Europhys. Lett., 54 (6) , pp. 813-819 (2001)
Magnetic stability of nano-particles: The role of dipolar instability pocketsM. Grimsditch1, A. Berger1, J. Johnson1, V. Metlushko2, B. Ilic3, P. Neuzil4 and R. Kumar4
1 Materials Science Division, Argonne National Laboratory Argonne, IL 60439-4845, USA
2 Department of Electrical Engineering and Computer Science University of Illinois at Chicago - Chicago, IL 60607, USA
3 School of Applied and Engineering Physics, Cornell University Ithaca, NY 14853, USA
4 Institute of Microelectronics, 11 Science Park Rd., Singapore, 117685
(Received 4 December 2000; accepted in final form 5 April 2001)
We show that the magnetic stability of nano-particles, with regard to magnetization reversal or domain formation, is controlled by dipolar instability pockets. These pockets are regions in which the local dipolar fields (i.e. shape-dependent effects) favor a spin reorientation. Calculated shape-dependent demagnetizing fields coupled with exchange contributions combine to yield the field at which a magnon mode attains zero frequency implying the onset of reversal or domain formation. Calculated switching-onset fields are found to explain experimental data as a function of: material, thickness, aspect ratio, and shape.
75.60.Ej - Magnetization curves, hysteresis, Barkhausen and related effects.
75.70.Kw - Domain structure (including magnetic bubbles).
© EDP Sciences 2001