Magnetic organometallosiloxanes

The generalized analysis of a change in magnetic properties of organometallosiloxanes as a function of the number of metal atoms in their molecules (on going from mono- and binuclear to polynuclear crystalline and polymeric compounds) is presented. The relation between the magnetic characteristics and structural parameters of metal-containing fragments is studied. The factors affecting the formation of exchange-coupled ionic pairs and clusters in polymeric systems are analyzed. The ways to the organization of magnetic phases in polymeric systems are considered: the choice of conditions of chemical synthesis, the organization of metal atoms in a common spin system upon incorporation of conducting coordinating additives, and thermocondensation and reduction processes leading to the formation of a metallic phase dispersed in a silicon dioxide matrix. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1432–1442, August, 1997.     

Integrating Photoluminescence and Ferromagnetism in Carbon Quantum Dot/ZnO by Interfacial Orbital Hybridization for Multifunctional Bioprobes

Integrating ferromagnetism (FM) and photoluminescence (PL) into one particular nanostructure as biological probe plays an irreplaceable role in accurate clinical diagnosis combining magnetic resonance and photoluminescence imaging technology. However, magnetic emergence generally needs a spin polarization at Fermi level to display a half-metallic electronic feature, which is not beneficial for preserving radiation recombination ability of photo-excited electron-hole carriers. To overcome this intrinsic difficulty, we propose a feasible atomic-hybridization strategy to anchor carbon quantum dots (CQDs) onto ZnO microsphere surface via breakage of C=O bonds at CQDs and subsequent Zn-3d and C-2p orbital hybridization, which not only ensures the carrier recombination but also leads to a room-temperature magnetism. Herein, the photoluminescence and magnetism coexist in this multifunctional heterojunction with outstanding biocompatibility. This work suggests that integration of magnetism and photoluminescence could be accomplished by particular interfacial orbital hybridization.     

Ferromagnetic Interactions in Highly Stable,Partially Reduced TiO2: The S=2 State in Anatase

We report direct evidence for quintuplet spin states in a particular kind of reduced TiO₂ anatase obtained by the mild oxidation of TiB₂ under hydrothermal conditions. Continuous‐wave and pulse EPR spectroscopy at X and Q band frequencies provide compelling evidence for the presence of S= 2 states, stable in a wide range of temperatures up to room temperature. A tentative model, corroborated by spin‐polarized DFT calculations, is proposed, which consists of four ferromagnetically interacting Ti³⁺ ions with distances ranging from 0.5 nm to 0.8 nm and tetrahedral arrangement.     

Magnetic Properties Near the Ferromagnetic-Nonferromagnetic Phase Boundary in Potassium Clusters Incorporated into Zeolite LTA

Abstract

Magnetic and optical properties are investigated for K clusters incorporated into zeolite LTA at loading densities of K atoms, n, between 1.0 and 3.2 per cluster. No magnetic ordering is observed at n < 2. The spontaneous magnetization due to ferromagnetism is observed suddenly at n > 2. It is confirmed that the 1p-like quantum electronic state of K cluster plays an essential role in the ferromagnetic phase.     

Hyperfine Interactions and Magnetism of 3d Transition-Metal-Impurities in II–VI and III–V Compound-Based Diluted Magnetic Semiconductors

The electronic structure of II–VI and III–V compound-based diluted magnetic semiconductors is calculated based on the local density approximation (LDA) using the Korringa–Kohn–Rostoker method combined with the coherent potential approximation. The magnetism of 3d transition-metal-atom-doped ZnO, ZnS, ZnSe, ZnTe, GaN, GaAs is investigated from first-principles. It is suggested that the double exchange mechanism stabilizes the ferromagnetism in these DMSs. In order to obtain microscopic information on the electronic structure of transition-metal-impurities in semiconductors, the hyperfine field of respective impurities in each host material is calculated. It is found that the agreement with the experimental values is not good, probably because the LDA is not sufficient to describe the core states of transition metals. However, it is suggested that the hyperfine fields clearly reflect the local magnetic moments for 3d impurities. This revised version was published online in September 2006 with corrections to the Cover Date.     

Experimental and first‐principle investigation of Cu‐doped ZnO ferromagnetic powders

Zn_1‐xCu_x O powders were synthesized by using sol‐gel method. Electronic band structure and ferromagnetic properties of Zn_1‐xCu_x O powders were studied experimentally and theoretically. The simulations are based upon the Perdew‐Burke‐Ernzerhof form of generalized gradient approximation within the density functional theory. Zn_1‐xCu_x O shows dilute ferromagnetism, as a saturated magnetization of 0.9×10^‐3emu/g was observed for Zn_0.95Cu_0.05O powders. The strong p ‐d hybridization between Cu and its four neighbouring O atoms is responsible for the ferromagnetism. Comparing with ZnO whose Fermi level locates at the valence band maximum, the Fermi level of the Zn_1‐xCu_x O shifts upward into the valence band and hence the Zn_1‐xCu_x O system exhibits theoretically a p ‐type metallic semiconducting property. The Zn_1‐xCu_x O system may be a potential candidate in spintronics. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetizations and magneto-transport properties of Ni-doped PrFe03 thin films

The present study reports the magnetizations and magneto-transport properties of PrFel_xNixO3 thin films grown by pulsed laser ablation technique on LaA103 snbstrates. From DC M/H plots of these films, weak ferromagnetism or ferrimagnetism behaviors are observed. With Ni substitution, reduction in saturation magnetization is also seen. With Ni doping, variations in saturation field （Hs）, coercive field （Hc）, Weiss temperature （0）, and effective magnetic moment （Pelf） are seen. A small change of magnetoresitance with application of higher field is observed. Various essential parameters like density of state （Nf） at Fermi level, Mott＇s characteristic temperature （To）, and activation energy （Ea） in the presence of and in the absence of magnetic field are calculated. The present observed magnetic properties are related to the change of Fe-O bond length （causing an overlap between the oxygen p orbital and iron d orbital） and the deviation of the Fe-O-Fe angle from 180~. Reduction of magnetic domain after Ni doping is also explored to explain the present observed magnetic behavior of the system. The influence of doping on various transport properties in these thin films indicates a distortion in the lattice structure and single particle band width, owing to stress-induced reduction in unit cell volume.     

Evidences of defect contribution in magnetically ordered Sm-implanted GaN

Samarium (Sm) ions of 200 keV in energy were implanted into highly-resistive molecular-beam-epitaxy grown GaN thin films with a focused-ion-beam implanter at room temperature. The implantation doses range between 10¹⁴ and 10¹⁶ cm⁻². X-ray diffraction revealed Sm incorporation into GaN matrix without secondary phase. Raman-scattering spectroscopy identified impurity-independent defect-related oscillation modes. Slight decrease in band gap and significant reduction in transmittance were observed by optical transmission spectroscopy. Photoluminescence spectra showed emission peaks related to background p-type impurity. Ferromagnetic hysteresis loops were recorded from GaN implanted with highest Sm dose, and magnetic ordering was observed from Sm-implanted GaN with dose of and above 10¹⁵ cm⁻². The long-range magnetic ordering can be attributed to interaction of Sm ions through the implantation-induced Ga vacancy.