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1.
A crystal and magnetic structure of manganites Pr0.7Ca0.3Mn1?y Fe y O3 (y = 0, 0.1) has been studied by means of powder neutron diffraction at pressures up to 4 GPa in the temperature range 15-300 K. Under high pressure, an appearance of A-type antiferromagnetic state in both systems was observed. Both compounds exhibit anisotropic compression of the lattice which leads to the apical compression of MnO6 octahedra along the crystallographic b-axis. The calculated from obtained structural data pressure dependence of the charge-carrier bandwidth is in a qualitative agreement with observed pressure behavior of insulator-metal transition temperature within the framework of the double-exchange model. 相似文献
2.
Jiangying Wang Xiaoying Zhang Jingji Zhang Huiling Li Zhengfa Li 《Journal of Physics and Chemistry of Solids》2012,73(7):957-960
Dielectric and piezoelectric properties of (1?x)Ba0.7Sr0.3TiO3?xBa0.7Ca0.3TiO3 (BST?xBCT) (x=0.2–0.9) perovskite ceramics have been investigated. BCT has fully incorporated into BST lattice, forming a complete perovskite solid solution, whose lattice constant χ decreases almost linearly with increase in x from 0.2 to 0.4, while showing an anomalous expansion at 0.4<x≤0.6. This, together with the deviation of tetragonal–orthorhombic phase transition temperature (TO–T) from the linear relation TO–T (K)=?103.7x+239.3 at x=0.5, suggests that a small amount of Ca2+ has substituted for Ti4+. Curie temperature TC increases linearly with increase in x from 0.2 to 0.9, which is mainly contributed to the increase of the Ba/Sr ratio. The calculated degree of relaxation (γ) is in the range of 1.41–1.53, indicating that the BST–xBCT ceramics are ferroelectric materials with diffuse phase transition. Strain and piezoelectric constant (d33) decrease with increasing x, whereas planar electromechanical coefficient (kp) reaches a maximum (17.0%) at x=0.6. 相似文献
3.
T. S. Orlova J. -Y. Laval V. S. Zakhvalinskiĭ Yu. P. Stepanov 《Physics of the Solid State》2006,48(11):2115-2124
The formation and specific features of the superstructure in La0.33Ca0.67Mn1?y Fe y O3 (y = 0, 0.05) manganites doped with iron are investigated using transmission electron microscopy. The electron diffraction patterns of the manganites are studied in the temperature range 90–300 K, and the high-resolution electron microscope images recorded at temperatures of 91–92 K are analyzed. In both manganites, the structural transition that is accompanied by the formation of the superstructure and which is directly observed from the appearance of additional peaks in the electron diffraction patterns occurs at a temperature that is in close agreement with the charge ordering temperature T CO determined from the temperature dependences of the magnetization M(T). In the temperature range 90 < T < 200 K, the undoped compound has a commensurate superstructure characterized by the vector q = 1/3a* and triple the unit cell «3a × b × c» (where a ≈ b ≈ √2a c , c ≈ 2a c , and a c ~ 3.9 Å is the lattice parameter of a simple perovskite). The doping with iron (5 at. %) brings about a decrease in the charge ordering temperature T CO by 50 K and the formation of an incommensurate structure for which the magnitude of the vector q is smaller by approximately 15%. The unit cell of the superstructure in the iron-doped compound is not triple the unit cell but involves defects of ordering, such as quadrupling of the unit cell, numerous translations by a c √2 along the a direction, and dislocation-type defects in the stripe structure of the charge ordering. These pseudoperiodic defects lead to a decrease in the magnitude of the vector q and are responsible for the incommensurability of the structure. A decrease in the charge ordering temperature T CO due to the doping with iron and the incommensurability of the superstructure correlate with the change in the concentration of Mn3+ Jahn-Teller ions as a result of their replacement by Fe3+ non-Jahn-Teller ions. 相似文献
4.
I. O. Troyanchuk D. D. Khalyavin S. V. Trukhanov G. N. Chobot H. Szymczak 《JETP Letters》1999,70(9):590-594
The magnetization and magnetoresistance are studied in La0.5Ca0.5MnO3−γ as a function of oxygen content. It is found that as the oxygen content is decreased, this compound undergoes a sequence
of transitions from an antiferromagnetic to a ferromagnetic state (γ⩾0.04), from the ferromagnetic to a spin-glass state (γ
⩾0.14), and from the spin glass to an inhomogeneous ferromagnetic state (γ⩾0.25). Strongly reduced samples (γ⩾0.25) show a
large magnetoresistance despite the absence of Mn3+–Mn4+ pairs. It is suggested that the oxygen vacancies in the strongly reduced samples (γ⩾0.25) are long-range ordered.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 9, 583–587 (10 November 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
5.
