Enhanced Interface-Driven Perpendicular Magnetic Anisotropy by Symmetry Control in Oxide Superlattices

Perpendicular magnetic anisotropy (PMA) has recently been shown to emerge at interfaces of 3d and 5d transition-metal oxides (TMOs). However, strategies to systematically stabilize such interface-driven PMA still remains elusive, hindering further applications of this design approach. Here, tuning crystal symmetry is shown to be an effective means to engineer this interfacial phenomenon. The evolution of PMA strength as a function of ferromagnetic oxide thickness quantitatively reveals the competition between volume- and interface-specific contributions that determine the magnetic anisotropy. By applying different degrees of epitaxial strain, the relative contributions to PMA are modulated, clearly revealing their correlations with crystal symmetries. To be more specific, the volume anisotropy energy is found to be correlated with the tetragonal distortion of the ferromagnetic layer, while the interface anisotropy energy is mainly modulated by the octahedral tilting at the interface. With these insights, superlattices with enhanced interface-driven PMA and higher Curie temperature are realized. These findings reveal a route to engineering interface-driven PMA and associated magnetic phenomena in TMO heterostructures for future spintronic applications.

Figure 1

(a) Schematic of $[(\mathrm{LSMO}{)}_m(\mathrm{SIO}{)}_n{]}_N$ superlattices (SLs) on STO and LSAT substrates. (b) High-angle annular dark-field (HAADF) STEM image of a $[(\mathrm{LSMO}{)}_4(\mathrm{SIO}{)}_1{]}_{10}$ on STO. $\mathrm{Ir}$ cations show the brightest contrast. (c) Representative θ-2θ x-ray diffraction spectra of the SLs with different LSMO thickness (m) on STO (top) and LSAT (bottom).

Figure 2

Ferromagnetic Curie temperature (T_c, top) and saturation magnetization (M_s, bottom) as a function of LSMO thickness (m) for the $[(\mathrm{LSMO}{)}_m(\mathrm{SIO}{)}_1{]}_N$ superlattices on STO (green) and LSAT (red) substrates.

Figure 3

X-ray linear dichroism spectra of $[(\mathrm{LSMO}{)}_m(\mathrm{SIO}{)}_1{]}_N$ superlattices on LSAT with m = 1 (red), m = 2 (blue), and m = 4 (green), superlattices on STO with m = 1 (black) and LSMO films on LSAT (gray). These spectra are measured at 300 K.

Figure 4

(a) Magnetic hysteresis loops at 10 K and (b) temperature dependence of magnetization along in-plane (IP [100]) and out-of-plane (OOP [001]) directions of an m = 3 superlattice (SL) on LSAT. (c) Magnetic hysteresis loops along OOP direction (m = 3) at different temperatures. (d)−(e) Magnetic hysteresis loops of SLs with m = 4 on (d) LSAT and (e) STO. (f) Evolution of uniaxial magnetic anisotropy energy (K_u) as a function of LSMO thickness (m) on the two substrates.

Figure 5

(a) Uniaxial magnetic anisotropy energy (K_u) times the LSMO thickness (t) versus t for the superlattices on two substrates at 10 K. The solid lines show the linear fitting by using the formula K_ut = K_vt + 2K_s, where K_v and K_s refer to the volume and interface anisotropy energy. (b) Schematic of correlation between the two anisotropy energies (K_v and K_s) and the corresponding crystalline symmetries (tetragonal distortion and octahedral tilting).