Growth and electrical transport properties of ${\mathbf{La}}_{0.7}{\mathbf{Sr}}_{0.3}{\mathbf{MnO}}_3$ thin films on ${\mathbf{Sr}}_2{\mathbf{IrO}}_4$ single crystals

We report the physical properties of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ thin films on ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ single crystals. The manganite films are deposited using oxide molecular beam epitaxy on flux-grown (001)-oriented iridate crystals. Temperature-dependent magnetotransport and x-ray magnetic circular dichroism measurements reveal the presence of a ferromagnetic metallic ground state in the films, consistent with films grown on ${\mathrm{SrTiO}}_3$ and ${\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7}{\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}{\mathrm{O}}_3$. A parallel resistance model is used to separate conduction effects within the ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ substrate and the ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ thin films, revealing that the measured resistance maximum does not correspond to the manganite Curie temperature but results from a convolution of properties of the near-insulating substrate and metallic film. The ability to grow and characterize epitaxial perovskites on ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ crystals enables a new route for studying magnetism at oxide interfaces in the presence of strong spin-orbit interactions.

Figure 1

Powder x-ray-diffraction data for ground crystals of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$. Rietveld refinement (labeled “Calc”) demonstrates the desired phase purity and crystal structure.

Figure 2

(a) Temperature dependence of the magnetization for various ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ crystals; data collected upon cooling. These panels compare the behavior observed in various samples from multiple growth batches; the crystals are found to be consistent between and within different growths. (b) Isothermal magnetization curves for single-crystalline ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ demonstrating the critical field and anisotropy of the induced magnetization. (c) Electrical resistance within the $ab$ plane of various ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ crystals.

Figure 3

(a) X-ray reflectivity measured from LSMO films grown on STO and LSAT substrates and a SIO crystal. The solid lines are the fits to a model by genx software. (b) X-ray diffraction measured from LSMO films on STO and LSAT substrates and a SIO crystal. (c) Atomic force microscopy image showing a step height in the LSMO/SIO film and (d) an example region between the step heights; line scans obtained from the dotted yellow lines are shown in (c) and (d).

Figure 4

Temperature-dependent resistivity measured in a zero magnetic field (filled symbols) and 7 T (open symbols) of LSMO films grown on (a) STO and LSAT substrates and (b) a SIO crystal. (c) Simulation results from the parallel resistor model obtained using $A_S=A_L=1$ (curve A); $A_S=1/4,A_L=4$ (curve B); $A_S=4,A_L=1/4$ (curve C). The gray line in (c) is the absolute resistance measured for LSMO/STO presented in panel (a). (d) Field-dependent magnetoresistance measured from the LSMO/SIO sample.

Figure 5

Mn $L$-edge x-ray absorption (XA) and XMCD of LSMO grown on SIO (red) and LSAT (black). (a) XA at 80 K and XMCD at (b) 300 K and (c) 80 K.