Quantum decay of metastable states in small magnetic particles

Abstract

We present an imaginary-time path-integral study of the problem of quantum decay of a metastable state of a uniaxial magnetic particle placed in the magnetic field at an arbitrary angle. Our findings agree with earlier results of Zaslavskii obtained by mapping the spin Hamiltonian onto a particle Hamiltonian. In the limit of low barrier, weak dependence of the decay rate on the angle is found, except for the field which is almost normal to the anisotropy axis, where the rate is sharply peaked, and for the field approaching the parallel orientation, where the rate rapidly goes to zero. This distinct angular dependence, together with the dependence of the rate on the field strength, provides an independent test for macroscopic spin tunneling. ͓S0163-1829͑96͒05625-1͔

Classical and Quantum Magnetization Reversal Studied in Nanometer‐Sized Particles and Clusters

“…The crossover temperature T c can be defined as the temperature where the quantum switching rate equals the thermal one. The case of a magnetic particle, as a function of the applied field direction, has been considered by several authors [175,176,177]. We have chosen the result for a particle with biaxial anisotropy as the effective anisotropy of most particles can be approximately described by strong uniaxial and weak transverse anisotropy.…”

Magnetic reversal of a quantum nanoferromagnet

“…Though very slow, this process should be significant at very low temperature. At this point, one can stress that this process is different from quantum tunneling, 4,[60][61][62] which is also invoked in a magnetization switch at very low temperatures; indeed, in contrast to quantum tunneling, the present process involves (1) a collision with an electron and (2) a dissipation, i.e., an energy change between the initial and final magnetization states that is balanced by heating a substrate electron. In a classical view, there is still a barrier separating the two magnetization states, lowered by the E contribution; the system does not tunnel through the barrier at constant energy, but, due to the symmetry lowering introduced by E, collision with a substrate electron is able to induce a direct transition between the two magnetization states.…”

Macroscopic Quantum Tunneling of Magnetization of Single Ferrimagnetic Nanoparticles of Barium Ferrite

“…The angular dependence of the crossover temperature of a ferromagnetic particle [22] was considered by several authors [23][24][25]. As the BaFeCoTiO particles have a strong uniaxial anisotropy and weak in-plane anisotropy, we compared our measurements by taking into account only uniaxial anisotropy [24]:…”

“…As the BaFeCoTiO particles have a strong uniaxial anisotropy and weak in-plane anisotropy, we compared our measurements by taking into account only uniaxial anisotropy [24]:…”