Controlling competing interactions at oxide interfaces: Enhanced anisotropy in La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ films via interface engineering

We investigated thin La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$-SrTiO${}_3$ heterostructures, where the band alignment is engineered by a variation of La/Sr stoichiometry only at the interface. In thin films, the engineered interface leads to an enhancement of the reversed spin configuration that mimics bulk behavior. Microscopically, this enhancement is closely connected with an increased magnetic anisotropy as well as intercoupling between an $e_g$ orbital reconstruction and a corresponding anisotropic lattice fluctuation. Furthermore, a reentrant-type behavior, triggered by this intercoupling, is observed in the remanent spin state. This microscopic perspective leads to insights on developing new strategies for maintaining bulk-like properties even in very thin La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ heterostructures.

Figure 1

(a) Representations of Mn valence states in ideal (abrupt) and natural interfaces. (b) Engineered interfaces. (c) Schematics of band alignment on natural interface and engineered interface. Plots of the layer-resolved DOS in LSMO/STO(001) and LSMO/La${}_{0.5}$Sr${}_{0.5}$MnO${}_3$(1 UC)/STO heterostructures that represent the natural and engineered interface, respectively. Yellow, orange, and violet color codes for the DOS are for bulk-like Mn in LSMO, enriched Mn${}^{3+}$, and Mn in the $\delta$ layer, respectively. Dashed lines indicate the band bending effect, which is obtained from the valence band maximum and conduction band minimum. (d) Oxygen XAS spectra of the engineered heterostructures with $x_{\delta }=0.15$, 0.3, and 0.67. The reference spectra, CaMnO${}_3$ and LaMnO${}_3$, are selected to represent the Mn${}^{4+}$ and Mn${}^{3+}$ states, respectively.

Figure 2

X-ray magnetic circular dichroism on LSMO(19 UC)/La${}_{1-x}$Sr${}_x$MnO${}_3$(1 UC)/STO[001] heterostructures with (a) $x$ $=$ 0.15, (b) 0.3, and (c) 0.67. Two different $H$ field modes: $h$ XMCD and $p$ XMCD (top), and temperature dependent $p$ XMCD around Mn $L_3$-edge region (bottom).

Figure 3

(a) $T$ dependence of $H_c$ behavior on LSMO(19 UC)/La${}_{0.33}$Sr${}_{0.67}$MnO${}_3$(1 UC)/STO[001]. Dashed and solid lines are guide to the eye. (b) $p$ XMCD around Mn $L_3$ region of the $x_{\delta }=0.67$ case within full temperature range. Arrows denote transitions. (c) Variations in intensities at $L_3$ edge. The dashed lines and arrows are guides to the eye. The inset schematic indicate the character of the $e_g$ orbital.

Figure 4

XRD results on LSMO(90 UC)/STO[001] as a function of temperature. (a) Bragg peaks on STO(002) and STO(112): top, and LSMO(002) and LSMO(112): bottom. The solid lines are fits to the data. (b) $T$ dependence of the ratios between the 2$\theta$ positions of STO(002) and LSMO(002) (left axis). The ratio of (112) positions (right axis). The thick solid lines are added as a guide to the eye.