Anisotropy Field Of Particles Research Articles

Quasistatic hysteresis loops of magnetic nanoparticles in a rotating magnetic field

Quasistatic hysteresis loops of a single-domain magnetic nanoparticle with uniaxial anisotropy in a rotating magnetic field have been calculated. Magnetic hysteresis is shown to exist only in a limited range of reduced magnetic field amplitudes, 0.5 < h0 < 1, where h0 = H0/Ha, H0 is the amplitude of the rotating magnetic field, Ha being the particle anisotropy field. An analytical formula is obtained for the particle coercive force as a function of the reduced field amplitude. In the domain h0 < 0.5 the magnetization reversal of a particle is impossible, since the final energy barrier exists between the potential wells of the particle for all orientations of applied magnetic field. On the other hand, in the domain h0 > 1 the total energy of the nanoparticle has a single energy minimum, so that there is no magnetic hysteresis. Quasistatic hysteresis loops of a randomly oriented assembly of non interacting nanoparticles in a rotating magnetic field are also obtained.

Parametric amplification of reversible transverse susceptibility in single domain magnetic nanoparticles

We propose, model, and experimentally demonstrate the enhancement of reversible transverse susceptibility in single domain magnetic nanoparticles through the principle of parametric amplification. It has previously been demonstrated that properly oriented anisotropic single domain magnetic nanoparticles have an appreciable peak in transverse susceptibility at the particle anisotropy field. Here we show theoretically and experimentally that an additional parametric AC magnetic field applied at a proper phase and at twice the frequency (2f) of the transverse field further enhances transverse susceptibility peaks through the process of parametric amplification. We model this effect numerically and describe it through the energy formalism of the single magnetic domain Stoner-Wohlfarth model. The proper phase relationships of the transverse and parametric fields to obtain either parametric amplification or attenuation of the transverse susceptibility signals are also described. We experimentally demonstrate such parametric tuning of transverse susceptibility in single domain magnetic nanoparticles of a commercial audio tape in a prototypical inductive transverse susceptibility set-up.

Critical magnetization and hysteresis of nanogranular films with perpendicular anisotropy

The magnetic-field dependences of the stability boundaries of the nonequilibrium magnetic states that exist in a nanogranular film with perpendicular anisotropy in tilted magnetic fields are theoretically described, and the corresponding critical magnetization is calculated. The field dependences of the critical magnetization of the film are analyzed at various ratios of the anisotropy field of particles to the maximum possible demagnetizing field of the film. In a tilted magnetic field, the magnetization reversal curves, which include hysteresis loops, are shown to consist of segments of the following three types: equilibrium stable magnetization, nonequilibrium stable magnetization, and critical type of magnetization.

The complex transverse susceptibility

Previous attempts to explain the dependence of the transverse susceptibility (TS) on the DC field predict the occurence of a maximum at the particle anisotropy field ( H K ). We demonstrate that the TS is also very sensitive to the particle volume distribution, which strongly influences the magnitude of the TS peak and the corresponding value of the DC field. The DC field has the same effect on the TS as the temperature on the AC susceptibility, giving rise to a complex TS with invaluable applications for recording media, like the determination of the particle volume and anisotropy field distributions.

Relationship Between Hk Distribution of Media and High Density Recording Characteristics

A new parameter, the ΔH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> of minor M-H curves, is introduced in order to estimate the standard deviation of the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> distribution. AHC correlates strongly to the coercivity squareness S* and the half-maximum width of the switching field distribution SFD, and need not be compensated for the demagnetizing field in perpendicular recording media. It was shown by computer simulation analysis that the magnetic recording performance depends greatly upon the particle's anisotropy field H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> distribution in the recording medium, as well as the coercivity and saturation magnetization. The narrow H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> distribution of Co-Cr sputtered media derives from the high crystallinity, and leads to superior performance in high density recording.

磁気記録媒体におけるＨｋ分布と高密度特性の関連

A new parameter ΔHc on M-H minor curves is introduced to estimate the standard deviation of the Hk distribution. The ΔHc correlates strongly to coercivity squareness s* and half-width of switching field distribution SFD. and needs no compensating for the demagnetizing field in perpendicular recording media. It was shown by computer simulation analysis that the magnetic recording performance depends greatly upon the particle's anisotropy field Hk distribution in recording media as well as coercivity and saturation magnetization. The narrow Hk distribution of Co-Cr sputtered media is derived from the high crystallinity, and leads to superior performance in high density recording.