Magnetoelastic effects in low-dimensional magnetic systems

We consider a new realization of magnetoelastic interactions in low-dimensional magnetic systems. We show that low-dimensional spin systems are unstable with respect to the spontaneous appearance of alternating distortions of the positions of the three-dimensional nonmagnetic atoms (ligands), that surround the magnetic ions. Those distortions are supplemented by the spontaneous onset of alternating effective g factors of the magnetic ions in the phase with short-range interactions. We discuss the possibility of observing the effect in an uniform external magnetic field, which in the situation considered produces both magnetization and staggered magnetization of the magnetic subsystem. The connection of the proposed theory with recent experiments on effectively low-dimensional magnetic systems (organic spin chains, heavy-fermion compounds, rare-earth molybdates) is discussed

Magnetic field-induced phase transitions in the antiferromagnet Nd₀.₆Dy₀.₄Fe₃(BO₃)₄

Low-temperature studies of elastic and magnetic characteristics of the single crystal Nd₀.₆Dy₀.₄Fe₃(BO₃)₄ have been performed. A transition to the antiferromagnetically ordered state of the magnetic subsystem has been manifested in the temperature behavior of the velocity and attenuation of acoustic modes and magnetization. Spin-reorientation phase transitions, which reveal themselves as anomalies in the behavior of elastic and magnetic characteristics of the crystal in the external magnetic field applied along the axis of the trigonal symmetry of the crystal have been discovered. The phase H–T diagram for H || С₃ has been constructed

Magnetic phase transitions in the NdFe₃(BO₃)₄ multiferroic

Low-temperature studies of the behavior of the sound velocity and attenuation of acoustic modes have been performed on a single crystal NdFe₃(BO₃)₄ Transitions of the magnetic subsystem to the antiferromagnetically ordered state at TN ≈ 30.6 K have been revealed in the temperature behavior of the elastic characteristics. The features in the temperature behavior of elastic characteristics of the neodymium ferroborate and its behavior in the external magnetic field, applied in the basic plane of the crystal, permit us to suppose that the transition to an incommensurate spiral phase is realized in the system. This phase transition behaves as the first order one. H–T phase diagrams for the cases H || a and H || b have been constructed. The phenomenological theory, which explains observed features, has been developed

Magnetoelastic studies of Nd₀,₇₅Dy₀,₂₅Fe₃(BO₃)₄ in the external magnetic field: Magnetic phase transitions

We report on results of sound-velocity and sound-attenuation measurements in the Nd₀,₇₅Dy₀,₂₅Fe₃(BO₃)₄ in external magnetic fields up to 5 T, applied along several directions with respect to crystallographic axes, and at temperatures down to 1.7 K. The experimental data are analyzed with a microscopic theory based on exchange-striction coupling and phenomenological theory resulting in a qualitative agreement between theoretical results and experimental data