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We investigate the structural, magnetic, dielectric properties, and scaling behaviors of Aurivillius compounds Bi6-x/3Fe2Ti3-2x(WCo)xO18 (0 ⩽ x ⩽ 0.15). The room-temperature weak ferromagnetism is observed for the W/Co co-doped samples. The results of the dielectric constant εr, complex impedance Z", the dc conductivity σdc, and hopping frequency fH manifest that the dielectric relaxation of the x = 0 sample and the doped samples in the dielectric anomaly region (450-750 K) can be ascribed to the trap-controlled ac conduction around the doubly ionized oxygen vacancies and the localized hopping process of oxygen vacancies, respectively. The scaling behaviors reveal that the dynamic process of both electrons in the x = 0 sample and oxygen vacancies in the doped samples is temperature independent. The ferroelectric Curie-temperature Tc decreases slightly from 973K to 947K with increasing the doping level of W/Co. In addition, the dielectric loss exhibits a dielectric relaxation above 800K with the rather large activation energies (1.95 eV ⩽ Ea ⩽ 2.72 eV). [ABSTRACT FROM AUTHOR]

The antiperovskite intermetallic compounds AgN1-xCxMn3 (0⩽x⩽0.15) have been synthesized. As x increases, the temperature coefficient of resistivity (TCR) above room temperature decreases monotonically and finally changes the sign from positive to negative above x=0.1. Meanwhile, the temperature range is gradually broadened. For x=0.07, TCR is ∼3.1 ppm/K between 280K and 375 K. Both the resistivity and its slope are insensitive to the external magnetic field, indicating an insignificant contribution from magnetic scattering or short-range magnetic ordering to the observed low-TCR. As manifested by the Hall effect, the charge carrier density in the paramagnetic state for x=0.15 is reduced by an order of magnitude in comparison with that for x=0. The reduction of carrier density and the enhancive disorders when x increases was proposed to be responsible for the decrease in TCR and its sign switch. [ABSTRACT FROM AUTHOR]

We report a systematic study of the specific heat and dc magnetic susceptibility on the paramagnetic to ferrimagnetic transition (TC~141 K) in CuNMn3. A large magnetocaloric effect (MCE) at TC is observed with the entropy change of 3.49 J/kg K (6.38 J/kg K) for the field change of ΔH=20 kOe (45 kOe). The analysis of the isothermal magnetizations, including the derived Arrott plots and magnetic entropy change, shows a second-order like transition at TC. However, the existence of latent heat around TC is unambiguously manifested by the reduced slope of the temperature-time relaxations recorded during the specific heat measurement, indicating the transition is in fact weakly first-order in nature. The large MCE comparable with those observed the antiperovskite manganese carbides suggests it is equivalently interesting to explore the MCE in the antiperovskite manganese nitrides as in the carbides. [ABSTRACT FROM AUTHOR]

In this paper, we report the effects of carbon content on crystal structure, magnetic and electrical/thermal transport properties in antiperovskite compounds GaCxFe3 (0.15 ≤ x ≤ 0.3). Our experimental results indicate that all the physical properties we measured are sensitive to the carbon concentration for GaCxFe3. With decreasing the carbon content x, the Curie temperature (TC), saturated magnetization, and coercive force (HC) increase while the lattice constant, Debye temperature, and resistivity decrease gradually. Further analysis suggests that the serial GaCxFe3 can be a new kind of promising high-temperature soft magnetic material considering their high-TC (∼788 K) and low-HC (∼22 Oe). Interestingly, the low-temperature resistivity exhibits an abnormal semiconducting behavior below a characteristic temperature for each of GaCxFe3 (0.15 ≤ x ≤ 0.3). This abnormality of resistivity may be attributed to a combination of the renormalized electron-electron interaction and the weak-localization. Furthermore, the studies of the thermal transport and the Hall measurement suggest that the type of dominant carriers in GaCxFe3 changes gradually from hole- to electron-type with decreasing x. [ABSTRACT FROM AUTHOR]

