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Presents a study which examined the energy barriers for thermal reversal of interacting single domain ferromagnetic particles. Energy surfaces for various interaction strengths; Analytical solutions; Calculation of an effective volume.

A capped composite patterned medium design is described which comprises an array of hard elements exchange coupled to a continuous cap layer. The role of the cap layer is to lower the write field of the individual hard element and introduce ferromagnetic exchange interactions between hard elements to compensate the magnetostatic interactions. Modeling results show significant reduction in the reversal field distributions caused by the magnetization states in the array which is important to prevent bit errors and increase achievable recording densities. [ABSTRACT FROM AUTHOR]

The single-particle energy surface model is utilized to study the switching field limit and the magnetization ringing in the dynamic reversal process. A simple analysis of magnetization ringing is shown and a method to reduce magnetization ringing in dynamic switching is suggested. We show that for the applied field smaller than the grain anisotropy field, the magnetization ringing is reduced with decreasing applied field magnitude. The energy surface model also predicts that for high data rate magnetic recording, the dynamic switching field may be well below the Stoner–Wohlfarth value. The magnetic write width can be much larger than the physical write pole width in perpendicular magnetic recording systems. [ABSTRACT FROM AUTHOR]

Dynamic relaxation for nonlinear magnetization excitation is analyzed. For direct processes, such as magnon-electron scattering and two-magnon scattering, the relaxation rate is determined from the linear case simply by utilizing the magnetization oscillation frequency for nonlinear excitation. For an indirect process, such as slow-relaxing impurities, the analysis gives an additional relaxation term proportional to the excitation level. In all cases the effective magnetization damping is increased compared to Landau-Lifshitz-Gilbert damping. [ABSTRACT FROM AUTHOR]

Presents a study which examined ferromagnetic switching in elongated iron oxide particles. Method of the study; Results and discussion; Conclusion.

It is conceivable that early generations of patterned media will utilize read heads whose dimensions are several times larger than an ‘island’ of magnetization. For such a scenario, we propose a ‘multiple islands per read head’ model where the output from the read head is a function of the magnetization from several independently written tracks of islands. In particular, we focus on a ‘3 islands per read head’ model where the output from the read head is a function of the magnetization from three independently written tracks of islands. The readback signal is determined from a finite track-width magnetoresistive (MR) head model using reciprocity calculations, and two noise sources—island position jitter and AWGN electronics noise—are considered. By sampling the noisy signal at intervals corresponding to the down-track island separation, we obtain a discrete-time readback channel model whose performance is obtained under maximum-likelihood sequence detection. [ABSTRACT FROM AUTHOR]

Magnetic reversal in exchange-coupled composite elements under microwave fields is characterized by several unique properties including reduced reversal fields, microwave fields, microwave resonant frequencies, and reduced sensitivity to anisotropy distributions as compared to homogeneous elements. We find that reversal can occur in uniform and nonuniform regimes. The uniform regime is characterized by coherent spin precession enhancement by the microwave field. In the nonuniform regime domain walls in the soft layer mediate reversal and under linearly polarized microwave fields, can lead to a formation of localized reversal/nonreversal areas in the “applied field-frequency” phase plane. [ABSTRACT FROM AUTHOR]

Patterned media elements comprising coupled magnetically hard and soft sections of different horizontal size, referred to as ledge elements, are characterized by several unique properties. These elements allow for remarkably reduced reversal fields, which are an order of magnitude below the Stoner-Wohlfarth limit. They also allow for precessional reversal to occur for practical field rise times (100–200 ps), which are two orders of magnitude larger than those in the case of homogeneous elements (∼2 ps). These attractive properties are obtained even for elements of small height (4–8 nm). Patterned media implementing such ledge elements can allow for recording densities above 10 Tbit/in2. [ABSTRACT FROM AUTHOR]

The energy barrier to be overcome for thermal reversal, the reversal mode and the effective particle volume involved are determined by the saddle points of the energy surface. We investigate the influence of field misorientation, exchange-coupling and magnetostatic interaction for a 2:1 aspect ratio particle discretized into two subunits. typically, increasing the field angle from 0° to 45° enhances the effective volume in both cases by more than 20%. [ABSTRACT FROM AUTHOR]

A micromagnetic model for the writing process in perpendicular magnetic recording is developed to study the effect of the soft underlayer on the dynamic reversal of the recording layer. The upper part of the soft material is discretized micromagnetically, each spin following LLG dynamics; the remaining part has infinite permeability. The validity of the model is tested in the static case. Dynamically, high-frequency spin motion is observed in the soft layer. Nevertheless, the field inside the data layer follows the time dependence of the input waveform. [ABSTRACT FROM AUTHOR]