Probing the magnetic ground state of stretched diamond lattices NdTaOand NdNbO: impact of spin-orbit coupling and crystal electric field.

Magnetic systems, wherein competing degree of freedoms arising from spin orbit coupling and crystal electric field lead to non-trivial magnetic ground states, remains in the forefront of research in condensed matter physics. Here, we present a comprehensive investigation on three-dimensional rare-earth based spin systems NdTaOand NdNbO, where the Nd ions sit on a stretched diamond lattice. No signatures of long-range ordering and spin freezing are observed down to 1.8 K, in both cases. The low temperature Curie-Weiss analysis indicate towards the dominance of antiferromagnetic interactions between Nd spins. A three-level CEF model clearly explain the nature of susceptibility curve. At low temperatures, heat capacity data exhibit two-level Schottky anomaly associated with ground state Kramer's doublet. Additionally, the low temperature magnetic behaviour is found reliable to effective spin () = ½ ground state, suggesting the presence of quantum fluctuations in both cases. First-principle calculations reveal a significant value of orbital moment with inclusion of spin orbit coupling and reinforce the= ½ nature of the ground state.