부산대학교 도서관

In this article, magnetic and structural characteristics of CoFe 2 O 4 nanopowders with mean diameter 17.8(4) and 63.7(2.4) nm [denoted as NM(18) and CP(60), respectively] were studied by applying X-ray diffraction method (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). It was established that for NM(18), the nanoparticle size corresponds to one crystallite while CP(60) nanoparticle forms a multi-crystallite system which means certain kind of averaging of magnetic moments. Magnetic analysis was performed according to the ZFC-FC protocol in the temperature range of 10–380 K, and magnetization curves $M(H)$ were recorded at the magnetic field up to 7 T. It was shown that, independently on nanoparticle size distribution, the magnetic response of both nanopowders is mainly determined by superspin glass type interaction of magnetic moments corresponding to a single crystallite. In addition, basic magnetic characteristics such as anisotropy constant $K_{1} =$ (3.9–12.5) $\times 10^{5}$ J/ $\text{m}^{3}$ , anisotropy field $\mu _{0}H_{\mathrm {A}} = 1.80$ –5.80 T, or magnetic moment per formula unit $\mu =3.45$ (5) $\mu _{\mathrm {B}}$ [for CP(60)] and $\mu =3.50$ (5) $\mu _{\mathrm {B}}$ [for NM(18)] were also determined and discussed.