Interfacial Exchange Phenomena Driven by Ferromagnetic Domains

Abstract

to control most of the new properties observed in these artificial systems. [1] Despite the increasing progress in applications, a satisfactory microscopic knowledge of some fundamental physical aspects is still lacking. Paradigmatic is the case of the exchange interaction at the interface between an antiferromagnet (AFM) and a ferromagnet (FM), [2] which is used in most spintronic devices to pin (or stabilize) the magnetization of the adjacent thin FM film although there are still puzzles and experimental contradictions not well understood about its origin and effects. [2,3] The interfacial exchange coupling in AFM/FM systems was discovered and initially described by Meiklejohn and Bean in 1956. [4] Experimentally, when an AFM/ FM heterostructure is field cooled (FC) from above the Néel temperature (T N ) of the AFM layer, [2,4] and this undergoes the phase transition with the FM layer oriented in a certain direction, [5] an interfacial unidirectional anisotropy (K E ) is induced, which shifts the hysteresis loop away from zero field by the exchange bias field H E . The naivest picture fails in predicting a value of H E orders of magnitude larger than observed, or its vanishing at T N (while it often occurs at a smaller temperature, referred as blocking temperature T B ≤ T N .) The simple picture does not explain effects on the coercive field Interfacial proximity effects in antiferromagnetic/ferromagnetic (AFM/FM) bilayers control the exchange-bias (EB) phenomena exploited in most spintronic devices, although still is lack of full understanding. Discordant results, including different exchange-bias field (H E ), coercivity (H C ), or blocking temperature (T B ) found even in similar systems, are usually ascribed to uncontrolled parameters, namely dissimilar interfacial defects, structure, and thicknesses. Here, it is shown in the very same sample that the magnetic domain structure during the magnetization reversal of the FM layer controls those mentioned effects. Simultaneous transport and vectorial-resolved magnetic measurements performed in a V 2 O 3 /Co system during warming after different field cooling (FC) procedures exhibit a strong dependence on the FC angle and the domain structure of the FM layer. Remarkably, magnetization reversal analysis reveals 35 K of variation in T B and up to a factor of two in H E . These observations can be explained within the random-field model for the interfacial exchange coupling with a fixed AFM domain structure in contact with a variable (angle-dependent) FM domain structure. The results highlight the importance of the domain structure and magnetization reversal of the FM layer (not previously considered) in the EB phenomena, with potential to tailor interfacial effects in future spintronic devices.

Influence of a Thin V2O3 Spacer on Interlayer Interactions in Fe-Ni/V2O3/FeNi Film Structures

“…Such a layer is suggested to arise due to the effect of magnetic proximity, similar to the process in a two-layer V 2 O 3 /Co system [21]. In this case, the structure of magnetic domains at the interface during magnetization reversal of the ferromagnetic layer controls the effects: fields of the exchange bias, coercive force or blocking temperature.…”

Atomic-Scale Structural Properties in NiCo₂O₄/CuFe₂O₄ Bilayer Heterostructures on (001)-MgAl₂O₄ Substrate Regulated by Film Thickness

“…The NCO and CFO films grown on MAO (001) substrate form a bilayer subferromagnetic heterojunction, further generating exchange bias effect, which plays a crucial role in spintronics devices [13], also occurring in spinel oxide system [14][15][16]. The factors affecting the exchange bias effect are the respective structural characteristics and magnetic properties of the bilayer films, as well as the microstructure of the interface [17][18][19]. Particularly, the antiferromagnetic APBs bound to the 2 interfacial dislocations normally form in the spinel film, in which the density and distribution of APBs would effectively affect the general magnetic properties [20,21].…”