Fluctuations of the anisotropy energy in nanoscale ferromagnetic particles

Abstract

What are the properties of individual states in the electronic spectrum of a nanometer size ferromagnetic particle? — Besides the intrinsic scientific interest in understanding ferromagnetism on the nanometer scale, this question might also be of technological interest, since the size of memory elements in magnetic storage technologies is decreasing extremely rapidly [1], and particles as small as 4 nm are coming under investigation [2]. In a ferromagnetic single electron transistor (SET) with leads and/or island made from itinerant ferromagnetic materials such as Co, Fe or Ni, which have different densities of states for spin-up (majority band) and spin-down (minority band) electrons, transport becomes spin dependent. This leads to a number of interesting new phenomena, such as tunneling magneto resistance, TMR [3], (the resistance of the SET depends on the relative orientation of the magnetic moments of leads and island) or Coulomb oscillations as a function of the applied magnetic field [4]. Such single electron tunneling effects in ferromagnetic systems are part of a new branch in mesoscopic physics called magneto electronics or spintronics, bringing together magnetism (spin) and electronics.