AbstractIn this work, La0.75Ca0.25FeO3?δ perovskite sample was prepared by the coprecipitation method. The nanoparticle was found to crystallize in the orthorhombic (Pbnm) phase as confirmed by X-ray diffraction (XRD) and transmission electron microscopic (TEM). The oxygen non-stoichiometry (δ) and magnetic states of iron ions (three magnetic sextets and non-magnetic doublet) were investigated by Mössbauer spectroscopy at room temperature (RT). The shape of the magnetic hysteresis loop of the sample reveals the existence of a weak ferromagnetism at RT. The magnetization vs. temperature curves, measured in the 9 to 200 K range, showed that the sample exhibits two magnetic-phase transition temperatures at 29 K (Tg) and 120 K (TCO). The magnetization isotherms, M (H), around these magnetic-phase transition temperatures for the sample are analyzed. 相似文献
6.
Ji Ma Mya Theingi Hui Zhang Qingming Chen Xiang Liu 《Applied Physics A: Materials Science & Processing》2014,114(4):1075-1078
Tilted La1?x Ca x MnO3 (0.1 ≤ x ≤ 0.7) thin films have been grown on vicinal cut LaAlO3 (100) substrate by pulsed laser deposition. The laser-induced voltage effect was studied at room temperature with the KrF excimer laser using as the thermal source. The relationships between Ca doping level and voltage signal, response time and anisotropy Seebeck coefficient were established. The voltage signal and anisotropy Seebeck coefficient increase at first with increasing Ca doping level, reach a maximum at the same Ca content around x = 0.5, and then decrease. The respond time decreases with the Ca concentration increasing, and changes very little after x = 0.5. The figure of merit F m was also the largest at this doping level, indicating a potential good performance of the photodetector devices. The variation of intrinsic structural and transport anisotropy induced by the change of Ca concentration has been proposed to account for the different LIV effects observed in LCMO thin films. 相似文献
7.
Anowar Tozri Moez Bejar Essebti Dhahri EL Kébir Hlil 《Central European Journal of Physics》2009,7(1):89-95
X-ray powder diffraction (XRD) and magnetic measurements were performed in order to investigate the effect of Na+ ion substitution for Ca2+ ions on the crystallographic structure, the character of magnetic ordering, and the effect of transition temperature in La0.7Ca0.3−x
Na
x
MnO3 manganites series (0 ⩽ × ⩽ 0.2). All samples crystallise in an orthorhombic structure with the Pnma space group. We have found a strong dependence of structural and magnetic properties on the cation-size disorder parameter
σ
2. The temperature dependence of magnetization of all samples obeys the Bloch T
3/2 law. The values of the spin wave constant at low temperature B increase with the increase of x and the Curie temperature decreases. It is concluded that the substitution of Ca by Na+ ions causes a decrease in total exchange integral Aof the samples.
相似文献
8.
9.
《Solid State Communications》2002,121(9-10):537-542
The structural, magnetic and electrical properties of the hole doped cobaltites, with compositions (La1−xRx)0.7Ba0.3CoO3 (0.0≤x≤1.0; R=Pr, Nd), have been studied. Substitutions of Pr and Nd for La destabilize the stoichiometric perovskite structure at the benefit of the ordered oxygen deficient perovskite ‘112’-type structure, due to decrease in size of the rare earth ion. Our studies show that for our synthesis condition, the samples of nominal compositions, R1−yBayCoO3 (R=Pr, Nd), can form with the perovskite structure only for y<0.3. In the single-phase regions, the thermo-magnetic irreversibility and coercive field increase with the substitution of Pr and Nd for La. The low temperature resistivity minimum and negative magneto-resistance in the insulating regions of these polycrystalline compounds have been ascribed to grain boundary effects. 相似文献
10.
N. A. Teplyakova N. V. Sidorov M. N. Palatnikov 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(4):304-306
The ferroelectric-antiferroelectric concentration phase transitions in solid solutions of Li x Na1 ? x Ta y Nb1 ? y O3, which are promising environmentally friendly (lead-free) ferropiezoelectric materials, are studied by means of Raman spectroscopy. 相似文献
11.
