Effect of Ni doping on the microstructure and high Curie temperature ferromagnetism in sol-gel derived titania powders

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• 作者：Nupur Bahadur ; ^{nupurbahadur@ymail.com} ; Renu Pasricha ; Govind ; Suresh Chand ; Ravinder Kumar Kotnala
• 关键词：Oxides ; Sol&ndash ; gel growth ; Magnetic force microscopy (MFM) ; Magnetic properties
• 刊名：Materials Chemistry and Physics
• 出版年：2012
• 期刊代码：58_02540584
• 类别：ms
• 出版时间：15 March, 2012
• 卷：133
• 期：1
• 页码：471-479
• 文件大小：1315 K

摘要

Undoped, 0.05 and 0.5 mol%Ni-doped TiO₂ powders were prepared by a modified sol-gel route. The doping effects on the microstructure and magnetism for the powdered samples have been systematically investigated. Doping of Ni in TiO₂ inhibited rutile crystal growth. The probable reason for this is discussed on the basis of band calculation based analysis of electronic structures of 3d transition metal-doped TiO₂ and the energetic, transformation kinetics and phase stability of anatase over rutile as the function of particle size. Room temperature ferromagnetism (RTFM) with the saturation magnetization of 12 m emu g^鈭? and Curie temperature as high as 820 K is observed only in case of 0.05 mol%Ni:TiO₂ powdered sample, whereas undoped TiO₂ was diamagnetic and 0.5 mol%Ni:TiO₂ was paramagnetic in nature. The role of any magnetic impurity or any Ni metal in the origin of the RTFM has been ruled out by energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) analysis, whereas magnetic force microscopy (MFM) established the presence of magnetic domains, supporting the intrinsic diluted magnetic semiconductor behavior. The observed ferromagnetism has been attributed to the spin ordering through exchange interaction between holes trapped in oxygen orbitals adjacent to Ni substitutional sites.