Yukai An

Local Mn structure and room temperature ferromagnetism in Mn-doped In2O3 films

Local Mn structure, magnetic, and transport properties in Mn-doped In2O3 films were investigated systematically. The detailed structural analysis and multiple-scattering calculations reveal that Mn2+ ions substitute for In3+ sites of the In2O3 lattice and form MnIn2+ + VO complex with the O vacancy in the nearest coordination shell. All films show clear room temperature ferromagnetism and Mott variable range hopping transport behavior. The saturation magnetization of films increases first, and then decreases with Mn doping, while carrier concentration nc decreases monotonically, implying that the ferromagnetism is not mediated by the charge carriers. These results provide strong evidence that oxygen vacancies play an important role in activating the ferromagnetic interactions in Mn-doped In2O3 films.

The local structure, magnetic, and transport properties of Cr-doped In2O3 films

Cr-doped In2O3 films were deposited on Si (100) substrates by RF-magnetron sputtering technique. The local structure, magnetic, and transport properties of films are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption fine structure, Hall effect, R-T, and magnetic measurements. Structural analysis clearly indicates that Cr ions substitute for In3+ sites of the In2O3 lattice in the valence of +2 states and Cr-related secondary phases or clusters as the source of ferromagnetism is safely ruled out. The films with low Cr concentration show a crossover from semiconducting to metallic transport behavior, whereas only semiconducting behavior is observed in high Cr concentration films. The transport property of all films is governed by Mott variable range hopping behavior, suggesting that the carriers are strongly localized. Magnetic characterizations show that the saturated magnetization of films increases first, and then decreases with Cr doping, while carrier concentration nc...

Investigation of structure, magnetic, and transport properties of Mn-doped SiC films

Mn-doped SiC films were fabricated by radio frequency magnetron sputtering technique. The structure, composition, and magnetic and transport properties of the films were investigated. The results show the films have the 3C-SiC crystal structure and the doped Mn atoms in the form of Mn2+ ions substitute for C sites in SiC lattice. All the films are ferromagnetic at 300 K, and the ferromagnetism in films arises from the doped Mn atoms and some extended defects. In addition, the saturation magnetization increases with the Mn-doped concentration increasing. The Mn doping does not change the semiconductor characteristics of the SiC films.

Influence of (Ni81Fe19)100−xCrx seed layer on structure and magnetic properties of NiFe/PtMn bilayers

Influence of (Ni81Fe19)100−xCrx seed layer on structure and magnetic properties of NiFe/PtMn bilayers was systemically investigated by magnetic measurements and x-ray diffraction. The results indicated that the pinning field Hex of NiFe/PtMn bilayers has a strong correlation with the Cr content of (Ni81Fe19)100−xCrx seed layer, which can effectively influence grain size, crystal texture, and L10 ordering phase transformation of PtMn. When the Cr content is 40%, PtMn shows strong (111) texture and large grain size, but the L10 ordering phase transformation is weak after annealing, which resulting in a low pinning field Hex. When the Cr content is 34% and 50%, PtMn has weak (111) texture and small grain size, but these are in favor of the L10 ordering phase transformation after annealing, resulting in a high pinning field Hex.

Evidence of the oxygen vacancies-induced room-temperature ferromagnetism in the (In0.97−xFexSn0.03)2O3 films

(In0.97−xFexSn0.03)2O3 films with x = 0.023, 0.05, 0.07 and 0.085 were prepared by RF-magnetron sputtering. The effects of Fe doping and oxygen vacancies on the magnetic and transport properties of the (In0.97−xFexSn0.03)2O3 films are studied systematically by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), Hall effect, R-T and magnetic measurements. Combining X-ray absorption spectroscopy with full multiple-scattering ab initio calculations, it reveals that Fe dopant ions substitute In3+ sites of the In2O3 lattice with a mixed-valence (Fe2+/Fe3+) and form FeIn1 + 2VO complex with O vacancy in the nearest coordination shell. Magnetic characterizations show that all the films display a clear room-temperature (RT) ferromagnetic behavior and the saturated magnetization decreases monotonically with an increase in Fe concentration. Temperature dependent resistivity data suggest the conduction mechanism of the Mott variable range hopping and Hard band gap hopping. The strong localization of carriers suggests the bound magnetic polarons scenario. It can be concluded that the local lattice distortion and oxygen vacancies around the Fe atoms play a key role in the observed intrinsic RT ferromagnetism in the (In0.97−xFexSn0.03)2O3 films. The monotonic reduction in Ms with Fe doping has a strong correlation with the localization radius ξ of variable range hopping of carriers, indicating that the variation in the localization effect could strongly modify the ferromagnetism of (In0.97−xFexSn0.03)2O3 films.

