents the resolution of APD from thermal drift. Therefore, such exclusion is necessary to measure XMCD of a single particle in the nano-crystalline magnet. In addition, for the measurement in the magnetic field, a combination system of superconductive magnet and use of non-magnetic parts and devices is preferable.

(22) A bulk sample of Nd.sub.2Fe.sub.14B or Sm.sub.2Fe.sub.17N.sub.3 is used as the sample. The sample is fabricated using focused ion beams, followed by measuring X-ray transmittance at each sample position. The measurement of X-ray transmittance for the Nd.sub.2Fe.sub.14B sample or Sm.sub.2Fe.sub.17N.sub.3 sample is based on the Nd-absorption-edge X-ray energy (980.4 eV) or Sm-absorption-edge X-ray energy (1083.3 eV), respectively. The result is shown in FIG. 7.

(23) From the result of FIG. 7, it is found that the Nd.sub.2Fe.sub.14B sample is measurable in the range 750 nm or less, 500 nm or less, 100 nm or less in thickness and that the Sm.sub.2Fe.sub.17N.sub.3 sample is measurable in the range 1000 nm or less, 500 nm or less, 100 nm or less in thickness.

(24) A bulk sample of NdFeB magnet is used for the sample is observed. From FIG. 8, the observed crystalline particle is estimated to be about 50 nm-100 nm in size.

(25) Next, the fabricated sample as shown in FIG. 9 is etched using focused ion beam. X-ray transmittance of the obtained sample is measured, followed by determining thickness distribution as shown in FIG. 10. The thickness of the sample can be determined from the following equation.
t= ln(I.sub.0/I)
where, t is a sample thickness, is substance-specific X-ray transmittance, I.sub.0 is intensity of X-ray irradiation, I is intensity of transmission X-ray.

(26) As shown in FIG. 10, the sample is found to be fabricated into 50 nm1000 nm in thickness.

(27) Next, the fabricated sample is irradiated with circular polarization X-ray, followed by measuring magnetic characteristic. FIG. 11 shows a XMCD space distribution. In FIG. 11, the difference in contrasting density of white and black colors shows the difference for the direction of magnetic moment corresponding to the magnetic domain phase of magnetic body. The magnetic characteristic at the part (A) in FIG. 11 is found to have two peaks at 981 eV and 1003 eV, respectively, as shown in FIG. 12. From the spectrum analysis, it is found that the magnetism property such as spin magnetic momentum and orbital magnetic momentum can be measured for a single crystal particle.

EXPLANATION OF REFERENCE CHARACTERS

(28) 1 sample 1 2 focused ion beam 3 X-ray