Thermally Assisted Macroscopic Quantum Tunneling of a Ferromagnetic Particle in a Magnetic Field at an Arbitrary Angle
نویسنده
چکیده
At finite temperature we study the quantum tunneling of magnetization for a small ferromagnetic particle with the biaxial symmetry placed in a magnetic field at an arbitrary angle. We present numerical WKB exponent below the crossover temperature in which the quantum tunneling is affected by the thermal activation, and the approximate form of the WKB exponent around the crossover region. The effect of quantum fluctuations on the thermal activation rate beyond the crossover regime are discussed. PACS numbers: 75.45.+j, 73.40.Gk, 75.30.Gw, 75.50.Gg Typeset using REVTEX
منابع مشابه
Magnetic Field Dependence of Macroscopic Quantum Tunneling and Coherence of Ferromagnetic Particle
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 fie...
متن کاملQuantum Nucleation in a Ferromagnetic Film Placed in a Magnetic Field at an Arbitrary Angle
We study the quantum nucleation in a thin ferromagnetic film placed in a magnetic field at an arbitrary angle. The dependence of the quantum nucleation and the temperature of the crossover from thermal to quantum regime on the direction and the strength of the applied field are presented. It is found that the maximal value of the rate and that of the crossover temperature are obtained at a some...
متن کاملMacroscopic measurement of resonant magnetization tunneling in high-spin molecules.
We report the observation of steps at regular intervals of magnetic field in the hysteresis loop of a macroscopic sample of oriented Mn12O12(CH3COO)16(H2O)4 crystals. The magnetic relaxation rate increases substantially when the field is tuned to a step. We propose that these effects are manifestations of thermally assisted, field-tuned resonant tunneling between quantum spin states, and attrib...
متن کاملKl-th 96/6 Application of Instantons: Quenching of Macroscopic Quantum Coherence and Macroscopic Fermi–particle Configurations
Starting from the coherent state representation of the evolution operator with the help of the path–integral, we derive a formula for the low–lying levels E = ǫ0 − 2△ǫ cos(s+ ξ)π of a quantum spin system. The quenching of macroscopic quantum coherence is understood as the vanishing of cos(s+ ξ)π in disagreement with the suppression of tunneling (i.e. △ǫ = 0) as claimed in the literature. A new ...
متن کاملMagnetic relaxations of antiferromagnetic nanoparticles in magnetic fields.
We reexamine anomalous magnetic relaxations of ferritin in magnetic fields, the presence of which has been regarded as evidence suggesting the existence of thermally assisted macroscopic quantum tunneling in antiferromagnetic nanoparticles. In the present study, relaxation curves of ferritin are examined using an approach that is free from assumptions regarding distributions of various paramete...
متن کامل