共查询到20条相似文献,搜索用时 12 毫秒
1.
P. Nisha S. Savitha Pillai Azad Darbandi Manoj Raama Varma K.G. Suresh Horst Hahn 《Materials Chemistry and Physics》2012
The structure, critical exponents and magnetocaloric effect (MCE) of Nebulized Spray Pyrolysis (NSP) synthesized nano crystalline La0.67Ca0.33Mn1−xFexO3 (x = 0.05, 0.2) were investigated. The Reitveld refinement of XRD patterns show that the samples adopt an orthorhombic structure with Pnma space group. TEM inspection reveals that the average particle size is about 15 nm and 42 nm for NSP synthesized LCMFe0.05 and LCMFe0.2 samples respectively. The temperature and field dependent magnetization studies reveal the superparamagnetic state of La0.67Ca0.33Mn0.95Fe0.05O3 and spin-glass-like state of La0.67Ca0.33Mn0.8Fe0.2O3. The critical behaviour at the transition region studied using modified Arrott plot provides a second order nature of phase transition for both samples. The magnetocaloric studies show the maximum value of magnetic entropy change (ΔSmax) is in the range 2.3 J kg−1 K−1 at 158 K for LCMFe0.05 and 0.3 J kg−1 K at 92 K for LCMFe0.2 respectively at 5 T field. The field dependence of the magnetic entropy changes are also analysed, which show a power law dependence (ΔSM ∞ Hn, n = 0.72 (2)) at transition temperature, TC = 162 K for LCMFe0.05 and n = 1.11(3) at 92 K for LCMFe0.2. 相似文献
2.
Crystal structures of BiMn0.97Al0.03O3 (I) at 300 and 470 K and BiMn0.9Al0.1O3 (II) at 90 and 300 K were studied with synchrotron X-ray powder diffraction. The strong Jahn-Teller distortion, observed at 300 K in I and associated with orbital order, disappeared at 470 K completely for one site and partially for the second site. The Mn/Al-O distances were very close to each other in I at 470 K and in II at 90 and 300 K indicating that orbital order did not appear in II even at 90 K. Magnetic properties of I and II were investigated with specific heat, high-temperature dc magnetic susceptibility, and ac magnetic susceptibility using different driving ac and applied dc magnetic fields and different ac magnetic field frequencies. The anomaly on the specific heat associated with a magnetic transition was strongly suppressed in II compared with that of I and BiMnO3. 相似文献
3.
W.L. Zhu M.Z. Wu H. Li S. Cao W.J. Yin K. Yang G.H. Zheng Z.Q. Sun 《Materials Research Bulletin》2009,44(9):1867-350
The optical spectra have been investigated for a prototypical double exchange ferromagnetic La0.67Ca0.33MnO3 with Mn substituted by V above the paramagnetic-magnetic transition temperature TC. The excitation spectra under the probe wavelength of λem = 473 nm for all samples exhibit two activation bands around 360 and 294 nm, involving an electron transfer from oxygen 2p states to the Mn d states in MnO6 octahedra. The photoluminescence spectra at λex = 290 nm have the similar spectral features for all samples. The photoluminescence spectral peaks located at 400, 473, 534, 670, 738 and 770 nm, and the corresponding photon energy is in a broad range of 3.1-1.6 eV, indicating that the PL bands could have the different origin: the self-trapped excitons localized on MnO6 octahedra; the interband transition between the O 2p and Mn 3d bands; the transition between the 3d electron states of Mn ions. So, it can be clearly seen that the electronic behavior above TC is very complicated. Our results suggest that the charge transfer from O 2p to Mn 3d has the important effects on the electronic structure, and it not only contributes to the optical transition but is helpful and even important to understand the electric, magnetic and thermal properties etc. due to the strong correlation among charge, spin and lattice in perovskite manganites. 相似文献
4.
A family of Sr-doped perovskite compounds Ln1−xSrxCoO3−δ (Ln = La3+, Pr3+ and Nd3+; x > 0.60), were prepared by sol-gel chemistry and reaction at 1100 °C under 1 atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm3+ and an upper limit of Sr2+ solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancy ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln3+/Sr2+ cation ordering was observed. 相似文献
5.
