The zero-field glassy ground state and field-induced ferromagnetic transition in(La0.4Pr0.6)1.2Sr1.8Mn2O7

Abstract

We have investigated glassy magnetic freezing in(La0.4Pr0.6)1.2Sr1.8Mn2O7 single crystals together with the field-induced transition to a metastable ferromagneticphase using ac magnetic susceptibility and heat capacity measurements. The magnetizationmeasurements show evidence for the development of a zero-field glassy groundstate below 45 K along with a hysteretic, field-induced change in susceptibilityassociated with the transition to the ferromagnetic phase above 5 T. The heatcapacity develops a clear peak at higher temperatures with the application oflarge magnetic fields, consistent with the development of a ferromagnetic order,while at low temperatures the Sommerfeld coefficient is monotonically reduced byan applied field, suggesting suppression of spin fluctuations. The heat capacityshows hysteretic behaviour, accompanied by a sharp decrease at a critical field,when held at fixed temperature, which does not recover on reducing the fieldback to zero. These measurements suggest that the zero-field ground state for(La0.4Pr0.6)1.2Sr1.8Mn2O7 consists of frozen disordered spin clusters, which develop into a metastable ferromagneticstate in modest magnetic fields.