Magnetic anisotropy in the ferromagnetic Cu-doped ZnO nanoneedles

Copper-doped ZnO (ZnO:Cu) nanoneedles exhibiting room-temperature ferromagnetism were fabricated by an ion beam technique using Cu plate and ZnO film. A saturated magnetization moment of 0.698 emu cm3 was found in the nanoneedles when a field of 10 kOe was applied perpendicular to the substrate, which was 15% larger than the field applied parallel to the substrate. The magnetic ordering of the nanoneedles was enhanced significantly to 0.968 emu cm3 after annealing of 400°C for 20 min. However, the magnetic anisotropy at high field is vanished but an "easy plane" ferromagnetism becomes apparent at low field region. The possible mechanisms of the magnetic ordering and anisotropy in the ZnO:Cu nanoneedles are discussed.