Local mechanism for magnetoelastic coupling and magnetic frustration in high-pressure synthetized NixTi2S4 intercalated sulfide

Abstract

Transition-metal dichalcogenides (TMDCs) have been investigated for their versatile properties and remarkable tunability. Recently, there has been a resurgence of interest in magnetically intercalated TMDCs, driven by their potential applications in spintronic devices. In this paper, we describe a novel high-pressure synthesis procedure, yielding nominal Ni_xTi₂S₄ compositions in a one-step straightforward procedure, starting from TiS₂ and Ni metal. According to the Rietveld-refined synchrotron X-ray diffraction data, the compound crystallizes into a trigonal space group Pm1 (No. 164) with a crystallographic formula of Ni_0.8Ti₂S₄. We observe anomalies in the thermal evolution of the Ni–S pair-bond at ∼8 K, which were correlated to a minor deviation of ∼0.05% below 25 K from the Grüneisen model for the zero-pressure equation of state that describes the thermal expansion of the unit-cell volume. Extended X-ray absorption fine structure (EXAFS) analysis probed the local atomic dynamics surrounding the Ni atoms (Ni K-edge). A careful examination of the bond variance in paths within the first shell indicated an increase in the covalent bonding between Ni and Ti, in contrast to other intercalated sulfides such as Fe_xTi₂S₄. The investigated magnetic properties and specific heat do not demonstrate a long-range magnetic order. Instead, we observed a cluster glass-like behavior around 16 K, which suggests the coexistence of anti/ferromagnetic short-range magnetic interactions at low temperatures mediated by electron hopping between Ni e_g states due to magnetic frustration in the system. The local atomic arrangement correlates to the short-range magnetic interactions, which suggests the occurrence of magnetoelastic coupling in Ni_0.8Ti₂S₄.