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Periodic Instanton Calculations of Quantum-Classical Transitions in Spin Systems |
| ZHANG Yun-bo1,2;NIE Yi-hang2;KOU Su-peng1,2;WANG Xiao-bing3;LIANG Jiu-qing1,2;PU Fu-ke1,4 |
| 1Institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100080
2Department of Physics, Shanxi University, Taiyuan 030006
3Center for Advanced Study, Tsinghua University, Beijing 100084
4Department of Physics, Guangzhou Normal College, Guangzhou 510400
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| Cite this article: |
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ZHANG Yun-bo, NIE Yi-hang, KOU Su-peng et al 1998 Chin. Phys. Lett. 15 683-685 |
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Abstract The quantum-classical transitions of the escape rates in the molecular magnet Mnl2Ac and a biaxial anisotropic ferromagnetic spin model are investigated by applying the periodic instanton method. The effective free energies are expanded around the top of the potential barrier in analogy to the Landau theory of phase transitions. We show that the first-order transitions occur below the critical external magnetic field hx = 1/4 for Mnl2Ac and beyond the critical anisotropy constant ratio λ = 1/2 for the biaxial ferromagnetic grains, which is in good agreement with earlier studies.
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| Keywords:
75.45.+j
75.50.Tt
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Published: 01 September 1998
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| PACS: |
75.45.+j
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(Macroscopic quantum phenomena in magnetic systems)
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75.50.Tt
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(Fine-particle systems; nanocrystalline materials)
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