10th International Symposium on Hysteresis Modeling and Micromagnetics (HMM 2015)

Abstract

In this paper, we present a detailed analysis on temperature and magnetic field dependences of the magnetic entropy change (ΔSm) near the ferromagnetic (FM)–paramagnetic (PM) phase transition of a La1.2Sr1.8Mn2O7 single crystal. Experimental results reveal the material exhibiting a FM–PM phase transition at TC=85 K, and belongs to a second-order phase transition (SOPT). Around TC, −ΔSm reaches the maximum value (|ΔSmax|), which increases with increasing an applied magnetic field change, ΔH. The |ΔSmax| values found are about 0.93, 1.73, 2.38, 2.91, and 3.33 J kg−1 K−1 for ΔH=10, 20, 30, 40, and 50 kOe, respectively. However, the peak position of the −ΔSm(T) curves is effectively shifted to higher temperatures when ΔH increases. Additionally, the ΔSm(T) curves measured at different ΔH values do not collapse into a universal curve when they are normalized to their respective ΔSmax value, and Prod. Type: rescaled the temperature axis with θ1=(T−TC)/(Tr−TC) for a reference temperature Tr>TC or Tr<TC. Nevertheless, they can be collapsed into a unique curve in the whole temperature range if using two separated reference temperatures, Tr1 and Tr2, with θ2=−(T−TC)/(Tr1−TC) for T≤TC and θ2=(T−TC)/(Tr2−TC) for T>TC.