Volume 86, Issue 8, 15 October 1999
Index of content:
- MAGNETISM AND SUPERCONDUCTIVITY (PACS 74-76)
86(1999); http://dx.doi.org/10.1063/1.371397View Description Hide Description
The microstructure and the room-temperature hysteretic magnetic properties of sputtered, 10 nm thin films of equiatomic binary alloys of CoPt and FePt were characterized using transmission electron microscopy(TEM) and a superconducting quantum interference device(SQUID) magnetometer. A transformation from an atomically disordered, face-centered-cubic structure to the ordered structure occurred during postdeposition annealing and was characterized using digital analysis of dark-field TEM images. The transformation was observed to follow first-order nucleation and growth kinetics, and the ordered volume fraction transformed was quantified at numerous points during the transformation. The ordered volume fraction was then compared to the magnetic coercivity data obtained from the SQUID magnetometer. In contrast to the relationship most commonly described in the literature, that the highest coercivity corresponds to a two phase ordered/disordered mixture, the maximum value for coercivity in this study was found to correspond to the fully ordered state. Furthermore, in samples that were less than fully ordered, a direct relationship between ordered volume fraction and coercivity was observed for both CoPt and FePt. The proposed mechanism for the high coercivity in these films is an increasing density of magnetic domain wall pinning sites concurrent with an increasing fraction of ordered phase.
Comparison of the magnetic and transport properties of Ga-, Ni-, and Fe-doped perovskite manganese oxides86(1999); http://dx.doi.org/10.1063/1.371398View Description Hide Description
A comparative study on magnetic and transport properties has been performed for B-site substituted perovskites (B=Ga, Ni, and Fe). The doped samples show a notable decrease of the Curie Temperature, from 365 K of the undoped sample to 290 K (Ga), 292 K (Ni), and 265 K (Fe). Furthermore, the metal–semiconductor transition peaks in the doped samples shift to lower temperature, from above 300 K (undoped) to 212 K (Ga), 237 K (Ni), and 195 K (Fe). This considerable differences in magnetic and transport properties between doped and undoped samples and the diversity among the doped samples can be explained by the destruction of the partial double-exchange interactions and the exchange couplings between Mn and doped ions.
86(1999); http://dx.doi.org/10.1063/1.371399View Description Hide Description
PolycrystallinePermalloyfilms were deposited onto silicon substrates by rf sputtering. Arrays of cylindrical dots with diameter d between 150 and 550 nm were patterned by optical holographiclithography. The dots were arranged on a square lattice with period p, ranging from 310 to 1030 nm. The height h of dots, given by the thickness of the permalloyfilms, ranged between 10 and 80 nm. The shape of the magnetization loops of the dot arrays depends strongly on the aspect ratio The in-plane saturation field is given by the intrinsic demagnetization field of single, isolated dots. The dipolar interaction between the dots is negligible. For cylinders with elliptical base plane, the magnetization loop depends on the field direction. The measured magnetization loops of the arrays are the superposition of the magnetization loops of the single dots without dipolar interaction. A model of magnetization reversal in applied fields is given.
The effect of boron on the uniaxial magnetic anisotropy energy and the polar Kerr rotation in amorphous NdFe films86(1999); http://dx.doi.org/10.1063/1.371400View Description Hide Description
Amorphous light rare earth–transition metal alloys are candidates for magneto-optical recording materials in the wavelength region of a blue laser beam (λ≈400 nm) due to the large Kerr rotation angle However, the large demagnetizing energy (shape anisotropy) prevents the films from developing an effective perpendicular anisotropy. The addition of boron to the amorphous Nd Fe matrix reduces the magnetization, enhances the effective perpendicular anisotropy, and enhances the Kerr rotation angle
86(1999); http://dx.doi.org/10.1063/1.371401View Description Hide Description
A method for computing local magnetic field for the case of small permeability or susceptibility contrast is described. The method is illustrated by using an example of a periodic array of cylinders which affords the simplest yet a representative case for visualizing the local fields. The cylinders represent material of one susceptibility such as solid grains in a rock matrix (or tissues in biological systems) and the space outside represents material of another susceptibility such as fluid which fills the pore space (or fluids outside tissues). We calculate the position dependent correction from the continuum to the local field inhomogeneity and go beyond the standard uniform field term. A simple (separate) illustration when the local field diverges is given.