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Zeitschriftenartikel:

D.C. Crew, Er. Girt, D. Süss, T. Schrefl, K.M. Krishnan, G. Thomas, M. Guilot:
"Magnetic interactions and reversal behavior of NdFeB particles diluted in a Nd matrix";
Physical Review B, 66 (2002), S. 184418-1 - 184418-13.



Kurzfassung englisch:
Magnetic interactions and reversal behavior of Nd2Fe14B particles diluted in a Nd matrix

D. C. Crew,1,2 Er. Girt,3 D. Suess,4 T. Schrefl,4 K. M. Krishnan,5 G. Thomas,5,6 and M. Guilot7 1 Materials and Chemical Sciences Division, Energy Science and Technology Department, Brookhaven National Laboratory, Upton, New York 11973
2Department of Physics, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
3Seagate Technology, 47010 Kato Road, Fremont, California
4Institute of Applied and Technical Physics, Vienna University of Technology, Haupstr. 8?10, A?1040 Vienna, Austria
5Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
6Department of Material Science and Engineering, University of California, Berkeley, California 94720
7Laboratoire des Champs Magnétiques Intenses, CNRS/MPI, 38042 Grenoble, France

(Received 6 June 2002; published 18 November 2002)

Reversible magnetization measurements, micromagnetic modeling, the temperature dependence of coercivity, and magnetic viscosity measurements have been used to clarify the magnetic reversal mechanism of Nd2Fe14B particles contained in a Nd matrix. The coercivity was observed to increase markedly as the dilution of the Nd2Fe14B phase was increased. The increase in coercivity was accompanied by a change in the reversal mechanism. In the least dilute samples, domain wall motion involving several grains governed by intergrain interactions was active. In the most dilute samples nonuniform reversal of individual grains was dominant, reversal occurring particle by particle and resembling the behavior of isolated Stoner-Wohlfarth particles. The value of the coercivity in the most dilute sample was in excellent agreement with micromagnetic modeling results for isolated particles when the effect of thermal activation of magnetization reversal was accounted for. Despite the single particle reversal mechanism of the most dilute samples, a linear dependence of coercivity on packing fraction was not observed. This is attributed to a clustering of the grains in the samples and changes in grain shape with composition. In all samples, regardless of dilution, the initial magnetic state after thermal demagnetization was found to be one in which a substantial proportion of grains were in a multidomain state. However, micromagnetic simulations for isolated particles of similar shape to those in the most dilute sample showed that the single domain state is the lowest energy state. It is concluded that thermal demagnetization can result in the system remaining in a local metastable state and not the global energy minimum. Micromagnetic calculations showed that one or more domain walls can arise in a grain during thermal demagnetization and that magnetostatic effects provide a significant energy barrier in zero field to the removal of a domain wall once it is formed. ©2002 The American Physical Society


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