D. L. Nagy

57Co emission studies of cupric oxide

Results on the incorporation, valence and spin states of Fe(Co) in CuO (with reference to similar studies on high temperature superconductors) and coupling of the Fe(Co) moment to the Cu magnetism in CuO are presented. Freshly prepared57Co: CuO shows two quadrupole doublets D1 and D2 withQ.S. of 2.49 and 1.52,I.S. of 0.35 and 0.70 mm/s and relative abundance of 74% and 26%, respectively at room temperature, the abundance being dependent on time in a sample exposed to ambient conditions and reaching 38 to 62% fifteen months after preparation. Below,TN=2251K, a typical combined magnetic-quadrupole interaction pattern is observed with a single saturation magnetic hfs of 25.6 T, central shift of 0.82 mm/s and a single |EQ|=1.62 mm/s at 4.2 K. External magnetic field spectra reveal an antiferromagnetic behaviour of the Fe(Co) ion. Temperature dependence of the magnetic hfs is fitted in the framework of the molecular field approximation allowing different spins and coupling constants for Cu and Fe(Co).

Magnetic field and temperature dependence of the anomalous emission line intensities in LiNbO3:57Co-initial population and relaxation

The magnetic field dependence of the anomalous Fe3+ emission line intensities in LiNbO3:57Co cannot be due to a direct spin-lattice relaxation process in the6S ground state. Raman and Orbach processes in the ground state are ruled out by the temperature independent behaviour of the spectra. The observed line intensities are proportional to the initial populations of the corresponding Zeeman levels.

Nonequilibrium Quantum Criticality and Non-Markovian Environment: Critical Exponent of a Quantum Phase Transition.

We show that the critical exponent of a quantum phase transition in a damped-driven open system is determined by the spectral density function of the reservoir. We consider the open-system variant of the Dicke model, where the driven boson mode and also the large N-spin couple to independent reservoirs at zero temperature. The critical exponent, which is 1 if there is no spin-bath coupling, decreases below 1 when the spin couples to a sub-Ohmic reservoir.

Calculation of emission spectra in terms of a stochastic relaxation model: Fe3+ in LiNbO3

AbstractMössbauer emission spectra of LiNbO3:57Co single crystals at 100 K in a magnetic field of 4 T show Fe3+ line intensities corresponding to a nearly Boltzmann population of the6A1g Zeeman sublevels. Supposing that this is due to a spin-lattice relaxation in the ground state, no relaxation matrix can reproduce the shape of the spectrum. We conclude that the initial populations are temperature dependent due to spin-lattice relaxation within the

Non-equilibrum population of the Fe3+ electronic states after the electron capture in57Co: LiTaO3

\Gamma _6 ^T

Switching reciprocity on and off in a magneto-optical x-ray scattering experiment using nuclear resonance of α-(57)Fe foils.

excited doublet.

On the applicability of the model of competing acceptors to Fe1+ in 57Co:ZnSe

Mössbauer spectra of57Co: LiTaO3 single crystals were recorded in an external longitudinal magnetic field of 6 T at different temperatures between 4.2 K and 150 K. The spectra were taken at two different orientations of the crystallographicc-axis relative to the magnetic field. The line intensities of the Fe3+-subspectra show a temperature dependent anomalous population of the three Kramers doublets of the Fe3+ spinS=5/2 ground state. A relaxation broadening is observed at higher temperatures, which cannot successfully be reproduced within a relaxation model taking into account only the six lowest lying electronic states.

Relaxation within the electronic ground state of the ferrous ion in [Fe(H2O)6]K2(SO4)2 single crystals at low temperatures

Mössbauer emission spectra of57Co: LiTaO3 show as a consequence of the nuclear decay anomalous emission line intensities in the subspectra of Fe2+ and Fe3+. Magnetic field and angle dependence of Fe3+ intensities can be explained by taking into account polarization-and crystal-field effects in the excited states. The experimental results for LiTaO3 are in good agreement with theory and previous measurements on LiNbO3.