Structural modulation of spinel ZnCr2Se4 in the vicinity of antiferromagnetic phase transition induced by an applied magnetic field

摘要

Magnetic and structural phase transitions of normal-type spinel ZnCr2Se4 have been studied as functions of applied magnetic field and temperature by means of neutron diffraction. It is found that the spiral spin order of Cr3+ ions is largely affected by the magnetic field, and the satellite-like magnetic reflections are largely decreased in the magnetic field of 0.6 T < H < 1.2 T and disappear at H greater than or equal to 1.2 T, when the magnetic field was applied vertically to an orthorhombic axis [001]. This means that the spiral configuration of the ferromagnetic CrSe4 chains is perfectly disordered around two-fold screw axes in an orthorhombic symmetry phase (Fddd structure) by the magnetic field H greater than or equal to 1.2 T, though the structural phase transition (T-C) between cubic and orthorhombic symmetry phases simultaneously occurs at the antiferromagnetic phase transition temperature (T-N approximate to 21 K) in no magnetic field. It is also found that the main reflections show a magnetic field dependence similar to that of the magnetic reflections. Pseudo-tetragonal displacements of Se ions below T-N are modulated by the applied magnetic field. The 3 T magnetic field induces a metastable structural transition at about 15 K, after initially cooling down to about 2 K in no applied magnetic field. The transition is related to the modulation from pseudo-tetragonal to pseudo-cubic displacements of Se ions. [References: 20]