Mesoscopic fluctuations of the anisotropy tensor in ferromagnetic nanoparticles

GONZALO USAJ; U BARANGER, HAROLD

EUROPHYSICS LETTERS

Año: 2005 vol. 72 p. 110 - 116

0295-5075

We calculate the mesoscopic fluctuations of the magnetic anisotropy of ferromagnetic nanoparticles;that is, the effect of single-particle interference on the direction of the collective magnetic moment. A microscopic spin-orbit Hamiltonian considered as a perturbationof the much stronger exchange interaction first yields an explicit expression for the anisotropy tensor. Then, assuming a simple random matrix model for the spin-orbit coupling allows us to describe the fluctuation of such a tensor analytically. In the case of uniaxial anisotropy, we calculate the distribution of the anisotropy constant for a given number of electrons, and its variation upon increasing this number by one. The magnitude of the latter scales inverselywith the number of atoms in the particle and is sufficient to account for the experimental data.