Local structure and p–d hybridization of Mn-doped In2O3 films

Mn-doped In2O3 films were deposited on Si (1 0 0) substrates by the RF-magnetron sputtering technique. The influence of Mn-doping concentration on the local structure and degree of p-d hybridization was investigated by x-ray absorption spectroscopy at the Mn K-edge and L-2,L-3-edge. The results show that Mn ions dissolve in In2O3 and substitute for In3+ sites in the +2 valence states. With the increase in Mn-doping concentration, the Mn-O bonding distance increases monotonically, but integrated intensities of L-2,L-3 edges increase first and then decrease. It can be concluded that there exists an optimal Mn-O bonding distance for the transition probabilities from the 2p state to the p-d hybridization state, which results in increasing degree of p-d hybridization. So the Mn-doping concentration has a significant effect on the local structure and degree of p-d hybridization in Mn-doped In2O3 films.

Effect of Mn doping on the structural, optical, and magnetic properties of In2O3 films

(In1-xMnx)(2)O-3 films were grown by radio frequency-magnetron sputtering technique. Effect of Mn doping on the structural, optical, and magnetic properties of films is investigated systematically. The detailed structure analyses suggest that Mn ions substitute for In3+ sites of the In2O3 lattice in the valence of +2 states, and Mn-related secondary phases or clusters as the source of ferromagnetism is safely ruled out. All films show typical room temperature ferromagnetism. The saturation magnetization M-s increases first, and then decreases, while carrier concentration n(c) decreases monotonically with Mn doping, implying that the ferromagnetism is not directly induced by the mediated carriers. The optical bandgap E-g of films decreases monotonically with the increase of Mn concentration, and there exists a linear functional dependence between E-g and n(c)(2/3), which is consistent with Burstein-Moss shift arguments. It can be concluded that the ferromagnetic order in Mn-doped In2O3 films is intrinsic, arising from Mn atoms substitution for the In sites of In2O3 lattice. The oxygen vacancies play a mediation role on the ferromagnetic couplings between the Mn ions

Effect of grain size on the properties of NiFe/PtMn bilayers

The structural and magnetic properties of NiFe/PtMn bilayers with a (Ni81Fe19)100−xCrx seed layer were investigated. It is found that the pinning field Hex of NiFe/PtMn bilayers is very sensitive to the Cr content of the (Ni81Fe19)100−xCrx seed layer, which can effectively influence the grain size, L10 ordering phase transformation and the critical thickness of PtMn as well as the blocking temperature (Tb). When the Cr content is 40 at%, PtMn shows a large grain size, a small critical thickness and a high blocking temperature, but the degree of L10 ordering phase transformation is weak after annealing, which results in a low pinning field Hex. When the Cr content is below 34 at% or above 50 at%, PtMn has a small grain size, a large critical thickness and a low blocking temperature, but the degree of L10 ordering phase transformation is very good after annealing, resulting in a high pinning field Hex. These results indicate that (Ni81Fe19)100−xCrx can be a promising seed layer in spin valves based on Mn-alloyed antiferromagnets.

Characterization and photoluminescence of Co-doped SiC films

Co-doped SiC films are fabricated on Si (100) substrates by radio frequency magnetron sputtering, and the crystal structure, composition, element valences, local structure, and photoluminescence of the films are studied. Crystal structure analysis identifies the film structure as 3C-SiC and shows that the Co dopant atoms form CoSi secondary phase compounds in the films. The composition and element valence analysis show that the Co dopant atoms substituting for C sites in the SiC lattice exist in the form of Co2+ ions, and that C clusters are present in the films, which increase in amount with increasing Co dopant concentration. The analysis of local structure reveals that Co clusters, CoO and Co3O4, are not present in the films, and CoSi secondary phase compounds exist. All of the films show a violet photoluminescence peak located at 413 nm, which becomes stronger with increased Co dopant concentration and annealing temperature, and is found to originate from the C clusters.

Effect of annealing on magnetotransport and structural properties of Ni70Co30/Cu multilayers

The effect of annealing on magnetotransport and structural properties of Ni70Co30/Cu multilayers is investigated. The GMR signal remains stable up to 175??C and almost disappears at 285??C. The total resistivity of multilayers is nearly constant below 175??C and rapidly increases after annealing at 285??C. By the combination of x-ray reflectivity, x-ray diffuse scattering and extended x-ray absorption fine structure (EXAFS) techniques, it is found that Ni atoms and Cu atoms occupy preferentially the interfacial position of the multilayer and the interface roughness is mainly caused through the diffusion of Cu and Ni in the grain boundary during the deposition. After 285??C annealing, the interface roughness increases remarkably and the interfacial lateral correlation length and the fractal exponent of Co, Ni and Cu decrease significantly. At the same time, the differences in the interfacial lateral correlation lengths of Co, Ni and Cu also becomes smaller. This suggests that the intermixing of adjacent layers takes place. It can be concluded that the degradation mechanism of the GMR effect on the annealed Ni70Co30/Cu multilayer is the compositional mixing at the interfaces, rather than the interlayer diffusion of atoms along the grain boundary.