9 research outputs found
Spin excitations of magnetoelectric LiNiPO in multiple magnetic phases
Spin excitations of magnetoelectric LiNiPO are studied by infrared
absorption spectroscopy in the THz spectral range as a function of magnetic
field through various commensurate and incommensurate magnetically ordered
phases up to 33\,T. Six spin resonances and a strong two-magnon continuum are
observed in zero magnetic field. Our systematic polarization study reveals that
some of the excitations are usual magnetic-dipole active magnon modes, while
others are either electromagnons, electric-dipole active, or magnetoelectric,
both electric- and magnetic-dipole active spin excitations. Field-induced
shifts of the modes for all three orientations of the field along the
orthorhombic axes allow us to refine the values of the relevant exchange
couplings, single-ion anisotropies, and the Dzyaloshinskii-Moriya interaction
on the level of a four-sublattice mean-field spin model. This model also
reproduces the spectral shape of the two-magnon absorption continuum, found to
be electric-dipole active in the experiment
Squeezing the periodicity of Néel-type magnetic modulations by enhanced Dzyaloshinskii-Moriya interaction of 4d electrons
In polar magnets, such as GaVS, GaVSe and VOSeO, modulated magnetic phases namely the cycloidal and the Néel-type skyrmion lattice states were identified over extended temperature ranges, even down to zero Kelvin. Our combined small-angle neutron scattering and magnetization study shows the robustness of the Néel-type magnetic modulations also against magnetic fields up to 2 T in the polar GaMoS. In addition to the large upper critical field, enhanced spin-orbit coupling stabilize cycloidal, Néel skyrmion lattice phases with sub-10 nm periodicity and a peculiar distribution of the magnetic modulation vectors. Moreover, we detected an additional single-q state not observed in any other polar magnets. Thus, our work demonstrates that non-centrosymmetric magnets with 4d and 5d electron systems may give rise to various highly compressed modulated states
Magnetic resonances of multiferroic TbFe3(BO3)4
Low-energy magnetic excitations of the easy-axis antiferromagnet
TbFe(BO) are investigated by far-infrared absorption and reflection
spectroscopy in high magnetic fields up to 30 T. The observed field dependence
of the resonance frequencies and the magnetization are reproduced by a
mean-field spin model for magnetic fields applied both along and perpendicular
to the easy axis. Based on this model we determined the full set of magnetic
interactions, including Fe-Fe and Fe-Tb exchange interactions, single-ion
anisotropy for Tb ions and -factors, which describe the ground-state spin
texture and the low-energy spin excitations of TbFe(BO). Compared
to earlier studies we allow a small canting of the nearly Ising-like Tb moments
to achieve a quantitative agreement with the magnetic susceptibility
measurements. The additional high energy magnetic resonance lines observed,
besides the two resonances expected for a two-sublattice antiferromagnet,
suggest a more complex six-sublattice magnetic ground state for
TbFe(BO)