We report inelastic neutron scattering measurements of the phonon spectrum of the pressure-induced ferromagnetic superconductor UGe$_{2}$. No changes of the spectrum were found on cooling down to low temperature. The phonon contribution to the specific heat was estimated from a fit to our data. The excess specific heat previously noted at around $T_{x} approx$ 30 K is not due to phonons but is well described by the temperature dependence of the magnetic order parameter at the molecular field level.
The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe$_2$. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature $T^{*}$ where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at $T^{*}$ at least under high pressure slightly below $P_{c}^{*}$ where $T^{*}$ becomes zero. The heat-capacity anomaly associated with the superconducting transition is also investigated, where a clear peak of $C/T$ is observed in a narrow pressure region ($Delta P sim 0.1$ GPa) around $P_{c}^{*}$ contrary to the previous results of the resistivity measurement. Present results suggest the importance of the thermodynamic critical point $P_{c}^{*}$ for the appearance of the superconductivity.
Inelastic neutron scattering was used to study the low energy magnetic excitations of the ferromagnetic superconductor UGe$_{2}$. The ferromagnetic fluctuations are of Ising nature with a non-conserved magnetization and have an intermediate behavior between localized and itinerant magnetism.
We performed the DC-magnetization and neutron scattering experiments under pressure {it P} for a pressure-induced superconductor UGe$_2$. We found that the magnetic moment is enhanced at a characteristic temperature {it T}$^{*}$ in the ferromagnetic state, where {it T}$^{*}$ is smaller than a Curie temperature {it T}$_{rm C}$. This enhancement becomes remarkable in the vicinity of {it P}$_{rm C}^{*}$ = 1.20 GPa, where {it T}$^{*}$ becomes 0 K and the superconducting transition temperature {it T}$_{rm SC}$ shows a maximum. The characteristic temperature {it T}$^{*}$, which decreases with increasing pressure, also depends on the magnetic field.
The specific heat-phonon spectrum inversion has played a significant role in solid physics. But for this inherently ill-posed problem, most of the known solutions are complex both in form and content, although they are rigorous and perfect. Here we suggest another simpler series solution to this problem, which can be easily calculated if the ratio of specific heat to temperature can be expanded into a power series, or specific heat can be expanded asymptotically and conditionally. Furthermore, we suggest similar solutions to the black-body radiation inversion.
Elementary excitations in the spin-ice compound Dy$_2$Ti$_2$O$_7$ can be described as magnetic monopoles propagating independently within the pyrochlore lattice formed by magnetic Dy ions. We studied the magnetic-field dependence of the thermal conductivity {kappa}(B) for B || [001] and observe clear evidence for magnetic heat transport originating from the monopole excitations. The magnetic contribution {kappa}_{mag} is strongly field-dependent and correlates with the magnetization M(B). The diffusion coefficient obtained from the ratio of {kappa}_{mag} and the magnetic specific heat is strongly enhanced below 1 K indicating a high mobility of the monopole excitations in the spin-ice state.