We report the magnetic phase diagram of antiperovskite compounds Zn1-xSnxCFe3 (0 ≤ x ≤ 1). The effects of the ratio of Zn/Sn on the structure, magnetic and electrical transport properties have been investigated systematically. With increasing the Sn content x, the lattice constant increases while both the Curie temperature (TC) and the saturated magnetization decrease gradually. All the resistivity curves of Zn1-xSnxCFe3 show a metal-like behavior in measured temperature range (2-350 K). In particular, the T2-power-law dependence of the electrical resistivity is obtained at low temperatures for all samples with x ≤ 0.3. It is noteworthy that, for x = 0.1, the TC is tuned just at the room temperature (∼300 K). Around TC, the magnetocaloric effect is considerably large with a magnetic entropy change of 2.78 J/kg K (ΔH = 45 kOe) as well as a relative cooling power (RCP) of 320 J/kg (ΔH = 45 kOe). Considering the considerably large RCP, suitable working temperature, inexpensive and innoxious raw materials, Zn0.9Sn0.1CFe3 is suggested to be a promising candidate for practical application in magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The effects of carbon concentration on the crystal structure, magnetic, and electrical/thermal transport properties of ZnCxFe3 (1.0 ≤ x ≤ 1.5) have been investigated systematically. Both the Curie temperature and the saturated magnetization decrease firstly and then reach saturation with increasing x. The investigations of heat capacity and resistivity indicate that ZnC1.2Fe3 displays a strongly correlated Fermi liquid behavior considering its Kadowaki-Woods ratio (∼0.64 a0). Around the ferromagnetic-paramagnetic phase transition (∼358 K), a reversible room-temperature magnetocaloric effect is observed. The relative cooling power (RCP) is ∼164 J/kg (∼385 J/kg) with the magnetic field change ΔH = 20 kOe (45 kOe). Considering the considerable large RCP, inexpensive and innoxious raw materials, ZnC1.2Fe3 is suggested to be a promising candidate for room-temperature magnetic refrigeration. Furthermore, the studies of thermal transport properties indicate that ZnC1.2Fe3 can also be a potential thermoelectric material with the dimensionless figure of merit (ZT = α2T/ρk) reaching its maximum of 0.0112 around 170 K. [ABSTRACT FROM AUTHOR]

The structural, magnetic, and transport properties of the electron-doped perovskites cobalt oxides La1-xTexCoO3 (0≤x≤0.25) have been investigated. For the structural properties, the room temperature structural transition from rhombohedra (R3C) to orthorhombic (Pbnm) symmetry is found in these samples with x>=0.10 by the Rietveld refinement of x-ray powder diffraction patterns, which is ascribed to the smaller ionic radius of Te. As for the magnetic properties, firstly the spin state transition of Co3+ ions is observed in all samples, and the transition temperature shifts up to higher temperature with Te doping, which is ascribed to the smaller ionic radius and the strong acidity of Te. Secondly, it is interesting that there exists paramagnetic to ferromagnetic phase transition in the Te-doped samples. It is suggested that such a phase transition results from the introduction of Co2+ ions and the appearance of double exchange interaction between Co2+ and Co3+ due to Te doping. Moreover, Curie temperature TC increases with the increase of the Te doping level x (for x≤0.10), and then decreases with the further increase of x. About the transport properties, the temperature dependence of the resistivity ρ shows that all samples display semiconducting behavior in the whole measured temperature region. And it can be seen that the resistivity first decreases with increasing Te doping level from x=0 to 0.10, then increases as x>=0.15. Such variations of TC and ρ with x are suggested to be related to the structure transition. [ABSTRACT FROM AUTHOR]

The effect of Mn doping on structural, magnetic, electronic transport, and specific heat properties in 4d perovskites SrMo1-xMnxO3(0≤x≤0.20) has been investigated. The Mn doping at the Mo site does not change the space group of the samples, but increases the structural parameter a monotonically. All Mn-doped samples show Curie-Weiss paramagnetic behaviors due to the appearance of localized moment, and the magnetic susceptibility χ increases with increasing the Mn-doping content. Samples (x≥0.03) exhibit semiconducting transport behavior, while x=0.01 shows a metallic behavior with an upturn below T1. The magnitude of resistivity monotonically increases with increasing Mn-doping content. The evolution of the resistive properties is discussed according to the competition among Kondo scattering, electron-electron interaction, and the disorder effect. In addition, the electron-electron interaction intensity increases with the increasing of Mn-doping content according to the study of specific heat properties. [ABSTRACT FROM AUTHOR]

