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Register a new userMagnetic-field-induced transition in BaVS3
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Added by
Gy\\\"orgy Mih\\'aly Prof
Publication date
2006
fields
Physics
and research's language is
English
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The metal-insulator transition (MIT) of BaVS3 is suppressed under pressure and above the critical pressure of p~2GPa the metallic phase is stabilized. We present the results of detailed magnetoresistivity measurements carried out at pressures near the critical value, in magnetic fields up to B=12T. We found that slightly below the critical pressure the structural tetramerization -- which drives the MIT -- is combined with the onset of magnetic correlations. If the zero-field transition temperature is suppressed to a sufficiently low value (T_MI<15K), the system can be driven into the metallic state by application of magnetic field. The main effect is not the reduction of T_MI with increasing B, but rather the broadening of the transition due to the applied magnetic field. We tentatively ascribe this phenomenon to the influence on the magnetic structure coupled to the bond-order of the tetramers.
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We study vanadium spinels $A$V$_2$O$_4$ ($A$ = Cd, Mg) in pulsed magnetic fields up to 65 T. A jump in magnetization at $mu_0 H approx$ 40 T is observed in the single-crystal MgV$_2$O$_4$, indicating a field induced quantum phase transition between two distinct magnetic orders. In the multiferroic CdV$_2$O$_4$, the field-induced transition is accompanied by a suppression of the electric polarization. By modeling the magnetic properties in the presence of strong spin-orbit coupling characteristic of vanadium spinels, we show that both features of the field-induced transition can be successfully explained by including the effects of the local trigonal crystal field.
Cubic spinel GeNi2O4 exhibits intriguing magnetic properties with two successive antiferromagnetic phase transitions (TN1 12.1 and TN2 11.4 K) with the absence of any structural transition. We have performed detailed heat capacity and magnetic measurements in different crystallographic orientations. A new magnetic phase in presence of magnetic field (H > 4 T) along the [111] direction is revealed, which is not observed when the magnetic field is applied along the [100] and [110] directions. High field neutron powder diffraction measurements confirm such a change in magnetic phase, which could be ascribed to a spin reorientation in the presence of magnetic field. A strong magnetic anisotropy and competing magnetic interactions play a crucial role on the complex magnetic behavior in this cubic system.
The charge response in the barium vanadium sulfide (BaVS3) single crystals is characterized by dc resistivity and low frequency dielectric spectroscopy. A broad relaxation mode in MHz range with huge dielectric constant ~= 10^6 emerges at the metal-to-insulator phase transition TMI ~= 67 K, weakens with lowering temperature and eventually levels off below the magnetic transition Tchi ~= 30 K. The mean relaxation time is thermally activated in a manner similar to the dc resistivity. These features are interpreted as signatures of the collective charge excitations characteristic for the orbital ordering that gradually develops below TMI and stabilizes at long-range scale below Tchi.
We investigated the effect of magnetic field on the highly correlated metal near the Mott transition in the quasi-two-dimensional layered organic conductor, $kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl, by the resistance measurements under control of temperature, pressure, and magnetic field. It was demonstrated that the marginal metallic phase near the Mott transition is susceptible to the field-induced localization transition of the first order, as was predicted theoretically. The thermodynamic consideration of the present results gives a conceptual pressure-field phase diagram of the Mott transition at low temperatures.
We report the first high-field x-ray diffraction experiment using synchrotron x-rays and pulsed magnetic fields exceeding 30 T. Lattice deformation due to a magnetic-field-induced valence transition in YbInCu4 is studied. It has been found that the Bragg reflection profile at 32 K changes significantly at around 27 T due to the structural transition. In the vicinity of the transition field the low-field and the high-field phases are observed simultaneously as the two distinct Bragg reflection peaks: This is a direct evidence of the fact that the field-induced valence state transition is the first order phase transition. The field-dependence of the low-field-phase Bragg peak intensity is found to be scaled with the magnetization.
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