Strain-induced magnetic phase transition in ${\mathrm{SrCoO}}_{3-\delta }$ thin films

It has been well established that both in bulk at ambient pressure and for films under modest strains, cubic ${\mathrm{SrCoO}}_{3-\delta }$ ($\delta <0.2$) is a ferromagnetic metal. Recent theoretical work, however, indicates that a magnetic phase transition to an antiferromagnetic structure could occur under large strain accompanied by a metal-insulator transition. We have observed a strain-induced ferromagnetic-to-antiferromagnetic phase transition in ${\mathrm{SrCoO}}_{3-\delta }$ films grown on ${\mathrm{DyScO}}_3$ substrates, which provide a large tensile epitaxial strain, as compared to ferromagnetic films under lower tensile strain on ${\mathrm{SrTiO}}_3$ substrates. Magnetometry results demonstrate the existence of antiferromagnetic spin correlations and neutron diffraction experiments provide a direct evidence for a $G$-type antiferromagnetic structure with Neél temperatures between $T_N\sim 135\pm 10\text{K}$ and $\sim 325\pm 10\text{K}$, depending on the oxygen content of the samples. Therefore, our data experimentally confirm the predicted strain-induced magnetic phase transition to an antiferromagnetic state for ${\mathrm{SrCoO}}_{3-\delta }$ thin films under large epitaxial strain.

Figure 1

(a) Schematic of the lattice directions of the SCO film and DSO substrate. (b) X-ray diffraction of SCO/DSO (black) and SCO/STO (red) showing the (002)${}_{pc}$ substrate peaks and (002)${}_{pc}$ film peaks. The dashed line denotes the location of the bulk (002)${}_{pc}$ SCO peak. The inset presents the entire scan along the (pseudo)cubic (00l)${}_{pc}$ directions of the substrates. (c) X-ray reflectivity of the 20 nm thick SCO/DSO film. (d) The scattering length density (SLD) across the SCO/DSO film [resulting from the analysis of (c)].

Figure 2

(a) Temperature dependence of the neutron diffraction intensity of the (001)${}_{pc}$ Bragg peak for the 400 nm thick SCO/STO sample. The black line serves as a guide to the eye (inset: raw data with Gaussian fits for selected temperatures). (b) In-plane measurement of the magnetic moment as a function of temperature (black squares) and integrated intensity of the (001) neutron diffraction scans (red circles).

Figure 3

$1/\chi$ measured for the [110] ([001] ${}_{pc}$) out-of-plane direction of the 20 nm thick SCO/DSO film. The red line shows the Curie-Weiss fit to the high temperature data. The inset shows the corresponding susceptibility $\chi$.

Figure 4

(a) Neutron diffraction scans of the ${\left(\frac{1}{2}\frac{1}{2}\frac{1}{2}\right)}_{pc}$ SCO Bragg peak of the 20 nm thick SCO film grown on DSO. Intensity of the ${\left(\frac{1}{2}\frac{1}{2}\frac{1}{2}\right)}_{pc}$ reflection of the SCO/DSO film (b) 3 days, (c) 2 weeks, and (d) 9 months postdeposition. The black squares are peak intensities of the scans derived from Gaussian fits to the data as indicated in (a). The solid line in (c) corresponds to the intensity of the peak maximum recorded as the temperature was raised from 5 K to room temperature. The dashed red lines serve as guides to the eye.