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High-Accuracy Magnetic Property Measurement Method by Separating Spin and Orbital Magnetic Moments (Press Release)

Release Date
04 Mar, 2013
  • BL08W (High Energy Inelastic Scattering)
- Promising tool for evaluating and developing high-performance magnets -

Japan Synchrotron Radiation Research Institute (JASRI)
University of Hyogo

A joint research group of JASRI and the University of Hyogo combined magnetic Compton scattering*1 with the conventional measurement method for magnetization. This has led to the successful development of a high-accuracy magnetic property measurement method for separately measuring the magnetic hysteresis loop*3 of the spin magnetic moment*2 and that of the orbital magnetic moment.*4

The magnetic force of magnets used in motors provides two moments: one is the spin magnetic moment, which is from the electrons themselves in the materials constituting the magnets, and the other is the orbital magnetic moment, which is generated by the electrons orbiting the nucleus. The orbital magnetic moment is considered to be a factor determining the magnetic intensity of magnets and the direction of the magnetic field in crystals and greatly depends on the type and arrangement of atoms constituting the magnetic material. Hence, the orbital magnetic moment can be used as a key index to evaluate the performance of magnetic materials and in the design of materials used for high-performance magnets. However, only the magnitude of the total magnetic moment consisting of the spin and orbital magnetic moments can be measured by the conventional measurement methods. The development of a method for separately measuring these magnetic moments has been required.

Using the high-energy circularly polarized X-rays*6 at the High-Energy Inelastic Scattering Beamline (BL08W) of SPring-8,*5 the research group successfully measured the spin magnetic moment with high accuracy by magnetic Compton scattering, thus realizing the high-accuracy separate measurement of the spin and orbital magnetic moments.

The method developed for separate measurement can be used as a powerful tool for designing magnetic materials and evaluating their performance. This achievement is expected to accelerate the development of high-performance magnets that do not require expensive rare-earth elements.

This study was carried out by the joint research group of Masayoshi Ito (associate senior scientist) and Yoshiharu Sakurai (associate chief scientist) of JASRI and Akihisa Koizumi (associate professor) of the University of Hyogo. The results were published online in the American scientific journal Applied Physics Letters on 27 February 2013.

Publication:
"Spin and orbital magnetization loops obtained using magnetic Compton scattering"
M. Itou, A. Koizumi, Y. Sakurai
Applied Physics Letters 102 082403, published online 27 February 2013.

<<Figures>>

Fig. 1
Fig. 1

When a bar magnet is divided into two, two smaller magnets are obtained. Further dividing these magnets results in atoms that serve as magnets, which are called atomic magnets.

Fig. 2
Fig. 2

Electrons are responsible for the magnetic force of atomic magnets. The electrons are magnetized by spinning at a constant rate as well as by orbiting the nucleus. The magnitude of the magnetism due to the spinning electrons is called the spin magnetic moment, whereas that due to the orbiting electrons is called the orbital magnetic moment. The orbital magnetic moment can be used as a key index to evaluate the performance of magnets and in the design of their materials.

Fig. 3 Magnetic Compton scattering system
Fig. 3 Magnetic Compton scattering system

Circularly polarized X-rays with an energy of 182 keV are selected from among the high-energy circularly polarized X-rays radiated from an inserted light source called an elliptical multipole wiggler*7 and are introduced into the magnetic Compton scattering system. A sample is placed in the magnetic field of a superconducting electromagnet. X-rays scattered at the sample are detected by an X-ray detector.

Fig. 4 Separate magnetic hysteresis loops of spin and orbital magnetic moments
Fig. 4 Separate magnetic hysteresis loops of spin and orbital magnetic moments

<<Glossary>>
*1 Magnetic Compton scattering
Magnetic Compton scattering can be used as an experimental technique for determining the properties of atomic magnets by detecting circularly polarized X-rays scattered at spinning electrons. The spin magnetic moment can be quantitatively measured by this technique.

*2 Spin magnetic moment
An electron spinning at a constant rate acts as a magnet. The magnitude of the magnetism of the spinning electron is called the spin magnetic moment.

*3 Magnetic hysteresis loop
When the sign of an external magnetic field applied to a magnet is changed between positive and negative, the magnitude of the magnetization of the magnet draws different curves to form a loop, which is called a magnetic hysteresis loop. Magnetic hysteresis loops are widely used as curves that characterize magnets.

*4　Orbital magnetic moment
An electron orbits the nucleus, giving rise to magnetism. The magnitude of the magnetism of the orbiting electron is called the orbital magnetic moment.

*5 SPring-8
SPring-8 is a synchrotron radiation facility that provides the world’s highest-brilliance synchrotron radiation. It is owned by RIKEN and located in Harima Science Park City, Hyogo Prefecture, Japan. JASRI is responsible for the operation, management, and promotion of the use of SPring-8. The name “SPring-8” is derived from “Super Photon ring-8 GeV”. When the direction of the electron beams accelerated to nearly the speed of light is changed by magnets, electromagnetic waves are emitted in the tangential direction; these waves are synchrotron radiation. When the electron beam has a higher energy and the change in the traveling direction is large, synchrotron radiation contains shorter-wavelength lights such as X-rays. In particular, the following three facilities are known as the third-generation large synchrotron facilities: SPring-8 in Japan, the Advanced Photon Source (APS) in the USA, and the European Synchrotron Radiation Facility (ESRF) in France. Because the ring at SPring-8 enables an electron acceleration energy of 8 giga-electronvolts to be generated, synchrotron radiation in a wide range of wavelengths can be obtained including far-infrared light, visible light, vacuum ultraviolet light, soft X-rays, and hard X-rays. SPring-8 is used by researchers both in Japan and overseas for joint research in various fields such as materials science, earth science, life science, environmental science, and industrial applications.

*6 Circularly polarized X-rays
X-rays are electromagnetic waves that have both electric and magnetic fields, which oscillate perpendicularly to each other. X-rays that travel with an electric field whose oscillating plane unidirectionally rotates at a constant rate are referred to as circularly polarized X-rays, and can be used as a probe for examining the properties of magnets. X-rays that travel with an electric field whose oscillating plane does not rotate and has a fixed direction are referred to as linearly polarized X-rays.

*7 Elliptical Multipole wiggler
An elliptical multipole wiggler is a piece of equipment used for producing circularly polarized X-rays by forcing electrons accelerated to nearly the speed of light to move along an elliptic orbital on the plane perpendicular to their traveling direction. Since the X-rays produced by the wiggler are a mixture of circularly and linearly polarized X-rays, the wiggler is called an elliptically polarized wiggler.


For more information, please contact:
  Dr. Masayoshi Ito (JASRI)
    E-mail : mail1

  Associate Prof. Akihisa Koizumi (University of Hyogo)
    E-mail : mail1