Strain-induced magnetic anisotropy via the Jahn-Teller effect and the magnetoelastic coupling of tetragonally distorted (Cu,Co)Fe2O4 particles

Coercivity analysis of cubic and tetragonal (Cu,Co) ferrite particles within the global model

“…Taking into consideration intergranular exchange coupling gives very good agreement with the experimental data. For this tetragonally distorted sample, the anisotropy field H A ≈ 1.9 MA m −1 is derived from the parameters M s = 0.158 × 10 6 A m −1 and K = 0.19 × 10 6 J m −3 at 300 K. This value is in fair agreement with the room temperature anisotropy field estimated via the rotational hysteresis and inverse applied field, W r vs 1/H plot from room temperature torque measurements (H A torq ≈ 1.6 MA m −1 ) [11]. The experimental M(H) curves were measured in the range 3-300 K and the fitting parameters obtained from the M(H app ) analysis are plotted as a function of temperature in figure 2(b).…”

“…Two samples of Co x Cu 1−x Fe 2 O 4 particles where x = 0.1 and x = 0.2 were prepared via coprecipitation and flux methods, as detailed in [11]. Analysis of x-ray diffraction patterns showed that the x = 0.1 sample consists of a single phase tetragonal structure with distinct JT distortion (c/a > 1), whereas the x = 0.2 sample consists of a single phase cubic structure with no distinct global JT distortion.…”

“…Such an approach has been reported for cubic Co doped spinel ferrite particles, where the enhanced coercivity was proportional to the Co content [8,9]. Another novel approach is the application of Jahn-Teller (JT) distortion of Cu 2+ or Mn 3+ ions to realize so-called tetragonal ferrite, coupled with the magnetoelastic effect of Co 2+ ions, to realize high magnetic anisotropy [10][11][12]. In the cases of (Cu,Co)Fe 2 O 4 and Co(Mn,Fe) 2 O 4 , two different types of cations play specific roles in enhancing the magnetic anisotropy.…”

“…While the Cu 2+ and/or Mn 3+ ions are responsible for the JT distortion, the Co 2+ ions increase the magnetic anisotropy via a magnetoelastic effect. It was demonstrated in [11] that the magnetic anisotropy of Cu 1−x Co x Fe 2 O 4 is simply proportional to χx where χ denotes the tetragonality of the spinel structure, indicating that the JT distortion and the magnetoelastic effect of the Co ions are strongly coupled.…”

“…In [11], we have reported in detail on the intrinsic properties including magnetic anisotropy of tetragonal ferrite. The main motivation of this study is to investigate the extrinsic properties, in particular coercivity, which is a critical property for the industrial application of hard magnetic materials.…”