Layered antiferromagnetic spin structures of expanded face-centered-tetragonal Mn(001) as an origin of exchange bias coupling to the magnetic Co layer

Abstract

Spin structures of an exchange-coupled-bilayer system of expanded-face-centered-tetragonal (e-fct) Mn(001) ultrathin films grown on Co/Cu(001) were resolved by means of spin-polarized scanning-tunneling microscopy. With an in-plane spin-sensitive probe, a layered antiferromagnetic-spin ordering of Mn overlayers was evidenced directly. In addition, the spin frustration across the same Mn layer creating a narrow domain wall down to nanometer scale was also observed along the buried step of Co underlayers. According to the micromagnetic simulation, the step-induced domain-wall width is in agreement with the experimental results. Such in-plane layered antiferromagnetic-spin structures of e-fct Mn(001) provide uncompensated spins at the interface with Co underlayers and elucidate the mechanism of the corresponding exchange-bias field observed in the previous studies.

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

“…As mentioned in the previous section, the results obtained in the current study support an in-plane layered AFM structure for the fcc-like Mn thin films grown on in-plane magnetic FM films (or vice versa) [10,23,24,29]. In the case of the fcc-Mn thin film, a previous XMCD-PEEM study on in-plane magnetic Fe/fcc-Mn/Cu 3 Au(001) reported the presence of uncompensated magnetic moments in the Mn layer [10]; this study also observed the presence of an uncompensatedcompensated transition of the Mn magnetic interface along with the continuous variation of t Mn .…”

“…This could substantially reduce the domain size of the adjacent FM layer because of the established collinear coupling and biquadratic coupling. Because the experimental results obtained in previous studies have indicated a layered-AFM structure of Mn films in fcc-like Mn/FM bilayers [10,29], in the current study, the strength of the long-range lateral exchange coupling between fcc-Mn and fct-Mn films can be distinguished by monitoring the features of the AFM-induced domain evolution.…”

“…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.…”

General nature of the step-induced frustration at ferromagnetic/antiferromagnetic interfaces: topological origin and quantitative understanding

“…In an independent study, Yamada et al repeated the same measurement on a system with Mn on top of Fe(001), but found the domain-wall width to be nearly independent of the Mn thickness [19]. Similar frustrated spin configurations have also been reported in other systems [8,9,[20][21][22][23][24][25][26][27][28][29][30]. The frustration induced domain wall in nanorings is considered to lead to potential logic and memory applications [31].…”

“…Indeed, surface defects of this type are practically unavoidable. Their presence at magnetically active interfaces often leads to nonnegligible magnetic frustration, resulting in complex spin textures [1][2][3][4][5][6][7][8][9]. This is especially true for most of the cases of practical relevance, where the exchange coupling across the AFM/FM interface is quite strong and is of primary importance for the understanding and design of various front-edge applications, such as magnetic storage, magnetic sensors, etc [10][11][12].…”