Variable variance Preisach model for multilayers with perpendicular magnetic anisotropy (original) (raw)
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Perpendicular magnetic anisotropy and magnetization process in CoFeB/Pd multilayer films
Perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal process in [CoFeB t nm/Pd 1.0 nm] n (t = 0.4, 0.6, 0.8, 1.0, and 1.2 nm; n = 2 -20) multilayer films have been studied by means of magnetic hysteresis and Kerr effect measurements. Strong and controllable PMA with an effective uniaxial anisotropy up to 7.7×10 6 J.m -3 and a saturation magnetization as low as 200 emu/cc are achieved. Surface/interfacial anisotropy of CoFeB/Pd interfaces, the main contribution to the PMA, is separated from the effective uniaxial anisotropy of the films, and appears to increase with the number of the CoFeB/Pd bilayers. Observation of the magnetic domains during a magnetization reversal process using polar magneto-optical Kerr microscopy shows the detailed behavior of nucleation and displacement of the domain walls.
Hysteresis loops of magnetic thin films with perpendicular anisotropy
Phys Rev B, 2005
We model the magnetization of quasi-two-dimensional systems with easy perpendicular (z) axis anisotropy upon change of the external magnetic field along z . The model is a generalization of the scalar “phi-fourth” model that considers only the z component of the magnetization, and includes magnetic exchange, dipolar interactions, structural disorder, and an external z -oriented magnetic field. The phase diagram in the disorder/interaction strength plane is presented, and the different qualitative regimes are analyzed, mainly focusing on the existence or not of an abrupt nucleation step in the process of magnetization reversal. The results compare very well with observed experimental hysteresis loops and spatial magnetization patterns, as for instance in the case of Co-Pt multilayers.
Hysteresis loops of Co–Pt perpendicular magnetic multilayers
Journal of Physics: Condensed Matter, 2004
We develop a phenomenological model to study magnetic hysteresis in two samples designed as possible perpendicular recording media. A stochastic cellular automata model captures cooperative behavior in the nucleation of magnetic domains. We show how this simple model turns broad hysteresis loops into loops with sharp drops like those observed in these samples, and explains their unusual features. We also present, and experimentally verify, predictions of this model, and suggest how insights from this model may apply more generally.
Magnetization Dynamics in CoFeB Buffered Perpendicularly Magnetized Co/Pd Multilayer
IEEE Transactions on Magnetics, 2000
The magnetic properties of CoFeB buffered [Co(0 3 nm) Pd(nm)] 6 multilayer films have been investigated. It is found that the magnetic properties of the multilayer depended on the Pd thickness and for thickness below 0.5 nm no perperdicular anisotropy is observed. Magnetization dynamics in perpendicularly magnetized CoFeB-[Co/Pd] multilayer films are investigated using time-resolved magneto-optical Kerr effect (TRMOKE). The variation of precession frequency with external magnetic field for different palladium thickness is quantitatively understood using the macrospin approximation of the Landau-Lifshitz-Gilbert equation of motion. The Gilbert damping constant , in the range 0.04-0.1, varying with the palladium thickness is reported. The observed value is comparable to the damping coefficient of bulk Ni, and much lower than the reported values for perpendicularly magnetized films. The CoFeB buffer layer with in-plane anisotropy appears to significantly affect the precession frequency and thus the damping constant of the films.
Thickness dependent magnetization dynamics of perpendicular anisotropy Co/Pd multilayer films
Journal of Magnetism and Magnetic Materials, 2011
We present the measurements of the picosecond magnetization dynamics of Co/Pd multilayer films. The dynamic magnetization properties of sputtered multilayer films were analyzed as a function of Co layer thicknesses and applied bias field. Both the eigenfrequencies of the magnetization precession in the multilayers and the associated Gilbert damping exhibit extreme sensitivity to the magnetic layer thickness on an atomic monolayer scale. The eigenfrequency increases more than threefold when the Co thickness decreases from 7.5 to 2.8Å, mainly due to the changes in effective saturation magnetization and perpendicular anisotropy constant. A concomitant 2.6-fold increase in the damping of the oscillations is observed and attributed to stronger interface dissipation in thinner Co layers. In addition, we introduce a quasi-1D micromagnetic model in which the multilayer stack is described as a onedimensional chain of macrospins that represent each Co layer. This model yields excellent agreement with the observed resonance frequencies without any free parameters, while being much simpler and faster than full 3D micromagnetic modeling.
Perpendicular Magnetic Anisotropy in CoFeB/Pd Bilayers
Magnetics, IEEE …, 2010
Perpendicular magnetic anisotropy is observed in ultrathin (~ 0.6 nm) amorphous Co40Fe40B20 when sputtered on an MgO (001) buffer layer and capped with Pd. The layers are superparamagnetic with a blocking temperature of ~ 230 K, below which they show an exponential temperature dependence of coercivity. Perpendicular magnetic anisotropy is observed in the as-deposited state and the mechanism is different from that of CoFeB/Pt, which requires postannealing. These ultrathin layers could be a model system for studies of electric field effects on magnetic anisotropy.
Physical Review B, 2006
A shift in the hysteresis loop of a NiFe thin film ͑with in-plane anisotropy͒ exchange coupled to a ͓Pt/ Co͔ multilayer ͑with out-of-plane anisotropy͒ is observed after in-plane saturation of the system. The origin of this effect and the related magnetic properties are investigated by means of in-plane and out-of-plane magnetometry techniques, magnetic force microscopy imaging, and micromagnetic simulations. Both the number of Pt/ Co repetitions in the multilayer and the NiFe thickness are found to have an influence on the magnitude of the loop shift and the in-plane and out-of-plane coercivity values of the system. This is correlated with variations in the number and average size of the magnetic domains formed in the ͓Pt/ Co͔ multilayer which, as revealed by micromagnetic simulations, pin the NiFe magnetization via formation of closure domains with a preferential orientation at the interface between the ͓Pt/ Co͔ multilayer and the NiFe.