ELFT HÍRADÓ

[szpl <szpl AT metal.elte.hu>]

ELTE Fizikai Intézet

                                ORTVAY KOLLOKVIUM

                    2016. április 14., csütörtök, 15:00-kor
                Az ELTE Pázmány Péter s. 1/A alatti épületében
                           földszinti 0.81 előadóban

                                Szunyogh László
                        (BME, Elméleti Fizika Tanszék)

            "Chiral twist of magnetic domain walls in ultrathin films"


Kivonatos ismertetés:
Breaking of inversion symmetry at surfaces or interfaces of magnetic solids 
and the presence of spin-orbit coupling can generate remarkably large 
Dzyaloshinskii-Moriya (DM) interaction that leads to numerous intriguing 
phenomena in nanomagnetism. In this talk, first I give a short overview 
about effects induced by DMI, like the stabilization of exotic spin textures 
(spin-spirals, magnetic skyrmions), asymmetry of the spin-wave dispersion, 
homochirality of magnetic domain walls, or exchange bias due to DMI.

A vast number of recent experimental and theoretical works focused on 
manipulating the DMI by varying the geometry and chemical composition of 
magnetic multilayers. Motivated by this challenge, I present a study of 
domain walls in Co/Irn/Pt(111) (n = 0-6) magnetic thin films by a combined 
approach of first-principles calculations and spin-dynamics simulations. We 
determine the tensorial exchange interactions and the magnetic anisotropies 
for the Co overlayer, depending on the thickness of Ir buffer layers. We find 
strong nearest neighbor ferromagnetic isotropic exchange interactions between 
the Co atoms and an out-of-plane magnetic anisotropy for the majority of the 
studied thin films. We show that the Néel type of magnetic domain walls (DWs) 
change their rotational sense (chirality) upon the insertion of an Ir buffer 
layer as compared to Co/Pt(111).

Quite unexpectedly, our spin-dynamics simulations indicate a twist of the 
DW profile off the plane normal to the surface. This feature can uniquely be 
attributed to the out-of-plane components of the DM vectors. Using symmetry 
arguments, we discuss the appearance of this twist for DWs propagating along 
different directions on a hexagonal lattice. In terms of an appropriate 
micromagnetic model we argue that the system gains energy through twisting 
of the DW profile. We show that the twisting amplitude proportionally depends 
on the size of the out-of-plane component of the effective DM vector, Δζ, 
while the direction of the twisting is determined by the sign of Δζ. [1]



[1] Gy. J. Vida, E. Simon, K. Palotás, and L. Szunyogh, preprint just before 
submission (2016).