Magnetic anisotropy — How much is enough for a permanent magnet?

Abstract

Material choices for permanent magnets are analyzed in terms of energy product, anisotropy and hardness parameter. Energy product is the main consideration for permanent magnets, because the purpose of a magnet is to store magnetostatic energy and create as much flux as possible in the surrounding space. Magnet processing is easiest if the hardness parameter is significantly greater than one. The anisotropy requirement becomes increasingly stringent for large M s and K 1 values of 1 to 2 MJ/m 3 may be insufficient. Some potential new magnets and alternative strategies to develop magnetic hardness are discussed.

Morphology and magnetic properties of α”-Fe₁₆N₂ nanoparticles synthesized from iron hydroxide and iron oxides

“…3.4 Toward an increase in the coercivity of α"-Fe16N2 nanoparticle assemblies The empirical figure known as the magnetic hardness parameter = (K1/μ0Ms 2 ) 1/2 is a useful parameter to consider how to approach the construction of modern permanent magnet 15) . The  value for Nd2Fe14B as a typical modern magnet, is 1.54, while that for α"-Fe16N2 is 0.53.…”

Research Progress of Stress-Induced Magnetic Anisotropy in Fe-Based Amorphous and Nanocrystalline Alloys

“…This surface charge distribution is a source of magnetic field and it is known as the demagnetizing field since it acts in opposition to the magnetic field which produces it [19]. The unique feature of permanent magnets is their ability to store magnetostatic energy and their shapes were dictated by the low coercivity H c of the ferromagnetic materials available over a 100 years ago, which limited the tolerable demagnetizing field in the second quadrant of the M(H) hysteresis loop where the working point of a magnet is inevitably located [20].…”

“…Shape anisotropy is only fully effective in regions where the magnetization remains uniform and rotates coherently without breaking upinto domains [20].…”

Optimization of the magnetic properties of nanostructured Y-Co-Fe alloys for permanent magnets

“…[1][2][3] The main concern in the material choice is the energy product, which quantifies the ability of the magnet to store magnetostatic energy and create flux in the surrounding space. 4 Improving extrinsic and intrinsic properties by nanostructuring and atomic structuring (crystal structure, composition) is the way to maximize the energy product. 5 The maximum possible value (BH) MAX = 1 /4 µ 0 M 2 s is reached with a demagnetization factor N = 1 /2.…”

“…For this H c must be greater than M s /2 where M s is related to the intrinsic atomic and crystal structure and H c originates from the magnetic anisotropy K. Typically its value will not exceed 25% of the anisotropy field H a = 2K/µ 0 M s . 4,6 Furthermore, H c depends on grain size, microscopic defects and the thermal history of a sample. Usually it is inversely related to the grain size, and large coerciviy is obtained when the crystallites are small and single-domain.…”