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We have studied a range of pseudo-ternaries derived from the parent compound PrMn2Ge2, substituting for each constituent element with a smaller one to contract the lattice. This enables us to observe the magneto-elastic transitions that occur as the Mn-Mn nearest neighbour distance is reduced and to assess the role of Pr on the magnetism. Here, we report on the PrMn2Ge2-xSix, Pr1-xYxMn2Ge2, and PrMn2-xFexGe2 systems. The pressure produced by chemical substitution in these pseudo-ternaries is inherently non-uniform, with local pressure variations dependent on the local atomic distribution. We find that concentrated chemical substitution on the R or X site (e.g., in Pr0.5Y0.5Mn2Ge2 and PrMn2Ge0.8Si1.2) can produce a separation into two distinct magnetic phases, canted ferromagnetic and canted antiferromagnetic, with a commensurate phase gap in the crystalline lattice. This phase gap is a consequence of the combination of phase separation and spontaneous magnetostriction, which is positive on transition to the canted ferromagnetic phase and negative on transition to the canted antiferromagnetic phase. Our results show that co-existence of canted ferromagnetic and antiferromagnetic phases depends on chemical pressure from the rare earth and metalloid sites, on local lattice strain distributions and on applied magnetic field. We demonstrate that the effects of chemical pressure bear close resemblance to those of mechanical pressure on the parent compound. [ABSTRACT FROM AUTHOR]

We present the studies of structural, electrical, and magnetic properties of bulk Cd1-xMnxGeAs2 crystals with low Mn content, x, varying from 0 to 0.037. The studied samples have excellent crystallographic quality indicated by the presence of diffraction patterns never before observed experimentally for this compound. The electrical transport in our samples is dominated by thermal activation of conducting holes from the impurity states to the valence band with activation energy of about 200 meV. The defect states acting as ionic scattering centers with concentration in the range from 6 to 15 × 1017 cm-3 are observed. The effective Mn content in our samples, xθ, determined from fit of the susceptibility data to the Curie-Weiss law, is very close to the average chemical content, x. It indicates that the Mn ions are distributed randomly, substituting the Cd sites in the host CdGeAs2 lattice. We observe a negative Curie-Weiss temperature, ∣θ∣ ⩽ 3:1K, increasing as a function of x. This indicates the significance of the short-range interactions between the Mn ions. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

We present systematic studies of magnetic and transport properties of Zn1-xMnxGeAs2 semimagnetic semiconductor with the chemical composition varying between 0.053≤x≤0.182. The transport characterization showed that all investigated samples had p-type conductivity strongly depending on the chemical composition of the alloy. The Hall effect measurements revealed carrier concentrations p≥1019 cm-3 and relatively low mobilities, μ≤15 cm2/(V s), also chemical composition dependent. The magnetic investigations showed the presence of paramagnet-ferromagnet phase transitions with transition temperatures greater than 300 K for the samples with x≥0.078. We prove by means of x-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy techniques that the observed room temperature ferromagnetism is due to the presence of MnAs inclusions. The high field magnetoresistance showed the presence of giant magnetoresistance effect with maximum amplitudes around 50% due to the presence of nanosize ferromagnetic grains. [ABSTRACT FROM AUTHOR]

The influences of Mn doping on the electrical and optical properties of the Zn1-xMnxO:N films have been investigated. Mn incorporation occupying on the Zn site has led the lattice constants and the bandgap of the films increased with the structural quality deteriorated. The electrical properties have been found to change significantly with the content of Mn in the films, due to the changes in the amount of the NO acceptors and CN compensation centers formed in the films by Mn incorporation as revealed by x-ray photoelectron spectrometry measurements. The chemical states of Mn have been identified as Mn2+ and Mn4+, corresponding to Mn occupying on the Zn site and MnO2 second phase, respectively. The conductive type and the Mn2+ content of the films show a strong effect on the magnetic properties, which can be explained from the theoretical predication on the Mn 3d and N 2p ferromagnetic (hole) coupling on the ferromagnetism. However, uncompensated spins from nonuniform distribution of Mn atoms in ZnO may also be responsible for the observation of ferromagnetism signature at least on the high resistant samples. [ABSTRACT FROM AUTHOR]

Local crystal structures associated with nanoscale variations of the concentration ratio of Fe ions to Mn ions in each single Li1.2Mn0.4Fe0.4O2 particle have been studied by nanobeam electron diffraction, high-resolution transmission electron microscopy, and electron energy-loss spectroscopy combined with scanning transmission electron microscopy. We have found the direct evidence that the Li1.2Mn0.4Fe0.4O2 particle is comprised of Mn-rich nanodomains with the layered rocksalt structure and Fe-rich nanodomains with the cubic rocksalt structure featured by the cation short-range order, within a common oxygen lattice framework of the cubic close-packed structure. Possible oxygen-centered octahedra in the present material are suggested. We discuss both origin and stability of the chemical-nanodomain structure. [ABSTRACT FROM AUTHOR]

