Impurity effects of the 3d transition metal atoms on the first-order magnetic and electrical transition in NiS

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Abstract
In the NiAs‐type Ni1−xMxS (M: the 3d transition metal impurities), the solubility limits xL are determined to be 0.077±0.005 for M:Ti, 0.04±0.01 for M:Cr, 0.001±0.002 for M:Mn, 0.060±0.005 for M:Co, and 0.015±0.005 for M:Cu. The first‐order transition temperature Tt (between the antiferromagnetic less‐conductive and the Pauli‐paramagnetic high‐conductive states) is investigated as a function of x for M:Ti, Cr, Co, and Cu (as described on M:V in our previous paper). The lattice parameters c and a are also investigated. The larger x gives the lower Tt for these M, except in the lower x for M:V or Cr. The following features are found on M:Ti (similar to V and Cr): a Curie–Weiss‐type susceptibility is superimposed on the constant Pauli‐paramagnetic one in temperatures above Tt; the sign of dθ(T<Tt)/dT (θ: thermoelectric motive force) changes from plus to minus at a critical concentration. The ratio c/a hardly depends on x in the cases of more than half filled M (Co and Cu), while it increases in x in the less than half filled M (Ti, V, and Cr). Correlations between these experimental results and the nuclear charges of M atoms or the exchange splitting energies of M(3s) bands in MS compounds are discussed on the basis of the Friedel‐type dilute‐alloy model. It is additionally noted that Ni0.96Co0.04S exhibits an anomalous temperature behavior of susceptibility just above Tt. This behavior indicates the presence of an intermediate state, between the above two magnetic states, in the high x region for M:Co.

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