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We review magnetic and superconducting properties of UT2Al3 (T = Pd, Ni) and UGe2 together with URu2Si2. For UPd2Al3, we have suggested that the superconducting attractive paring interaction is mediated by magnetic excitons. Knight shift measurements of UNi2Al3 show an odd parity pairing in contrast to an even parity formation in UPd2Al3. The ac magnetic susceptibility measurements of UGe2 indicate that the volume fraction of superconductivity grows with increasing pressure, suggesting inhomogeneous coexistence of superconductivity and ferromagnetism. Recent dc magnetization measurements on UGe2 exhibit a step like hysteresis loop at low temperatures. An analysis of the data suggests that a magnetic domain size is smaller than a superconducting coherence length. Finally, we report the observation of an anomaly appearing in the thermal expansion of URu2Si2 under high pressures, which can be ascribed to the phase transition between a hidden and antiferromagnetic order. [Copyright &y& Elsevier]

Abstract: Elastic neutron scattering experiments on the pressure-induced ferromagnetic superconductor have been carried out under pressures P up to 1.6GPa at temperatures T down to 60mK, to study the correlation between superconductivity and ferromagnetism. No change was observed in ferromagnetic Bragg peak intensities nor a line width at through the superconducting transition temperature under and 1.25GPa, suggesting that the ferromagnetism is not affected by the onset of superconductivity under these two pressures. [Copyright &y& Elsevier]

We have measured magnetization curves of the pressure-induced ferromagnetic superconductor UGe2 at temperatures down to 0.5 K under various pressures. The ferromagnetic hysteresis loop is smooth down to about 1 K, but on further decreasing temperature, the hysteresis suddenly changes into a staircase-like curve, and the jump occurs at regular interval of magnetic field. We ascribe this novel finding to the macroscopic quantum tunneling effect (MQT). An analysis based on MQT suggests tiny magnetic domain formation whose size is smaller than the superconducting coherence length. [Copyright &y& Elsevier]

We have measured ac magnetic susceptibility of the ferromagnet UGe2 which shows superconductivity in an external pressure range, P1⩽P⩽P2, in the ferromagnetic phase. When P is close to P1 (∼7 kbar in the present study) in the superconducting phase, the ac magnetic susceptibility indicates an imperfect superconducting shielding effect. It increases with pressure and shows nearly the perfect shielding effect around ∼12 kbar. We have also found that a superconducting onset temperature seems to be almost independent of the pressure below ∼12 kbar. [Copyright &y& Elsevier]

Volume expansion measurements of single crystalline UGe2 samples have been made under pressure. The linear coefficient αV(T) at ambient pressure shows a broad hump at around Tx∼25 K and a sharp transition at TC=52 K. We have observed that the anomaly in ΔαV at Tx becomes prominent and increases in magnitude with increasing pressure. [Copyright &y& Elsevier]