RESUMEN
We report on a new effect caused by the electron-phonon coupling in a stoichiometric rare-earth antiferromagnetic crystal subjected to an external magnetic field, namely, the appearance of a nonzero gap in the spectrum of electronic excitations in an arbitrarily small field. The effect was registered in the low-temperature far-infrared (terahertz) reflection spectra of an easy-axis antiferromagnet PrFe_{3}(BO_{3})_{4} in magnetic fields B_{ext}â¥c. Both paramagnetic and magnetically ordered phases (including a spin-flop one) were studied in magnetic fields up to 30 T, and two bifurcation points were observed. We show that the field behavior of the coupled modes can be successfully explained and modeled on the basis of the equation derived in the framework of the theory of coupled electron-phonon modes, with the same field-independent electron-phonon interaction constant |W|=14.8 cm^{-1}.
RESUMEN
The ac magnetoconductance of bulk InSb at THz frequencies in high magnetic fields, as measured by the transmission of THz radiation, shows a field-induced transmission, which at high temperatures (≈100 K) is well explained with classical magnetoplasma effects (helicon waves). However, at low temperatures (4 K), the transmitted radiation intensity shows magnetoquantum oscillations that represent the Shubnikov-de Haas effect at THz frequencies. At frequencies above 0.9 THz, when the radiation period is shorter than the Drude scattering time, an anomalously high transmission is observed in the magnetic quantum limit that can be interpreted as carrier localization at high frequencies.
RESUMEN
Spin-1/2 Heisenberg antiferromagnets Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures are studied by means of electron spin resonance spectroscopy in magnetic fields up to the saturation field and above. In the magnetically saturated phase, quantum fluctuations are fully suppressed, and the spin dynamics is defined by ordinary magnons. This allows us to accurately describe the magnetic excitation spectra in both materials and, using the harmonic spin-wave theory, to determine their exchange parameters. The viability of the proposed method was proven by applying it to Cs2CuCl4, yielding J/kB=4.7(2) K, J'/kB=1.42(7) K, [J'/J≃0.30] and revealing good agreement with inelastic neutron-scattering results. For the isostructural Cs2CuBr4, we obtain J/kB=14.9(7) K, J'/kB=6.1(3) K, [J'/J≃0.41], providing exact and conclusive information on the exchange couplings in this frustrated spin system.
RESUMEN
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.
RESUMEN
We report a systematic study of low-energy lattice vibrations in the layered systems KY(MoO4)2, KDy(MoO4)2, KEr(MoO4)2, and KTm(MoO4)2. A layered crystal structure and low symmetry of the local environment of the rare-earth ion cause the appearance of vibrational and electronic excitations in Terahertz frequencies. The interaction between these excitations leads to sophisticated dynamical properties, including non-linear effects in paramagnetic resonance spectra. The THz study in magnetic field allows for the clear distinction between lattice vibrations and electronic excitations. We measured the THz transmission spectra and show that the low energy lattice vibrations in binary molybdates can be well described within the quasi-one-dimensional model. The developed model describes the measured far-infrared spectra, and results of our calculations agree with previous Raman and ultrasound studies.
RESUMEN
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.