Magnetic properties of CeCu2 tested by muon-spin rotation and relaxation

Monocrystalline CeCu 2 has been studied by muon-spin rotation and relaxation (μSR) spectroscopy, using transverse- and longitudinal-field techniques between 5 and 300 K for the paramagnetic state, and in zero field (ZF) for the ordered antiferromagnetic (AF) phase, T N 3.6 K. As in the isostructural orthorhombic compounds GdCu 2 and PrCu 2 , in CeCu 2 the μ + is found at a 4e site. Bulk magnetic susceptibility and local susceptibility (extracted from the μ + Knight shift) are found to differ, most probably because of a change in crystalline electric field splitting of the Ce 3+ ions next to the muon. The relaxation of the μ + -spin polarization shows heavily anisotropic magnetic field fluctuations, explained by a dominant moment fluctuation amplitude along the crystallographic b axis. Below T N , ZF measurements reveal a spontaneous μ + precession frequency. The corresponding static magnetic field pattern is consistent with the known AF structure; fields at the μ + and Ce moments are parallel to the ±c axis. The temperature dependence of the μSR frequency is fitted by a two T-regime model, reflecting critical behaviour near T N and magnon excitation at low T. The oriented Ce moment values extracted from neutron diffraction measurements are not consistent with the μSR results. Part of the discrepancy could possibly be explained by a change of the contact-hyperfine coupling parameter A 0 at low temperature.