Structural, magnetic, and magnetocaloric properties in perovskite manganites La1-xPbxMn1-y-zCuyO3 (x~0.14, y=0, 0.01, 0.02, z=0.02, 0.08, 0.11) single crystals have been investigated. The Curie temperature TC decreases monotonously with increasing Cu-doping concentration. A sharp downturn in the inverse magnetic susceptibility 1/χm vs T plot at Griffiths temperature TG well above TC was observed for the free-doped sample, which can be attributed to the appearance of spin cluster in the paramagnetic state. The temperature interval between TG and TC decreases with increasing Cu-doping level and almost disappears as Cu concentration reaches 0.02. Large magnetic entropy change ΔSM occurs near TC and ΔSM approaches a maximum value for the sample with Cu-doping level y=0.01. The result can be explained based on the competing effect between the double-exchange interaction and the lattice distortion induced by Cu doping. [ABSTRACT FROM AUTHOR]

The persistent photoconductivity (PPC) effect has been observed in trilayered films made of perovskite manganites La[sub 2/3]Ca[sub 1/3]MnO[sub 3]/(La[sub 0.3]Nd[sub 0.7])[sub 2.3]Ca[sub 1/3]MnO[sub 3]La[sub 2/3]Ca[sub 1/3]MnO[sub 3](LNL) induced by He-Ne laser with wavelength of 632.8 nm. According to the result obtained in the thin film of (La[sub 0.3]Nd[sub 0.7])[sub 2/3]Ca[sub 1/3]MnO[sub 3](LNCMO), which the PPC effect is also observed below ∼50 K, the PPC effect observed in trilayered film LNL should originate from the middle layer LNCMO. Compared with the thin film of LNCMO, the PPC effect of the trilayered film LNL appears at ∼86 K, which is higher than that of LNCMO at ∼50 K. The PPC effect of LNL can be quenched on thermal cycling in the vicinity of 98 K, which is also higher than that of LNCMO at ∼77 K. The difference of PPC behavior between the thin films of LNCMO and LNL can be attributed to the variation of cluster-glass state in the trilay! ered films of LNL caused by the strong coupling of interlayer between the middle layer LNCMO and the top/bottom layers LCMO. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of Li doping on the charge ordering (CO) state in perovskite-type manganates La[sub 0.5]Ca[sub 0.5-x]Li[sub x]MnO[sub 3] with x=0, 0.05, 0.1, 0.15, 0.2 is investigated by transport and magnetic property measurements. The resistivity of the samples decreases with the increase of the Li-doped level. As x>=0.1, the insulator-metal (IM) transition has been induced. Accompanying the variation of transport properties, the sample undergoes the variation from antiferromagnetic order for x<0.05 to ferromagnetic (FM) order for x>=0.1. The experimental results indicate that the Li doping can destroy the CO state and induce the FM metallic (FMM) phase. These phenomena can be interpreted in terms of the strong competition between the CO state and FM phase induced by the Li[sup +] ions substitution for the Ca[sup 2+] ions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polycrystalline double perovskites A[sub 2]FeMoO[sub 6] (A=Ca, Sr, Ba) with nanometer-scale grain size have been synthesized using a sol-gel method. The grain size of the samples is controlled within nanometer scale by sintering at different temperatures. The phase purity and the crystal structure of the samples are analyzed by x-ray powder diffraction measurements. The electrotransport and magnetic properties are also measured in this article. In comparison with the large grain samples with micrometer scale, the nanometer-scale grain samples have different magnetic properties, such as lower magnetic transition temperatures and larger magnetoresistance, which can be explained in terms of size effect. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Negative thermal expansion (NTE) was investigated for Ga1-xMnxN0.8Mn3 (0.1⩽x⩽0.3). As x increases, the temperature range where lattice contracts upon heating becomes broad and shifts to lower temperatures. The coefficient of linear thermal expansion beyond -40 ppm/K with a temperature interval of ~50K was obtained around room temperature in x=0.2 and 0.25. Local lattice distortion which was thought to be intimately related to NTE is invisible in the X-ray pair distribution function of x=0.3. Furthermore, a zero-field-cooling exchange bias was observed as a result of competing ferromagnetic (FM) and antiferromagnetic (AFM) orders. The concomitant FM order serves as an impediment to the growth of the AFM order, and thus broadens the temperature range of NTE. Our result suggests that NTE can be achieved in antiperovskite manganese nitrides by manipulating the magnetic orders without distorting the local structure. [ABSTRACT FROM AUTHOR]

