Nowak, Ulrich


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Geometric control of the magnetization reversal in antidot lattices with perpendicular magnetic anisotropy

2016-03-28, Gräfe, Joachim, Weigand, Markus, Träger, Nick, Schütz, Gisela, Goering, Eberhard J., Skripnik, Maxim, Nowak, Ulrich, Haering, Felix, Ziemann, Paul, Wiedwald, Ulf

While the magnetic properties of nanoscaled antidot lattices in in-plane magnetized materials have widely been investigated, much less is known about the microscopic effect of hexagonal antidot lattice patterning on materials with perpendicular magnetic anisotropy. By using a combination of first-order reversal curve measurements, magnetic x-ray microscopy, and micromagnetic simulations we elucidate the microscopic origins of the switching field distributions that arise from the introduction of antidot lattices into out-of-plane magnetized GdFe thin films. Depending on the geometric parameters of the antidot lattice we find two regimes with different magnetization reversal processes. For small antidots, the reversal process is dominated by the exchange interaction and domain wall pinning at the antidots drives up the coercivity of the system. On the other hand, for large antidots the dipolar interaction is dominating which leads to fragmentation of the system into very small domains that can be envisaged as a basis for a bit patterned media.


Atomistic spin model simulation of magnetic reversal modes near the Curie point

2010, Barker, Joe, Evans, Richard Francis L., Chantrell, Roy W., Hinzke, Denise, Nowak, Ulrich

The so-called linear reversal mode is demonstrated in spin model simulations of the high anisotropy material L10 FePt. Reversal of the magnetization is found to readily occur in the linear regime despite an energy barrier (KV/kBT) that would conventionally ensure stability on this timescale. The timescale for the reversal is also established with a comparison to the Landau Lifshitz Bloch equation showing good agreement.

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Behavior of the antiferromagnetic layer during training in exchange-biased bilayers within the domain state model

2010, Biternas, Andreas G, Chantrell, Roy W., Nowak, Ulrich

An analysis of the antiferromagnetic spins is used to study the training effect in exchange bias bilayers. We use an atomistic model for the magnetic interactions within a classical Heisenberg spin Hamiltonian for the investigation of the temperature dependence of the training effect. Various exchange bias bilayers with different kinds of anisotropy are presented. The spins in the antiferromaget are grouped as stable and unstable according to their behavior during the reversal. It is found that their population changes during the training effect. The stable spins result in a magnetization which is shown to be related to the exchange bias field behavior. The behavior of the interface spins is shown to be determined predominantly by the degree of geometric spin frustration at the interface.