NdRhSn: A ferromagnet with an antiferromagnetic precursor

NdRhSn has a ferromagnetic ground state [T_t=7.6(1) K] with a magnetic moment equal to 2/3 of the free Nd3⁺-ion moment. Upon cooling from the paramagnetic state, the ferromagnetism is preceded by an incommensurate antiferromagnetic state between T_N=9.8(1) K and T _t. In both magnetic phases the magnetic moments are locked along the c axis, which is the easy-magnetization axis of the system. We have investigated this unusual situation by measuring anomalies of several bulk physical properties characteristic for the magnetic phase transitions at T_N and T_t and the response of these properties to an applied magnetic field. Neutron-diffraction experiments have been also performed at low temperatures. Furthermore, in order to understand better the physical properties of NdRhSn, single crystals have been studied under external hydrostatic and uniaxial pressure and in high magnetic fields. An antiferromagnetic phase with a propagation vector (0 0 1/11) has been found between T_N and T _t. The magnetic-ordering temperatures T_N and T_t are sensitive to both hydrostatic and uniaxial pressures, but in a different manner. Application of hydrostatic pressure leads to a reduction of the ordering temperatures at rates ΔT_N/Δp=-0.76(5) K/GPa and ΔT_t/Δp=-0.9(2) K/GPa while uniaxial pressure applied along the c axis leads to an increase of the ordering temperatures at rates ΔT_N/Δp=+1.2(5) K/GPa and ΔT_t/Δp= +2.7(4) K/GPa. No considerable influence of pressure on the antiferromagnetic propagation vector has been found. The peculiar evolution of magnetism in NdRhSn with temperature indicates a complex hierarchy of exchange interactions.