Hou Denglu

Preisach Modelling on the Magnetic Properties of Nano-Particle Fe3O4

A sample of nano-particle Fe3O4 was synthesized using coprecipitation, and characterized by zero field cooling (ZFC) and field cooling (FC) magnetic moments and the major hysteresis loops. The data are analysed within the framework of a generalized Preisach model, which provides an excellent description of the experimental data. The simulated results are in good agreement with the experimental data. Using the model, we obtain that the blocking temperature of Fe3O4 nano-particles with diameter of 8.4 nm is 105 K, and the interaction field distribution between the particles is 550 Oe.

Large Tunability of Physical Properties of Manganite Thin Films by Epitaxial Strain

Physical properties of strongly correlated manganites are known to depend sensitively on lattice parameters. We show that in thin film form, the magnetic and transport properties of manganites can be tuned in a wide range using epitaxial strain. Specifically, by systematically varying the strain from negative to positive, we have observed 65%, −33%, 650%, and −17% changes for the saturation magnetization field Hs, saturation magnetization Ms, resistivity, and metal-insulator transition temperature. We explain these results with density functional theory calculations.

Room-temperature ferromagnetism observed in Si-Al 2 O 3 composite film

Room-temperature ferromagnetism (FM) is observed in Si-Al 2 O 3 amorphous composite film. The magnetic moment is the highest in the case of the Si-Al 2 O 3 composite films with the Si content being 15 vol.%, and distinct domains are detected in our films. The difference in magnetism property between sample annealed in Ar atmosphere and untreated composite film indicates that the observed ferromagnetism does not originate primarily from oxygen defects. It is concluded that the ferromagnetism arises from the direct coupling between defects. These defects orignate from the interface between Si particles and Al 2 O 3 matrix. By varying the Si content in the film, one can change the defect density and thereby control the strength of the ferromagnetic coupling.

Magnetic and Microstructure of Triple C/Co73Cr22Ta5/Ti for Perpendicular Media

The magnetic properties and microstructure of triple C/CoCrTa/Ti perpendicular recording films have been studied. Magnetic measurements show that the optimal thickness of Ti underlayer is 40 nm and that of CoCrTa is 35 nm. The optimal value of substrate temperature is found to be 400°C. A suitable Ti underlayer causes a magnetic layer to have a near-perfect hcp texture, with Co grains in the (002) preferred orientation. The film with needle-like grains is more suitable for perpendicular recording films.