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1.
采用溶胶-凝胶法制备出钙钛矿型纳米BaFeO3粉末,利用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)分析研究了其微观结构及形貌,结果表明:胶体试样经800℃退火处理后,形成了20nm左右的钙钛矿型BaFeO3粉末,其(110)面晶面间距为0.280nm左右,(100)面晶面间距为0.401nm左右.利用振动样品磁强计(VSM)研究了纳米BaFeO3粉末的室温铁磁性能,测量结果表明:在室温条件下,纳米BaFeO关键词:
溶胶-凝胶法
3')" href="#">钙钛矿型纳米BaFeO3
铁磁性
氧空位 相似文献
2.
Polycrystalline LaFe1?xNixO3 (x = 0.0, 0.1, 0.3 and 0.5) have been prepared by the standard solid state reactions method. The phase formation has been confirmed by the powerful synchrotron X-ray diffraction experiment. In order to investigate the effects of Ni doping on the oxidation state, spin state and the magnetic ordering of the iron cations, 57Fe Mössbauer Spectroscopy has been carried out at room temperature. Iron is present as Fe3+ in high spin state in LaFeO3. Ni doping has no effect on the spin state of the Fe3+ cations. However, a progressive increase in the concentration of Fe4+ cations has been inferred. Relatively stronger covalent character of the Fe4+–O?2 bond causes a progressive collapse in the magnetic ordering and delocalization of the hole states. 相似文献
3.
The magnetic property of double doped manganite Nd0.5(1+x)Ca0.5(1−x)Mn(1−x)CrxO3 with a fixed ratio of Mn3+:Mn4+=1:1 has been investigated. For the undoped sample, it undergoes one transition from charge disordering to charge ordering (CO) associated with paramagnetic (PM)-antiferromagnetic (AFM) phase transition at T<250 K. The long range AFM ordering seems to form at 35 K, rather than previously reported 150 K. At low temperature, an asymmetrical M-H hysteresis loop occurs due to weak AFM coupling. For the doped samples, the substitution of Cr3+ for Mn3+ ions causes the increase of magnetization and the rise of Tc. As the Cr3+ concentration increases, the CO domain gradually becomes smaller and the CO melting process emerges. At low temperature, the FM superexchange interaction between Mn3+ and Cr3+ ions causes a magnetic upturn, namely, the second FM phase transition. 相似文献
4.
Thin films of Ge100−xFex (x in at%) alloys, fabricated by thermal co-evaporation, have an amorphous structure at compositions x<∼40, although an unidentified crystalline phase with an FCC symmetry also exists at low Fe content. Magnetization versus temperature curves show that saturation magnetization is non-zero (1 to 2.5 emu/cm3) and remains nearly unchanged up to the highest measured temperature of 350 K. Magnetic hysteresis loops at room temperature show a typical ferromagnetic shape, complete saturation occurring by 1–2 kOe. These results may indicate ferromagnetic ordering at room temperature. No definite tendency is observed in the compositional dependence of saturation magnetization. 相似文献
5.
Mössbauer spectroscopic studies of BaFeO4 and K2FeO4 as prepared, then either sealed, or exposed to air, or exposed to moist air for a period up to more than one year, were performed at room temperature as a function of time. Some of the samples were studied as a function of temperature down to 4.2 K. K2FeO4 and BaFeO4 after preparation, exhibit a pure Fe6+ spectrum. K2FeO4 shows low stability. After a period of 14 months in a sealed sample holder, the spectrum exhibits 83% noncrystalline Fe3+, as Fe2O3 nanoparticles, and only 17% of the original Fe6+. BaFeO4 sealed, or exposed to dry air disintegrates slowly, exhibiting a spectrum composed of three subspectra. In addition to the original Fe6+ and final Fe3+ subspectra, a subspectrum, of an intermediate stage of a crystalline Fe4+ system, is present. In the first month the increase of the Fe3+ subspectrum is 15%, and that of the Fe4+ is 8%. BaFeO4 exposed to moist air, disintegrates at a very fast rate. The Fe3+ subspectrum, due to Fe2O3 nanoparticles, increases in the first days at the rapid rate of ∼13%/day, and there is no evidence for Fe4+ in the spectrum. The Fe6+ in BaFeO4, Fe3+ and Fe4+ in the disintegrated systems are all magnetically ordered at 4.2 K. Above 90 K the Fe3+ subspectra exhibit a superposition of a paramagnetic doublet and a diffuse magnetic sextet, with relative intensities changing with temperature, and changing from sample to sample according to their blocking temperatures, which are determined by the distribution in size of the nanoparticles. 相似文献
6.
