Magnetic anisotropy and anisotropic magnetoresistance in strongly phase separated manganite thin films

摘要

The present study reports the impact of magnetic anisotropy (MA) on magnetotransport properties such as the magnetic transitions, magnetic liquid behavior, glass transition and anisotropic magnetoresistance (AMR) in epitaxial film (thickness 42 nm) of strongly phase separated manganite La_(5/8-y)Pr_yCa_(3/8)MnO_3 (y ≈ 0.4). Angle dependent magnetization measurement confirms the out-of-plane magnetic anisotropy with the magnetic easy axes aligned in the plane of the film and the magnetic hard axis along the normal to the film plane. The more prominent divergence between the zero filed cooled (ZFC) and field cooled warming (FCW) and the stronger hysteresis between the field cooled cooling (FCC) and FCW magnetization for H‖ shows the weakening of the magnetic liquid along the magnetic hard axis. The peak at T_P ≈ 42 K in FCW magnetization, which characterizes the onset of spin freezing shifts down to T_P ≈ 18 K as the field direction is switched from the easy axes (H‖) to the hard axis (H⊥). The glass transition, which appears at T_g ≈ 28 K for H‖| disappears for H⊥. The easy axis magnetization (M_‖) appears to saturate around H～20 kOe, but the hard axis counterpart ( M_⊥) does not show such tendency even up to H=50 kOe. MA appears well above the ferromagnetic (FM) transition at T ≈ 170 K, which is nearly the same as the Neel temperature (T_N) of M_⊥-T. The temperature dependent resistivity measured at H= 10 kOe applied along the easy axis (ρ_‖ - T) and the hard axis (ρ_⊥ - T) shows insulator metal transition (IMT) at ≈ 106 K and ≈ 99 K in the cooling cycle, respectively. The large difference between ρ_⊥ - T and ρ_‖ - T during the cooling cycle and in the vicinity of IMT results in huge AMR of ≈ -142% and -115%. The observed properties have been explained in terms of the MA induced variation in the relative fraction of the coexisting magnetic phases.