Strain-induced specific orbital control in a Heusler alloy-based interfacial multiferroics

For the development of spintronic devices, the control of magnetization by a low electric field is necessary. The microscopic origin of manipulating spins relies on the control of orbital magnetic moments ( m orb ) by strain; this is essential for the high performance magnetoelectric (ME) effect. Herein, electric-field induced X-ray magnetic circular dichroism (XMCD) is used to determine the changes in m orb by piezoelectric strain and clarify the relationship between the strain and m orb in an interfacial multiferroics system with a significant ME effect; the system consists of the Heusler alloy Co 2 FeSi on a ferroelectric Pb(Mg 1 / 3 Nb 2 / 3 )O 3 -PbTiO 3 substrate. Element-specific investigations of the orbital states by operando XMCD and the local environment via extended X-ray absorption fine structure (EXAFS) analysis show that the modulation of only the Fe sites in Co 2 FeSi primarily contributes to the giant ME effect. The density functional theory calculations corroborate this finding, and the growth of the high index (422) plane in Co 2 FeSi results in a giant ME effect. These findings elucidate the element-specific orbital control using reversible strain, called the ‘orbital elastic effect,’ and can provide guidelines for material designs with a giant ME effect.