Transition metal oxyborates M-3(BO3)(2) (M = Mn, Co, Ni) belong to a group of materials with the kotoite structure and many of them demonstrate complex magnetic behavior as a result of competing interactions between magnetic ions in nonequivalent crystallographic positions. In this paper, we report results of the detailed infrared and Raman spectroscopic studies of a Co-3(BO3)(2) single crystal. Most of the phonons are observed and identified. Unusually large phonon shifts, in comparison to isostructural compound Ni-3(BO3)(2), were registered in the low- and mid-infrared frequency range (100-700 cm(-1)) of the spectra. The experimental findings are supported by the ab initio simulations of the lattice dynamics, which allow us to propose the normal-mode assignments. We argue that the large phonon shift between cobalt and nickel compounds are associated with changes of force constants induced by the changes of M-O bond lengths within the two types of octahedral MO6 groups. In addition to the first-order Raman scattering, intense second-order Raman scattering was detected due to the resonant enhancement regime. Furthermore, we performed the single crystal XRD experiments which did not show any detected evidences of magneto-structural phase transition previously observed in Ni-3(BO3)(2). (C) 2021 Elsevier B.V. All rights reserved.

ZnO films obtained by high-frequency magnetron sputtering and doped with a Fe 57 metallic 3 d impurity by the diffusion method are studied. The type of local environment of Fe 57 impurity atoms on varying the deposition parameters of ZnO films is determined by Mössbauer spectroscopy. It is established that the ground state of Fe 57 impurity atoms corresponds to metallic iron in the magnetically ordered state and there is a small fraction of Fe 57 atoms with a local environment corresponding to the complex oxide Fe 3 O 4 , having the magnetically ordered state; there is also a fraction of iron atoms in the paramagnetic state. The magnetic and magnetooptical parameters of the films were measured using magnetooptic Kerr effect. The spectral dependences of the polar magnetooptic Kerr effect in ZnO(Fe 57 ) films are measured in a photon energy range of 1.5–4.5 eV and simulated by the effective-medium method. It is established that ZnO(Fe 57 ) possess an easy-plane magnetic anisotropy with a magnetization lying in the film plane.

A time-resolved optical pump-probe technique has been applied for studying the ultrafast dynamics in the magnetic semiconductor EuTe near the absorption band gap. We show that application of external magnetic field up to 6 T results in crossover from the inverse Faraday effect taking place on the femtosecond time scale to the optical orientation phenomenon with an evolution in the picosecond time domain. We propose a model which includes both these processes possessing different spectral and temporal properties. The circularly polarized optical pumping induces the optical electronic transition $4f^75d^0 \rightarrow 4f^65d^1$ forming the absorption band gap in EuTe. The observed crossover is related to a strong magnetic-field shift of the band gap in EuTe at low temperatures. It was found that manipulation of spin states on intrinsic defect levels takes place on a time scale of 19 ps in the applied magnetic field of 6 T.

AbstractZnO films obtained by high-frequency magnetron sputtering and doped with a Fe^57 metallic 3 d impurity by the diffusion method are studied. The type of local environment of Fe^57 impurity atoms on varying the deposition parameters of ZnO films is determined by Mössbauer spectroscopy. It is established that the ground state of Fe^57 impurity atoms corresponds to metallic iron in the magnetically ordered state and there is a small fraction of Fe^57 atoms with a local environment corresponding to the complex oxide Fe_3O_4, having the magnetically ordered state; there is also a fraction of iron atoms in the paramagnetic state. The magnetic and magnetooptical parameters of the films were measured using magnetooptic Kerr effect. The spectral dependences of the polar magnetooptic Kerr effect in ZnO(Fe^57) films are measured in a photon energy range of 1.5–4.5 eV and simulated by the effective-medium method. It is established that ZnO(Fe^57) possess an easy-plane magnetic anisotropy with a magnetization lying in the film plane.

Abstract —The optical and magneto-optical properties of the metal–dielectric multilayer [Co/TiO_2]_ n structures with 2–4-nm-thick layers prepared on a silicon substrate Si(001) by ion-beam deposition have been studied. The complex permittivity of multilayer [Co/TiO_2]_ n structures has been measured by the optical ellipsometry technique in the spectral range of 0.6–5.6 eV and analyzed using the optical reflection matrices for isotropic multilayer dielectric structures taking into account the optical losses and also using the method of anisotropic effective medium. The magneto-optical Kerr effect has been measured by the polarimetric technique in the spectral range of 1.2–4.5 eV in the polar and longitudinal geometries. The magnetic anisotropy type is determined on the base of the field dependences of the magneto-optical Kerr effect. It is found that the nanosized [Co/TiO_2]_ n structures can be considered as artificial optically uniaxial media with a strong magnetic and optical anisotropy at room temperature.