Flipping magnetization induced by noncollinear ferromagnetic-antiferromagnetic exchange coupling

Abstract

We present a direct observation of a flipping magnetization of a uniform Fe film/wedged-Mn bilayer induced by a biquadratic-type exchange coupling established at the interface. The element-resolved magnetic imaging shows that the Fe film exhibited a flipping of magnetization between the [100] and [010] directions with a periodicity of one monolayer Mn thickness as below a critical temperature. The enhancement of the variation angle with the increase of Mn thickness follows the tendency of the finite-size effect of antiferromagnetism on interface exchange coupling. The flipping magnetization emerging coincidentally with the uncompensated-compensated transition of Mn magnetic surface indicates a frustration-induced biquadratic-type interface exchange coupling, and suggests a layered-like uncompensated AFM ordering for the Mn layer.

Probing magnetoelastic effects of ultrathin antiferromagnets via magnetic domain imaging in ferromagnetic-antiferromagnetic bilayers

“…Magnetic ultrathin films were prepared in an ultrahigh vacuum NTU-NSRRC nanomagnetism preparation chamber through thermal evaporation at a base pressure of 2 × 10 −10 Torr. Single crystals of Cu 3 Au(001)(a = 3.75Å) and Cu(001) (a = 3.61Å) with a 0.1 • miscut were used as the substrates, and they were prepared using procedures described in previous reports [10,16,17]. Depending on the objectives of different experiments, either uniform or wedge-shaped Mn/Co bilayers were deposited on the substrates at room temperature.…”

“…In magnetologic devices such as the spin valve, the effects of exchange bias fields and coercivity enhancement are extensively used for "pinning" the magnetization of magnetic reference layers [1][2][3][4][5]. Recent studies have reported that antiferromagnetic (AFM) thin films can alter the magnetization direction of the adjacent FM layer, leading to a spin reorientation transition (SRT) that depends on the characteristics or symmetry of the interfacial moments [6][7][8][9][10][11][12]. Such a mechanism can even induce perpendicular magnetization [11][12][13][14], thus enhancing the functionality of AFM thin films.…”

“…For AFM thin films, direct probing of antiferromagnetism is extremely challenging because of the lack of macroscopic magnetization. Although the antiferromagnetism of AFM films may be inferred from the magnetic response of FM films in AFM-FM bilayers [6][7][8][9][10], the effects on FM films themselves and the possible morphological (or interface) effects must be appropriately excluded when studying the magnetoelastic effects of AFM films. Our knowledge of magnetoelastic effects of AFM films is limited, probably because of the challenges involved in experimentally probing the correlation between variations in the crystallinity and antiferromagnetism.…”

“…Among various antiferromagnets, face-centered-cubic (fcc)-like Mn thin films are considered to be highly attractive systems because they can be fabricated with current epitaxial growth techniques [19][20][21][22][23][24][25][26]. Although theoretical studies have suggested that the behavior of bulk fcc-like Mn could be a function of the lattice parameters, on the basis of the rich magnetic phase diagram of bulk fcc-like Mn [27,28], for Mn thin films directly grown on FM films with stable in-plane magnetization (or vice versa), experiments involving spinpolarized scanning tunneling microscopy (SP-STM) and x-ray magnetic circular dichroism (XMCD)-based photoemission microscopy (PEEM) have supported in-plane layered AFM structures [10,23,24,29]. The similar AFM structure of Mn films in fcc-like Mn/FM bilayers renders them relatively simple model systems that can be used for exploring the magnetoelastic effects of antiferromagnets.…”

“…The similar AFM structure of Mn films in fcc-like Mn/FM bilayers renders them relatively simple model systems that can be used for exploring the magnetoelastic effects of antiferromagnets. Because the phenomenon of antiferromagnetism-induced SRT in AFM/FM bilayers has been reported to be highly sensitive to variations in the magnetic anisotropy or spin ordering of the AFM ultrathin film [6][7][8]10], this phenomenon can be possibly used to determine the magnetoelastic effects of fcc-like Mn ultrathin antiferromagnets.…”