Multicritical phase diagram of PrMn1-xSb2 with two interacting magnetic elements

We carried out systematic magnetotransport measurements to study the magnetic phase diagram of PrMn1-xSb2, where two antiferromagnetic orders associated with the moments of Pr and Mn coexist. When the magnetic field (H) was applied parallel to the crystallographic c axis, we found a tricritical point where a first-to-second order changeover takes place as in ordinary metamagnets. On the other hand, the metamagnetic transition field decreased unexpectedly with decreasing the temperature at low temperatures for H II [110]. Further, the transition line associated with the metamagnetic transition terminated at low temperature, where a multicritical point was formed. Starting from a three-dimensional phase diagram predicted from a simple model and modifying it to fit our experimental results, we argue that the magnetic interaction between the two magnetic elements is responsible for forming the new critical point and influences the shape of the phase boundaries.