Synthesizing New Half-Metallic Material with High Magnetic Transition Temperature- New material applicable to spintronic devices including ultrahigh -density magnetic memories– (Press Release)
- Release Date
- 23 May, 2014
- BL25SU (Soft X-ray Spectroscopy of Solid)
Kyoto University
Japan Synchrotron Radiation Research Institute (JASRI)
Japan Science and Technology Agency (JST)
Key points
• Synthesizing a new material applicable to future devices in the field of spintronics
• Achieving a high transition temperature and a large magnetic moment by controlling the ordered arrangement of magnetic ions
• Demonstrating the spin polarization of conduction electrons by experiments and theoretical calculations
• Expanding the variety of materials that can be used in functional oxide electronics
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A research group led by Yuichi Shimakawa (professor) of the Institute for Chemical Research, Kyoto University, and Masaichiro Mizumaki (associate senior scientist) of SPring-8, JASRI, in collaboration with a research group for the Centre for Science at Extreme Conditions and School of Chemistry, the University of Edinburgh in the UK, has succeeded in synthesizing a new A- and B-site-ordered perovskite oxide*2 that can be used in future devices in the field of spintronics*1 such as high-density magnetic memories and high-sensitivity sensors. Spintronics has been attracting interest as a technology developed by the fusion of electronics and magnetic properties, and is used in devices such as ultrahigh-density magnetic memories. The conduction electrons in the materials used in such devices should have a high spin polarization*3. Also, the temperature at which the conduction electrons are spin-polarized (magnetic transition temperature) should be sufficiently higher than room temperature for the stable operation of such devices, and the development of such materials has been desired. The research group of this study succeeded in synthesizing a new A- and B-site-ordered perovskite oxide CaCu3Fe2Re2O12 in which multiple elements are regularly arranged in the A and B sites, and found that this material is a ferrimagnetic*4 metal with a magnetic transition temperature much higher than room temperature and a large magnetization. On the basis of theoretical calculations of the electronic state and the measurement of the polycrystalline grain-boundary tunneling magnetoresistance effect*5, they also demonstrated that this material is a half metal*6 in which the spins of the conduction electrons are polarized. These results were achieved through the development of materials by using the principles of solid-state chemistry to design and synthesize ordered arrangements of the constituent elements of materials. The discovery of the new material is expected to significantly promote research and development in the field of oxide electronics, expanding the variety of oxide electronic materials with various integrated functions. The achievements of this study were published in the British online journal Nature Communications, a publication of Nature Publishing Group, on 22 May 2014. Publication： |
<<Caption>>
2+and Cu2+ions at a ratio of 1:3 in the A sites and that of Fe3+and Re5+ions at a ratio of 1: 1 in the B sites are characteristics of the perovskite structure.
The large magnetization observed at 560 K and below indicates that the magnetic transition temperature of this material is much higher than room temperature (~300 K).
Because the Cu2+in the A sites and the Fe3+in the B sites showed the same negative and positive MCD spectra at the two absorption edges, L3 and L2, the magnetic moments of these two types of ions are ferromagnetically aligned in the same direction.
The new material synthesized in this study shown in (c) is a ferrimagnetic oxide in which the spins of Cu2+ in the A sites and Fe3+ in the B sites are ferromagnetically aligned in the same direction because of the antiferromagnetic interactions between the spins of Re5+ introduced in the B sites and the spins of both Cu2+ in the A sites and Fe3+in the B sites.
From theoretical calculations of the ground-state electronic structure, a gap is observed to exist in the spin-up electron bands and only spin-down electron bands are observed to cross the Fermi level (EF). These results suggest a half-metallic electronic state with only spin-down conduction electrons.
When the electrical resistance of polycrystalline samples is measured in a magnetic field, the grain-boundary tunneling magnetoresistance effect, namely, a change in the resistance depending on the direction and magnitude of the magnetic field, is observed in a weak magnetic field ≤3 kOe because of the spin-polarized conduction electrons.
<<Glossary>>
*1 Spintronics
A new electronic and magnetic control technology integrating electronics to control electronic devices through the control of electrons and magnetic engineering to control the spins of electrons.
*2 Perovskite oxide
Oxides with the formula ABO3having a crystal structure with a corner-sharing octahedral network in which transition metal ions in the B sites are surrounded by oxygen atoms.
*3 Spin polarization
The difference between the numbers of spin-up and spin-down electrons among the conduction electrons.
*4 Ferrimagnetic
A magnetic property of materials having two or more types of magnetic ions with their magnetic moments aligned in opposite directions but showing overall ferromagnetic magnetization because of the difference in the magnitude of the magnetic moments.
*5 Magnetoresistance effect
A change in the electrical resistance caused by a change in the magnetic field. In particular, a significant change in the electrical resistance is called the giant magnetoresistance (GMR) effect, for which the French scientist Albert Fert and the German scientist Peter Grünberg won the 2007 Nobel Prize for Physics. A change in the electrical resistance depending on the direction of spins aligned by a magnetic field when spin-polarized electrons conduct through a thin insulating layer (a layer normally blocking electricity) by the tunneling effect is called the tunneling magnetoresistance effect. In polycrystalline samples consisting of small crystal grains, crystal grain boundaries are considered to play the role of insulating tunnel barriers.
*6 Half metal
Ferromagnetic metal materials consisting of conduction electrons with spins aligned in one direction. Ideally, such materials have a spin polarization of 100%. Significant changes in spin-dependent properties such as the magnetoresistance effect are easily measured in such materials because of their high spin polarization. Therefore, half-metallic materials have an advantage over existing materials for use in spintronic devices such as high-density magnetic memories and high-sensitivity sensors.
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