Electron spin resonance in Ge0.99Mn0.01 nanowires

Electron spin resonance (ESR) is measured in arrays of Ge_0.99Mn_0.01 nanowires (NWs). We show that the ESR spectrum comprises four lines corresponding to the different magnetic subsystems. Two lines are attributed to spin-wave excitations in the Mn⁺³ ion subsystem. The third component corresponds to the resonance in the Mn⁺² ions. The last component has an asymmetric Dyson form and characterizes the resonance in the mobile paramagnetic centers. We demonstrate that temperature dependences of ESR parameters are correlated in subsystems of the localized magnetic centers (Mn⁺³ and Mn⁺² ions) and delocalized band carriers. It implies the presence of exchange interactions between the localized Mn ions and spin-polarized carriers.     

Electron spin resonance in oriented nanowires Ge0.99Cr0.01

Physics of the Solid State - The electron spin resonance in Ge0.99Cr0.01 nanowires grown in nanopores of anodized aluminum oxide is investigated. At temperatures in the range 4–300 K, the...     

Excitons and photoluminescence in ZnO and Zn0.99Mn0.01O nanocrystals

The photoluminescence and photoluminescence excitation spectra for Zn_1?x Mn _x O nanocrystals are presented. After annealing of powders in air, the intensity of the bands attributable to manganese decreases noticeably. This suggests that the oxygen vacancies affect the Zhang-Rice-like states appearing due to strong d-p-hybridization, which is confirmed by an increase in the band gap of Zn_1?x Mn _x O for low x. The origin of the 2.9-eV peak and the shape of its excitation spectrum are discussed qualitatively. For Zn_1?x Mn _x O nanocrystals, the shape of the excitation spectrum is as unusual as the intense absorption in the range (2.2–3.0) eV.     

Microwave magnetoresistance and electron spin resonance in Ge:Mn thin films and nanowires

Resonant and nonresonant absorption of microwave radiation is found to occur in germanium films implanted with manganese at concentrations of 2, 4, and 8 at %. Electron spin resonance is observed in two temperature ranges: (i) in the vicinity of the phase transition of Mn₅Ge₃ clusters to the ferromagnetic state at T = 295 K; and (ii) in the range of temperatures below 60 K, at which collective ordering of Mn spins in the crystal lattice and spin-wave resonance take place. The dependence of the nonresonant signal of the microwave magnetoresistance on the magnetic field exhibits a nonmonotonic behavior identical for the X and K microwave bands. An analysis of the field dependence of the microwave magnetoresistance makes it possible to separate two components of the derivative of the magnetoresistance: the quasi-linear Lorentzian component observed in strong fields and the negative exponential anisotropic component determined by spin-dependent scattering of charge carriers from magnetic impurities. The length of the phase relaxation of charge carriers is estimated to be 350 nm at T = 2 K and exceeds the thickness of the film (120 nm) and the sizes of clusters and precipitates (3–5 nm). In quasi-one-dimensional nanowires of the composition Ge:Mn at the same impurity concentrations, microwave magnetoresistance is absent. These facts suggest that conduction in thin films has a quasi-two-dimensional character and that the measured microwave magnetoresistance is associated with charge carriers in the crystal lattice rather than with impurity clusters.     

Magnetic patterns and flux pinning in Pd0.99Fe0.01-Nb hybrid structures

The magnetic properties of hybrid thin-film Pd_0.99Fe_0.01-Nb structures are studied by a magneto-optical technique. It is shown that, below 14 K, the samples exhibit the ferromagnetic ordering corresponding to the formation of weakly coupled ferromagnetic nanoclusters. In the clusters, the effective spin polarization of Fe ions is about 4μ_B, corresponding to that in the bulk Pd₃Fe alloy. The proximity of the ferromagnetic layer does not suppress the superconductivity in niobium. It does not affect the superconducting transition temperature but leads to an enhanced pinning and results in an increase in the critical current by about 30%. This behavior agrees well with the existence of the nanocluster structure in the ferromagnetic film.     