Magnetization and susceptibility were investigated as a function of temperature and magnetic field in polycrystalline Mn[Cr0.5Ga1.5]S4 spinel. The dc susceptibility measurements at 919 Oe showed a disordered ferrimagnetic behaviour with a Curie-Weiss temperature θCW=−55 K and an effective magnetic moment of 5.96 μB close to the spin-only value of 6.52 μB for Cr3+ and Mn2+ ions in the 3d3 and 3d5 configurations, respectively. The magnetization measured at 100 Oe revealed the multiple magnetic transitions with a sharp maximum at the Néel temperature TN=3.9 K, a minimum at the Yafet-Kittel temperature TYK=5 K, a broad maximum at the freezing temperature Tf=7.9 K, and an inflection point at the Curie temperature TC=48 K indicating a transition to paramagnetic phase. A large splitting between the zero-field-cooled (ZFC) and field-cooled (FC) magnetizations at a temperature smaller than TC suggests the presence of spin-glass-like behaviour. This behaviour is considered in a framework of competing interactions between the antiferromagnetic ordering of the A(Mn) sublattice and the ferromagnetic ordering of the B(Cr) sublattice. 相似文献
7.
Temperature and field-dependent magnetization measurements on polycrystalline CeMnCuSi2 reveal that the Mn moments in this compound exhibit ordering with a ferromagnetic (FM) component ordered instead of the previously reported purely antiferromagnetic (AFM) ordering. The FM ordering temperature, Tc, is about 120 K and almost unchanged with external fields up to 50 kOe. Furthermore, an AFM component (such as in a canted spin structure) is observed to be present in this phase, and its orientation is modified rapidly by the external magnetic field. The Ce L3-edge X-ray absorption result shows that the Ce ions in this compound are nearly trivalent, very similar to that in the heavy fermion system CeCu2Si2. Large thermomagnetic irreversibility is observed between the zero-field-cooled (ZFC) and field-cooled (FC) M(T) curves below Tc indicating strong magnetocrystalline anisotropy in the ordered phase. At 5 K, a metamagnetic-type transition is observed to occur at a critical field of about 8 kOe, and this critical field decreases with increasing temperature. The FM ordering of the Mn moments in CeMnCuSi2 is consistent with the value of the intralayer Mn–Mn distance RaMn–Mn=2.890 Å, which is greater than the critical value 2.865 Å for FM ordering. Finally, a magnetic phase diagram is constructed for CeMnCuSi2. 相似文献
8.
E. M. Alakshin E. I. Kondratyeva V. V. Kuzmin K. R. Safiullin A. A. Stanislavovas A. V. Savinkov A. V. Klochkov M. S. Tagirov 《JETP Letters》2018,107(2):111-114
The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.67%) and DyF3 (0.33%) micropowders at temperatures of 1.5–3 K has been studied by pulsed nuclear magnetic resonance (NMR). The DyF3 is a dipolar dielectric ferromagnet with the phase transition temperature Tc= 2.55 K, whereas the diamagnetic fluoride LaF3 is a diluting substance for the optimal observation conditions of 3Не NMR in powder pores. The magnetic phase transition in DyF3 is accompanied by a considerable change in the character of fluctuations of the magnetic moments of dysprosium ions, which affect the spin kinetics of 3Не in contact with the substrate. Significant changes in the relaxations rates of the longitudinal and transverse magnetizations of 3Не have been discovered in the region of magnetic ordering of the solid matrix. The technique of studying the static and fluctuating magnetic fields of a solid matrix at low temperatures using liquid 3He as a probe has been proposed. 相似文献
9.
