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Register a new userAngular Dependence of the High-Magnetic-Field Phase Diagram of URu2Si2
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Gernot Werner Scheerer
Publication date
2012
fields
Physics
and research's language is
English
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We present measurements of the magnetoresistivity RHOxx of URu2Si2 single crystals in high magnetic fields up to 60 T and at temperatures from 1.4 K to 40 K. Different orientations of the magnetic field have been investigated permitting to follow the dependence on Q of all magnetic phase transitions and crossovers, where Q is the angle between the magnetic field and the easy-axis c. We find out that all magnetic transitions and crossovers follow a simple 1/cos(Q) -law, indicating that they are controlled by the projection of the field on the c-axis.
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The pressure-temperature phase diagram of the heavy-electron superconductor URu2Si2 has been reinvestigated by ac-susceptibility and elastic neutron-scattering (NS) measurements performed on a small single-crystalline rod (2 mm in diameter, 6 mm in length) in a Cu-Be clamp-type high-pressure cell (P < 1.1 GPa). At ambient pressure, this sample shows the weakest antiferromagnetic (AF) Bragg reflections reported so far, corresponding to the volume-averaged staggered moment of mord ~ 0.011 mB/U. Under applied pressure, the AF scattering intensity exhibits a sharp increase at P ~ 0.7 GPa at low temperatures. The saturation value of the AF scattering intensity above 0.7 GPa corresponds to mord ~ 0.41 mB/U, which is in good agreement with that (~ 0.39 mB/U) observed above 1.5 GPa in our previous NS measurements. The superconductivity is dramatically suppressed by the evolution of AF phase, indicating that the superconducting state coexists only with the hidden order phase. The presence of parasitic ferro- and/or antiferromagnetic phases with transition temperatures T1star =120(5) K, T2star = 36(3) K and T3star = 16.5(5) K and their relationship to the low-T ordered phases are also discussed.
We report high magnetic field (up to 45 T) c-axis thermal expansion and magnetostriction experiments on URu2Si2 single crystals. The sample length change associated with the transition to the hidden order phase becomes increasingly discontinous as the magnetic field is raised above 25 T. The re-entrant ordered phase III is clearly observed in both the thermal expansion and magnetostriction above 36 T, in good agreement with previous results. The sample length is also discontinuous at the boundaries of this phase, mainly at the upper boundary. A change in the sign of the coefficient of thermal-expansion is observed at the metamagnetic transition (B_M = 38 T) which is likely related to the existence of a quantum critical end point.
We report the magnetic phase diagram of single-crystalline LiFePO$_4$ in magnetic fields up to 58~T and present a detailed study of magneto-elastic coupling by means of high-resolution capacitance dilatometry. Large anomalies at tn in the thermal expansion coefficient $alpha$ imply pronounced magneto-elastic coupling. Quantitative analysis yields the magnetic Gruneisen parameter $gamma_{rm mag}=6.7(5)cdot 10^{-7}$~mol/J. The positive hydrostatic pressure dependence $dT_{rm N}/dp = 1.46(11)$~K/GPa is dominated by uniaxial effects along the $a$-axis. Failure of Gruneisen scaling below $approx 40$~K, i.e., below the peak temperature in the magneto-electric coupling coefficient [onlinecite{toft2015anomalous}], implies several competing degrees of freedom and indicates relevance of recently observed hybrid excitations~[onlinecite{yiu2017hybrid}]. A broad and strongly magnetic-field-dependent anomaly in $alpha$ in this temperature regime highlight the relevance of structure changes. Upon application of magnetic fields $B||b$-axis, a pronounced jump in the magnetisation implies spin-reorientation at $B_{rm SF} = 32$~T as well as a precursing phase at 29~T and $T=1.5$~K. In a two-sublattice mean-field model, the saturation field $B_{rm sat,b} = 64(2)$~T enables the determination of the effective antiferromagnetic exchange interaction $J_{rm af} = 2.68(5)$~meV as well as the anisotropies $D_{rm b} = -0.53(4)$~meV and $D_{rm c} = 0.44(8)$~meV.
Recently, Yb-based triangular lattice antiferromagnets have garnered significant interest as possible quantum spin liquid candidates. One example is YbMgGaO4, which showed many promising spin liquid features, but also possesses a high degree of disorder owing to site-mixing between the non-magnetic cations. To further elucidate the role of chemical disorder and to explore the phase diagram of these materials in applied field, we present neutron scattering and sensitive magnetometry measurements of the closely related compound, YbZnGaO4. Our results suggest a difference in magnetic anisotropy between the two compounds, and we use key observations of the magnetic phase crossover to motivate an exploration of the field- and exchange parameter-dependent phase diagram, providing an expanded view of the available magnetic states in applied field. This enriched map of the phase space serves as a basis to restrict the values of parameters describing the magnetic Hamiltonian with broad application to recently discovered related materials.
We have measured the magnetic field dependence of the paramagnetic to the field-induced high temperature antiferroquadrupolar magnetically ordered phase transition is CeB6 from 0 to 60 T using a variety of techniques. It is found that the field-dependent phase separation line becomes re-entrant above 35 T and below 10 K. Measurements of resonant ultra-sound, specific heat and neutron diffraction show conclusively that the zero-field temperature-dependent phase transition is to a state with no ordered dipole moments, but with second order transition signatures in both sound attenuation and specific heat.
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