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Abstract Magnetic vortices are topological spin structures frequently found in ferromagnets, yet novel to antiferromagnets. By combining experiment and theory, it is demonstrated that in a nanostructured antiferromagnetic‐ferromagnetic NiO(111)‐Fe(110) bilayer, a magnetic vortex is naturally stabilized by magnetostatic interactions in the ferromagnet and is imprinted onto the adjacent antiferromagnet via interface exchange coupling. Micromagnetic simulations are used to construct a corresponding phase diagram of the stability of the imprinted antiferromagnetic vortex state. The in‐depth analysis reveals that the interplay between interface exchange coupling and the antiferromagnet magnetic anisotropy plays a crucial role in locally reorienting the Néel vector out‐of‐plane in the prototypical in‐plane antiferromagnet NiO and thereby stabilizing the vortices in the antiferromagnet.

Abstract The magnetic properties of Co(10 Å)/NiO(40 Å)/Fe trilayer epitaxially grown on W(110) substrate were investigated with use of x-ray magnetic linear dichroism (XMLD) and x-ray magnetic circular dichroism (XMCD). We showed that magnetic anisotropy of Fe film that can be controlled by a thickness-driven spin reorientation transition is transferred via interfacial exchange coupling not only to NiO layer but further to ferromagnetic Co overlayer as well. Similarly, a temperature driven spin reorientation of Fe sublayer induces a reorientation of NiO spin orientation and simultaneous switching of the Co magnetization direction. Finally, by element specific XMCD and XMLD magnetic hysteresis loop measurements we proved that external magnetic field driven reorientation of Fe and Co magnetizations as well as NiO Néel vector are strictly correlated and magnetic anisotropy fields of Fe and Co sublayers are identical despite the different crystal structures.

Abstract We show that the interaction between ferromagnetic Fe(110) and antiferromagnetic CoO(111) sublayers can be mediated and precisely tuned by a nonmagnetic Au spacer. Our results prove that the thickness of the Fe and Au layers can be chosen to modify the effective anisotropy of the Fe layer and the strength of the exchange bias interaction between Fe and CoO sublayers. Well-defined and tailorable magnetic anisotropy of the ferromagnet above Néel temperature of the antiferromagnet is a determining factor that governs exchange bias and interfacial CoO spins orientation at low temperatures. In particular, depending on the room temperature magnetic state of Fe, the low-temperature exchange bias in a zero-field cooled system can be turned “off” or “on”. The other way around, we show that exchange bias can be the dominating magnetic anisotropy source for the ferromagnet and it is feasible to induce a 90-degree rotation of the easy axis as compared to the initial, exchange bias-free easy axis orientation.

Abstract We report on the magnetic properties of antiferromagnetic NiO(001) thin films in epitaxially grown NiO/MgO(d MgO )/Cr/MgO(001) system for different thicknesses of MgO, d MgO . Results of X-ray Magnetic Linear Dichroism show that together with an increase of d MgO , rotation of NiO spins from in-plane towards out-of-plane direction occurs. Furthermore, we investigated how the proximity of Fe modifies the magnetic state of NiO in Fe/NiO/MgO(d MgO )/Cr/MgO(001). We proved the existence of a multidomain state in NiO as a result of competition between the ferromagnet/antiferromagnet exchange coupling and strain exerted on the NiO by the MgO buffer layer.

Magnetic vortices are topological spin structures frequently found in ferromagnets, yet novel to antiferromagnets. By combining experiment and theory, it is demonstrated that in a nanostructured antiferromagnetic‐ferromagnetic NiO(111)‐Fe(110) bilayer, a magnetic vortex is naturally stabilized by magnetostatic interactions in the ferromagnet and is imprinted onto the adjacent antiferromagnet via interface exchange coupling. Micromagnetic simulations are used to construct a corresponding phase diagram of the stability of the imprinted antiferromagnetic vortex state. The in‐depth analysis reveals that the interplay between interface exchange coupling and the antiferromagnet magnetic anisotropy plays a crucial role in locally reorienting the Néel vector out‐of‐plane in the prototypical in‐plane antiferromagnet NiO and thereby stabilizing the vortices in the antiferromagnet. [ABSTRACT FROM AUTHOR]

A ferromagnet/antiferromagnet (FM/AFM) Fe/NiO bilayer was grown using molecular beam epitaxy on MgO(001) and Cr buffered MgO(001) substrates. X-ray linear dichroism measurements showed a dominating out-of-plane component for the NiO spins in Fe/NiO/MgO and an in-plane spin direction for NiO layers grown on the Cr buffer. Furthermore, systematic studies on the magnetic properties of Fe/NiO grown on the wedge-shaped Cr buffer revealed a continuous strain-induced spin reorientation transition from out-of-plane to in-plane NiO spin directions when the Cr thickness increased from 0 nm to 3.5 nm. The analysis of the in-plane magnetic structure of NiO in Fe/NiO/Cr showed a pronounced uniaxial anisotropy in thin AFM layers. The AFM spins are perpendicular to the Fe spins due to spin–flop interaction. These results demonstrate the feasibility of using strain and coupling with FMs to manipulate spin structures in NiO.

Abstract Recently, perpendicular magnetic anisotropy (PMA) and its voltage control (VC) was demonstrated for Cr/Fe/MgO. In this study, we shed light on the origin of large voltage-induced anisotropy change in Cr/Fe/MgO. Analysis of the chemical structure of Cr/Fe/MgO revealed the existence of Cr atoms in the proximity of the Fe/MgO interface, which can affect both magnetic anisotropy (MA) and its VC. We showed that PMA and its VC can be enhanced by controlled Cr doping at the Fe/MgO interface. For Cr/Fe (5.9 Å)/Cr (0.7 Å)/MgO with an effective PMA of 0.8 MJ/m3, a maximum value of the voltage-controlled magnetic anisotropy (VCMA) effect of 370 fJ/Vm was demonstrated due to Cr insertion.

We demonstrate that FeRh layers can be implemented to the epitaxial Fe/Au/FeRh spin valve structures grown on MgO(001). Owing to the AFM-FM phase transition in the FeRh film, the magnetic structure of our Fe/Au/FeRh system can be temperature controlled. The indirect exchange coupling between Fe and FeRh films mediated by the Au spacer enables to control the relative orientation of the Fe and FeRh magnetizations by the Au spacer thickness between ferromagnetic and non-collinear with nearly orthogonal magnetizations. Moreover, the evolution of magnetic structure of the Fe/Au/FeRh system along with the AFM-FM transition is accompanied by the reversible in-plane rotation of the top Fe-layer magnetization.

The relationship between the magnetic properties and MgO buffer layer thickness d was studied in epitaxial MgO/Fe(t)/Cr/MgO(d) layers grown on MgO(001) substrate in which the Fe thickness t ranged from 0.4 nm to 1.1 nm. For 0.4 nm ≤ t ≤0.7 nm, a non-monotonic coercivity dependence on the MgO buffer thickness was shown by perpendicular magneto-optic Kerr effect magnetometry. For thicker Fe films, an increase in the buffer layer thickness resulted in a spin reorientation transition from perpendicular to the in-plane magnetization direction. Possible origins of these unusual behaviors were discussed in terms of the suppression of carbon contamination at the Fe surface and changes in the magnetoelastic anisotropy in the system. These results illustrate a method to control magnetic anisotropy in MgO/Fe/Cr/MgO(d) via an appropriate choice of MgO buffer layer thickness d. [ABSTRACT FROM AUTHOR]