We have performed first-principles calculations to obtain magnetic moment, magnetocrystalline anisotropy energy (MAE), i.e., the magnetic crystalline anisotropy constant (K), and the Curie temperature (T_c) of low temperature phase (LTP) MnBi and also estimated the maximum energy product (BH)_max at elevated temperatures. The full-potential linearized augmented plane wave (FPLAPW) method, based on density functional theory (DFT) within the local spin density approximation (LSDA), was used to calculate the electronic structure of LPM MnBi. The T_c was calculated by the mean field theory. The calculated magnetic moment, MAE, and T_c are 3.63 μ_B/f.u. (formula unit) (79 emu/g or 714 emu/cm³), −0.163 meV/u.c. (or K = −0.275 × 10⁶ J/m³) and 711 K, respectively. The (BH)_max at the elevated temperatures was estimated by combining experimental coercivity (H_ci) and the temperature dependence of magnetization (M_s(T)). The (BH)_max is 17.7 MGOe at 300 K, which is in good agreement with the experimental result for directionally-solidified LTP MnBi (17 MGOe). In addition, a study of electron density maps and the lattice constant c/a ratio dependence of the magnetic moment suggested that doping of a third element into interstitial sites of LTP MnBi can increase the M_s.

We report 24-30 nm spherical barium ferrite (S-BaFe) particles having extremely narrow size distribution without any superparamagnetic phase. We have converted spherical magnetite (S-Mag) nanoparticles to S-BaFe nanoparticles using a unique adsorption-diffusion process. The synthesized S-BaFe nanoparticles were characterized by X-ray diffractometer, Mossbauer spectrometer, transmission electron microscope (TEM), and vibrating magnetometer (VSM) for magnetic and physical properties. Saturation magnetization and coercivity of the S-BaFe nanoparticles were found to be 41.4 emu/g and 4075 Oe, respectively. The thermal stability of K_u V/k_B T ap 107 was estimated for the S-BaFe nanoparticles from time-dependent remanent coercivity measurement.