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

• Published in: NPG Asia materials Vol. 16; no. 1; pp. 3 - 10
• Main Authors: Okabayashi, Jun, Usami, Takamasa, Mahfudh Yatmeidhy, Amran, Murakami, Yuichi, Shiratsuchi, Yu, Nakatani, Ryoichi, Gohda, Yoshihiro, Hamaya, Kohei
• Format: Journal Article
• Language: English
• Published: Tokyo Springer Japan 10-01-2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/119/996; 639/766/119/996; Biomaterials; Chemistry and Materials Science; Cobalt; Density functional theory; Dichroism; Electric fields; Energy Systems; Ferroelectric materials; Ferroelectricity; Fine structure; Heusler alloys; Iron; Line shape; Magnetic anisotropy; Magnetic moments; Materials Science; Multiferroic materials; Optical and Electronic Materials; Piezoelectricity; Strain; Structural Materials; Substrates; Surface and Interface Science; Thin Films; X ray absorption
• ISSN: 1884-4057; 1884-4049; 1884-4057
• DOI: 10.1038/s41427-023-00524-6

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.
Schematic illustrations of the changes in the magnetic anisotropy by an applied electric field (
E
) in the strain directions are displayed. Under an applied
E
, the piezoelectric stress in the ferroelectric PMN-PT could be introduced in the tensile and compressive directions using positive and negative bias voltages, respectively, resulting in the changes in the magnetic anisotropy in the Co
2
FeSi layer. The XMCD spectra of Fe and Co
L
-edges in Co
2
FeSi under applying
E
showed the line shape changes only in the Fe site, which corresponds to the changes of orbital magnetic moment in Fe, while that in Co remains unchanged.