Anomalous magnetic properties in LaFe11.5Al1.5.

We report the magnetic relaxation, DC magnetization, heat capacity, and X-ray powder diffraction studies of a melt-spun LaFe11.5Al1.5 compound executed across a temperature range of 5 to 300 K. We have found three magnetic transitions (at temperatures T1, T2, and Tord) in this compound in the zero-field cooled (ZFC) mode, and two magnetic transitions (at T2 and Tord) in the field-cooled cooling/warming (FCC/FCW) mode. The ferromagnetic transition (FM) at temperature T2 indicating hysteresis alludes to a magnetic transition of the first-order (FOT) at lower temperatures. The magnetization study reveals that meta-stable states exist in the low-temperature antiferromagnetically ordered state. Partially reversible behaviour is also observed in the 120-140 K temperature range. The heat capacity data indicates that the magnetic state of this compound is clearly different from that of spin glasses. The magnetocaloric properties of the compound are determined in the form of the isothermal magnetic entropy change (SM) and the adiabatic temperature change (ΔTad) and the utmost values of SM and Tad for a field variation of 25 kOe observed were 3.1 J kg-1 K-1 and 1.12 K respectively. The relative cooling power (RCP) is ascertained to be 216 J kg-1 for an enforced field of 25 kOe.