In this study, bulk ceramics with general formula Bi1−ySryFe(1−y)(1−x)Sc(1−y)xTiyO3 (x = 0-0.2, y = 0.1-0.3 mol%) were prepared by traditional solid-state reaction method. As a comparison, bulk BiFeO3 (BF) was also sintered by rapid sintering method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that apart from a small amount of secondary phase detected in BF, all other samples crystallized in pure perovskite structure and maintained original R3c space group. The room temperature M-H curves were obtained. While BF had a coercive magnetic field (Hc) of 150 Oe, Bi1−ySryFe1−yTiyO3 solid solutions had a much larger value (for y = 0.1, 0.2, 0.3, Hc were 4537, 5230 and 3578 Oe, respectively). Sc3+ substitution decreased the Hc values of these solid solutions remarkably, and resulted in soft magnetic properties, as well as a decrease of the dielectric loss. At 1 MHz, the tan δ of Bi0.7Sr0.3Fe0.7(1−x)Sc0.7xTi0.3O3 with x = 0.05, 0.1, 0.15, 0.2 were 0.1545, 0.1078, 0.1046 and 0.1701, respectively. 相似文献
6.
The effect of Al2O3 content on the structure, electrical properties, magnetic properties, and interparticle exchange interactions of (Fe65Co35)1 − x(Al2O3)x films with Al2O3 volume fractions x ranging from 0 to 0.50 was systematically investigated. Among the films with x between 0 and 0.25, the lowest coercivity of 0.56 kA/m was achieved in the (Fe65Co35)0.82(Al2O3)0.18 film. This is ascribed to the strongest exchange interactions between the Fe65Co35 nanoparticles in this film. Combined with the microstructure analysis of the (Fe65Co35)1 − x(Al2O3)x films, the modified Herzer's model was extended to interpret the variation of the coercivity with x and analyze the effect of the exchange interactions between the Fe65Co35 nanoparticles on the magnetic softness. The remanence curves confirm the existence of the exchange interactions and reveal the evolution of the exchange interaction strength with Al2O3 content. 相似文献
7.
We report formation of new noncentrosymmetric oxides of the formula, R3Mn1.5CuV0.5O9 for R = Y, Ho, Er, Tm, Yb and Lu, possessing the hexagonal RMnO3 (space group P63cm) structure. These oxides could be regarded as the x = 0.5 members of a general series R3Mn3−3xCu2xVxO9. Investigation of the Lu-Mn-Cu-V-O system reveals the existence of isostructural solid solution series, Lu3Mn3−3xCu2xVxO9 for 0 < x ≤ 0.75. Magnetic and dielectric properties of the oxides are consistent with a random distribution of Mn3+, Cu2+ and V5+ atoms that preserve the noncentrosymmetric RMnO3 structure. 相似文献
8.
The role of GB in Mg-substituted lanthanum-strontium manganite ceramics is studied with microstructural details. At higher concentrations of Mg (x>0.05), where the average grain size is ∼1 μm, the M-I transition is shifted from 348 to 110 K. Annealing in lower pO2 (10−6 atm) at 1375 K for 1 h obliterates the M-I transition and brings in insulating behaviour throughout the temperature of measurement. Re-annealing in oxygen atmosphere for 10-25 min reintroduces the M-I transition, indicating that the electrical transport properties depend on the chemical inhomogeneity introduced by the in- or out-diffusion of oxygen through the GB regions. Samples with larger grain size (∼35 μm) do not exhibit major modifications in electrical resistivity on annealing in different pO2. The insulating manganites display non-linear J-E characteristics below the magnetic transition temperature at electric field strengths <50 V/cm. The non-linear behaviour is explained on the basis of the inelastic tunnelling through the multiple localised states in the insulating GB regions. The external magnetic field lowers the voltage at which the non-linearity sets in. The tunnelling therefore may be not only through independent defect centres of oxygen vacancies (VO), but possibly from defect complexes such as Mn3+-VO or Mn2+-VO, where spin-dependent tunnelling can take place. 相似文献
9.
Chromium (Cr) is doped at the Mn site of La0.85Ca0.15MnO3 system to explore its complex ferromagnetic insulating (FMI) state. The Rietveld refinement of neutron diffraction data indicates that there is no structural change owing to Cr substitution in La0.85Ca0.15Mn1 − xCrxO3 (0 ≤ x ≤ 0.1). Nevertheless, it strengthens the magnetic couplings and the system shifts towards enhanced ferromagnetic (FM) ordering. Doping with Cr is found to stabilise the FMI state at low temperatures. The magnetic moment of the parent compound (for x = 0) obtained from neutron diffraction data recorded at low temperature (17 K) is found to be ~ 3.53(5) μB and is close to the theoretically estimated value of 3.85 μB. This value is higher than previously reported value of 2.90 μB. 相似文献
10.
