S. Colis

Antiferromagnetism in bulk Zn1−xCoxO magnetic semiconductors prepared by the coprecipitation technique

Polycrystalline Zn1−xCoxO diluted magnetic semiconductors have been prepared by coprecipitation technique in the concentration range 0⩽x⩽0.1. Structure, composition analysis, and optical absorption measurements revealed that cobalt is incorporated into the lattice, as Co2+ substituting Zn2+ ions, forming a solid solution with wurtzite structure instead of Co precipitates. Room- and low-temperature magnetization measurements reveal a paramagnetic behavior for the Co-doped ZnO samples with a paramagnetic Co amount smaller than the nominal concentration. χT versus T evidenced that the remaining Co is antiferromagnetically coupled through oxygen. This is further supported by a simple model that shows that as the Co concentration increases the amount of nearest neighbors Co atoms increases thus giving antiferromagnetic coupling and reducing the paramagnetic contribution.

Absence of ferromagnetism in Al-doped Zn0.9Co0.10O diluted magnetic semiconductors

A 0.5% Al-doped Zn0.895Co0.100O polycrystalline powder was synthesized by the co-precipitation method. Raman spectroscopy revealed that divalent cobalt ions were substituted for Zn2+ ions into the ZnO matrix and that Al ions activate additional modes which are nonspecific to the dopant. These additional modes disappear after annealing at 1373K for 1h under Ar flow. We suggest that the electrical dopant becomes active in substitutional sites after annealing. Resistance measurements confirm that free carriers were created in our sample. Nevertheless, the sample shows the same magnetic properties: a mixture of paramagnetism and antiferromagnetism.

Paramagnetism of the Co sublattice in ferromagnetic Zn1 xCoxO films

Using the spectroscopies based on x-ray absorption, we have studied the structural and magnetic properties of

Extrinsic origin of ferromagnetism in ZnO and Zn0.9Co0.1O magnetic semiconductor films prepared by sol-gel technique

{\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{O}

Pure paramagnetic behavior in Mn-doped ZnO semiconductors

films (

Evidence of superparamagnetic co clusters in pulsed laser deposition-grown Zn0.9Co0.1O thin films using atom probe tomography.

x=0.1

Structural, optical, and electrical properties of Yb-doped ZnO thin films prepared by spray pyrolysis method

and 0.25) produced by reactive magnetron sputtering. These films show ferromagnetism with a Curie temperature

Structural and photoluminescence properties of ZnO thin films prepared by sol-gel process

{T}_{C}

Room temperature ZnO growth by rf magnetron sputtering on top of photoactive P3HT: PCBM for organic solar cells

above room temperature in bulk magnetization measurements. Our results show that the Co atoms are in a divalent state and in tetrahedral coordination, thus substituting Zn in the wurtzite-type structure of ZnO. However, x-ray magnetic circular dichroism at the

Co and Al co-doping for ferromagnetism in ZnO:Co diluted magnetic semiconductors

\mathrm{Co}\phantom{\rule{0.2em}{0ex}}{L}_{2,3}