Tomoya Fukui

Magnetization Process and the Associated Lattice Deformations in an Intermetallic Compound Gd5Ge3

The results of magnetization and synchrotron X-ray diffraction measurements on Gd 5 Ge 3 subject to a pulsed high magnetic field are reported. When the magnetic field, H , is applied parallel to the a -axis, a sudden increase in magnetization, M , has been observed at ∼3.8 T. For H ∥ c , M increases monotonically with H . The magnetization becomes saturated above about 30 T for the two orientations. The lattice constant, a elongates, while c shrinks with increasing H . We calculate the exchange energy under applied magnetic fields based on the proposed magnetic structure assuming an antiferromagnetic exchange interaction in the a – a plane and a ferromagnetic one along the c -axis. We are successful in explaining the opposing behavior of the lattice deformations. Our calculation shows that the change in the lattice constants is proportional to M 2 , in agreement with the observation.

Lattice Deformations Induced by an Applied Magnetic Field in the Frustrated Antiferromagnet HgCr2O4

The way geometric frustration in the pyrochlore antiferromagnet HgCr 2 O 4 is relieved by an applied magnetic field is studied by synchrotron X-ray diffraction. The material shows a structural chan...

1/3 Magnetization Plateau in Spin-1/2 Square Lattice Antiferromagnet (CuBr)Sr2Nb3O10

A new triple-layered perovskite (CuBr)Sr 2 Nb 3 O 10 with the S = 1/2 square lattice has been prepared through a chimie douce route. Presence of strong spin frustration is inferred from zero-field specific heat measurements which exhibit successive phase transitions at 9.3 and 7.5 K. Application of magnetic fields merges the transition temperatures at 3 T, suggesting that the intermediate phase is of magnetic origin with fluctuating spin–spin correlation. Despite the square geometry, magnetization curves have revealed a metamagnetic transition to a novel phase characterized by a 1/3 plateau of the saturated magnetization.

Magnetic Ordering and Tunable Structural Phase Transition in the Chromic Compound CuMoO4

We report the first observation of long-range magnetic order in the chromic compound CuMoO 4 at 1.75 K by means of a specific heat measurement in zero magnetic field. Magnetization measurements performed up to 57 T at 4.2 K indicate a plateau at 1/3 of the saturated magnetization consistent with a simple magnetic model of two non-interacting Cu 2+ spins and two isolated antiferromagnetic dimers ( J / k B = 26 K). A large temperature-hysteresis in the magnetic susceptibility is observed to originate from the structural phase transition and to be closely related to chromism between α-CuMoO 4 (green) and γ-CuMoO 4 (brownish-red). This discontinuous phase transition is tunable using substitutional effects in Cu 1- x Zn x MoO 4 (0≤ x ≤0.1) and CuMo 1- y W y O 4 (0≤ y ≤0.1) over a wide range of temperatures.

Magnetization Process in GdB4

Magnetization measurements are made on single crystal samples of GdB 4 under static fields up to 14 T and pulsed fields up to ∼60 T. When the external magnetic field, H , is applied along the [110] spin easy axis, the magnetization increases non-linearly at around 12 T, indicating a spin reorientation from the easy axis to the direction perpendicular to H . The values of saturation field, H s , are, H s [110] ≃52 T, H s [100] ≃52 T and H s [001] ≃54 T. We analyze the results based on the two-dimensional model proposed by Shastry and Sutherland [B. S. Shastry and B. Sutherland: Physica B 108 (1981) 1069]. We obtain J 1 / k B =-8.9 K and J 2 / k B =-0.68 K, where, J 1 and J 2 are the diagonal exchange interaction and the exchange interaction along the edges of a square, respectively.

Structure and Magnetic Properties of New Trigonal Iron-Boracite, Fe3B7O13(OH)

The magnetic properties of a newly synthesized compound, Fe 3 B 7 O 13 (OH), are reported. The space group and lattice constants at room temperature are R 3 c H ( trigonal , #161), a = 8.590(3) A and c = 21.107(7) A. In this compound, three Fe 2+ ions form an equilateral triangular trimer sharing a hydroxide ion, and the trimers further construct a trigonal lattice. The magnetic susceptibility exhibits an antiferromagnetic phase transition accompanied by a steep drop in susceptibility at T N ≈4.8 K under small magnetic fields. Mossbauer spectroscopy indicates that Fe ions are divalent. It also suggests a simple spin structure in which all of the spins are equally canted from the principal axis of the electric-field gradient below T N . This magnetic ground state is, however, easily destroyed by almost 1 T of magnetic field regardless of its direction. In addition to this transition, successive metamagnetic transitions are induced by larger magnetic fields. The additional transitions are strongly dependent...