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Register a new userMagnetic field induced phenomena in UIrGe in fields applied along b axis
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The metamagnetic transition between the antiferromagnetic and paramagnetic state in UIrGe has been studied at various temperatures by magnetization, heat capacity and magnetocaloric-effect measurements on a single crystal in static and pulsed magnetic fields applied along the orthorhombic b-axis. A first-order transition is observed at temperatures below 13 K and a second-order one at higher temperatures up to the Neel temperature (TN = 16.5 K). The first-order transition is accompanied by a dramatic increase of the Sommerfeld coefficient. Magnetization measurements extended to the paramagnetic range revealed an anomalous S-shape (inflection point at a magnetic field Hm) in magnetization isotherms at temperatures above 13 K and a temperature dependence of susceptibility with a maximum at Tmax well above TN. The lines representing the temperature-induced evolution of Hm and field-induced evolution of Tmax, respectively, are bound for the point in the magnetic phase diagram at which the order of metamagnetic transition changes. A tentative scenario explaining these anomalies by antiferromagnetic correlations or short-range order in the paramagnetic state is discussed.
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We have studied the magnetization and magnetoresistance of CeRu2Al10 in the applied magnetic field H along the c-axis up to ~ 55 T. The magnetization M at low temperatures shows an H-linear increase with a small slope of M/H than that for H // a-axis up to ~ 55 T after showing a small anomaly at H ~ 4 T, which indicates that the critical field to the paramagnetic phase H_c^p is higher than 55 T for H // c-axis. The magnetization curves for H // a- and c-axes below the antiferro magnetic (AFM) transition temperature T0 behave as if the magnetic anisotropy in the AFM-ordered phase is small, although there exists a large magnetic anisotropy in the paramagnetic phase, which favors the easy magnetization axis along the a-axis. On the other hand, very recently, Khalyavin et al. have reported that the AFM order where the magnetic moment is parallel to the c-axis takes place below T0. These results indicate that the AFM order in this compound is not a simple one. The longitudinal magnetoresistance for H // c-axis at low temperatures shows no anomaly originating from the phase transition, but shows oscillations below 4.2 K. This oscillatory behavior below 4.2 K originates from the Shubnikov-de Haas oscillations, from which the cross section of the Fermi surface normal to the c-axis is estimated to be 1.0*10^14 cm-2, with no large effective mass. This is the first direct evidence of the existence of the Fermi surface below T0.
We present magnetoresistivity measurements on the heavy-fermion superconductor UTe$_{2}$ in pulsed magnetic fields $mu_0H$ up to 68~T and temperatures $T$ from 1.4 to 80~K. Magnetic fields applied along the three crystallographic directions $mathbf{a}$ (easy magnetic axis), $mathbf{b}$, and $mathbf{c}$ (hard magnetic axes), are found to induce different phenomena - depending on the field direction - beyond the low-field suppression of the superconducting state. For $mathbf{H}parallelmathbf{a}$, a broad anomaly in the resistivity is observed at $mu_0H^*simeq10$~T and $T = 1.4$~K. For $mathbf{H}parallelmathbf{c}$, no magnetic transition nor crossover are observed. For $mathbf{H}parallelmathbf{b}$, a sharp first-order-like step in the resistivity indicates a metamagnetic transition at the field $mu_0H_m simeq 35$~T. When the temperature is raised signature of first-order metamagnetism is observed up to a critical endpoint at $T_{CEP}simeq7$~K. At higher temperatures a crossover persists up to 28~K, i.e., below the temperature $T_chi^{max} = 35$~K where the magnetic susceptibility is maximal. A sharp maximum in the Fermi-liquid quadratic coefficient $A$ of the low-temperature resistivity is found at $H_m$. It indicates an enhanced effective mass associated with critical magnetic fluctuations, possibly coupled with a Fermi surface instability. Similarly to the URhGe case, we show that UTe$_{2}$ is a candidate for field-induced reentrant superconductivity in the proximity of $H_m$.
The field distribution in the vortex lattice of a pure niobium single crystal with an external field applied along a three-fold axis has been investigated by the transverse-field muon-spin-rotation (TF-$mu$SR) technique over a wide range of temperatures and fields. The experimental data have been analyzed with the Delrieus solution for the form factor supplemented by phenomenological formulas for the parameters. This has enabled us to experimentally establish the temperatures and fields for the Delrieus, Ginzburg-Landaus, and Kleins regions of the vortex lattice. Using the numerical solution of the quasiclassical Eilenbergers equation the experimental results have been reasonably understood. They should apply to all clean BCS superconductors. The analytical Delrieus model supplemented by phenomenological formulas for its parameters is found to be reliable for analyzing TF-$mu$SR experimental data for a substantial part of the mixed phase. The Abrikosovs limit is contained in it.
We review our recent studies on ferromagnetic superconductors, UGe2, URhGe and UCoGe, where the spin-triplet state with the so-called equal spin pairing is realized. We focus on experimental results of URhGe and UCoGe in which the superconductivity occurs already at ambient pressure. The huge upper critical field Hc2 on UCoGe for the field along the hard magnetization axis (b-axis) is confirmed by the AC susceptibility measurements by the fine tuning of field angle. Contrary to the huge Hc2 along the hard-magnetization axis, Hc2 along the easy-magnetization axis (c-axis) is relatively small in value. However, the initial slope of Hc2, namely dHc2/dT (H -> 0) both in UCoGe and in URhGe indicates the large value, which can be explained by the magnetic domain effect detected in the magnetization measurements. The specific heat measurements using a high quality single crystal of UCoGe demonstrate the bulk superconductivity, which is extended under magnetic field for the field along c-axis.
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.
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