The interest in magnetic properties of DO_{3}-type alloys stems from their ability to exhibit dependence of magnetic moments on local environment. It is shown that both, static and dynamic properties of the alloys based on Fe_{3}Si and Fe_{3}Al require further investigations. This concerns mainly the problem of selective substitution of chromium for iron, as well as spin dynamics, the latter problem is illustrated on the example of measured spin waves in Sendust.
A combination of infrared and inelastic incoherent neutron scattering spectroscopies with the density functional theory and semi-empirical calculations was applied to propose an assignment of the vibrational spectra of 4-aminopyridine chloroantimonate(IV).
Molecular vibrational spectra in 3, 3-dimethyl-1-butanol, (CH_3)_3 CCH_2CH_2OH, and 3, 3-dimethyl-2-butanol, (CH_3)_3CCHOHCH_3, were measured by the inelastic incoherent neutron scattering and mid infrared spectroscopy and for 3, 3-dimethyl-2-butanol additionally by the far infrared absorption method. Experimental results were discussed and compared with the results of the quantum chemical calculations performed by the density functional theory (DFT/B3LYP/6-311G**) and semi-empirical PM3 calculation methods assuming the isolated molecule approximation.
The low temperature magnetic response of Mn(III)F(salen), salen = H_{14}C_{16}N_{2}O_{2}, an S=2 linear-chain system, has been studied. Using a single crystal with the field applied perpendicular to the chain direction, torque magnetometry, down to 20 mK and up to 18 T, revealed a feature at 3.8 T when T ≤ 400 mK. ESR ( ≈200 GHz) studies, using single crystals at 4 K and in 5 T, have not detected any signal. In 10 mT, the temperature dependence of the susceptibility of powder-like samples can be reasonably fit when J/k_{B}=50 K and g=2. In addition, these data are unchanged for P ≤1.0 GPa. Using a randomly-oriented, powder-like, deuterated (12 of 14 H replaced by D) sample of 2.2 g at 270 mK, neutron scattering data, acquired with the Cold Neutron Chopper Spectrometer at the Spallation Neutron Source, show several well defined excitations that may be from the zero-field energy levels of antiferromagnetic S=2 spins with g=2, J/k_{B}=50 K, D/k_{B}=2.8 K, and E/k_{B}=0.5 K.
Magnetic ordering in TbB_{66} and GdB_{66} was investigated at very low temperatures. Measurements of ac susceptibility have shown rather clear features of magnetic ordering below 1 K, at 0.34 K for TbB_{66} and at 0.20 K for GdB_{66}. However, no clear evidence of long range magnetic order was found by neutron scattering experiments. Reasons leading to these observations are discussed.
Inelastic neutron scattering infrared and Raman spectra of the crystalline 1,3,5-trimethoxybenzene were measured and compared with simulated ones by using the Gaussian 98 and DMol3 programs at density functional theory methods. Application of the double numerical plus polarization basis set for the crystalline state within the local density Perdew and Wang (PWC functionals) approximation quite well reproduces the low frequency bands related to the methyl group librational modes, which are very sensitive to molecular interactions. Infrared spectra for the crystalline sample and CCl_4 solution show spectacularly the change of low frequency modes by going from the symmetric D_{3h} molecules in the gas phase to asymmetric ones in the crystal.
The influence of spinodal decomposition on the spin wave characteristics in the Mn_{0.75}Cu_{0.25} alloy was studied with inelastic neutron scattering. The measurements were performed on the quenched and annealed samples at a few temperatures. Parameters of spin-wave dispersion-relation for small wave-vector were derived. The values of spin wave velocity and energy gap obtained at reduced temperature T/T_{N} ≈ 0.65 are after decomposition twice higher than for the quenched sample. For the decomposed sample the values of both parameters are close to the results published for the Mn_{0.9}Cu_{0.1} alloy. This fact confirms that after decomposition spin waves are present in the sample regions of Cu concentration close to 0.1 and that the neighborhood of regions with high Cu content seems not to influence them. The spin wave velocity for the quenched sample is lower than observed in any other manganese alloy.
Dynamics of 2,2-dimethylbutan-1-ol and 2,3-dimethylbutan-2-ol have been studied by experimental spectroscopy methods, i.e., inelastic incoherent neutron scattering and infrared absorption. Experimental results were discussed and compared with the results of the quantum chemical calculations performed by semi-empirical PM3 and the density functional theory methods assuming the isolated molecule and dimer, trimer and tetramer clusters. The density functional theory modelling of vibrational spectra of monomers and OH bonded molecular clusters allows to assign the inter- and intermolecular vibrational modes observed in density of states and absorption spectra.
We have confirmed the significant anisotropy of the generalised magnetic susceptibility in the paramagnetic and antiferromagnetic phase of the fcc Mn-Ni alloys. In this paper the detailed account of the experiments performed on the Mn_{0.71}Ni_{0.29} alloy is given. Our main result for the paramagnetic phase is that the correlation length is larger for the direction parallel to the anisotropy axis than for the perpendicular one by a factor of 1.6. The spin-wave velocity observed at 15 K is higher for the direction parallel to the anisotropy axis than that for the perpendicular direction by a factor of 1.2. These results are similar to that for the Mn_{0.62}Ni_{0.38} alloy. Our results indicate that the magnetic carriers are more localized and the magnetic interactions are less extended in alloys with higher Ni concentration.
By a direct derivation of the equations of motion for the spins in CsNiF_3 we show that the extensively used sine-Gordon equation fails to describe the dynamics of this 1D magnet. Instead of this soliton-bearing model we use the spin-wave theory and, without going to the continuum approximation, calculate the dynamic structure factors of the scattering of neutrons on CsNiF_3. Complete analytical solutions for the dynamic structure factors in the frequency domain are obtained both within the classical consideration and with quantum corrections.
We report on the transitions between the ferromagnetic order, spin-glass behavior, heavy fermion and fluctuating valence state in a series of isostructural compounds CeT_4M (T = Ni, Cu; M = Al, Ga, Mn). The dilution of Ce or the T and M elements allowed us to follow the physical properties evolution employing the measurements of the heat capacity, dc magnetic susceptibility, frequency dependent ac magnetic susceptibility, magnetization relaxation, inelastic neutron scattering and also the X-ray photoemission spectroscopy. It is shown that the Mn rich compounds lean towards the spin glass behavior. For the compounds governed by the close to localization Ce 4f states the effect of the crystal electric field has been studied. It has been shown that the spin glass-like behavior can significantly influence the physics of the CeT_4M compounds.
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