Magnetic Relaxation in Fine‐Particle Systems

Magneto-optical Kerr effect, is used to investigate the magnetization of film made of uncoalesced cobalt and cobalt‐platinum nanocrystals. For the pure cobalt nanocrystals, different film morphologies are obtained through application of magnetic field during deposition. These morphologies have quite different magnetic properties, which is rationalized by considering dipolar interactions and the associated demagnetizing factor. We show that fast annealing can be used to trigger changes in the particles’ crystalline structure while largely avoiding their coalescence. With increasing the annealing temperature, 2.7 nm CoPt nanocrystals show a transition from the magnetically soft face-centered-cubic phase to the hard face-centered-tetragonal L1 0 phase. In particular fast annealing to 950 K is shown to produce largely uncoalesced nanocrystals ferromagnetic at room temperature. With 7 nm cobalt nanocrystals, fast annealing at 500 K equally results in ferromagnetism at room temperature without inducing coalescence between the nanocrystals in the film. © 2004 American Institute of Physics. @DOI: 10.1063/1.1686906#

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Magnetic properties of cobalt and cobalt-platinum nanocrystals investigated by magneto-optical Kerr effect

A thermal variable variance Preisach-Neel model was developed. The effect of the applied field and of the interaction variance was studied in zero field cooled simulated processes using different expressions for the thermal barrier expression and different ways of Preisach distribution modification due to thermal effects. The advantages and disadvantages of using each variant of the model were investigated.

A Preisach-Neel model with thermally variable variance

Experimental evidence of ferromagnetic behavior of liquid droplets produced by laser ablation from amorphous alloys is presented. Thin films of amorphous magnetic materials were fabricated by laser ablation deposition in the presence and in the absence of a magnetic field. The difference in parameters of deposited films is attributed to ferromagnetic properties of small size liquid droplets.

Evidence of ferromagnetic behavior of small liquid droplets produced from amorphous alloys by laser ablation

Experimental evidence for ferromagnetic behavior of liquid droplets produced by laser ablation from amorphous alloys is presented for the first time. Thin films of amorphous magnetic materials are fabricated by a laser deposition technique in the presence and in the absence of magnetic field. The differences in the parameters of deposited films are attributed to the ferromagnetic properties of small liquid droplets.

Ferromagnetic liquid droplets

γ-Fe2O3 nanoparticle zero field cooled magnetization: Variation of the superparamagnetic θsp Curie temperature with the measurement geometry and the applied field

J.P. Jolivet

Papers

γ-Fe2O3 nanoparticle zero field cooled magnetization: Variation of the superparamagnetic θsp Curie temperature with the measurement geometry and the applied field