In-plane magnetic anisotropy and magnetization reversal in phase-separated ${\left({\mathrm{La}}_{0.5}{\mathrm{Pr}}_{0.5}\right)}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_3$ thin films

The dynamics and interaction of different electronic phases near the metal-to-insulator transition of the phase-separated ${\left({\mathrm{La}}_{0.5}{\mathrm{Pr}}_{0.5}\right)}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_3$ (LPCMO) thin film grown on NGO substrate was studied using the first-order reversal curves (FORC) diagram method for electric transport measurements. The in-plane angle-dependent remanence and coercivity field in the region of the ferromagnet metallic phase was measured using the macroscopic magnetization technique. These measurements suggest an in-plane uniaxial magnetic anisotropy for the film with a uniaxial anisotropic constant (Ku) of $\sim 1.2\times {10}^6\mathrm{erg}/\mathrm{c}{\mathrm{m}}^3$ at 20 K. The angle dependence of the coercivity is best described by 1/cosθ dependence indicating that the magnetization reversal occurs mainly through the depinning of the domain wall, a signature of nucleation and propagation mechanism. The correlation of FORC measurements, resistance relaxation, and macroscopic magnetic measurements indicate a fast reversal of electronic and magnetic phases towards the denser phase region and strong interaction of different phases for the LPCMO system.

Figure 1

Specular XRR measurements from LPCMO film. The inset (lower) of (a) shows the reflectivity geometry in reciprocal space. Inset (upper) of (a) shows the electron scattering length density (ESLD) depth profile of the film. Diffuse (off-specular) XRR data (open circles) and corresponding fit (solid lines) from the film at two different angles of incidences with $Q_z=0.179{\AA }^{-1}$ (b) and $0.216{\AA }^{-1}$ (c). (d) Normalized spin asymmetry (NSA) data (symbols) with the corresponding fit (solid lines) for the film at 200 and 20 K. (e) nuclear and magnetic SLD depth profiles of the sample at 20 K.

Figure 2

(a) Resistance ratio as a function of temperature [$R\left(T\right)/R$ (25 K)] for the film along two perpendicular in-plane directions. The inset shows the two perpendicular in-plane directions [(001) and $\left(1\overline{1}0\right)$] of NGO substrates on which LPCMO film is grown. (b) The ($1/R$) $dR/dT$ curves for resistance data suggest different metal-to-insulator $(T_{\mathrm{MI}}=\sim 114\mathrm{K})$ and insulator-to-metal $(T_{\mathrm{IM}}=\sim 108\mathrm{K})$ transition temperatures. (c) Resistance vs temperature during the cooling cycle at different applied magnetic fields. A magnetic field is applied along $\left(1\overline{1}0\right)$] of NGO and resistance are also measured along the same directions. Inset shows the variation of $T_{\mathrm{MI}}$ as a function of the applied field. (d) MR (%) value at different fields for the cooling cycle.

Figure 3

(a) First-order reversal curves $\left[R\left(T_R,T\right)\right]$ for LPCMO film. The closed star (violet) points on the $R\left(T\right)$ curve during the warming cycle are the temperatures at which we measured the resistance relaxation. $T_R$ is the reversal temperature, and temperature direction is changed for FORC measurements (see text). (b) The corresponding contour plot distribution (2D FORC diagram). (c) Relative variation of resistance of LPCMO film as a function of time for different temperatures.

Figure 4

(a) Hysteresis loops [$M\left(H\right)$ curve] for the LPCMO film at 20 K measured by applying an in-plane magnetic field ($H$) along the (001) and $\left(1\overline{1}0\right)$ NGO directions, suggesting $\left(1\overline{1}0\right)$ NGO is an easy axis. $M\left(H\right)$ curves along the in-plane easy axis at different temperatures upon (b) field-cooled cooling (FCC) and (c) field-cooled warming (FCW) cycles. (d) Comparison of hysteresis loop at 110 K in FCC and FCW cycle.

Figure 5

Temperature-dependent variation of (a) magnetization ratio [$M\left(T\right)/M\left(20\mathrm{K}\right)$], (b) coercive field $\left(H_{\mathrm{c}}\right)$, and (c) ratio of remanent magnetization and saturation magnetization [$M_{\mathrm{r}}/M_{\mathrm{s}}$] along the easy axis ($\left[1\overline{1}0\right]$ NGO direction), upon field-cooled cooling (FCC) and field-cooled warming (FCW) cycles. The transport measurements upon cooling and warming are also plotted in (a). The inset of (a) shows the temperature variation of $\left(1/M\right)dM/dT$ data suggesting a transition temperature of $\sim 132\mathrm{K}$.

Figure 6

(a) Reduced $M\left(H\right)$ curves at 20 K along different angles from the in-plane easy axis. The inset shows the direction of the angle at which the field was applied. Variation of (b) $H_{\mathrm{c}}$ and (c) $M_{\mathrm{r}}/M_{\mathrm{s}}$, at 20 K with the in-plane angle of applied filed with respect to the easy axis.