As a type of perovskite transparent conducting oxides, La-doped BaSnO3 is considered as a very important material to construct all transparent perovskite devices. The difficulty in achievement of large-area films with high electrical mobility has hindered the development of La-doped BaSnO3 films. Here, we report the results about chemical solution deposition of Ba0.92La0.08SnO3-δ (BLSO) films. The post-annealing and atmosphere as well as lattice mismatch have been investigated. Post-annealing at 1000 °C can obviously improve the performance due to the enhanced crystallization. Under post-annealing in N2 atmosphere the room-temperature resistivity and electrical mobility can achieve 3.25 mΩ cm and 11.09 cm² V-1 s-1, respectively, for the BLSO on LaAlO3 single crystal substrates due to the enhanced oxygen deficiencies. BLSO films with different orientation can be easily obtained by selection of the substrates, showing isotropic physical properties. Furthermore, the room-temperature resistivity and mobility are optimized to 1.8 mΩ cm and 23.04 cm² V-1 s-1 when SrTiO3 single crystal substrates with smaller lattice mismatch are used due to the decreased dislocation density. The results will provide an alternative route to fabricate large-area transparent conducting alkaline-earth stannate films with high performance using low-cost chemical solution deposition. [ABSTRACT FROM AUTHOR]

The antiperovskite functional compound CuNMn3 exhibits magnetostriction below the non-collinear ferromagnetic (FM)-paramagnetic (PM) transition (accompanied by a martensitic transformation). After the substitution of Mn for Cu, martensitic transformation is decoupled from FM transition. Meanwhile, the tetragonality of the martensitic phase and the magnetostriction are weakened. The combined analysis indicates that the spin, charge, and lattice are closely coupled around martensitic transformation temperature (TMS). The low-temperature martensitic phase is associated with a metastable magnetic state characterized by small magnetocrystalline anisotropy. Additionally, the depression of TMS with introducing the Mn dopant is revelatory for the development of low-temperature negative thermal expansion material. [ABSTRACT FROM AUTHOR]

The persistent photoconductivity (PPC) induced by visible light of a He–Ne laser with a wavelength of 632.8 nm in perovskite manganite films of (La[sub 0.3]Nd[sub 0.7])[sub 2/3]Ca[sub 1/3]MnO[sub 3] at low temperatures, below ∼50 K, was observed. Based on the measurements of transport and magnetic properties, it is suggested that the samples undergo a transition of cluster-glass state below ∼50 K. The PPC phenomenon can be qualitatively explained in terms of a photoinduced ferromagnetic cluster growth model. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report a systematic study of the specific heat and dc magnetic susceptibility on the paramagnetic to ferrimagnetic transition (TC~141 K) in CuNMn3. A large magnetocaloric effect (MCE) at TC is observed with the entropy change of 3.49 J/kg K (6.38 J/kg K) for the field change of ΔH=20 kOe (45 kOe). The analysis of the isothermal magnetizations, including the derived Arrott plots and magnetic entropy change, shows a second-order like transition at TC. However, the existence of latent heat around TC is unambiguously manifested by the reduced slope of the temperature-time relaxations recorded during the specific heat measurement, indicating the transition is in fact weakly first-order in nature. The large MCE comparable with those observed the antiperovskite manganese carbides suggests it is equivalently interesting to explore the MCE in the antiperovskite manganese nitrides as in the carbides. [ABSTRACT FROM AUTHOR]