Interplay among spin, orbital, and lattice degrees of freedom in a frustrated spinel Mn3O4

Abstract

We have investigated magnetic-field (H [100]) effect on a spin-frustrated tetragonally distorted spinel Mn 3 O 4 by measurements of magnetization, dielectric constant, and strain as well as synchrotron x-ray and neutron diffraction. In two low-temperature phases below 40 K, long-wavelength lattice modulations coupled with magnetic order have been confirmed, revealing spin-lattice coupling caused by the exchange striction in the geometrically frustrated Mn 3+ spin moments on the distorted pyrochlore lattice. A magnetic-field-induced phase transition has been found at low temperatures, which involves an abrupt change in both structural and magnetic configurations. The magnetostructural phase transition by the application of a magnetic field H [100] is discussed in terms of interplay among spin, orbital, and lattice degrees of freedom.

Effects of magnetic field and twin domains on magnetostructural phase mixture inMn3O4: Raman scattering studies of untwinned crystals

“…A structural modulation with a propagation vector identical to that of the magnetic modulation has also been observed, 24 demonstrating the strong spin-lattice coupling in Mn 3 O 4 . This strong coupling is proposed to originate from the geometric frustration of the Mn 3+ spins, which is only partially relieved by the hightemperature, cubic-to-tetragonal distortion.…”

“…13,23,24 Magneticfield-induced changes in the low-frequency dielectric constant and crystal dimensions have been attributed to field-induced transitions between two distinct magnetostructural phases, which are discussed below. 24 A highresolution x-ray diffraction study recently revealed that these two magnetostructural phases in fact coexist below the Néel temperature in polycrystalline Mn 3 O 4 , 25 demonstrating the near degeneracy of their free energies. Thus, Mn 3 O 4 belongs to the class of strongly correlated materials whose bulk physical parameters are 'tunable' due to distinct phases existing in close proximity.…”

“…This strong coupling is proposed to originate from the geometric frustration of the Mn 3+ spins, which is only partially relieved by the hightemperature, cubic-to-tetragonal distortion. 24,29 The resultant exchange striction in the magnetically-ordered state leads to a cell-doubled-orthorhombic (CDO) structure whose modulation is of the form pictured in Fig. 1(b netic fields applied in the (001) plane (magnetic easy plane).…”

“…2, left) utilizes the as-grown crystal face, which presents a (101) (or, equivalently, (011) ) axis in the magnetically ordered state causes these directions to become magnetically and structurally inequivalent, as the crystal elongates along the direction of the applied magnetic field. 24 We refer to this elongated direction as the [110] direction.…”

“…10,24,30 For example, cooling a sample in the presence of a H = 1 T magnetic field applied along the [110] direction drives a uniform orthorhombic distortion of the lattice via spin-orbit coupling and inverse exchange striction. 24 The resultant face-centeredorthorhombic (FCO) structure is proposed to be of the form pictured in Fig. 1(c) (T melt > 1800 K); however, such crystals may display twin domains due to the T = 1440 K cubic-to-tetragonal transition in this material.…”