Nonreciprocal flexural dynamics of Dzyaloshinskii domain walls

We revisit the description of ferromagnetic domain wall dynamics through an extended one-dimensional model by allowing flexural distortions of the wall during its motion. This is taken into account by allowing the domain wall center and internal angle to be functions of position in the direction parallel to the wall. In the limit of small applied fields, this model accounts for the nonreciprocity in the propagation of wall modes and their stability in the presence of the Dzyaloshinskii-Moriya interaction and in-plane magnetic field.Comment: 8 pages, 8 figure

Semiparametric point process and time series models for series of events

We are dealing with series of events occurring at random times #tau#_n and carrying further quantitive information #xi#_n. Examples are sequences of extrasystoles in ECG-records. We will present two approaches for analyzing such (typically long) sequences (#tau#_n, #xi#_n), n=1, 2,.... (i) A point process model is based on an intensity of the form #alpha#(t) x b_t(#theta#), t#>=#0, with b_t a stochastic intensity of the self-exciting type. (ii) A time series approach is based on a transitional GLM. The conditional expectation of the waiting time #sigma#_n_+_1=#tau#_n_+_1-#tau#_n is set to be #nu#(#tau#_n) x h(#eta#_n(#theta#)), with h a response function and #eta#_n a regression term. The deterministic functions #alpha# and #nu#, respectively, describe the long-term trend of the process. (orig.)SIGLEAvailable from TIB Hannover: RR 6137(114) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Optical Microscopy Using the Faraday Effect Reveals in Situ Magnetization Dynamics of Magnetic Nanoparticles in Biological Samples

The study of exogenous and endogenous nanoscale magnetic material in biology is important for developing biomedical nanotechnology as well as for understanding fundamental biological processes such as iron metabolism and biomineralization. Here, we exploit the magneto-optical Faraday effect to probe intracellular magnetic properties and perform magnetic imaging, revealing the location-specific magnetization dynamics of exogenous magnetic nanoparticles within cells. The opportunities enabled by this method are shown in the context of magnetic hyperthermia; an effect where local heating is generated in magnetic nanoparticles exposed to high-frequency AC magnetic fields. Magnetic hyperthermia has the potential to be used as a cellular-level thermotherapy for cancer, as well as for other biomedical applications that target heat-sensitive cellular function. However, previous experiments have suggested that the cellular environment modifies the magnetization dynamics of nanoparticles, thus dramatically altering their heating efficiency. By combining magneto-optical and fluorescence measurements, we demonstrate a form of biological microscopy that we used here to study the magnetization dynamics of nanoparticles in situ, in both histological samples and living cancer cells. Correlative magnetic and fluorescence imaging identified aggregated magnetic nanoparticles colocalized with cellular lysosomes. Nanoparticles aggregated within these lysosomes displayed reduced AC magnetic coercivity compared to the same particles measured in an aqueous suspension or aggregated in other areas of the cells. Such measurements reveal the power of this approach, enabling investigations of how cellular location, nanoparticle aggregation, and interparticle magnetic interactions affect the magnetization dynamics and consequently the heating response of nanoparticles in the biological milieu