Magnetic Field Dependence of Macroscopic Quantum Tunneling and Coherence of Ferromagnetic Particle
نویسندگان
چکیده
We calculate the quantum tunneling rate of a ferromagnetic particle of ∼ 100Å diameter in a magnetic field of arbitrary angle. We consider the magnetocrystalline anisotropy with the biaxial symmetry and that with the tetragonal symmetry. Using the spin-coherent-state path integral, we obtain approximate analytic formulas of the tunneling rates in the small ǫ(= 1−H/Hc)-limit for the magnetic field normal to the easy axis (θH = π/2), for the field opposite to the initial easy axis (θH = π), and for the field at an angle between these two orientations (π/2 ≪ θH ≪ π). In addition, we obtain numerically the tunneling rates for the biaxial symmetry in the full range of the angle θH of the magnetic field (π/2 < θH ≤ π), for the values of ǫ = 0.01 and 0.001. PACS numbers: 75.45.+j, 73.40.Gk, 75.30.Gw, 75.50.Gg a e-mail: [email protected] b e-mail: [email protected] Typeset using REVTEX
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