Evidence for carrier-mediated magnetism in Mn-doped ZnO thin films (original) (raw)
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Applied Physics Letters, 2009
Spin electronics or spintronics, is an advanced technology which exploits the quantum spin states of electrons as well as making use of their charge state. Electron spin has two possible states, either "up" or "down." Aligning spins in a material creates magnetism. Moreover, magnetic fields affect the passage of "up" and "down" electrons differently. Controlling the spin of electrons within a device can produce surprising and substantial changes in its properties. Scientists have proposed the miniature of numerous spintronic devices, such as the magnetoresistive random access memory (MRAM), spin field effect transistor (Spin-FET), spin light emitting diode (Spin-LED), and quantum computer. The integration of magnetism, optics and electronics for the development of advanced spintronic devices is an extremely important research topic.
Room temperature ferromagnetism in Mn-doped ZnO films mediated by acceptor defects
Applied Physics Letters, 2007
This work probes the relevance of oxygen vacancies in the formation of local ferromagnetic coupling between Fe ions at octahedral sites in zinc ferrites. This coupling gives rise to a ferrimagnetic ordering with the Curie temperatures above room temperature in an otherwise antiferromagnetic compound. This conclusion is based on experimental results from x-ray magnetic circular dichroism measurements at the Fe L 2,3 edges and magnetization measurements performed on zinc ferrites, nanoparticles, and films, with different cation distributions and oxygen vacancy concentrations. Our observations are confirmed by density-functional-theory calculations and indicate that the enhanced ferrimagnetic response observed in some nominally nonmagnetic or antiferromagnetic ferrites can be taken as a further example of the defect-induced magnetism phenomenon.
Electron concentration dependent magnetization and magnetic anisotropy in ZnO:Mn thin films
Applied Physics Letters, 2008
Well-above room temperature and electron concentration dependent ferromagnetism was observed in n-type ZnO:Mn films, indicating long-range ferromagnetic order. Magnetic anisotropy was also observed in these ZnO:Mn films, which is another indication for intrinsic ferromagnetism. The electron-mediated ferromagnetism in n-type ZnO:Mn contradicts the existing theory that the magnetic exchange in ZnO:Mn materials is mediated by holes.
Investigation of the room temperature ferro-magnetism in transition metal-doped ZnO thin films
Applied Physics A, 2020
In the present work, we report the ferromagnetic (Fe, Ni) co-doped Zn 1-x-y Ni y Fe x O (y = 0.01 and x = 0.01, 0.03, 0.05) thin films fabricated through the RF magnetron sputtering on Silicon (400) substrate. Structural studies of prepared thin films through X-ray Diffraction (XRD) reveal the formation of a single-phased hexagonal structure of films. Atomic Force Microscopy (AFM) confirms the decrease in surface roughness with the increase in Fe doping. The optical band gap of the thin films analyzed through the UV-Vis spectroscopy suggests the appropriateness of prepared thin films to be utilized in optoelectronic devices. The magnetic study of these thin films confirmed the room temperature ferromagnetic (RTFM) behavior for prepared thin films. The observed magnetic behavior has been described in view of polaron percolation theory.
Structural; morphological; optical and magnetic properties of Mn doped ferromagnetic ZnO thin film
Applied Surface Science, 2012
The structural, optical and magnetic properties of the Zn 1-x Mn x O (0 < x < 0.05) thin films synthesized by sol-gel technique have been analyzed in the light of modification of the electronic structure and disorder developed in the samples due to Mn doping. The films are of single phase in nature and no formation of any secondary phase has been detected from structural analysis. Absence of magnetic impurity phase in these films confirmed from morphological study also. Increasing tendency of lattice parameters and unit cell volume has been observed with increasing Mn doping concentration. The incorporation of Mn 2+ ions introduces disorder in the system. That also leads to slight degradation in crystalline quality of the films with increasing doping. The grain size reduces with increase in Mn doping proportion. The band gaps shows red shift with doping and the width of localized states shows an increasing tendency with doping concentration. It is due to the formation of impurity band and trapping of Mn atoms, which leads to the generation of the defect states within the forbidden band. Photoluminescence (PL) spectra shows gradual decrease of intensity of exitonic and defect related peaks with increasing Mn doping. Defect mediated intrinsic ferromagnetism has been observed even at room temperature for 5at% Mn doped ZnO film. The strong presence of antiferromagnetic (AFM) interaction reduces the observed ferromagnetic moments.
Journal of Applied Physics, 2008
Diluted magnetic semiconducting ZnO:Co thin films with above room-temperature TC were prepared. Transmission electron microscopy and x-ray diffraction studies indicate the ZnO:Co thin films are free of secondary phases. The magnetization of the ZnO:Co thin films shows a free electron carrier concentration dependence, which increases dramatically when the free electron carrier concentration exceeds ∼1019 cm−3, indicating a carrier-mediated mechanism for ferromagnetism. The anomalous Hall effect is observed in the ZnO:Co thin films. The anomalous Hall coefficient and its dependence on longitudinal resistivity were analyzed. The presence of a side-jump contribution further supports an intrinsic origin for ferromagnetism in ZnO:Co thin films. These observations together with the magnetic anisotropy and magnetoresistance results support an intrinsic carrier-mediated mechanism for ferromagnetic exchange in ZnO:Co diluted magnetic semiconductor materials.
Electrical and Magnetic Properties of Mn-Doped ZnO
Ferroelectrics, 2002
We have studied electrical and magnetic properties of x at% Mn-doped Si thin films with high Mn concentrations (x at% ¼ 7.5, 9.1, and 11.3), which were prepared by molecular beam epitaxy. Our data reveals that the films are p-type semiconductors at room temperature, and their hole density is about 10 20 cm À3. When temperature increases from 5 to 300 K, the resistivity of 7.5 at% Mn film decreases and can be described by Mott's variable-range-hopping model. The resistivity of 9.1 at% Mn film does not change remarkably. In contrast, the resistivity of 11.3 at% Mn film increases, indicating metallic characteristics at temperatures below 240 K. Magnetic measurements reveal that the films exhibit the low-temperature ferromagnetic ordering, which is largely related to the presence of secondary phase.
Journal of Magnetism and Magnetic Materials, 2013
The presence of structural defects degrade the crystalline quality of ZnO:Mn thin films and affects the magneto-optical properties of ZnO:Mn thin films. The donor defects in ZnO, which are known to be the source of n-type conductivity in ZnO host matrix, play an important role in limiting the ferromagnetism to lower temperatures. A systematic study of structural, optical and magnetic properties was carried out with the primary focus on understanding the relationship between the defect concentration, material composition and ferromagnetic properties. Single phase ZnO:Mn thin films with wurtzite structure were grown under ambient argon-oxygen admixture to investigate the effect of stoichiometry and interstitial oxygen on magnetic properties. A consistent increase in crystallinity of ZnO:Mn thin films (without precipitation of Mn) with increasing argon-oxygen admixture gas pressure was observed. Extended near band edge (NBE) emission spectra with marked decrease in photoluminescence (PL) ratio in optical characterization revealed improved optical quality of ZnO:Mn thin films. Magnetic measurements revealed enhanced room temperature ferromagnetism (RTFM) in sample grown at optimum argonoxygen ambient pressure. The enhancement was directly related to maximal core level X-ray photoelectron spectroscopic peak of stoichiometric ZnO which, in turn, favors strong hybridization of Mn in the ZnO host matrix.