Fe 2+ Contents and Magnetocrystalline Anisotropy in Iron Defect LiZnTiMn Ferrites
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J. Balmaseda Centro Nacional de Investigaciones Cientı´ficas, Ave 25 y calle 158, Cubanaca´n, Playa, La Habana 6990, Cuba
A. Gonza´lez Ariasa) Dpto. Fı´sica Aplicada, Facultad de Fı´sica, Universidad de La Habana, La Habana 10400, Cuba (Received 13 June 2001; accepted 15 April 2002)
An investigation of the effects of the iron defect k in LiZnTiMn ferrites using Mo¨ssbauer spectroscopy and ferromagnetic resonance techniques was carried out in single-phased samples. Results show that the isomer shifts have values corresponding to a compound with either low-spin Fe(II), low-spin Fe(III), or high-spin Fe(III). On the other hand, the Lande factor and the ferromagnetic resonance linewidth disclosed that g is always very close to 2, being equal to 2.02 when k ⳱ 0.06. A minimum in ⌬H was detected for this value of k. From these results, the possible presence of Fe2+ in the samples could be excluded, and it was concluded that the changes in ⌬H are due to the variation of the Fe(III) contents in the tetrahedral and octahedral sites. The existence of the minimum in ⌬H is due to a compensation point in the magnetocrystalline anisotropy.
I. INTRODUCTION
In a previous paper, referred to the effect on the microwave properties of the iron defect in LiZnTiMn ferrites, we reported the decrease of the saturation magnetization (Ms) and the ferromagnetic resonance line width (⌬H) with the increase of the iron defect parameter k, defined from the formula Li0.5(1−x+y)ZnxTiyFe[2.5−0.5(x+3y)−z−k]MnzO4
,
(1)
where x ⳱ 0.25, y ⳱ 0.83, z ⳱ 0.05, and 0 艋 k 艋 0.1. A similar behavior was observed for samples sintered in air and oxygen, measured at 0.8 GHz. Ms and ⌬H showed a marked decrease when k 艌 0.04, and ⌬H exhibited a minimum when k ⳱ 0.06. The values of ⌬H ranged from 4.25 kA/m, in the case of the air-sintered samples with k ⳱ 0.0, to 1.25 kA/m for the oxygensintered samples with k ⳱ 0.06. According to the general evidence in the ferrite literature, the decrease in ⌬H was attributed to a decrease of [Fe2+], the Fe2+ cation concentration in the sample, caused by the increase of k. Some additional changes in the magnetic and ferromagnetic resonance (FMR) properties were attributed to Li2O a)
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J. Mater. Res., Vol. 17, No. 7, Jul 2002 Downloaded: 14 Mar 2015
losses taking place in the sintering stage, as had been reported before by several authors in similar ferrite systems.1 However, thermogravimetry studies carried out in samples with the same chemical composition and sintered in pure oxygen showed evidence that the samples did not change their [Fe2+] contents when k increased. Instead, a drastic decrease of the vacancy concentration was detected in the same range of k values. The vacancy concentration dropped to zero when k was about 0.04, while the Fe2+ cation coefficient in the chemical formula kept constant, close to 0.02; it was pointed out that some variability may be expected in these reported val
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