  We address electron spin resonance of single magnetic moments in a tunnel
junction using time-dependent electric fields and spin-polarized current. We
show that the tunneling current directly depends on the local magnetic moment
and that the frequency of the external electric field mixes with the
characteristic Larmor frequency of the local spin. The importance of the
spin-polarized current induced anisotropy fields acting on the local spin
moment is, moreover, demonstrated. Our proposed model thus explains the absence
of an electron spin resonance for a half integer spin, in contrast with the
strong signal observed for an integer spin.
