Pseudo exchange bias due to rotational anisotropy

2017

AIP Advances

Co/CoO belongs to the typical exchange bias systems which have been investigated for decades. Surprisingly, Co/CoO thin film systems epitaxially grown on MgO(100) substrates show a strong influence of the relative orientation of the average uncompensated antiferromagnetic magnetization with respect to the cooling field direction, giving rise to unexpected asymmetric angular dependencies of the horizontal loop shift as well as the sign of the transverse magnetization peaks in magneto-optical Kerr effect (MOKE) experiments. In this paper, we provide a broad overview of the influence of cooling field orientation and sample orientation on magnetization reversal processes in this system.

Section: Resultsmentioning

confidence: 85%

Angle and rotational direction dependent horizontal loop shift in epitaxial Co/CoO bilayers on MgO(100)

2017

AIP Advances

“…The particles under simulation here had slightly different geometries ( Figure 1): one of them, defined as "square corner cuts," has an ideal structure which has shown to lead to two additional intermediate states at remanence [5], while the other one, denoted as "diagonal corner cuts," has a more realistic shape, as recognized in former lithographically produced nanostructures [19,20]. Lateral dimensions of each nanoparticle were 120 nm in the sample plane and 5 nm height, corresponding to the smallest samples used in former experimental investigations [19,20]. This value was chosen since the aim of this study is to find the highest possible particle density and thus the highest data density.…”

Section: Methodsmentioning

confidence: 99%

Influence of the Distance between Nanoparticles in Clusters on the Magnetization Reversal Process

Journal of Nanomaterials

2017

Fourfold magnetic nanoparticles, created from nanowires or in the form of an open square, offer the possibility of creating quaternary memory devices with four unambiguously distinguishable stable states at remanence. This feature, however, has been simulated for single magnetic nanoparticles or clusters with interparticle distances similar to the nanoparticle dimensions. For the possible use in bit-patterned media, it is important to understand the scaling behavior of the stability of the additional intermediate states with the interparticle distance. The paper investigates exemplarily nanoparticles of two shapes which were found to be optimum to gain four states at remanence. For clusters of these particles, the probability of reaching the additional intermediate states in all particles in the same field region is strongly reduced with decreased interparticle distance. The differences between both shapes indicate possible solutions for this problem in the form of new nanoparticle shapes.

“…Nanostructures of two different geometries were chosen for simulation ( Figure 1): one square ring with "ideal" square corner cuts which has shown to result in intermediate stable states at remanence [16] and one ring with "realistic" diagonal corner cuts which was gained in former lithographic processes [17,18]. Lateral dimensions were chosen as 200 nm diameter and 5 nm height, similar to real nanorings under experimental investigation [17,18].…”

Section: Methodsmentioning

confidence: 99%

“…In several situations, hysteresis loops with steps on both sides occur in theoretical and experimental investigations, allowing creating "quaternary" memory systems with four stable states at vanishing external magnetic field and thus the possibility of storing two bits in one position [16]. On the other hand, experimental investigation of these structures has revealed undesired modifications of the original rings' shapes in the lithography process, resulting in modified magnetization reversal processes [17,18]. This experience underlines the necessity of examining the influence of such shape modifications to allow creation of nanorings with reliable magnetic properties.…”

Section: Introductionmentioning

confidence: 99%

Magnetization Reversal in Ferromagnetic Nanorings of Fourfold Symmetries

Advances in Materials Science and Engineering

2017

Magnetic nanoparticles offer a broad spectrum of magnetization reversal processes and respective magnetic states, such as onion, horseshoe, or vortex states as well as various states including domain walls. These states can be correlated with stable intermediate states at remanence, enabling new quaternary memory devices storing two bits in one particle. The stability of these intermediated states was tested with respect to shape modifications, variations in the anisotropy axes, and rotations and fluctuations of the external magnetic field. In our micromagnetic simulations, 6 different stable intermediate states were observed at vanishing magnetic field in addition to the remanence state. The angular region of approx. 5 ∘ -12 ∘ between nanoring and external magnetic field was identified as being most stable with respect to all modifications, with an onion state as technologically best accessible intermediate state to create quaternary memory devices.