Kai-Zhong Gao

Recording potential of bit-patterned media

A comprehensive analysis of the areal density potential of bit-patterned media recording shows that the recording performance is dominated by written-in errors. The statistical fluctuations of the magnetic properties and the locations of the individual bits lead to error probabilities so that some dots are either not recorded at all or cannot be recorded in the time window necessary to ensure synchronized writing. The highest areal densities are obtained with a combination of a pole head, a soft magnetic underlayer, and a storage medium of the composite type. Areal density scenarios of up to 5Tbits∕in.2 are analyzed.

Slow magnetization relaxation and reversal in magnetic thin films

The slow magnetization dynamics in magnetic thin films has been investigated in this paper. It is shown that the experimental results of the time-dependent magnetization can be well described by the extended exponential function, exp(−(t/τ)β) with β>0, in a number of thin film systems. By investigating the characteristics of the magnetization process and examining the limitations of the present models, an explanation is provided based on the structural and dynamical properties of the magnetic domains. Meanwhile, some questions have been clarified in the study towards understanding the magnetization relaxation phenomenon in thin films.

Microwave generation by a direct current spin-polarized current in nanoscale square magnets

Theoretical calculation for a simple nanoscale magnetoelectronic device to function as a microwave generator based on the spin-transfer torque effect is presented. The device is unique because the output amplitude and frequency can be continuously tuned by the electrical current in the microwave frequency range. Analysis and discussion of the device structure, function, and realization are provided.

Precessional dynamics of single-domain magnetic nanoparticles driven by small ac magnetic fields

The magnetic and mechanical dynamics of nanometre-sized magnetic particles with a uniaxial anisotropy excited by ac magnetic fields is studied using the classical theory approach in the Lagrangian formalism. Through the magnetic anisotropy between the magnetic moment and the lattice, the nanoparticle is coupled with the magnetic moment and then driven into a mechanical precession mode by the ac magnetic fields. Mechanical resonance can be achieved along with the magnetic resonance at frequencies and with resonance amplitudes that depend strongly upon both the magnetic and the mechanical properties of the nanoparticles. The dynamics manifests itself in magnetic susceptibility and energy dissipation, which are discussed in great detail in this article.

Magneto-elastic coupling and Peierls-like phase transition of one-dimensional magnetic nanoparticle chains

The fine structure of magnetic nanoparticle periodic chains is studied by considering the competition between magnetic dipolar interaction and elastic interaction. A Peierls phase with a doubled unit cell length can be formed under proper conditions and a Peierls transition can be induced by temperature and by external magnetic field. Due to the coupling between the magnetic state and the structural state, the nanoparticle chains would possess distinct properties and exhibit interesting behaviour.

Hysteretic magnetization behaviour influenced by spin-currents in magnetic thin films with perpendicular anisotropy

While most recent studies of the spin-transfer torque effect mainly deal with magnetic structures with in-plane anisotropies and magnetizations, we theoretically investigate the magnetization behaviour driven by spin-currents in a trilayer structure with perpendicular anisotropy and magnetization using a modified Landau?Lifshitz?Gilbert equation. This study is particularly conducted for hysteresis loop measurements under spin-currents and current?voltage measurements in the presence of external magnetic fields, by which the unique magnetization rotations and reversals associated with the spin-transfer torque in the magnetic configuration can be captured.