Weak magnetism phenomena in heavy-fermion superconductors: selected $\mu$SR studies

Abstract

The behavior of the so-called weak moment antiferromagnetic states, observed in the heavy-fermion superconductors UPt${}_3$ and URu${}_2$Si${}_2$, is discussed in view of recent $\mu$SR results obtained as function of control parameters like chemical substitution and external pressure. In UPt${}_3$, the Pd substitution for Pt reveals the dynamical character of the weak moment order. On the other hand, $\mu$SR measurements performed on samples in which Th substitutes U suggest that crystallographic disorder on the magnetic sites deeply affects the fluctuation timescale. In URu${}_2$Si${}_2$, a phase separation between the so-called hidden order state, present at ambient pressure, and an antiferromagnetic state, occurring under pressure, is observed. In view of the pressure-temperature phase diagram obtained by $\mu$SR, it is deduced that the respective order parameters have different symmetries.

To appear in: J. Phys.: Cond. Matter