Development and processing temperature dependence of ferromagnetism in Zn0.98Co0.02O

被引:21
作者
Hays, J.
Thurber, A.
Reddy, K. M.
Punnoose, A. [1 ]
Engelhard, M. H.
机构
[1] Boise State Univ, Dept Phys, Boise, ID 83725 USA
[2] Pacific NW Natl Lab, Environm Mol Sci Lab, Richland, WA 99352 USA
基金
美国国家科学基金会;
关键词
D O I
10.1063/1.2173956
中图分类号
O59 [应用物理学];
学科分类号
摘要
We report the development of room-temperature ferromagnetism (FM), with coercivity H-c=2000 Oe and saturation magnetization M-s similar to 0.01 emu/g, in chemically synthesized powders of Zn0.98Co0.02O processed at 150 degrees C, and paramagnetism with antiferromagnetic interactions between the Co2+ spins (S=3/2) in samples processed at higher temperatures 200 <= T-P <= 900 degrees C. X-ray diffraction data show a decrease in the lattice parameters a and c with T-P, indicating a progressive incorporation of 0.58 angstrom sized tetrahedral Co2+ at the substitutional sites of 0.60 angstrom sized Zn2+. Diffuse reflectance spectra show three well defined absorption edges at 660, 615, and 568 nm due to the d-d crystal field transitions (4)A(2)(F)-> E-2(G),(4)A(2)(F)-> T-4(1)(P), and (4)A(2)(F)-> T-2(1)(G) of high spin (S=3/2)Co2+ in a tetrahedral crystal field, whose intensities increase with processing temperature. X-ray photoelectron spectroscopy shows that the doped Co2+ ions in the 150 degrees C processed samples are located mostly on the surface of the particles and they disperse into the entire volume of the particles when processed at higher temperatures. The observations suggest that the FM most likely results from Co2+ attached to the surface sites and it is lost in well dispersed samples formed at T-P>150 degrees C. (C) 2006 American Institute of Physics.
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