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Universal magnetic structure of the half-magnetization phase in Cr-based spinels determined using a neutron diffraction technique under a pulsed magnetic field up to 30 TJan. 22 , 2010A joint research group has established the neutron diffraction technique under pulsed high magnetic fields. Using this technique, magnetic structures in a magnetic field up to 30 tesla, which is as high as 0.75 million times of terrestrial magnetism, can be determined. The group consists of Prof. Hiroyuki Nojiri at Institute for Materials Research, Tohoku University, Dr. Masaaki Matsuda at Japan Atomic Energy Agency (JAEA) and Dr. Hiroaki Ueda at Institute for Solid State Physics, University of Tokyo. Cr-based spinel compounds ACr2O4 (A=Mg, Zn, Cd, and Hg) are so far the best model systems for a network of corner-sharing tetrahedrons with isotropic nearest-neighbor antiferromagnetic interactions, which gives rise to a strong magnetic frustration. The systems exhibit novel spin-Peierls phase transitions from cubic spin liquid to non-cubic Néel states at low temperatures, indicating a strong spin-lattice coupling. Bulk magnetization studies on ACr2O4 revealed the magnetic field-induced half-magnetization plateau states that are stable over a wide range of field, which also indicates a strong spin-lattice coupling. The research team determined the magnetic structure in the half-magnetization plateau phase in CdCr2O4. The result indicates that the observed P4332 state is the generic ground state of the field-induced phase of the Cr-spinels, despite their different zero-field spin-lattice states. This suggests that there is a universal field induced spin-lattice coupling mechanism at work in the Cr-based spinels. This study demonstrates that the new technique makes it possible to investigate novel field-induced states of complex materials that were beyond the reach of the steady magnetic field technology. It would contribute to designing and development of new magnetic materials for magnetic memory or sensor. The research results have been published in "Physical Review Letters" (a scientific journal issued by American Physical Society) on January 26, 2010. The paper’s title is "Universal magnetic structure of the half-magnetization phase in Cr-based spinels".
Magnetic field dependence of the peak intensity of the (a) (1.0675, -1.0125, 0.0275), (b) (1, -1, 0), and (c) (2, -2, 0) reflections measured at T=2.5 K with the ascending (filled circles) and descending (open circles) field. The incommensurate magnetic peak (1.0675, -1.0125, 0.0275) disappears and the commensurate magnetic peak (1, -1, 0) appears at the critical field, Hc = 28 T.
The magnetic structure of the Cr3+ spins in the magnetization plateau phase in CdCr2O4 determined by a neutron diffraction technique. Blue and red circles represent up and down spins, respectively. The distance between the blue circles is elongated and the distance between blue and red circles is contracted. This structural distortion stabilizes the magnetic structure, indicating a strong spin-lattice coupling. |