We have investigated structural, magnetic, optical, and electrical transport properties of Zn0.9-xFe0.1(Co/Mn)xO (x=0.05,0.1 for Co and x=0.1 for Mn) diluted magnetic semiconducting nanoparticles synthesized through low temperature chemical “pyrophoric reaction process.” From transmission electron micrograph, particle sizes are found to be in the nanometric regime (∼7 nm) and single crystalline in nature. The magnetization measurements reveal that doping of Co or Mn ions in ZnFeO nanometric matrix decreases the values of coercive field and average magnetization, not due to just increasing the total dopant concentration. It has been attributed to the formation of antiferromagnetic or paramagnetic states in ferromagnetic infinite cluster (spanning of magnetic polarons) by doping of Co or Mn ions. The strong irreversibility has been observed to persist at and above room temperature in magnetization versus temperature curve. The semiconducting band gap of those nanoparticles has been estimated using recorded absorbance spectra. The electrical behaviors of those samples have been investigated over the wide temperature and frequency range using ac complex impedance spectroscopy. [ABSTRACT FROM AUTHOR]

The magnetic and chemical interface properties of Mn–Ir/Co–Fe/Al+oxidation/Ni–Fe magnetic tunnel junctions are investigated for different barrier thickness, oxidation times, and annealing conditions by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. For underoxidized samples the formation of Co–Fe–Al alloy at the lower barrier interface during optimal annealing is observed. For optimally oxidized and overoxidized samples FeOx is formed during oxidation, which is reduced by Mn diffusing to the barrier during annealing. The reduction of FeOx is accompanied by an increase of the interfacial magnetic Fe moment, whereas the Co moments hardly change with the postannealing. Comparison of these results with transport properties of the junctions shows that their polycrystalline structure has to be taken into account to understand the annealing temperature and oxidation state dependence of the tunneling magnetoresistance effect. [ABSTRACT FROM AUTHOR]

We report a combined study of hydrostatic pressure (P ⩽ 25 kbar) and chemical substitution on the magnetic pair-breaking effect in Eu- and Mn-substituted BaFe2As2 single crystals. At ambient pressure, both substitutions suppress the superconducting (SC) transition temperature (Tc) of BaFe2-xCoxAs2 samples slightly under the optimally doped region, indicating the presence of a pair-breaking effect. At low pressures, an increase of Tc is observed for all studied compounds followed by an expected decrease at higher pressures. However, in the Eu dilute system, Tc further increases at higher pressure along with a narrowing of the SC transition, suggesting that a pair-breaking mechanism reminiscent of the Eu Kondo single impurity regime is being suppressed by pressure. Furthermore, Electron Spin Resonance (ESR) measurements indicate the presence of Mn2+ and Eu2+ local moments and the microscopic parameters extracted from the ESR analysis reveal that the Abrikosov-Gor'kov expression for magnetic pair-breaking in a conventional sign-preserving superconducting state cannot describe the observed reduction of Tc. [ABSTRACT FROM AUTHOR]

We report a combined study of hydrostatic pressure (P ⩽ 25 kbar) and chemical substitution on the magnetic pair-breaking effect in Eu- and Mn-substituted BaFe2As2 single crystals. At ambient pressure, both substitutions suppress the superconducting (SC) transition temperature (Tc) of BaFe2-xCoxAs2 samples slightly under the optimally doped region, indicating the presence of a pair-breaking effect. At low pressures, an increase of Tc is observed for all studied compounds followed by an expected decrease at higher pressures. However, in the Eu dilute system, Tc further increases at higher pressure along with a narrowing of the SC transition, suggesting that a pair-breaking mechanism reminiscent of the Eu Kondo single impurity regime is being suppressed by pressure. Furthermore, Electron Spin Resonance (ESR) measurements indicate the presence of Mn2+ and Eu2+ local moments and the microscopic parameters extracted from the ESR analysis reveal that the Abrikosov-Gor'kov expression for magnetic pair-breaking in a conventional sign-preserving superconducting state cannot describe the observed reduction of Tc. [ABSTRACT FROM AUTHOR]

Examines the tilted antiferromagnetic ordering of the methacrylonitrile (Mn )spins in polycrystalline Nd0.62Ca0.38MnO3. Information on the discovery of colossal magnetoresistance (CMR) in many systems; Preparation of polycrystalline samples; Observation of charge ordering, tilted antiferromagnetic ordering of the Mn spins.