Investigation of Magnetic Properties of MnBi/$\alpha$-Fe Nanocomposite Permanent Magnets by Micro-Magnetic Simulation

Abstract

In the present study, the demagnetization curves of MnBi/α-Fe nanocomposite permanent magnets were calculated by the micromagnetic finite element method. The effect of volume ratio between magnetically soft α-Fe phase and MnBi hard phase on the magnetic properties of magnets was investigated. The sample used in the present simulation was consisted of 91 spherical fourteen faces units of hard phase grains with diameter of 20 nm, and the soft matrix phase with the thickness (t) ranging from 1 to 6 nm. For the isotropic MnBi/α-Fe magnets, as increases, the remanence (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> )increases first, peaks at 0.855 T for t = 3 nm, then decreases again, while the coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</sub> ) drops monotonically from 691 kA/m for t = 1 nm to 94 kA/m for t = 6 nm. The sample with t = 2 nm has the optimal maximum energy product (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 55.15 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . For the anisotropic magnets, the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</sub> exhibit their t-dependent behavior similar to that of the isotropic ones. The optimal values of B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</sub> and (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> are 1.47 T, 3200 kA/m, and 322 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> when t = 5,1, and 3 nm, respectively, indicating a good potential of the anisotropic MnBi/α-Fe nanocomposite as practical permanent magnets.