Experimental evidence of orbital ferrimagnetism in ${\mathrm{CoMnO}}_3$(0001) epitaxial thin film

We have experimentally investigated the magnetic properties of ${\mathrm{CoMnO}}_3$(0001) epitaxial films known to exhibit orbital ferrimagnetism. The films were grown by the reactive rf magnetron sputtering method. X-ray magnetic circular dichroism revealed that the spin momenta of Mn and Co ions are oriented opposite to each other and a large orbital momentum comparable to the spin angular momentum emerges only on Co, indicating the orbital ferrimagnetic nature of ${\mathrm{CoMnO}}_3$. The magnetic anisotropy of ${\mathrm{CoMnO}}_3$(0001) thin films was found to have a large negative value of $K_u=-15.6\pm 0.8\mathrm{Merg}/{\mathrm{cm}}^3$ at 300 K. The saturation magnetization was slightly smaller than the reported values of tiny single crystals, due to the presence of a sizable dead layer.

Figure 1

Spin structure of ${\mathrm{CoMnO}}_3$ drawn by vesta [18].

Figure 2

(a)–(c) are the patterns of the scattering vector $\mathit{k}$ parallel to [0001], $\left[11\overline{2}0\right]$, and $\left[1\overline{1}00\right]$, respectively.

Figure 3

Left: Mn $K$ edge XANES spectra of (a) ${\mathrm{CoMnO}}_3$ film, (b) ${\mathrm{Li}}_2{\mathrm{MnO}}_3$ [29], and (c) ${\mathrm{Mn}}_2{\mathrm{O}}_3$ [29]. Right: Co $K$ edge XANES spectra of (d) ${\mathrm{CoMnO}}_3$ film, (e) CoO [30], and (f) ${\mathrm{Co}}_2{\mathrm{O}}_3$ [30].

Figure 4

(a) The in-plane $M\text{−}H$ loop of 90-nm-thick ${\mathrm{CoMnO}}_3$(0001) films on the ${\mathrm{Al}}_2{\mathrm{O}}_3$(0001) substrate at 300 K. (b) Plot of $M_S·t$ as a function of thickness $t$. The $x$-axis intercept and the slope indicate the dead layer of $21\pm 2$ nm and $M_S$ of $0.57\pm 0.04{\mu }_B/\mathrm{f}.\mathrm{u}.$ ($110\pm 7\mathrm{emu}/{\mathrm{cm}}^3$), respectively. The film thinner than the $x$-axis intercept is excluded when the fitting is performed.

Figure 5

Magnetotorque curve of a ${\mathrm{CoMnO}}_3$ thin film with a film effective thickness of 69 nm, and a nominal thickness of 90 nm at 90 kOe.

Figure 6

Mn and Co circularly polarized XAS (${\mu }^{+}$ and ${\mu }^{-}$), XMCD spectra (${\mu }^{+}-{\mu }^{-}$), and the integral of XMCD spectra.