Correlation between reentrant spin glass behavior and the magnetic order-disorder transition of the martensite phase in Ni-Co-Mn-Sb Heusler alloys

We have performed ac susceptibility and dc magnetization measurements in Ni50-xCoxMn38Sb12 Heusler alloys. From the ac susceptibility measurements, the existence of reentrant spin glass (RSG) state is observed for x = 0-5. It is found that the signature of RSG behavior diminishes with increase in x. This behavior is in contrast to the fact that the exchange bias field increases with x, which reveals that the origins of RSG and exchange bias are different in the present system. It is found that the system enters a frustrated ferromagnetic state just below the Curie temperature of the martensite phase (T-C(M)) and then the RSG state at low temperature. The strength of the RSG state is critically dependent on the sharpness of the magnetic transition at T-C(M). This proposition is further supported by the thermo-remanent magnetization and low field thermomagnetic measurements.