Anomalous magnetic properties in LaFe11.5Al1.5

Abstract

We report the magnetic relaxation, DC magnetization, heat capacity, and X-ray powder diffraction studies of a melt-spun LaFe_11.5Al_1.5 compound executed across a temperature range of 5 to 300 K. We have found three magnetic transitions (at temperatures T₁, T₂, and T_ord) in this compound in the zero-field cooled (ZFC) mode, and two magnetic transitions (at T₂ and T_ord) 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 (S_M) and the adiabatic temperature change (ΔT_ad) and the utmost values of S_M and T_ad 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.