We report on the specific heat, magnetization and ac susceptibility measurements of single crystals of hybrid frustrated magnets Gd1.8Tb0.2Ti2O7 and Gd1.5Tb0.5Ti2O7. The analysis of experimental data ...revealed that, although partial replacing of the Gd3+ ions by the Tb3+ ions in the Gd2Ti2O7 host lattice slightly enhances antiferromagnetic coupling, as inferred from the evolution of the paramagnetic Curie-Weiss temperature, the ordering temperature gradually decreases. Paramagnetic correlations introduced by the Tb3+ ions cause this perturbation, altering the effective further neighbor interactions and destabilizing the ground state in Gd2Ti2O7. In addition, the low-energy states of Gd2−xTbxTi2O7 are suggested to possess a nature different from those in parent members Tb2Ti2O7 and Gd2Ti2O7. Finally, the frequency-dependent magnetic susceptibility behavior in Gd1.5Tb0.5Ti2O7 is consistent with the formation of a spin-glass-like state indicating a pronounced slowing down of the dynamical response of the studied hybrid magnets.
The effect of substituting Rh in CeRh sub(1-x)Pd sub(x)In sub(5) with Pd up to x = 0.25 has been studied on single crystals. The crystals have been grown by means of the In self-flux method and ...characterized by x-ray diffraction and microprobe. The tetragonal HoCoGa sub(5)-type of structure and the c/a ratio of the parent compound remains intact by the Pd substitution; the unit cell volume increases by 0.6% with x = 0.25 of Pd. The low-temperature behavior of resistivity was studied also under hydrostatic pressure up to 2.25 GPa. The Pd substitution for Rh affects the magnetic behavior and the maximum value of the superconducting transition temperature measured at pressures above 2 GPa only negligibly. On the other hand, the results provide evidence that superconductivity in CeRh sub(0.75)Pd sub(0.25)In sub(5) is induced at significantly lower pressures, i.e. the Pd substitution for Rh shifts the CeRh sub(1-x)Pd sub(x)In sub(5) system closer to coexistence of magnetism and superconductivity at ambient pressure.
We report on the magnetic structures in the TbPd1-xNixAl compounds as determined by powder neutron diffraction. The development of magnetic structures in the Tb(Pd,Ni)Al series is relatively simple. ...All the compounds show the existence of two magnetic phases with almost unchanged Neel temperature K and an additional magnetic phase transition temperature K. The arrangement of the Tb moments between TN and T1 is identical for all the concentrations and is characterized by a () propagation vector with one-third of Tb moments frustrated to nearly zero. Certain concentration development occurs only below T1. Magnetic moments that are frustrated between TN and T1 change their propagation below T1 to commensurate () or incommensurate (), depending on the Ni concentration. The magnetic moments stay parallel to the hexagonal c axis for all concentrations and temperatures.
Physics of polymorphic transitions in CeRuSn Fikáček, J.; Prokleška, J.; Míšek, M. ...
Physical review. B, Condensed matter and materials physics,
08/2012, Letnik:
86, Številka:
5
Journal Article
Odprti dostop
We report a detailed study of the polymorphic transitions in ternary stannide CeRuSn on high quality single crystals through a combination of x-ray diffraction experiments conducted at 300, 275, and ...120 K, and measurements of the thermal expansion, magnetization, and resistivity, along main crystallographic axes. In addition, the transition was followed as a function of pressure up to 0.8 GPa. The present x-ray diffraction data show that the room temperature polymorph consists of the lattice doubled along the c axis with respect to the CeCoAl-type structure consistent with previous reports. Upon cooling, the compound undergoes two successive transitions, first to a quintuple (~ 290 K) and than to a triple CeCoAl superstructure at ~ 225 K. The transitions are accompanied by a tremendous volume change due to a strong shrinking of the lattice along the c axis, which is clearly observed in thermal expansion. We advance arguments that the volume collapse originates from an increasing number of crystallographically inequivalent Ce sites and the change of ratio between the short and long Ce-Ru bonds. The observed properties of the polymorphic transition in CeRuSn are reminiscent of the gamma arrow right alpha transition in elementary cerium, suggesting that similar physics, i.e., a Kondo influenced transition and strong lattice vibrations, might be the driving forces.
Dielectric response of perovskite Sr sub(1-x)Ba sub(x)MnO sub(3) (x = 0.43 and 0.45) ceramics was investigated using microwave, THz and infrared spectroscopic techniques in order to study the ...ferroelectric and antiferromagnetic phase transitions with critical temperatures T sub(C) approximately 350 K and T sub(N) approximately 200 K, respectively. The two lowest-frequency polar phonons are overdamped above T sub(N) and they exhibit pronounced softening on heating towards T sub(C). Nevertheless, permittivity epsilon ' in the THz range shows only a small anomaly at T sub(C) because the phonon contribution to epsilon ' is rather small. The phonons are coupled with a central mode which provides the main contribution to the dielectric anomaly at T sub(C). Thus, the ferroelectric phase transition has characteristics of a crossover from displacive to order-disorder type. At the same time, the intrinsic THz central peak is partially screened by conductivity and related Maxwell-Wagner relaxation, which dominates the microwave and lower-frequency spectra. Below T sub(N), the ferroelectric distortion markedly decreases, which has an influence on the frequencies of both the central and soft modes. Therefore, epsilon ' in the THz range increases at T sub(N) on cooling. In spite of the strong spin-phonon coupling near T sub(N), surprisingly no magnetodielectric effect was observed in the THz spectra upon applying magnetic field of up to 7 T, which is in contradiction with the theoretically expected huge magnetoelectric coupling. We explain this fact as due to the insensitivity of T sub(N) to magnetic field.
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 Nd3+ 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.
The evolution of magnetism and superconductivity in Ce sub(2)Rh sub(1-x)Pd sub(x)In sub(8) solid solutions has been studied within the entire concentration range by means of thermodynamic and ...magnetic measurements at ambient pressure and at temperatures between 0.35 K and room temperature. For this purpose, single crystals with Pd concentrations x = 0, 0.10, 0.15, 0.30, 0.45, 0.55, 0.85 and 1 have been grown from In self-flux and characterized by x-ray diffraction and microprobe analysis. Starting from the antiferromagnet Ce sub(2)RhIn sub(8), the Neel temperature gradually decreases with increasing Pd concentration and the anti-ferromagnetism has disappeared for x > or = 0.45. Superconductivity has been observed only
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