Observing Relationship between Perpendicular Magnetic Anisotropy and "Shape of Chemical Bonding" for the First Time in the World - New Guidelines for Developing High-Density Magnetic Recording Methods (Press Release)
- Release Date
- 12 Apr, 2010
- BL08W (High Energy Inelastic Scattering)
Japan Synchrotron Radiation Research Institute
Gunma University
University of Hyogo
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A joint research team consisting of scientists from Gunma University (Kuniaki Takata, President), Japan Synchrotron Radiation Research Institute (JASRI; Tetsuhisa Shirakawa, President), and University of Hyogo (Masayoshi Kiyohara, President) determined the relationship between perpendicular magnetic anisotropy and the shape of the charge density distribution of electrons associated with the chemical bonding (symmetry of wave function*2) in Co/Pt and Co/Pd artificial lattice*1 layers (nano-multilayers) at SPring-8 for the first time in the world. This was achieved by high-precision magnetic Compton scattering experiments*3 using the high-intensity high-energy X-rays produced at SPring-8. Perpendicular magnetic films utilizing the properties of perpendicular magnetic anisotropy were first applied to magnetic recording media of hard disc in practice in 2005 and are now widely used; however, the mechanism of perpendicular magnetic anisotropy has not yet been clarified. It is strongly expected that the results of this study will contribute to the design of device materials used for IT equipment with a large capacity and a high transfer rate. The study involved joint research by Hiroshi Sakurai, a professor of the Graduate School of Engineering at Gunma University; Masayoshi Ito, an associate senior scientist, and Yoshiharu Sakurai, an associate chief scientist, at JASRI; and Akihisa Koizumi, an associate professor of Graduate School of Materials Science at University of Hyogo. The achievements were published online in an American scientific journal, Applied Physics Letters, on 12 April 2010. Publication: |
<Figure>
Fig. 2 For perpendicular magnetic recording using a perpendicular magnetic film, bar magnets are aligned longitudinally, and more bar magnets can be aligned in a given area than in conventional horizontal magnetic recording.
Fig. 4 By changing the thickness of the Pt or Pd layer of the Co(0.8 nm)/Pt (x nm) or Co(0.8 nm)/Pd (x nm) (x=0.8-4.0) artificial lattice layer, the lattice constant of the Co layer changes, and the film becomes a perpendicular magnetic film (perpendicular and in-plane magnetizations when the perpendicular magnetic anisotropy energies per unit area are positive and negative, respectively).
Fig. 5 The research group found that the shape of chemical bonding (symmetry of wave function: percentage of the number of magnetic quanta) changes with the change in the lattice constant of the Co layer.
<Glossary>
*1 Artificial lattice
An artificial lattice contains thin alternately stacked layers of various types of atom with a thickness of 2-3 nm (a nanometer is a billionth of a meter), corresponding to the length of a sequence of more than ten atoms.
*2 Wave function
In quantum mechanics, it is impossible to determine the exact position of an electron in a material in the steady state, but the probability that the electron exists at a particular position can be determined. The mathematical formula used to express this probability is a function of the position and corresponds to a formula representing a wave. It is thus called a wave function and is generally expressed as Ψ(r). The charge density distribution is expressed as |Ψ(r)|2. The shape of chemical bonding is assumed to represent the shape of the charge density distribution of electrons associated with the chemical bonding.
*3 Magnetic Compton scattering experiments
Compton scattering is the elastic collision between electrons and X-ray photons, similar to that between billiard balls. By measuring the energy of X-ray photons scattered after the collision with electrons, the momentum (and thus the velocity) of the electrons before collision can be determined. Circularly polarized X-ray photons interact with electron spins in the material, by which the momentum resulting from magnetism can be measured. This phenomenon is called magnetic Compton scattering.
For more information, please contact: Dr. Yoshiharu SAKURAI |
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