Magnetoresistance of MnFeP/sub 0_55/As/sub 0_45/

We have measured the dependence on magnetic field and temperature of the electrical resistance and magnetization of MnFeP
_0.55
As
_0.45
, which undergoes a reversible first-order ferromagnetic-to-paramagnetic phase transition at a critical temperature T
_cr
= 231 K. The electrical resistance R(T) measured by cooling to low temperatures in zero magnetic field has a usual metallic character. The isothermal magnetic-field dependence of the magnetoresistance from 243 K to 265 K indicates the presence of temperature-dependent critical magnetic fields that transform the paramagnetic phase into the ferromagnetic phase. The critical-magnetic-field diagram determined from the isothermal magneticfield dependencies of the electrical resistance of MnFeP
_0.55
As
_0.45
shows that the field hysteresis is about 1 T between the increasingand decreasing-field cycles.