Magnetic susceptibility and nuclear magnetic resonance studies of transition-metal monophosphides

Abstract

The magnetic susceptibilities of the transition-metal monophosphides TiP, ZrP, HfP, VP, NbP, TaP, and CrP were measured between 78° and 400°K. Susceptibilities ranged from -0.70×10-6 cgs/gm for TaP to 3.4×10-6 cgs/g in CrP. Although small temperature variations of χ were observed in some cases, magnetic ordering was absent in these materials over the temperature range investigated. Shifts of the 3IP magnetic resonance relative to 85% H3PO4 were all to higher frequency (lower applied field) for the Group IVa and Va monophosphides, and temperature independent, varying from 0.001% in HfP to 0.059% for TiP. On the other hand, the 31P resonance in CrP exhibited an indirect Knight shift of K(297°K) = -0.149% which varied linearly with bulk magnetic susceptibility. From K(T) vs χ (T) data a value of -30±3 kOe/Bohr magneton was obtained for the phosphorus hyperfine field in CrP. Metal resonance shifts and quadrupole splittings were also measured in 51VP and 93NbP. Magnetic susceptibility results are shown to be consistent with the qualitative features of Goodenough's model in which narrow cation d bands lie in the energy gap between broad metal-phosphorus valence and conduction bands. The NMR findings in CrP and the isomorphic compounds MnP, FeP and CoP studied by previous workers suggest appreciable covalent mixing of phosphorus 3dπ states with cation t2g sublattice bands, and support the concept that the eg states are collective in the monophosphides.