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We report the synthesis, crystal structure, magnetic and electrical/thermal transport properties of antiperovskite nitrides ZnNFe 3 and AlNFe 3 . Both compounds display ferromagnetic (FM) ground state and transform into the paramagnetic phase at 762 K and 770 K, respectively. At FM phase, for ZnNFe 3 and AlNFe 3 , the saturated magnetizations at 5 K are 163 and 188 emu/g, which is the largest value among all the antiperovskite compounds; the minimal coercive forces ( H C ) are as low as 18.6 and 16.3 Oe; the low H C is almost constant covering a broad temperature range of 5–650 K. These characteristics indicate that both ZnNFe 3 and AlNFe 3 may be promising candidates of high-temperature soft magnetic material. In addition, electrons are dominant carriers owing to the negative Seebeck coefficient, the Fermi-liquid behavior is well presented via the investigation of low-temperature electrical transport, and the lattice thermal conductivity estimated by Wiedemann–Franz law is the main part of total thermal conductivity at high temperatures for both ZnNFe 3 and AlNFe 3 .

The effects of Cr doping on structural, magnetic, electrical and thermal transport properties of Ca3Co4−xCrxO9 (0 ⩽ x ⩽ 0.3) have been investigated systematically. Based on the analysis of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data, the Cr ions are suggested to be doped at Co4+-sites in CoO2 layers in the form of Cr6+. The introduction of the nonmagnetic Cr6+ ions results in the decrease of the average effective magnetic moment, which confirming that the ferrimagnetic state of Ca3Co4O9 system can be well suppressed by Cr doping. The magnitude of resistivity and the metal–insulator-transition temperature increase monotonously with increasing x, indicating the enhanced carrier localization and the more stable spin-density-wave state in these Cr-doped samples. As Cr6+ ions are doped into system, the thermopower increases obviously. Correspondingly, the room-temperature thermopower reaches the maximum value of 140 μV/K for x = 0.3 sample. These results of magnetism and electrical/thermal transport are mainly originated from the variations of carrier concentration and electronic correlation resulted from the partial substitution of Cr6+ for Co ions.

The effect of W-doping at Co-site on structural, magnetic, and transport properties in Ca3Co4−xWxO9 (0≤x≤0.4) polycrystalline samples has been studied. Based on the analysis of the structural parameter variations, the substitution is suggested to occur at Co-site in Ca2CoO3 layers. Magnetic results show that the low-temperature magnetic behavior of the series samples changes from a ferrimagnetic state of Ca3Co4O9 to a glass-like state for the W-doped samples. The result is suggested to originate from the variation of the average valence of Co ions induced by W-doping. All samples show metal-insulator transition at Tmin and Tmin increases monotonously with increasing W-doping level. The temperature range shows Fermi liquid transport behavior becomes narrower with increasing W-doping level, indicating an enhanced electron–electron correlation. Moreover, the resistivity increases and the transport mechanism changes from thermally activated model to the Mott’s variable range hoping model as W-doped into the system. The variation of the resistivity and the transport mechanism is ascribed to the increased distortion or disorder induced by W-doping.

The critical properties of the spinel vanadate MnV1.95Al0.05O4 have been investigated by the Kouvel–Fisher method, and critical isotherm analysis. Reliable critical exponents β=0.492(3), γ=0.969(1) and δ=2.951(4) are obtained. Based on these critical exponents, the magnetization-field–temperature data around TC collapse into two independent curves obeying the single scaling equation M(H,e)=eβf±(H/eβ+γ). Moreover, the critical exponents are confirmed by the field dependence of the magnetic entropy change relation Δ S M | T = T C ∝ H n with n=1+(β+1)/(β+γ). The critical behavior of MnV1.95Al0.05O4 agrees with the prediction of the mean-field model with long range interaction. Compared with MnV2O4, the different critical behavior of MnV1.95Al0.05O4 might be because the doped Al ions destroy the collective frustration interaction between V ions. The ferromagnetism of MnV1.95Al0.05O4 is mainly related to the long range ferromagnetic interaction of Mn ions.

Ca3Co4O9 thin films have been first prepared on polycrystalline Al2O3 substrates using chemical solution deposition method by multiple annealing processing. It is observed that the derived thin films are c-axis oriented although the substrates are polycrystalline Al2O3 substrates, suggesting the self-assembled c-axis orientation. The annealing temperature effects on the properties are investigated and discussed. The best performances are attributed to the 850 °C-annealed sample, whose resistivity, Seebeck coefficient and power factor at 300 K are 7.4 mΩ cm, 117 μV/K and 0.18 mW/m K−2 respectively, which is even better than those of the thin films deposited on single crystal substrates. The results will provide an effective route to optimize the properties of Ca3Co4O9 thin films using chemical solution deposition by multiple annealing processing even the substrates are polycrystalline.

The granular composites of (1−x)La0.7Sr0.3MnO3/xSrFe12O19 [(1−x)LSMO/xSFO] were prepared. The magnetic, electrical, and magnetoresistive properties of the composites were investigated systematically. Two magnetic transitions originating from LSMO and SFO are observed for x=0.05, 0.10, and 0.20. The addition of hard-magnetic SFO ferrite leads to the increased substantially resistivity of the composites and the shift of insulating-metallic transition temperature TIM correlated with LSMO. Enhanced low-field magnetoresistance (LFMR) in the composites can be mainly attributed to the enhanced spin disorder and spin-dependent tunneling at LSMO grain boundaries induced by the interaction between LSMO and SFO ferrite. The transport mechanisms in detail are analyzed in LSMO/SFO composite system.

Structural, magnetic, resistivity and thermal transport measurements have been performed to study the Mo-doping effect on a layered cobaltite Ca3Co4−xMoxO9 ( 0 ≤ x ≤ 0.4 ) system. The results indicate that the low-temperature magnetic behavior of the system changes from a ferrimagnetic state to a spin-glass-like state upon Mo doping, which is due to the decrease in the average valence of Co ions. Moreover, all the Mo-doped samples have a higher resistivity and larger thermopower S compared with the Mo-free sample. The variation in the resistivity and thermopower between the Mo-doped and the Mo-free samples is dominated by the change in the carrier concentration of the samples. In the Mo-doped samples with x ≥ 0.1 , both the resistivity and thermopower decrease gradually with increasing Mo-doping level, which is suggested to mainly originate from the variation in the carrier mobility of the samples. In addition, an obvious thermopower upturn is observed in the S ( T ) curve of all the Mo-doped samples, which can be explained by the enhancement of spin-fluctuation induced by Mo-doping.

La 0.6 Sr 0.4 MnO 3 (LSMO) particles were prepared by the sol–gel method with and without an external magnetic field (H ext = 4 kOe). Structural and magnetic properties were investigated. X-ray powder diffraction results show that both samples are single-phase. Field-emission scanning electronic microscopy shows that the mean particle size of LSMO particles synthesized under H ext = 4 kOe is larger than that of the sample without an external magnetic field. The enhanced magnetic properties are attributed to the magnetic-field effect.

GaN films on AlN buffer layers were grown on (111) silicon substrates in a vertical rotating disk metal–organic chemical-vapor deposition reactor (CVD, Inc.). The dependence of residual stress in GaN films on the V/III molar flow ratio was studied. The crystalline quality of GaN films was analyzed by x-ray diffractometry, and the x-ray lattice parameter method was used to determine the residual stress in the films by measuring the c-axis and a-axis strain separately. The x-ray results show that the residual stress decreases with an increasing V/III molar flow ratio if all other growth parameters are kept constant.