Topological phase interference induced by a magnetic field along hard anisotropy axis in nanospin

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Title: Topological phase interference induced by a magnetic field along hard anisotropy axis in nanospin
Author(s): Lu, Rong; Hu, Hui; Zhu, Jia-Lin; Wang, Xiao-Bing; Chang, Lee; Gu, Bing-Lin
Abstract: Based on the instanton technique in the spin-coherent-state path-integral representation, the spin-parity effects induced by the topological Wess-Zumino or Berry phase are studied theoretically in nanometer-scale single-domain ferromagnets in the presence of an external magnetic field along the hard anisotropy axis. We consider the magnetocrystalline anisotropy with the biaxial, trigonal, tetragonal, and hexagonal crystal symmetry, respectively. Both the Wentzel-Kramers-Brillouin (WKB) exponent and the preexponential factors are evaluated in the instanton's contribution to the ground-state tunnel splittings. The Euclidean transition amplitudes between energetically degenerate easy directions are obtained with the help of the dilute instanton gas approximation. The effective Hamiltonian approach is applied to present the final results of ground-state tunnel splittings for each kind of crystal symmetry. The Euclidean transition amplitudes and the ground-state tunnel splittings are found to depend on the parity of total spins of ferromagnets and oscillate with the external magnetic field for both the integer and half-integer total spins. We show that the topological phase interference or spin-parity effects can reflect in thermodynamic quantities of magnetic tunneling states. Possible relevance to experiments is also discussed.
Publication type: Journal article
Source: Physical Review B: Condensed Matter and Material Physics, Vol. 61, no. 21 (Jun 2000), pp. 14581-14591
Publication year: 2000
FOR Code(s): 01 Mathematical Sciences; 02 Physical Sciences; 09 Engineering
Keyword(s): Euclidean transition; Nanospin; Wentzel-Kramers-Brillouin exponent
Publisher: American Physical Society
ISSN: 1098-0121
Publisher URL: http://dx.doi.org/10.1103/PhysRevB.61.14581
Peer reviewed