Exchange-coupling behavior in SrTb0.01Tm0.01Fe11.98O19/(CoFe2O4)x hard/soft nanocomposites

Abstract

The magnetic and exchange-coupling properties of SrTb_0.01Tm_0.01Fe_11.98O₁₉/(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 SrTb_0.01Tm_0.01Fe_11.98O₁₉ 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 SrTb_0.01Tm_0.01Fe_11.98O₁₉/CoFe₂O₄ phases were efficiently exchange-coupled. A drastic increase in saturation magnetization (M_s), remanence (M_r) and coercivity (H_c) 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.