Properties of polycrystalline nanoparticles with uniaxial and cubic types of magnetic anisotropy of individual grains

• Published in: Journal of magnetism and magnetic materials Vol. 460; pp. 278 - 284
• Main Authors: Bautin, V.A., Seferyan, A.G., Nesmeyanov, M.S., Usov, N.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.08.2018; Elsevier BV
• Subjects: Anisotropy; Aspect ratio; Axes (reference lines); Chromium oxides; Cobalt; Cobalt ferrites; Computer simulation; Crystal structure; Granular materials; Inhomogeneity; Magnetic anisotropy; Magnetic properties; Magnetism; Magnetite; Mathematical models; Nanoparticles; Numerical simulation; Polycrystalline magnetic nanoparticles; Polycrystals; Single crystals; Single-domain diameter; Numerical simulation; Single-domain diameter; Polycrystalline magnetic nanoparticles; Magnetic anisotropy
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2018.04.019

•Single-domain diameters of polycrystalline particles are reduced.•Effective single-domain diameter decreases with magnetic hardness increase.•Structural defects are less important for particles with cubic anisotropy. The influence of the crystal structure inhomogeneities on the magnetic properties of cobalt nanoparticles with different aspect ratio and spherical nanoparticles of chromium dioxide, cobalt ferrite and magnetite has been studied by means of numerical simulation. The polycrystalline nanoparticles are modeled by means of subdivision of the nanoparticle volume into tightly bound single-crystal granules with randomly distributed directions of the easy anisotropy axes. The probability of appearance of quasi uniform and vortex states in sufficiently large assemblies of polycrystalline nanoparticles of various types have been calculated depending on the nanoparticle diameter. It is shown that the subdivision of a nanoparticle into single-crystal granules with different orientations of the easy anisotropy axes substantially reduces the effective single-domain diameters for particles with uniaxial type of anisotropy of individual granules. However, for particles with cubic type of magnetic anisotropy the influence of the crystal structure inhomogeneities on the equilibrium properties of the particles is not so important even for magnetically hard cobalt ferrite nanoparticles. It is practically absent for magnetically soft magnetite nanoparticles.