Nature of Ho Magnetism in Multiferroic ${\mathrm{HoMnO}}_3$

Using x-ray resonant magnetic scattering and x-ray magnetic circular dichroism, techniques that are element specific, we have elucidated the role of ${\mathrm{Ho}}^{3+}$ in multiferroic ${\mathrm{HoMnO}}_3$. In zero field, ${\mathrm{Ho}}^{3+}$ orders antiferromagnetically with moments aligned along the hexagonal $\mathbf{c}$ direction below 40 K, and undergoes a transition to another magnetic structure below 4.5 K. In applied electric fields of up to $1\times {10}^7\mathrm{V}/\mathrm{m}$, the magnetic structure of ${\mathrm{Ho}}^{3+}$ remains unchanged.

Figure 1

(a) Energy scans for the magnetic (0 0 9) reflection and the fluorescence spectra through the Ho $L_{\mathrm{III}}$ absorption edge. The solid lines are guides to the eye. The small peak marked by a vertical arrow is due to multiple charge scattering. (b) The XMCD and absorption spectra at the Ho $L_{\mathrm{III}}$ edge with applied magnetic, electric fields and without any fields, measured on a powder sample at 4ID-D. The solid line is a guide to the eye.

Figure 2

Temperature dependence of the magnetic peak intensity for the (0 0 9) and (1 0 9) reflections, measured for both the dipole and quadrupole resonances. The dipole resonance data are vertically displaced for clarity. Solid blue circles represent the integrated intensity of peaks measured at selected temperatures. The solid black lines are fits to the data in the intermediate magnetic phase as described in the text.

Figure 3

Effect of an applied electric field on the (0 0 9) antiferromagnetic peak. Inset: rocking scans at 0 and 1500 V for the quadrupole resonance at 7 K.