V. P. Pashchenko A. V. Pashchenko V. K. Prokopenko Yu. F. Revenko A. A. Shemyakov A. G. Sil’cheva 《Technical Physics》2012,57(11):1508-1513
Ceramic (La0.7Ca0.3)1 ? x Mn1 + x O3 samples are studied by X-ray diffraction, resistive, magnetic, 55Mn NMR, and magnetoresistance methods. The concentration changes of lattice parameter a of the cubic perovskite structure and its average ionic radius are in good agreement if the concentrations of anion and cation vacancies and nanostructured clusters with Mn2+ in the A positions increase with x. Phase transition temperatures T ms and T c weakly depend on x, and the electrical resistivity and the activation energy decrease substantially with increasing x due to a change in the imperfection of the perovskite structure. An analysis of the broad asymmetric 55Mn NMR spectra of the samples indicate a high-frequency Mn3+? Mn4+ electron superexchange and nonuniform magnetic and valence states of these ions because of a nonuniform distribution of ions and defects, which decrease the amplitude resonance frequency with increasing x. The magnetoresistive (MR) effect near phase-transition temperatures T ms and T c increases substantially with x and is caused by the effect of a magnetic field on the scattering of charge carriers by intracrystallite nanostructured heterogeneities of an imperfect perovskite structure. The second MR effect is located in the low-temperature range, is related to tunneling through mesostructural crystallite boundaries, and decreases weakly with increasing x. A correlation is found between the hyperstoichiometric manganese content, the imperfection of the perovskite structure, and the magnitude of the MR effect. 相似文献
12.
F. N. Bukhanko 《Journal of Experimental and Theoretical Physics》2013,116(4):593-603
The structural and magnetic phase transformations that occur in the system of self-doped La1 ? y Pr y MnO3 + δ (δ ≈ 0.1, 0 ≤ y ≤ 1) manganites in the temperature range 4.2–300 K are studied by X-ray diffraction and measuring the temperature and field dependences of dc magnetization. The low-temperature magnetic phase transformations induced by the substitution of Pr for La correlate well with the structural phase transformations at T = 300 K, which indicates a strong coupling of the electronic and magnetic subsystems of La1 ? y Pr y MnO3 + δ manganites with the crystal lattice. The anomalies of the magnetic and structural properties detected in this work in the form of peaks and inflection points in the concentration dependences of the magnetization and lattice parameters of the pseudocubic phase of La1 ? y Pr y MnO3 + δ (0.1 ≤ y ≤ 0.7) in the temperature range 4.2–300 K are explained in terms of the existing concepts of the effect of Fermi surface nesting on the renormalization of the density of states and the hole dispersion near E F in the presence of a strong coupling of holes with low-frequency optical phonons, which results in their transformation into quasiparticles. The narrow peak in the magnetization curve M(y) of La1 ? y Pr y MnO3 + δ that is detected near y = 0.3 at T = 4.2 K is assumed to correspond to the peak of coherence of quasiparticles with a low energy of coupling with the crystal lattice near E F, which was found earlier in the photoelectron emission spectra of manganites. The disappearance of the narrow magnetization peak with increasing Pr concentration is explained by the transition of charge carriers from the mode of “light” holes weakly coupled to one of the soft phonons to the mode of “heavy” holes strongly coupled to several phonons. The transition between phases with strongly different effective quasiparticle masses proceeds jumpwise; that is, it has features of the metal-insulator Mott transition and is accompanied by the transition from 3D to 2D quasiparticle motion in planes ab. 相似文献
13.
A. M. Kadomtseva Yu. F. Popov G. P. Vorob’ev K. I. Kamilov V. Yu. Ivanov A. A. Mukhin A. M. Balbashov 《Physics of the Solid State》2000,42(6):1110-1115
A study is reported on phase transitions in the La1?x SrxMnO3 system, both spontaneous and induced by a pulsed magnetic field of up to 250 kOe, accompanied by anomalies in magnetoelastic properties. The temperatures of the polaron (charge) and magnetic ordering, as well as those of structural transitions, are observed to be in good agreement with the results obtained by other methods. Jumps in the field dependence of longitudinal and transverse magnetostriction associated with field-induced orbital ordering have been found. A strong temperature dependence of the corresponding threshold fields is observed. 相似文献
14.
Roulin et al (1988), in one of their experimental papers, have presented a study of field-dependent entropy of high-purity YBa2Cu3O7???δ (YBCO) as a function of oxygen deficiency. In order to explain their experimental results, we have used phenomenological GL-theory of anisotropic HTSCs in the London limit in line with of our earlier paper (Pattanaik et al, Physica B405, 3234 (2010)). Moreover, to account for the applicability of the theory at high field, we have incorporated the effect of vortex overlapping in the London theory done by Nanda (1995). Here, we have presented the variation of change in entropy (ΔS) with magnetic field for different oxygen deficiencies δ?=?0, 0.04, and 0.06. On comparison, we found that our results are in good agreement with the experimental data of Roulin et al (1988). The variation of penetration depth (λ) and anisotropic ratio of effective masses (γ) with concentration is also presented. 相似文献
15.
