Exchange-coupling behavior in SrTb0.01Tm0.01Fe11.98O19/(CoFe2O4)x hard/soft nanocomposites
Abstract
The magnetic and exchange-coupling properties of SrTb0.01Tm0.01Fe11.98O19/(CoFe2O4)x (x = 1.0, 1.5, 2.0, 2.5, and 3.0) hard/soft nanocomposites produced via a one-pot sol–gel combustion route were investigated in detail. Their structures and morphologies were explored by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). The XRD results showed integration between hexaferrite and spinel ferrite phases. The SEM images exhibited hexagonal plate-shaped particles decorated with cubic particles relevant to SrTb0.01Tm0.01Fe11.98O19 and CoFe2O4, respectively. The magnetic properties of the prepared nanocomposite ferrites were also investigated. Smooth M–H hysteresis loops with no “bee waist” established that the hard/soft SrTb0.01Tm0.01Fe11.98O19/CoFe2O4 phases were efficiently exchange-coupled. A drastic increase in saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) was noticed on increasing the content of the soft phase (x). (BH)max (maximum energy product) showed maximum values of 19.9 and 87.2 kJ m−3 for the nanocomposite with x = 3.0 at 300 and 10 K, respectively. The exchange coupling among the soft and hard ferrite grains was proven by the switching field distribution (SDF) plots. Excellent exchange-coupling behavior was noticed for the nanocomposite with x = 3.0. The prepared hard/soft ferrite nanocomposites have been found to be promising candidate nanomaterials for permanent nanomagnets.