Impact of interface structure on magnetic exchange coupling in MnBi/FexCo1−x bilayers

Abstract

In this study we investigate the magnetic exchange coupling behavior in MnBi/FeCo system at the hard/soft interface. Exchange spring MnBi/FexCo1−x (x = 0.65 and 0.35) bilayers with various thicknesses of the soft magnetic layer were deposited onto quartz glass substrates in a DC magnetron sputtering unit from alloy targets. According to magnetic measurements, using a Co-rich layer leads to more coherent exchange coupling with optimum soft layer thickness of about 1 nm. In order to take into account the effect of structural factors at the hard/soft interface which can deteriorate the exchange coupling for thicker soft magnetic layers, we have combined cross-sectional High Resolution Transmission Electron Microscopy (HR-TEM) analysis with DFT calculations and micromagnetic simulations. DFT calculations predict formation of a polycrystalline FeCo layer with coexisting crystalline (110) and disordered (randomly-oriented) phases which is confirmed by HR-TEM images. Moreover, our micromagnetic simulations show how the thickness of the FeCo layer and the interface roughness between the hard and soft magnetic phases both control the effectiveness of exchange coupling in MnBi/FeCo system. Our method can be applied to study other exchange spring systems.

Rigid Exchange Coupling in Rare‐Earth‐Lean Amorphous Hard/Soft Nanocomposites

“…The samples under investigation consist of magnetically hard Sm 15 Co 85 (SmCo) and soft Co 85 (Al 70 Zr 30 ) 15 (CoAlZr) layers deposited by magnetron sputtering on Si substrates. The composites are in the form of a single bilayer SmCo(10 nm)/ CoAlZr(10 nm), and a multilayer stack of [SmCo (2 nm)/ CoAlZr (2 nm)]×5.…”

“…Reduced exchange interactions at the interfaces is a phenomenon that often occurs in conventional crystalline heterostructures due to structural transitions between the magnetic phases, interface disorder, and roughness. [15] The success of the continuous amorphous interface model in reproducing the experimental data, without reducing the exchange coupling at the interfaces, emphasizes the advantage of all-amorphous multilayers, where the absence of sharp structural interfaces preserves the exchange coupling over longer length scales compared to crystalline magnetic composite structures. [18] According to the Goto model for interfacial exchange-spring coupling between a soft and a hard phase, the two phases can reverse their moment coherently, that is, as a single component, only if the coupling is strong enough to extend from the interface throughout the full thickness of the soft phase.…”

“…In crystalline heterostructures, the exchange coupling is often reduced at the interfaces due to structural transitions, defects, or both. [ 14–16 ] Multilayers and composites made using amorphous alloys have the advantage that undesirable effects from, for example, atomic steps at interfaces and other structural defects are avoided simply by the amorphous nature, resulting in smooth and continuous interfaces. [ 17,18 ] The alternative, to produce high quality epitaxial heterostructures of hard/soft magnets, is a much more cumbersome route toward smooth interfaces.…”

Interfacial magnetic coupling and orbital hybridization for D022-Mn3Ga/Fe films

“…In contrast, AFM coupling usually reduces the saturation magnetization and increase the coercivity. Based on these characteristics, FM and AFM couplings between magnetic bilayers have been widely used in magnetic thin film devices, such as permanent magnets [8][9][10][11], perpendicular magnetic recording media [12][13][14] and spintronic devices [15,16]. Thus, a deep understanding for the magnetic exchange interaction of magnetic bilayers at the interface is a precondition to design and fabricate advanced magnetic materials.…”