R.V.K. Mangalam 《Materials Research Bulletin》2009,44(3):576-36
The ferromagnetic metallic oxide, SrRuO3 (TC ∼ 165 K) undergoes structural, magnetic and metal-insulator transitions upon substitution of Cu at the Ru-site. For x = 0.2 in SrRu1−xCuxO3, the structure becomes a tetragonal with the space group I4/mcm and there is a signature of both ferromagnetic (TC = 65 K) and antiferromagnetic (TN = 32 K) ordering due to possible magnetic phase separation. The antiferromagnetism arises due to short range ordering of Cu- and Ru-moments. Jahn-Teller distortion of (Ru,Cu)-O6 octahedra indicates that the copper ions are in 2+ oxidation state with 6t2g3eg electronic configuration. For x ≥ 0.1, narrowing of Ru-4d bandwidth by the substitution of Cu ions results in semiconducting behavior. For x = 0.3, the ac and dc susceptibility measurements indicate a spin glass behavior. The origin of spin glass behavior has been attributed to competing ferromagnetic and antiferromagnetic interactions. 相似文献
11.
Philipp M. Leufke Ajay Kumar MishraAndré Beck Di Wang Christian Kübel Robert KrukHorst Hahn 《Thin solid films》2012,520(17):5521-5527
Studies on large-distance sputtering as an effective alternative to molecular beam epitaxy, pulsed laser deposition or off-axis sputtering for the deposition of epitaxial La1 − xSrxMnO3 (LSMO) thin films, are reported. The focus of this study is on the quality of the samples and their structural and magnetic properties. The dependence of the characteristics of the LSMO films on the sputtering mode (rf, dc) and the sputtering parameters, in particular on the oxygen partial pressure is established and discussed. It is shown that large-distance sputtering can provide high quality LSMO thin films without the need for post-annealing. 相似文献
12.
Bulk metallic glasses (BMGs) Nd60Fe30 − xNixAl10 were prepared by suction cast method. The glass forming abilities (GFAs) and the hard magnetic properties of the BMGs were examined by differential scanning calorimeter (DSC) and vibrating sample magnetometer (VSM), respectively. The results show that the largest GFA (Tx / Tm = 0.61) of the alloys was obtained when Fe was substituted by 10% Ni and the rods of Nd60Fe20Ni10Al10 have the coercivity up to 323 kA/m and the remanence up to 9.41 Am2/kg as high as Nd-Fe-Co-Al, the Nd-Fe-based BMGs with highest hard magnetic properties up to date. The homogeneous distribution of Fe-rich nano-clusters, Nd(FeNiAl)2, in amorphous matrix is responsible for the enhancement. 相似文献
13.
La2−xBaxMo2O9−x/2 (x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La2−xBaxMo2O9−x/2 (x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18-0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La2Mo2O9 is defined in range of 0.18 < x < 0.2. As the replacement degree of La3+ by Ba2+ increases, the bulk conductivity of La2−xBaxMo2O9−x/2 (x ≤ 0.18) decreases initially and then increases, a minimum value at La1.9Ba0.1Mo2O8.95 exists. Hebb-Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La2−xBaxMo2O9−x/2 (x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La1.84Ba0.16Mo2O8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10−6 K−1 between 298 and 1173 K. 相似文献
14.
Ramakanta Naik 《Thin solid films》2010,518(19):5437-5441
In this paper, we report results of the optical properties of thermally deposited As2 − xS3 − xSbx thin films with x = 0.02, 0.07, 0.1 and 0.15. We have characterized the deposited films by Fourier Transform Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The relationship between the structural and optical properties and the compositional variation were investigated. It was found that the optical bandgap decreases with increase in Sb content. The XPS core level spectra show a decrease in As2S3 percentage with increase in Sb content. This is confirmed from the shifting of the Raman peak from AsS3 vibrational mode towards SbS3 vibrational mode. 相似文献
15.
Structure, magnetic and electrical transport properties of the polycrystalline (Fe3O4)100 − xPtx composite films fabricated using DC reactive magnetron sputtering at ambient temperature were investigated systematically. It is found that the films are composed of inverse-spinel-structured polycrystalline Fe3O4 and Pt. Pt addition proves the growth of Fe3O4 grains with the (111) orientation. All the films are ferromagnetic at room temperature. The dominant magnetic reversal mechanism turns from domain wall motion to Stoner-Wohlfarth rotation with the increasing x. The electrical transport mechanism also changes with the increasing x because Pt addition decreases the height of the tunneling barrier at the Fe3O4 grain boundaries, and makes the magnetoresistance of the films decrease. 相似文献
16.