X.H. Zhang Z.Q. Li W. Song P. Wu H.L. Bai E.Y. Jiang 《Solid State Communications》2005,135(6):356-360
The structural and magnetic properties of Pr0.75Na0.25MnO3 have been investigated experimentally. At room temperature, the compound shows paramagnetic characteristic. Along with decreasing temperature, a peak appears in the magnetization versus temperature curve around 220 K. To clarify whether this peak is associated with the ordering arrangement of Mn3+ and Mn4+ ions, electron diffraction experiments were carried out below and above 220 K respectively. Only basic Brag diffraction spots can be observed at high temperatures, however, superlattice diffraction appears below 220 K. This provides direct evidence for the existence of charge ordering in Pr0.75Na0.25MnO3. We find the Mn3+ and Mn4+ cations form zigzag chains in a-c plane by analyzing the diffraction patterns. Combining with the magnetization measurements and the results of electron spin resonance, we confirm the antiferromagnetic phase and ferromagnetic component coexist in Pr0.75Na0.25MnO3 below 120 K. 相似文献
10.
M.A. White N.W. Granville L.A.K. Staveley 《Journal of Physics and Chemistry of Solids》1982,43(4):341-349
The heat capacity of the layer compound, tetrachlorobis (methylammonium) manganese II, (CH3NH3)2MnCl4, has been measured over the range 10K <T<300K. In this region, two structural phase transitions have been observed previously by other techniques: one transition is from a monoclinic low temperature (MLT) phase to a tetragonal low temperature (TLT) phase, and the other is from TLT to an orthorhombic room temperature (ORT) phase. The present experiments have shown that the lower transition (MLT→TLT) occurs at T = 94.37±0.05K with ΔHt = 727±5 J mol?1 and ΔSt = 7.76±0.05 J K?1 mol?1, and the upper transition (TLT→ORT) takes place at T = 257.02±0.07K with ΔHt = 116±1J mol?1 and ΔSt = 0.451±0.004 J K?1mol?1. These results are discussed in the light of recent measurements on (CH3NH3)2CdCl4, and also with regard to a recent theoretical model of the structural phase transitions in compounds of this type.In addition to the structural phase transitions, (CH3NH3)2MnCl4 also undergoes magnetic ordering at T < 150K. The magnetic component to the heat capacity, as deduced from a corresponding states comparison of the heat capacity of the present compound with that of the Cd compound, is shown to be consistent with the behaviour expected for a quasi 2-dimensional Heisenberg antiferromagnet. 相似文献
11.
Daniel Martins de Almeida Carlos Angelo Nunes Gilberto Carvalho Coelho 《Journal of magnetism and magnetic materials》2009,321(17):2578-2581
In this work the Mn5Si3 and Mn5SiB2 phases were produced via arc melting and heat treatment at 1000 °C for 50 h under argon. A detailed microstructure characterization indicated the formation of single-phase Mn5Si3 and near single-phase Mn5SiB2 microstructures. The magnetic behavior of the Mn5Si3 phase was investigated and the results are in agreement with previous data from the literature, which indicates the existence of two anti-ferromagnetic structures for temperatures below 98 K. The Mn5SiB2 phase shows a ferromagnetic behavior presenting a saturation magnetization Ms of about 5.35×105 A/m (0.67 T) at room temperature and an estimated Curie temperature between 470 and 490 K. In addition, AC susceptibility data indicates no evidence of any other magnetic ordering in 4-300 K temperature range. The magnetization values are smaller than that calculated using the magnetic moment from previous literature NMR results. This result suggests a probable ferrimagnetic arrangement of the Mn moments. 相似文献
12.
