Exchange bias induced by O ion implantation in ferromagnetic thin films

Abstract

Exchange bias (EB) is induced by oxygen implantation in three different ferromagnetic materials: polycrystalline Co, highly textured Co and polycrystalline Ni. These systems are compared in order to study the influence of the grain boundary density and the intrinsic ferromagnet/antiferromagnet coupling strength on the implantation-induced EB. Special emphasis is given to the role of the implantation profile in the EB properties. The implantation profile is thoroughly characterized and its correlation with the magnetic depth profile, i.e. the magnetization as a function of depth, for different magnetic states is studied. This is achieved by modelling the implanted system as a layered system. In the three systems, the magnetization reversal mechanism is studied. In this way the effect of the implantation process on the reversal mechanism is unraveled. Irrespective of the particular system, the magnetization reverses solely by domain wall nucleation and motion, as opposed to Co/CoO bilayer systems, where a change in the reversal mechanism is observed upon the first reversal.

Interdependence between training and magnetization reversal in granular Co-CoO exchange bias systems

“…2, in contrast to O-implanted thin films with Gaussian-like O depth profiles that display inhomogeneous hysteresis loops [34,36,37], the loops are rather symmetric and characterized by sharp descending and ascending branches, indicating that magnetization reversal takes place at well-defined switching fields thus confirming the homogeneity of the O-induced profile. Interestingly, as shown in Fig.…”

“…Since surface oxidation is a self-limiting process, it results in an oxide thickness of only a few nanometers, which forms a single interface between Co and CoO. Ion implantation has been demonstrated to be a suitable procedure to control the amount of AFM and, ultimately, the EB properties of FM-AFM systems, such as Co-CoO [34][35][36][37] or Ni-NiO [37], by forming multiple FM-AFM interfaces (i.e., granularlike) controllably distributed throughout the FM matrix.…”

Tuning the ferromagnetic-antiferromagnetic interfaces of granular Co-CoO exchange bias systems by annealing

“…3 The majority of EB research has been focused on thin films, with Co-CoO bilayers constituting a valuable model system. 14 Alternatively, ion implantation has been demonstrated to be a suitable approach to control the EB properties of granular-like FM-AFM systems with multiple interfaces, such as Co-CoO [15][16][17][18] or Ni-NiO. 18 Recently, by the interplay between implantation conditions and sample design, it has been shown that the O-depth profile across the FM layer thickness can be controlled using a single-energy ion implantation approach.…”

“…14 Alternatively, ion implantation has been demonstrated to be a suitable approach to control the EB properties of granular-like FM-AFM systems with multiple interfaces, such as Co-CoO [15][16][17][18] or Ni-NiO. 18 Recently, by the interplay between implantation conditions and sample design, it has been shown that the O-depth profile across the FM layer thickness can be controlled using a single-energy ion implantation approach. 17 In particular, in contrast to both bilayers and FM films with a Gaussian-like O-depth profile, uniform O-depth distributions result in superior low-temperature EB properties, such as enhanced exchange-coupling strength, improved loop homogeneity or increased blocking temperature (T B ).…”

Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

“…7 Some iron oxide thin films prepared by radio frequency magnetron sputtering show more than one phase, the details of which are controlled by the bias voltage. 1 In other systems, oxygen ion implantation in single phase ferromagnetic thin films 8,9 and oxidation of grain boundaries can lead to unexpected exchange bias. 10 Here, we report an unusual exchange bias effect in magnetite thin films on silicon substrates which nominally show absence of a second crystalline phase.…”