Magnetic order in Nd2 PdSi3 investigated using neutron scattering and muon spin relaxation

The rare-earth-based ternary intermetallic compounds R2TX3 (R = rare earth, T = transition metal, X = Si, Ge, Ga, In) have attracted considerable interest due to a wide range of interesting low-temperature properties. Here we investigate the magnetic state of Nd2PdSi3 using neutron diffraction, muon spin relaxation (μSR), and inelastic neutron scattering (INS). This compound appears anomalous among the R2PdSi3 series since it was proposed to order ferromagnetically, whereas others in this series are antiferromagnets. Although some members of the R2TX3 series have been reported to form ordered superstructures, our data are well described by Nd2PdSi3 adopting the AlB2-type structure with a single Nd site, and we do not find evidence of superlattice peaks in neutron diffraction. Our results confirm the onset of long-range magnetic order below T0=17 K, where the whole sample enters the ordered state. Neutron diffraction measurements establish the presence of a ferromagnetic component in this compound, as well as an antiferromagnetic one which has a propagation vector k2=(1/2,1/2,1/4-δ) with a temperature-dependent δ≈0.02-0.04, and moments orientated exclusively along the c axis. μSR measurements suggest that these components coexist on a microscopic level, and therefore the magnetic structure of Nd2PdSi3 is predominantly ferromagnetic, with a sinusoidally modulated antiferromagnetic contribution which reaches a maximum amplitude at 11 K and becomes smaller upon further decreasing the temperature. INS results show the presence of crystalline electric field (CEF) excitations above T0, and from our analysis we propose a CEF level scheme.