The study of the structural and magnetic phase diagram of the manganites La1−xAgxMnO3 shows similarity with the La1−x′Srx′MnO3 series, involving a metallic ferromagnetic domain at relatively high temperature (≈300 K). The Ag-system differs from the Sr-one by a much smaller homogeneity range (x≤1/6) and the absence of charge ordering. But the most important feature of the Ag-manganites deals with the exceptionally high magnetoresistance (−25%) at room temperature under 1.2 T, that appears for the composition x=1/6. The latter is interpreted as the coincidence of the optimal double exchange condition (Mn3+:Mn4+=2) with Tmax=300 K (maximum of the ρ(T) curve in zero field). 相似文献
13.
I. de Pedro D.P. RojasJesús A. Blanco J. Rodríguez Fernández 《Journal of magnetism and magnetic materials》2011,323(10):1254-1257
The magnetic ionic liquids (MILs) are considered to open up a wide range of applications because of their magnetic and electrochromic switching. Until recently almost all magnetic ionic liquids containing tetrachloroferrate ion FeCl4− evidenced a paramagnetic temperature dependence of the magnetic susceptibility, with only small deviations from the Curie law at low temperatures. However, 1-ethyl-3-methylimidazolium tetrachloroferrate, Emim[FeCl4], clearly exhibits a long-range antiferromagnetic ordering below the Neel temperature TN≈3.8 K. In addition, the shape of the magnetic ordering depends on the cooling speed, indicating that the magnetic coupling could be modified. 相似文献
14.
《Journal of magnetism and magnetic materials》2003,262(3):458-464
The antiferromagnetic body-centred tetragonal compound GdNi2Ge2 orders at 28 K. Successive magnetic phase transitions are observed by specific-heat and magnetisation measurements as a function of temperature in different applied magnetic fields. Plots of M2 vs. B/M (Arrott-plots) show various anomalies. On the basis of the experimental results, a magnetic phase diagram is constructed. The multiple magnetic phase transitions are discussed in terms of competing ordering modes in the Gd sublattice. 相似文献
15.
S. ChattopadhyayT.K. Nath A.J. BehanJ.R. Neal D. ScoreQ. Feng A.M. FoxG.A. Gehring 《Journal of magnetism and magnetic materials》2011,323(8):1033-1039
Epitaxial films of ZnO doped with magnetic ion Fe and, in some cases, with 1% Al show clear evidence of room temperature ferromagnetic ordering. The Al doped optimized samples with carrier concentration nc∼8.0×1020 cm−3 show about 3 times enhanced saturation magnetization (0.58 μB/Fe2+) than the one with nc∼3.0×1020 cm−3 (0.18 μB/Fe2+). A clear correlation between the magnetization per transition metal ion and the ratio of the number of carriers to the number of donors have been found as is expected for carrier-induced room temperature ferromagnetism. The transport mechanism of the electrons in all the DMS films at low temperature range has been identified with the Efros's variable range hopping due to the electron-electron Coulomb interaction. 相似文献
16.
Polycrystalline double perovskite LaNi1−xMnxO3 (x=0.3, 0.4, 0.5 and 0.7, which is defined as Mn03, Mn04, Mn05 and Mn07, respectively) thin films are successfully deposited on Si (1 0 0) substrates via chemical solution deposition method. Their structural and magnetic properties are measured. All the thin films are of single phase. Raman spectra indicate that relative intensity of Mn05 is stronger than that of others that can be attributed to the higher degree of B-site ordering. The low temperature magnetic moment of Mn05 is about 500 emu/cm3, which is obviously larger than that of Mn03 and Mn07 because of the long-range ordering of Mn and Ni ions in Mn05. 相似文献
17.
