Interfacial Symmetry Control of Emergent Ferromagnetism at the Nanoscale

Abstract

The emergence of complex new ground states at interfaces has been identified as one of the most promising routes to highly tunable nanoscale materials. Despite recent progress, isolating and controlling the underlying mechanisms behind these emergent properties remains among the most challenging materials physics problems to date. In particular, generating ferromagnetism localized at the interface of two nonferromagnetic materials is of fundamental and technological interest. Moreover, the ability to turn the ferromagnetism on and off would shed light on the origin of such emergent phenomena and is promising for spintronic applications. We demonstrate that ferromagnetism confined within one unit cell at the interface of CaRuO3 and CaMnO3 can be switched on and off by changing the symmetry of the oxygen octahedra connectivity at the boundary. Interfaces that are symmetry-matched across the boundary exhibit interfacial CaMnO3 ferromagnetism while the ferromagnetism at symmetry-mismatched interfaces is suppressed. We attribute the suppression of ferromagnetic order to a reduction in charge transfer at symmetry-mismatched interfaces, where frustrated bonding weakens the orbital overlap. Thus, interfacial symmetry is a new route to control emergent ferromagnetism in materials such as CaMnO3 that exhibit antiferromagnetism in bulk form.

Strain-phonon coupling in (111)-oriented perovskite oxides

“…21,22 Furthermore, the different behavior between in-phase and out-of-phase rotations opens interesting vistas for tuning of perovskite iodides and bromides, where in-phase rotations are more common than in their oxide counterpart. 61 On the other hand, for the polar modes for ∼ 1, both the inplane and out-of-plane polarization is almost equally affected, and compressive (111)-strain suppresses the overall ferroelectricity.…”

“…Strain-phonon coupling, the effect of strain on the phonon modes, has been much studied for (001)-strain over the last decades. 3,[6][7][8][9][10][11][12] As shown in Figure 1, novel magnetic states, 21 which can induce a magnetic moment without charge transfer in (111)-oriented thin films. 22 Thus understanding general trends for how (111)-strain affects phonon frequencies, and developing routes to tailor soft and hard phonon modes in a material, is essential for rational design of new functional materials for electronic and spintronic applications.…”

Tuning Perpendicular Magnetic Anisotropy by Oxygen Octahedral Rotations in (La1−xSrxMnOYi1, Flint2, Balakrishnan3 et al. 2017Phys. Rev. Lett.1159911View full textAdd to dashboardCite

“…4(a) (x =0.5). Based on previous studies [42][43][44][45][46], we can identify the dominant rotation contributions for each peak. More specifically, the observation of the (1/2, 1/2, 3/2) peak corresponds to out-of-phase rotations along a, con- sistent with the absence of the (1/2, 1, 3/2) peak that corresponds to in-phase rotations along a.…”

Atomic-scale engineering of ferroelectric-ferromagnetic interfaces of epitaxial perovskite films for functional properties

“…Symmetry mismatch alone can also affect subsequent magnetic ordering at the interface. Very recently, symmetry-mismatch of the oxygen octahedra at the CaRu O 3 /CaMn O 3 interface was shown to switch off ferromagnetism 4 . Alteration of Mn-O-Ru bonding was proposed to reduce the orbital overlap and suppression of electron transfer stabilizes the AFM order in such systems.…”