Magnetic anisotropy in CsGd(MoO4)2 probed by EPR spectroscopy.

Here we report electron paramagnetic resonance (EPR) study of rare-earth paramagnet CsGd(MoO4)2. Multifrequency EPR measurements allowed us to directly probe the splitting of the lowest 8S7/2 multiplet of Gd3+ ion and revealed the rhombic type of single-ion anisotropy. An easy-axis anisotropy approximation with a rhombic distortion of the Gd3+ local environment describes obtained EPR spectra and yield energies of 8S7/2 splitting. Within this model, we discuss the configuration of the lowest Gd3+ multiplet, its zero-field splitting, and the anisotropy of magnetic properties in CsGd(MoO4)2. We argue that the zero-field splitting of 8S7/2 induces a multiple structure of EPR spectra in CsGd(MoO4)2.

Spin-glass polyamorphism induced by a magnetic field in LaMnO3 single crystal.

We present experimental evidence of field-driven transition in spin-glass state, similar to pressure-induced transition between amorphous phases in structural and metallic glasses, attributed to the polyamorphism phenomena. Cusp in temperature dependences of ac magnetic susceptibility of weakly disordered LaMnO3 single crystal is registered below the temperature of magnetic ordering. Frequency dependence of the cusp temperature proves its spin-glass origin. The transition induced by a magnetic field in spin-glass state, is manifested by peculiarity in dependence of cusp temperature on applied magnetic field. Field dependent maximum of heat capacity is observed in the same magnetic field and temperature range.

Slow spin relaxation induced by magnetic field in [NdCo(bpdo)(H2O)4(CN)6]⋠3H2O.

We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(H2O)4(CN)6]⋅3H2O (bpdo=4, 4'-bipyridine-N,N'-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S = 1/2 and a weak exchange interaction J/kB = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd(3+) ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field.

Multiple-timescale relaxation dynamics in CsGd(MoO4)2--a dipolar magnet with a highly anisotropic layered crystal structure.

The dynamic properties of the dipolar magnet CsGd(MoO4)2 have been studied. The frequency and temperature dependence of the AC susceptibility investigated in the paramagnetic region above 2 K revealed the co-existence of magnetic field induced slow and fast relaxation channels with a timescale differing by three orders of magnitude. The slow relaxation is determined by the properties of the first coordination sphere of the Gd(3+) ion and has the character of a two-phonon Orbach process. The fast relaxation is potentially attributed to a two-phonon Raman process realized via a localized phonon mode associated with the layered crystal structure. The temperature dependence of the phonon mean free path in zero magnetic field indicates significant phonon scattering below 1 K resulting from the combined effect of magnetic correlations and the scattering of dominant phonons with energies corresponding to the crystal-field levels.

Terahertz-range free-electron laser electron spin resonance spectroscopy: techniques and applications in high magnetic fields.

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave terahertz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The combination of two linac-based FELs (covering the wavelength range of 4-250 microm) with pulsed magnetic fields up to 70 T allows for multifrequency ESR spectroscopy in a frequency range of 1.2-75 THz with a spectral resolution better than 1%. The performance of the spectrometer is illustrated with ESR spectra obtained in the 2,2-diphenyl-1-picrylhydrazyl and the low-dimensional organic material (C6H9N2)CuCl3.