Inhomogeneous lattice distortions in the Zn0.99Cd0.01Se crystal

The structural state of a Zn_0.99Cd_0.01Se crystal at temperatures of 78 and 300 K has been investigated using thermal neutron diffraction. It has been found that the diffraction patterns of the crystal contain diffuse scattering regions in the vicinity of the basic structure reflections, which are independent of temperature. It has been shown that the effects of diffuse scattering are caused by transverse displacements of lattice atoms, which are induced by impurities of the Cd²⁺ ions whose sizes substantially exceed the sizes of the Zn²⁺ ions. The obtained results have been used to construct a picture of the influence of cadmium ions on the structural state of the crystal under study.     

Magnetic Anisotropy of the Low-Temperature Specific Heat of Ho0.01Lu0.99B12 with Dynamic Charge Stripes

JETP Letters - The specific heat of Ho0.01Lu0.99B12 single crystals with dynamic charge stripes is studied at low and ultralow temperatures (0.07–20 K) in applied magnetic fields of 0–9...     

Spin dynamics in oriented ferromagnetic nanowires Ge<Subscript>0.99</Subscript>Co<Subscript>0.01</Subscript>

The magnetic properties of one-dimensional oriented nanowires Ge_0.99Co_0.01 grown in pores of anodized aluminum oxide membranes are investigate using ferromagnetic resonance spectroscopy. The electron spin resonance signals of the magnetically ordered cobalt subsystem and the charge-carrier subsystem are identified. It is revealed that the anisotropy field at 4 K is equal to 400 Oe and aligned parallel to the nanowire axis. The transverse relaxation time of spin waves at 4 K is estimated to be ～10^?10 s. It is shown that the magnetic properties of nanowires are predominantly determined by the ferromagnetism of Co and GeCo alloy clusters.     

Electron spin resonance in amorphous Si and Ge doped with Mn

ESR signal with hyperfine structure due to Mn and that due to dangling bonds are observed. From the magnitude of the hyperfine structure constant, Mn is considered to locate within voids without making a covalent bond with the host atom in the form of Mn²⁺. The intensity of the ESR signal due to dangling bonds decreases with the increase of that due to Mn, so it is likely that electrons are transfered from Mn to dangling bonds and their unpaired electrons are paired up.     

C掺杂Mn3Ge的电子结构和磁性

采用第一性原理计算方法研究C掺杂对Mn₃Ge的影响.对Mn_3-xGeC_x的晶体结构进行几何优化,发现C原子最稳定的掺杂位置在正八面体的中心位置.研究其电子结构和总磁矩随C掺杂量的变化,发现总磁矩随着C浓度的增加先减小后增大,其中Mn₃GeC_0.4总磁矩接近零,可以实现完全的磁性补偿.研究Mn₃GeC_0.4多层膜的磁性,给出总磁矩接近零的Mn₃GeC_0.4多层膜结构,为Mn₃Ge的实际应用提供参考.     

Spin-Wave Resonance in Ge : Mn Thin Films with Percolation Magnetic Ordering

The mechanism of excitation and propagation of spin waves in Ge: Mn thin films with different nominal manganese concentrations (2, 4, and 8 at % Mn) with percolation magnetic ordering is explored. Concentration dependencies of Curie temperature T_C(n) and spin wave rigidity D(n) are determined, which enables to find the index of correlation distance. An exotic percolation magnetic state of samples of Ge: Mn thin films is confirmed by rectifying experimental dependences D(n) and D/T_C(n) in coordinates accepted in the percolation theory.     

Rietveld analysis of single phase Ba0.99Dy0.01TiO3 ceramic

Microstructure characterization of ball-milled powder mixtures was done by analyzing the X-ray powder diffraction data. Formation of single phase dysprosium-modified BaTiO₃ and structural and microstructural changes in terms of lattice imperfections have been estimated from the analysis of X-ray powder diffraction data of ball-milled powder mixtures by Rietveld’s powder structure refinement method. For the first time this type of analysis is reported for this material to the best of knowledge. The generated structure of Ba_0.99Dy_0.01TiO₃ ceramic in terms of bond lengths, bond angles and generated positions has been discussed.     

