DOI: 10.1209/epl/i2001-00326-y


Europhys. Lett., 54 (6) , pp. 813-819 (2001)

Magnetic stability of nano-particles: The role of dipolar instability pockets

M. Grimsditch¹, A. Berger¹, J. Johnson¹, V. Metlushko², B. Ilic³, P. Neuzil⁴ and R. Kumar<sup>4

1</sup>  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)

Abstract
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.

PACS
75.60.Ej - Magnetization curves, hysteresis, Barkhausen and related effects.
75.70.Kw - Domain structure (including magnetic bubbles).


© EDP Sciences 2001