Observation of perpendicular anisotropy in granular magnetic solids

Granular Co-Ag materials with low Co contents exhibit giant magnetoresistance and single-domain magnetic properties. In this paper, we discuss unusual hysteresis behavior that we have observed in Co-rich samples, where the magnetization is approximately linear with the applied field up to saturation, and the coercivity and remnant magnetization are both nearly zero. We attribute this unusual behavior to a perpendicular anisotropy that depends on the nanostructure in the phase-segregated materials. These results are corroborated by magnetic domain imaging using scanning electron microscopy with polarization analysis.