Stability of the ferromagnetic ground state of La${}_2$MnNiO${}_6$ against large compressive stress

The effect of quasi-hydrostatic pressure upon the ferromagnetic ground state of magnetodielectric, double-perovskite La${}_2$MnNiO${}_6$ is investigated using x-ray absorption spectroscopy and diffraction measurements in a diamond anvil cell. The Mn-O-Ni superexchange interaction that gives rise to ferromagnetism in this cation-ordered structure is stable to at least 38 GPa (380 000 atm). Such unusual stability of a ferromagnetic state to applied pressure can be rationalized in terms of the electronic and crystal structure and should help preserve the outstanding electronic and magnetic properties of this material when grown epitaxially under moderate compressive and tensile strain conditions.

Figure 1

(Top left) Crystal structure of La${}_2$MnNiO${}_6$. Mn (red, left) and Ni (green, center) cations occupy centers of corner-sharing oxygen octahedra. (Top right) Schematic representation of SE interactions in cation-ordered (a) vs cation-disordered (b), (c) FM and AFM structures, respectively. (Bottom) Mn (left) and Ni (right) $K$-edge XANES spectra in La${}_2$MnNiO${}_6$ and reference compounds.

Figure 2

Normalized La $L_{2,3}$ edge (top panel) and (Ni, Mn) $K$ edge (middle panel) XANES and XMCD data measured at ambient pressure in a $H=0.8$ T field. Bottom panel: Temperature-dependent SQUID magnetization data and integrated XMCD intensities.

Figure 3

Pressure dependence of Ni $K$-edge XMCD intensity at various temperatures, together with SQUID magnetization data (main panel). XANES data (insets) show the absence of valence transitions within this pressure range.

Figure 4

Pressure-volume relationship at $T=200$ K measured with powder XRD.