The magnetic anisotropy of Fe-SiO₂and Fe₂₀Ni₈₀-SiO₂granular solids

Abstract

Fe-SiO2 and Fe20Ni80-SiO2 granular solids have been prepared using a sol-gel method and investigated by X-ray diffractometry, Mossbauer spectroscopy and transmission electron microscopy. The magnetic properties were measured and the coercivity of these granular solid samples was found to be almost independent of temperature in the range 80-300 K. The effective magnetic anisotropy including shape anisotropy and strain anisotropy has been determined from the magnetizing curves of these granular solid samples using the law of approach to saturation. The obtained values of the effective magnetic anisotropy exceed 106 erg cm-3. The almost temperature-independent effective magnetic anisotropy can approximately explain the variation of Hc versus T for the granular solid samples. The shape anisotropy has been estimated assuming that the average axis ratio of the metal particles c/a is 1.2 and the strain anisotropy has been calculated from the effective anisotropy and the shape anisotropy. The magnitude of the strain anisotropy and the variation of the strain anisotropy with temperature are explained for the Fe-SiO2 and Fe20Ni80-SiO2 granular solid samples.

Magnetic anisotropy of the Fe-SiO/sub 2/ and Fe/sub 20/Ni/sub 80/-SiO/sub 2/ granular solid measured using the magnetic relaxation method

“…3 that the obtained values of the effective magnetic anisotropy are in the order of 106erg/cm3 for the two granular solid samples, which are far larger than the magnetocrystalline anisotropy for the bulk bcc structure Fe and fcc structure FezONisO alloy which is on the order of 105erg/cm3 [9] These values are very close to the previously reported values of the Fe-SiOz granular films [3], [4]. These values are also very close to the calculated results using the law of approach to saturation method [ 5 ] . The large effective magnetic anisotropy may come from the larger stress anisotropy besides the contribution of the magnetocrystalline anisotropy as the metal particles are tightly bonded to the silica matrix [2], [3].…”

“…In this work, the Fe-SiO, and Fe20Nix0-Si02 granular solid samples were prepared using a sol-gel method which has already been proved an effective and economical way to prepare the granular solids [ 5 ] , [8]. The fabrication of the bcc structure Fe and fcc structure Fe,0Ni80 nanoscale particles dispersed in Fe-SiO, and Fe20Nixo-Si02 granular solid are confirmed by the result of the XRD and the Mossbauer spectra.…”

“…The large effective magnetic anisotropy may come from the larger stress anisotropy besides the contribution of the magnetocrystalline anisotropy as the metal particles are tightly bonded to the silica matrix [2], [3]. Wang et a1 in reference [5] has already analyzed the effective magnetic anisotropy in granular solid and shown that the stress anisotropy is the main part of the effective magnetic anisotropy for the granular solid.…”

“…However, in the past, the magnetic anisotropy is studied seldom for the granular solid. Up to now, there are three methods to measure the magnetic anisotropy for the granular solid, the Mossbauer measurement [3], the ferromagnetic resonance measurement [4] and the method of using the law of approach to saturation [5]. In this paper, a method is reported by which the effective magnetic anisotxopy constant K can be calculated by using the equations for describing the relaxation process of single domain particles [6], [7] and the calculated magnetic anisotropy of the granular solid is discussed.…”

Preparation and Magnetic Properties of Fe0.7Co0.3–SiO2 Granular Alloy Solid

“…Various techniques [3 to 5] have been employed to prepare the granular alloy solids. Recently, a sol±gel method has been found effective for preparing dispersions of small alloy particles in nonmetallic matrices [6]. In the present work, we have successfully prepared the Fe 0X7 Co 0X3 ±SiO 2 granular alloy solid using the sol±gel method.…”