EFFECT OF EXTERNAL-PRESSURE AND CHEMICAL SUBSTITUTION ON THE PHASE-TRANSITIONS IN MNAS

The evolution of the phase transitions in Mn//1// minus //tT//tAs(T equals Ti, V, Cr, Fe, Co and Ni) with t at low substitution levels in correlated with the external pressure, temperature (P, T) phase diagram of MnAs using the chemical pressure (P*) concept. The study is based on data for transition temperatures and unit cell dimensions at atmospheric pressure and P, T phase diagrams of Mn//1// minus //tT//tAs with different T and t. Chemical pressure coefficients (ranging between epsilon equals minus 52 plus or minus 2 kbar for T equals Ti and epsilon equals 133 plus or minus 12 kbar for T equals Fe, assuming P* equals epsilon t) are estimated from the location of the boundary of the essentially pressure driven NiAs, F to MnP, P or MnP, H//a type transition in the individual P, T phase diagrams.