Evolution of Intrinsic and Magnetic Field-Induced Magnetic Anisotropies in Strongly Phase-Separated Manganite Thin Films

Abstract

Single crystalline thin film (∼ 100 nm) of La_0.18Pr_0.40Ca_0.42MnO₃ is grown on (001) oriented LaAlO₃ substrates and the evolution of anisotropy associated with the supercooling behaviour of the magnetic liquid is studied as a function of temperature and magnetic field. The angle-dependent magnetization measurements ascertain that the easy magnetic axis lies in the plane of the film while the hard axis is along the plane normal. The ratio of the easy and hard axes magnetizations (M_|| and M_⊥) measured at 10 K, viz., M_||/M_⊥ (10 K) = 2.6, confirms the strongly anisotropic nature of the film. The easy axis ferromagnetic (FM) transition temperature (T_C) is smaller than that along the hard axis. The giant hysteresis in FCC–FCW M–T, which manifests the magnetic liquid behaviour of the strongly phase-separated manganites is appreciably narrowed along the hard axis. The strain glass state is also less dominant along the easy axis. The analysis of the M–H data brings out that the easy axis remanence (M_r||) shows a nonlinear temperature dependence, while the one corresponding to the hard axis (M_r⊥) shows a nearly linear behaviour. The coercivity (H_C) follows a law of the type $H_{\mathrm {C}}\left (T \right )\mathrm {=}H_{\mathrm {C}}\mathrm {(0)(1-}{\text {AT}}^{b}\mathrm {)}$. The value of exponent b ∼ 0.5 for single-domain particles, but in the present case, the best fit to the experimental data yields the exponent b ≈ 0.25 for both H_C|| and H_C⊥. The smaller value of the exponent is attributed to the non-canonical nature of the ferromagnetic state and the associated strongly phase-separated nature of the LPCMO thin film.