Magnetic nanowires

We review recent developments in the research on magnetic nanowires electrodeposited into pores of membranes. Typical nanowires fabricated by this method have a diameter in the range 30–500 nm for a length of the order of 10 μm, and can be composed of a stack of layers of different metals with thicknesses in the nanometer range (multilayered nanowires). We describe the preparation methods and present typical examples of structural characterization. We review the magnetic properties with examples of results on both arrays of nanowires and isolated nanowires. We then describe the magnetoresistance properties of multilayered nanowires, and their interest for their understanding of the CPP–GMR and the determination of spin diffusion lengths. The last section is an overview on the perspectives of future research.     

Resistive anomalies in (Pd1−xAgx)0.99Fe0.01 ternary alloys

The resistivity of ternary alloys (Pd_1?xAg_x)_0.99Fe_0.01 and the corresponding binary hosts has been measured from 1.2 K to 300 K. For x = 50 the results suggest spin-glass behaviour resembling that in the Pd-H (1% Fe) system with H/M ≈ 0.6.     

Nuclear magnetic resonance in noncollinear antiferromagnet Mn3Al2Ge3O12

The ⁵⁵Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice antiferromagnet Mn₃Al₂Ge₃O₁₂ has been studied in the frequency range of 200–640 MHz in the external magnetic field H ‖ [001] at T = 1.2 K. Three absorption lines have been observed in fields less than the field of the reorientation transition H _c at the polarization h ‖ H of the rf field. Two lines have been observed at H > H _c and h ⊥ H. The spectral parameters indicate that the magnetic structure of manganese garnet differs slightly from the exchange triangular 120-degree structure. The anisotropy of the spin reduction and (or) weak antiferromagnetism that are allowed by the crystal symmetry lead to the difference of ≈3% in the magnetization of sublattices in the field H < H _c. When the spin plane rotates from the orientation perpendicular to the C ₃ axis to the orientation perpendicular to the C ₄ axis, all magnetic moments of the electronic subsystem decrease by ≈2% from the average value in the zero field.     

Magnetic and electrical transport properties of delta-doped amorphous Ge:Mn magnetic semiconductors

We report on the growth and characterization of delta-doped amorphous Ge:Mn diluted magnetic semiconductor thin films on GaAs (0 0 1) substrates. The fabricated samples exhibit different magnetic behaviors, depending on the Mn doping concentration. The Curie temperature was found to be dependent on both the Mn doping concentration and spacing between the doping layers. A sharp drop in magnetization and rise in resistivity are observed at low temperature in samples with high Mn doping concentrations, which is also accompanied by a negative thermal remanent magnetization (TRM) in the higher temperature range. The temperature at which the magnetization starts to drop and the negative TRM appears show a correlation with the Mn doping concentration. The experimental results are discussed based on the formation of ferromagnetic regions at high temperature and antiferromagnetic coupling between these regions at low temperature.     

Large quadratic electro-optic effect in K0.99Li0.01Ta0.60Nb0.40O3 single crystal

Single crystal paraelectric K_0.99Li_0.01Ta_0.60Nb_0.40O₃ is grown with a room-temperature Curie temperature (T_c). The parameters of the Sellmeier dispersion equation were determined. A large quadratic electro-optic (QEO) effect was observed. The QEO coefficient R₁₁ reaches as high as 2.48 × 10^?15 m² V^?2 around T_c. The induced refractive index change under an electric field of 500 V/mm is 40 times bigger than that of commonly used LiNbO₃. The large QEO coefficient makes single crystal K_0.99Li_0.01Ta_0.60Nb_0.40O₃ a promising candidate in optical devices.