Crystalline symmetry-dependent magnon formation in the itinerant ferromagnet $\mathrm{SrRu}{\mathrm{O}}_3$

$\mathrm{SrRu}{\mathrm{O}}_3$ (SRO) is an itinerant ferromagnet with strong coupling between the charge, spin, and lattice degrees of freedom. This strong coupling suggests that the electronic and magnetic behaviors of SRO are highly susceptible to changes in the lattice distortion. Here we show how the spin interaction and resultant magnon formation change with the modification in the crystallographic orientation of SRO thin films. We fabricated SRO epitaxial thin films with (100), (110), and (111) surface orientations, to systematically modulate the spin interaction and spin dimensionality. The reduced spin dimensionality and enhanced exchange interaction in the (111)-oriented SRO thin film significantly suppress magnon formation. Our study comprehensively demonstrates the facile tunability of magnon formation and spin interaction in correlated oxide thin films.

Figure 1

Lattice structures of (100)-, (110)-, and (111)-oriented SRO epitaxial thin films. (a)–(c) Schematic diagrams of the SRO thin films with distinct surface orientations. The bottom panel shows the top view, and hence, represents the in-plane geometry of the SRO films and substrates. The black square, rectangles, and triangles indicate the surface symmetry of each orientation. (d) XRD $\theta \text{–}2\theta$ scans of the SRO thin films on (100)-, (110)-, and (111)-oriented STO substrates, respectively. * and # indicate STO substrates and SRO thin films, respectively. (e) The reciprocal space maps of the (100)-, (110)-, and (111)-oriented SRO thin films, shown around the (103), (222), and (123) Bragg reflections of the STO substrate, respectively. (f) Interplanar distance ($d_{\mathrm{inter}}$) and perovskite pseudocubic unit cell volume ($V_{\mathrm{pc}}$) of the SRO thin films. The lines are guides to the eye and the sizes of the symbols represent the error bars.

Figure 2

$M\left(T\right)/M$ (2 K) of (a) (100)-, (b) (110)-, and (c) (111)-oriented SRO thin films. A 100-Oe magnetic field was applied along the out-of-plane direction. Green solid (black dashed) lines are the fits using the scaling law (Bloch's law). The arrows indicate $T_m$. (d) Critical exponent γ and exchange coupling constant $J$ of the SRO thin films. The lines are guides to the eye. (e) $\rho \left(T\right)/{\rho }_{300\mathrm{K}}$ for the (100)-, (110)-, and (111)-oriented SRO films. The arrows indicate $T_{\mathrm{c}}$. (f) The triangles and circles represent $T_{\mathrm{c}}$ obtained from $M$($T$) and $\rho \left(T\right)$, respectively.

Figure 3

(a) $T$ derivative of $\rho \left(T\right)$ for the SRO thin films. The arrows indicate the phase transition temperature $T^{*}$ between the NFL and FL phases. (b) Critical exponents $n$ as functions of $T$ are shown for the (100)-, (110)-, and (111)-oriented SRO thin films. The triangles, stars, and circles indicate $T_{\mathrm{c}}$, $T_m$, and $T^{*}$, respectively. (c) $T$ derivative of $\rho \left(T\right)$ for the SRO thin films under a high magnetic field $\left(H_{\perp }=5\mathrm{T}\right)$. (d) Critical exponents $n$ as a function of $T$ under a high magnetic field $\left(H_{\perp }=5\mathrm{T}\right)$.