Hysteresis anomalies and exchange bias in 6.6 nm CuO nanoparticles

In the 6.6 nm particles of CuO with Neel temperature T(N)similar or equal to40 K, hysteresis loops are observed up to 330 K. With decrease in temperature, the coercivity H-c increases slowly up to T-N below which rapid increases in H-c and exchange bias H-e are observed. At 5 K, the ratio H-e/H(c)similar or equal to2, decreasing to zero as T-->T-N. At 10 K, the variation of H-e, H-c, and the ratio H-e/H-c with the cooling field show behavior similar to that of the weak ferromagnetic moment resulting from the uncompensated surface spins. (C) 2002 American Institute of Physics.