Measurement and ab initio calculation of the structural parameters and physical properties of 3d transition intermetallics TiMP (M = Cr, Mn, Fe, Co, or Ni)

Abstract

In this study, 3d transition metal phosphides TiMP, where M = Cr, Mn, Fe, Co, or Ni, were synthesized via solid-state reactions. At 293 K, both TiCrP and TiMnP exhibited hexagonal symmetry with P6-2m space groups, while TiFeP, TiCoP, and TiNiP possessed orthorhombic symmetry with Pnma space groups. The electrical resistivity ρ of each compound was on the order of 10−5 Ω m and was relatively temperature independent above 2 K, except in the case of TiFeP, for which ρ linearly decreased with decreasing temperature. The absolute value of the Seebeck coefficient was small (<30 µV K−1) between 2 K and 300 K and exhibited linear temperature dependence except in the case of TiNiP. The magnetic susceptibilities χ for TiCrP, TiCoP, and TiNiP, which ranged from 1 × 10−4 emu mol−1 to 3 × 10−4 emu mol−1, were temperature independent above 2 K, indicating that these species exhibit Pauli paramagnetism. The temperature-independent χ of TiFeP was relatively high, ~2.5 × 10−3 emu mol−1. The Stoner enhancement factor estimated from the Pauli paramagnetic susceptibility that was determined based on the calculated density of states and the Wilson ratio were 21.2 and 14.1, respectively, for TiFeP, suggesting that the magnetism of TiFeP may be exchange-enhanced Pauli paramagnetism. In contrast, for TiMnP, χ obeyed a Curie–Weiss law, and an effective magnetic moment per TiMnP formula unit of 1.07 μB and a Weiss temperature of −8.0 K were obtained. The ab initio calculations for TiMnP yielded a predicted magnetic moment of 1.0 μB per TiMnP formula unit, which is consistent with the experimental result. On the other hand, the measured electronic specific heat coefficient of TiMnP (48.1 mJ mol−1 · K−2) was about seven times higher than that estimated based on the calculated density of states. These results for TiMnP imply that spin fluctuations may determine its properties.