Mn 0.9Co 0.1P in field parallel to hard direction: phase diagram and irreversibility of CONE phase

Abstract

A single crystal of Mn 0.9Co 0.1P, a homologue of MnP with disordered metal sublattice, has been studied by the ac susceptibility method in a steady field H . This report concerns H parallel to the orthorhombic a axis ( a > b > c ). The magnetic phase diagram is qualitatively similar to that of MnP, including the presence of a Lifshitz multicritical point ( T L = 98 K, H L = 42 kOe) at the confluence of the paramagnetic, ferromagnetic and modulated FAN phases. Contrary to pure MnP, irreversible behaviour was observed in the susceptibility of the modulated CONE phase. This phenomenon develops only for fields above 30 kOe, in contrast to the irreversibility of the FAN phase (reported previously for H ‖ b in the whole field range down to H = 0). New features of the presumably continuous CONE-FAN transition were also found.