  We measure the low-temperature resistance of permalloy break junctions as a
function of contact size and the magnetic field angle, in applied fields large
enough to saturate the magnetization. For both nanometer-scale metallic
contacts and tunneling devices we observe large changes in resistance with
angle, as large as 25% in the tunneling regime. The pattern of
magnetoresistance is sensitive to changes in bias on a scale of a few mV. We
interpret the effect as a consequence of conductance fluctuations due to
quantum interference.
