Electric dipole moment as descriptor for interfacial Dzyaloshinskii-Moriya interaction

Abstract

Chiral magnets are of fundamental interest and have important technological ramifications. The origin of chiral magnets lies in the Dzyaloshinskii-Moriya interaction (DMI), an interaction whose experimental and theoretical determination is laborious. We derive an expression that identifies the electric dipole moment as descriptor for the systematic design of chiral magnetic multilayers. Using density functional theory calculations, we determine the DMI of (111)-oriented metallic ferromagnetic Z/Co/Pt multilayers of ultrathin films. The non-magnetic layer Z determines the DMI at the Co-Pt interface. The results validate the electric and magnetic dipole moments as excellent descriptors. We found a linear relation between the electric dipole moment of Pt, the Allen electronegativity of Z, and the contribution of Pt to the total DMI.

Large Dzyaloshinskii-Moriya interaction induced by chemisorbed oxygen on a ferromagnet surface

“…The physical origin of the large magnitude of the oxygen-induced DMI is linked to the electric surface dipole moment induced by charge transfer and related hybridization between p -orbitals of oxygen and d -orbitals of ferromagnets ( 31 ). The charge transfer can be explained by the large difference in electronegativity, and therefore, our results provide experimental evidence for the recently predicted relationship between DMI and electronegativity ( 32 ). A large work function change (~0.7 eV) is observed for the Ni/Co/Pd/W system upon oxygen chemisorption (fig.…”

“…The large magnitude of the DMI induced by oxygen may be sufficient to stabilize magnetic chirality in a-few-nanometer-thick magnetic films; for instance, the chirality in typical perpendicular magnetic anisotropy multilayers [Co(1 ML)/Ni(2 ML)] n might be stabilized up to n = 5 (roughly 3 nm (31). The charge transfer can be explained by the large difference in electronegativity, and therefore, our results provide experimental evidence for the recently predicted relationship between DMI and electronegativity (32). A large work function change (~0.7 eV) is observed for the Ni/Co/ Pd/W system upon oxygen chemisorption (fig.…”

“…DMI induced by oxygen chemisorption on Fe films, different from the aforementioned oxide systems, has also been theoretically predicted with the DMI mechanism related to the hybridization and charge transfer between atomic oxygen and metal ( 31 ). Chemisorbed oxygen on a 3 d metal surface is an ideal system to test this picture, as well as the recent theoretical prediction of the relation between the DMI and the electric dipole moment ( 32 ), as the presence of atomic oxygen creates a strong internal electric field at the atomic oxygen/metal interface, because of the large difference of electronegativity between oxygen and 3 d ferromagnets (oxygen has a Pauling electronegativity of 3.44, and 3 d ferromagnets have a Pauling electronegativity of ~1.90), yet such experimental examinations are still missing so far.…”

Nature of Interfacial Dzyaloshinskii-Moriya Interactions in Graphene/Co/Pt(111) Multilayer Heterostructures

“…Alternatively, DMI strength and handedness can also be manipulated by adsorption of light element atoms, , hydrogen [22,23] and oxygen [24,25], or capping with graphene (Gr) [23,26] and hexagonal boron nitride [27]. This DMI variation upon adsorption stems from the charge density redistribution at the surface and it is correlated with the electric dipole at the surfaces [24], where the correlation is endorsed by an analytical expression [28]. The manifestation of DMI through other more accessible properties of the system, such as electrostatic ones, has motivated the search of DMI descriptors that allow its predictability in systems of potential interest.…”

Synthetic chiral magnets promoted by the Dzyaloshinskii–Moriya interaction

“…The DMI arises in magnetic systems that lack a centre of inversion and exhibit strong spin-orbit coupling. This can occur in bulk crystalline materials 25 , amorphous alloys with a composition gradient 26 , as well as in thin magnetic films where the conditions for the emergence of the DMI are naturally fulfilled at asymmetric interfaces, such as for ferromagnets in contact with heavy metals [27][28][29][30] or graphene 31,32 , and ferrimagnetic garnets grown on nonmagnetic substrates 33,34 . This interaction can be represented by the Hamiltonian HDMI =-ij Dij • (Si×Sj), where two neighbouring spins Si and Sj are indirectly coupled via a heavy metal atom.…”