Kamlesh Yadav M.P. Singh F.S. Razavi G.D. Varma 《Materials Science and Engineering: B》2012,177(14):1225-1231
The structural, magnetic, and electrical properties of Ln0.5Sr0.5Mn0.9Cu0.1O3 (Ln = La, Pr, Nd, or Ho) perovskite manganites have been investigated to explore the influence of A-site cation radius (〈rA〉) and the A-site cation size-disorder (σ2) on the various interdependent phenomena such as ferromagnetism (FM), phase separation (PS), and charge ordering (CO). The temperature dependence magnetization (M–T) curve of La-based sample shows four distinct points at ∼269 K, 255 K, 200 K, and 148 K corresponding to strong FM, cluster glass (CG), weak FM, and charged ordered antiferromagnetic (COAFM) transitions, respectively. Our investigation shows that Neel temperatures (TN) increases, whereas Curie (TC) and irreversibility temperatures (Tirr) decrease with decreasing 〈rA〉, i.e., with increasing σ2. Furthermore, the value of the magnetization decreases and resistivity increases with decreasing 〈rA〉. All samples exhibit insulating behavior in the temperature range 77–300 K and above 110 K the electronic conduction mechanism has been described within the framework of the variable range hopping (VRH) model. 相似文献
17.
Nanocrystalline La1−xCdxFeO3 (0.0 ≤ x ≤ 0.3) solid solutions have been synthesized by a single-step solution combustion method at a relatively low temperature of 400 °C. The combustion-synthesized solid solutions were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and magnetic measurements. The crystal structure examined by XRD indicates that the samples were single-phase, and crystallize in an orthorhombic (space group, Pbnm no. 62) structure. The parent and doped compounds showed canted antiferromagnetic behavior associated with an increase in magnetic moment with Cd doping. The changes in magnetic properties of the materials are correlated to the changes in structural features resulting from the Rietveld structural refinement of the materials. 相似文献
18.
We have investigated the magnetic and transport properties of the La0.5Ca0.5Mn1−xMoxO3 (0.0 ≤ x ≤ 0.1) compounds. Partial substitution of Mn by Mo destroys the charge-ordering (CO) phase and induces the ferromagnetic (FM) metallic transition at low temperatures in the samples. The thermo-magnetic irreversibility observed in both resistivity ρ (T) and magnetization M (T) curves suggest a competing scenario due to the coexistence of different phases in the Mo doped samples. In addition, a deviation from the Curie–Weiss behavior in the inverse susceptibility far above the Curie temperature (TC) indicates the existence of Griffiths phase (GP) in the Mo-doped compounds. The above results can be interpreted based on the induced Mn2+ species by Mo substitution in the La0.5Ca0.5Mn1−xMoxO3 system. 相似文献
19.
Cd1 − xZnxO nanocrystalline thin films with rock-salt structure were obtained through thermal decomposition of Cd1 − xZnxO2 (x = 0, 0.37, 0.57, 1) thin films which were electrodeposited from aqueous solution at room temperature. X-ray diffraction results showed that the Zn ions were incorporated into rock salt-structure of CdO and the crystal lattice parameters decreased with the increase of Zn contents. The bandgaps of the Cd1 − xZnxO thin films were obtained from optical transmission and were 2.40, 2.51, 2.63 and 3.25 eV, respectively. 相似文献
20.
We synthesized the spinel-type compounds belonging to the Mn2−xV1+xO4 series with x = 0, 1/3 and 1 as polycrystalline powders. Crystal and magnetic structures were refined using synchrotron X-ray and neutron powder diffraction. At 300 K all members crystallize in the cubic system, space group , and show a structural transition at low temperature, changing to a tetragonal symmetry (space group I41/amd). Cations distributions between octahedral and tetrahedral sites were refined from neutrons diffraction (ND) data and explained based on crystal field stabilization energies (CFSE) and ionic radii. The magnetic unit cell is the same as the crystallographic one, having identical symmetry relations. The magnetic structure was refined as an arrangement of collinear spins, antiferromagnetically ordered, parallel to the c-axis of the unit cell. The refined site magnetic moments are smaller than those obtained from hysteresis cycles of the M vs. H measurements, indicating that some non-collinear disordered component coexists with the ordered component along the c-axis. 相似文献