The Magnetic Properties of Sol-Gel Synthesized TM_0.03 Zn_0.97 O (TM: Mn, Fe, Co and Ni) Nanoparticles: Role of Different Transition Metals

Abstract

TM 0.03 Zn 0.97 O (TM: Mn, Fe, Co and Ni) nanoparticles have been synthesized using sol-gel technique. Structural study through X-ray diffraction (XRD) has revealed that all samples, except Ni:ZnO, possess single phase wurtzite structure of ZnO, whereas in Ni:ZnO, Ni ions have mainly segregated as NiO (a secondary phase). Morphological study through Field Effect Scanning Electron Microscopy (FESEM) has confirmed the formation of nanoparticles with particle sizes in the range of 30-61 nm. X-ray absorption spectroscopy (XAS) exhibits that Co ions substitutionally replace Zn ions, Mn ions partially occupy substitutional sites and partially interstitial positions, Fe ions mainly occupy interstitial positions, whereas Ni ions mainly chemically segregate with oxygen to form NiO phase. All TM:ZnO samples show reasonable ferromagnetism (FM) up to room temperature (RT) and except for the Ni:ZnO, the observed FM seems to be intrinsic in nature. Temperature dependent magnetization (MÀT) measurement of Ni:ZnO reveals a superparamagnetic behavior (with transition temperature higher than 300 K). In the regime of diluted magnetic semiconductors (DMSs) and as far as intrinsic FM is concerned, Fe:ZnO sample seems to be a good ferromagnet with appreciable saturation magnetization (M S ),whereas Co:ZnO shows hard FM (with significant irreversible magnetization). The higher capability of occupying substitutional position by Co ions enhances further the utility of Co:ZnO.

Removal of Ferrimagnetic ZnFe2O4 Impurity Phase by Li Co-Doping in Fe Doped ZnO

“…A significant concentration of interstitial TM dopants may lead to segregation to form secondary impurity phase. 12 Hence, a careful investigation is required to verify the nature of occupation of TM dopants in the host ZnO matrix. Such investigation can effectively be performed by thorough local structure study by XANES.…”

“…Such investigation can effectively be performed by thorough local structure study by XANES. [12][13][14] The report 12 of XANES for TM doped ZnO exhibits that the efficiency of substitutional occupation is appreciably high in Co doping, moderate in Mn doping, low in Fe doping and secondary oxide phase segregation occurs for Ni doping when maximum doping concentration is quite low (below 3 at%).…”