Kamlesh Yadav M. P. Singh H. K. Singh F. S. Razavi G. D. Varma 《Applied Physics A: Materials Science & Processing》2013,111(3):845-851
We have studied structure, magnetic and transport properties of polycrystalline Bi0.6?x Nd x Ca0.4MnO3 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6). Substitution of Nd at Bi sites induces a strong interplay between the magnetic and charge ordering. The charge-ordering temperature (T CO) decreases with increasing x. Further, the antiferromagnetic ordering temperature (T N) increases sharply at both extremes and remains nearly constant for x=0.2–0.4. At T<T N a transition to a metamagnetic glass-like state is also seen. Nd doping also leads to enhancement in the magnetic moment and a concomitant decrease in resistivity up to x=0.3 and then an increase in resistivity up to x=0.5. Furthermore, Nd doping promotes an antiferromagnetic to ferromagnetic type fluctuation in the materials at room temperature, as evidenced by the change in the value of the paramagnetic Curie temperature. We find that the local lattice distortion induced by the size mismatch between the A-site cations and the 6s2 character of Bi3+ lone pair electrons explains the observed peculiarity in magnetic and transport properties of Nd-doped Bi0.6Ca0.4MnO3. 相似文献
18.
A method based on strain-induced phase transformation was used to lower the ordering temperature of FePt films. The strain resulted from the lattice mismatch between the FePt film and the substrate or underlayer favored the ordering. The relationships between the lattice mismatch, the ordering of FePt film, and the corresponding magnetic anisotropic constant were investigated. A critical lattice mismatch near 6.33% was believed to be most suitable for improving the chemical ordering of the FePt films. CrX (X=Ru, Mo, W, Ti) alloys with (2 0 0) texture was used to control the easy axis and ordering temperature of FePt films on glass substrate. Large uniaxial anisotropy constant Ku?1×107 erg/cm3, good magnetic squareness (∼1) and FePt(0 0 1) texture (rocking curve −5°) were obtained at the temperature Ts?250 °C when using CrRu underlayer. The diffusion from overlying layers of Ag and Cu and an inserted Ag pinning layer were effective in reducing the exchange decoupling and changing the magnetization reversal. The media noise was effectively reduced and the SNR was remarkably enhanced when a 2 nm Ag was inserted. 相似文献
19.
A.P. Pyatakov A.M. Kadomtseva Yu.F. Popov A.K. Zvezdin M.M. Lukina 《Journal of magnetism and magnetic materials》2009,321(7):858-860
Complex magnetic, magnetoelectric and magnetoelastic studies of spontaneous and field-induced phase transitions in TmMn2O5 were carried out. In the vicinity of spontaneous phase transition temperatures (35 and 25 K) the magnetoelectric and magnetoelastic dependences demonstrated the jumps of polarization and magnetostriction induced by the field ∼150 kOe. These anomalies can be attributed to the influence of magnetic field on the conditions of incommensurate-commensurate phase transition at 35 K and the reverse one at 25 K. In b-axis dependences the magnetic field-induced spin-reorientation phase transition was also observed below 20 K. Finally the magnetoelectric anomaly associated with metamagnetic transition is observed below the temperature of rare-earth subsystem ordering at relatively small critical fields of 5 kOe. This variety of spontaneous and induced phase transitions in RMn2O5 stems from the interplay of three magnetic subsystems: Mn3+, Mn4+, R3+. The comparison with YMn2O5 highlights the role of rare earth in low-temperature region (metamagnetic and spin-reorientation phase transitions), while the phase transition at higher temperatures between incommensurate and commensurate phases should be ascribed to the different temperature dependences of Mn3+ and Mn4+ ions. The strong correlation of magnetoelastic and magnetoelectric properties observed in the whole class of RMn2O5 highlights their multiferroic nature. 相似文献
20.
The mechanical spectrum measurement was performed in ceramic La0.5Sr0.5FeO3?δ from liquid nitrogen temperature to room temperature at kilohertz frequencies. From temperature dependent reduced modulus, a kink (corresponding temperature labeled as TM) was observed which evidenced a phase transition by the mechanical spectrum at two flexural resonance frequencies. This elastic manifested phase transition is a charge disproportionation transition. Around 170 K, an internal friction peak (labeled as P1) was observed accompanied with a large modulus hardening with the decrease in temperature. Two mechanisms are proposed for P1 peak, one is elastic manifestation of magnetic freezing, and the other is the ordering or freezing of oxygen vacancies. 相似文献