Kh. G. Bogdanova A. R. Bulatov V. A. Golenishchev-Kutuzov M. M. Shakirzyanov 《Physics of the Solid State》2001,43(8):1572-1575
The propagation of ultrasonic waves at a frequency of 770 MHz in a La0.825Sr0.175MnO3 single crystal is investigated in the temperature range 350–150 K. It is found that the velocity, attenuation, and mode composition of ultrasonic waves change at temperatures of 315–280 and 220 K. These changes correlate with the structural and magnetic phase transitions and can be explained in terms of the Jahn-Teller distortions of the crystal lattice. 相似文献
16.
《Physics letters. A》1999,259(1):57-61
For insulating Eu1−xAxMnO3 (A = Ca, Sr; x = 0, 0.3) ceramics the magnetic properties depend on the thermomagnetic history of the sample and the maximum of initial magnetic susceptibility is located at T=TN, being independent of the AC field frequency. Magnetization isotherms are the superposition of the linear part and spontaneous magnetization. The maximum of electrical resistivity and colossal magnetoresistance are observed in the TN region. These properties are explained by the magnetic two-phase state. 相似文献
17.
Anuj Kumar Monika Mudgel V.P.S. Awana Hari Kishan 《Physica C: Superconductivity and its Applications》2010
In this paper we investigate the properties of polycrystalline series of Ru1?xCrxSr2Eu1.5Ce0.5Cu2O10?δ (0.0 ? x ? 0.40) by resistivity, XRD and dc magnetization measurements. EuRu-1222 is a reported magneto superconductor with Ru spins magnetic ordering at temperatures near 100 K and superconductivity occurs in Cu–O2 planes below Tc ? 40 K. The exact nature of Ru spins magnetic ordering is still being debated and no conclusion has been reached yet. In this work, we found the superconducting transition temperature Tc = 20 K from resistivity and dc magnetization measurements for pristine sample. DC magnetization measurements exhibited ferromagnetic like transition for all samples. 相似文献
18.
I.P. Studenyak M. Kranjčec V.E. Ponomaryov V.V. Panko L.M. Suslikov 《Phase Transitions》2013,86(6):497-502
Cu6PS5I1? ? ? x Cl x mixed crystals were grown using chemical vapour transport. Isoabsorption studies of optical absorption edge and optical polarization measurements were performed in the temperature range 77–320?K. The influence of anionic I?→?Cl substitution on the phase transitions in Cu6PS5I1? ? ? x Cl x mixed crystals is studied. Compositional dependence of the phase-transition temperatures is obtained and the x,T-diagram for Cu6PS5I1? ? ? x Cl x mixed crystals is constructed. 相似文献
19.
《Journal of magnetism and magnetic materials》1996,153(3):L260-L264
A powder neutron diffraction study on the giant magnetoresistive oxides Pr0.70Ca0.3−xSrxMnO3 has been performed versus temperature for x = 0.1 and 0.05. The first one, Pr0.7Ca0.3Sr0.1MnO3, exhibits the smaller R0/RH ratio (100 at 100 K) and evidences a transition from paramagnetic to ferromagnetic state as the temperature decreases (Tc = 170 K). The second sample, Pr0.70Ca0.25Sr0.05MnO3, that exhibits an extremely high R0/RH ratio (2.5 × 105 at 88 K), shows a transition from the paramagnetic state to an antiferromagnetic state and finally to a canted ferromagnetic state. The presence of an intermediate AF state explains the M(T) curves and the exceptional high magnetoresistive effect. The determination of the nuclear structure of these oxides confirms their ‘O3’ oxygen stoichiometry and evidences a contraction of the lattice parameters at the ferromagnetic transition. The evolution of the MnO distances shows a decrease of the Jahn-Teller distortion at the magnetic transition. 相似文献
20.
《Journal of Physics and Chemistry of Solids》2003,64(4):583-591
In this work we report crystallographic structure variations and the related modifications on the magnetic behavior of La0.7Ca0.3MnO3±δ introduced by heat-treatments in different synthesis atmospheric conditions. We have prepared polycrystalline ceramic samples using a modified polymeric precursors method, which produces highly homogeneous specimens.The use of argon atmosphere enlarges the crystalline c-axis as detected by Rietveld refinements. As a consequence, an improvement in the magnetic transition temperature TC of the samples was observed.Our results also indicate that different heat-treatment conditions change the magnetic interactions between the ferromagnetic (F) and antiferromagnetic (AF) structures of these systems. Our conclusions rely on the use of AC magnetic susceptibility measurements as the experimental tool for measuring these variations. 相似文献