Magnetic anisotropy variations and nonequilibrium tunneling in a cobalt nanoparticle - art. no. 226801

We present detailed measurements of the discrete electron-tunneling level s pectrum within nanometer-scale cobalt particles as a function of magnetic f ield and gate voltage, in this way probing individual quantum many-body eig enstates inside ferromagnetic samples. Variations among the observed levels indicate that different quantum states within one particle are subject to different magnetic anisotropy energies. Gate-voltage studies demonstrate th at the low-energy tunneling spectrum is affected dramatically by the presen ce of nonequilibrium spin excitations.