Prototypical topological orbital ferromagnet γ-FeMn

Abstract

We predict from first principles an entirely topological orbital magnetization in the noncoplanar bulk antiferromagnet γ-FeMn originating in the nontrivial topology of the underlying spin structure, without any reference to spin-orbit interaction. Studying the influence of strain, composition ratio, and spin texture on the topological orbital magnetization and the accompanying topological Hall effect, we promote the scalar spin chirality as key mechanism lifting the orbital degeneracy. The system is thus a prototypical topological orbital ferromagnet, the macroscopic orbital magnetization of which is prominent even without spin-orbit coupling. One of the remarkable features of γ-FeMn is the possibility for pronounced orbital magnetostriction mediated by the complex spin topology in real space.

The chiral biquadratic pair interaction

“…The competition between the DMI and the symmetric anisotropic exchange was recently found to explain the magnetic stability of decorated Fe trimers on the Pt(111) surface [34]. The intricate interplay of higher-order and anisotropic bilinear magnetic interactions generates various magnetic states: conical spin spirals [35] and more complex magnetic structures [31,36,37], such as an intricate nanoskyrmion lattice for a monolayer of Fe on the Ir(111) surface [38].…”

“…Prominent examples are the antiferromagnetic uuddstate (a 2Q-state) [20,21] and the 3Q-state [22]. Interestingly, this 3Q-state (also magnetic skyrmions [23,24] and bobbers [25,26]) is a noncoplanar magnetic state that hosts interesting Berry-phase physics arising from its nonvanishing scalar spin chirality S S S i j ḱ · ( ), such as topological orbital ferromagnetism and Hall effects [27][28][29][30][31]. The concept of vector spin chirality is embodied by the antisymmetric bilinear Dzyaloshinskii-Moriya interaction (DMI), D S S ij i j · ( ) [3,4], which arises due to the combination of spin-orbit coupling and absence of spatial inversion symmetry.…”

Topological–chiral magnetic interactions driven by emergent orbital magnetism

“…The 3D magnetization textures of 2D skyrmions gives rise to a scalar spin chirality, a driving force behind a plethora of macroscopic phenomena. Examples are the topological Hall effect 18,19 or a finite topological orbital moment (TOM) [20][21][22][23][24][25] , which can both serve as experimental fingerprints of skyrmions. Texture-induced contributions to these macroscopic phenomena were also predicted in frustrated magnets 26,27 , where they originate from the non-trivial spin topology associated with the real-space configuration of magnetic moments S i as reflected by the scalar spin chirality χ ijk = S i · (S j × S k ).…”

Spin glass transition in a thin-film NiO/permalloy bilayer

“…They have recently attracted a renewed attention thanks to the high dynamical magnetization frequencies of AFs, enabling applications in fast interconversion and transmission of spin signals [3], and THz optics [4]. Additionally, vanishing magnetization of AFs can enable enhanced spin-transfer efficiency in electronic manipulation of the magnetic states for ultrahigh-density information storage, avoiding the constraints imposed by the angular momentum conservation and the dipolar fields ubiquitous to ferromagnetic systems [5].A number of novel phenomena have been recently observed or predicted for thin AF films, including antiferromagnetic spin-orbit torques [6][7][8], AF magnetoresistance [9], enhanced interconversion between electron spin current and spin waves [3,10], generation of THz signals [4,11], AF exchange springs [12,13], and topological effects [14][15][16]. While some of these phenomena are expected even for standalone AFs, strong exchange coupling at AF/F interfaces provides one of the most efficient approaches to controlling and analyzing the magnetization states of AFs, with the state of F controlled by the magnetic field or spin current, and characterized by the magnetoelectronic or optical techniques.…”

“…A number of novel phenomena have been recently observed or predicted for thin AF films, including antiferromagnetic spin-orbit torques [6][7][8], AF magnetoresistance [9], enhanced interconversion between electron spin current and spin waves [3,10], generation of THz signals [4,11], AF exchange springs [12,13], and topological effects [14][15][16]. While some of these phenomena are expected even for standalone AFs, strong exchange coupling at AF/F interfaces provides one of the most efficient approaches to controlling and analyzing the magnetization states of AFs, with the state of F controlled by the magnetic field or spin current, and characterized by the magnetoelectronic or optical techniques.…”