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1.
Nabil Kallel Nejib Ihzaz Sami Kallel Ahmed Hagaza Mohamed Oumezzine 《Journal of magnetism and magnetic materials》2009,321(15):2285-2289
The structural, magnetic and transport properties of La0.5Sr0.5MnO2.88 and La0.5Sr0.5Mn0.5Ti0.5O3 samples have been investigated systematically. Indeed, this series has been considered to understand the influence of physical parameters such as oxygen deficiency and titanium doping effect in undoped La0.5Sr0.5MnO3 sample. Ceramic material based on La0.5Sr0.5MnO2.88 exhibits interesting behaviours of charge-ordering (CO), ferromagnetic (FM) states and a good conductivity down to the lowest temperatures. The substitution of Ti for Mn destroyed drastically the CO, damaged the motion of itinerant eg electrons and changed the local parameters of perovskite cell. A change of the structure from tetragonal to rhombohedral symmetry is observed causing a weakening of double-exchange interaction. The experiment results show that the suppression of the CO is sensitive to the variety of Mn3+/Mn4+ ratio. In a field of 8 T at 10 K, FM and CO phase can be evaluated to be ∼20:80 according to the μexp/μcal ratio for La0.5Sr0.5MnO2.88, whereas the CO state is suppressed for La0.5Sr0.5Mn0.5Ti0.5O3 sample, FM and anti-ferromagnetic (AFM) phase are coexisted and evaluated to be ∼54:46, respectively. 相似文献
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3.
Ru Xing Jian-jun Zhao Yi LuWu Hong-ye Lin Zheng Yang SunZhao-hua Cheng 《Physica B: Condensed Matter》2011,406(24):4569-4571
The magnetic properties of Ca-doped Nd0.5Sr0.5MnO3 have been studied by electron spin resonance (ESR) and dc magnetization measurements. The antiferromagnetic order and charge order are found to occur separately at TN=200 K and Tco=150 K, respectively. Compared to the undoped Nd0.5Sr0.5MnO3, the ferromagnetic correlations are suppressed by doping of the small Ca2+ ion. In addition, the antiferromagnetic transition temperature is enhanced to 200 K, which can be explained by an increase of superexchange interaction between Mn3+ and Mn4+ ions as their distance decreases. 相似文献
4.
F. Damay Z. Jirák M. Hervieu C. Martin A. Maignan B. Raveau G. André F. Bourée 《Journal of magnetism and magnetic materials》1998,190(3):221
The structural and magnetic transitions in Pr0.5Sr0.41Ca0.09MnO3 have been investigated by neutron diffraction and electron microscopy. Two structural transitions, Imma to I4/mcm and I4/mcm to Pmmn, are observed by decreasing the temperature. Two magnetic transitions, from a paramagnetic insulating to a ferromagnetic metallic and from a ferromagnetic metallic to an antiferromagnetic insulating states at TC=250 K and TN=180 K, respectively, are also observed. The structures of these three forms have been determined from neutron powder diffraction data. The first important result concerns the low temperature antiferromagnetic CE type and charge ordered structure, which has been refined in the Pmmn space group, without any constraint. This structure is completely long range ordered, with two Mn-sites, Mn3+ in tetragonally elongated octahedra, and Mn4+, off-centered in nearly regular octahedra. The second important point concerns the abrupt character of the structural transition from the I4/mcm to the Pmmn structure, without any appearance of incommensurability. The magnetic and transport properties of this compound are compared with those of Pr0.5Sr0.5MnO3. 相似文献
5.
Pawan Kumar R. PrasadR.K. Dwivedi H.K. Singh 《Journal of magnetism and magnetic materials》2011,323(21):2564-2568
A comparative study of the out-of-plane anisotropic magnetoresistance (AMR) in single crystalline and polycrystalline thin films of phase separated manganite Nd0.51Sr0.49MnO3 has been carried out. On-axis DC magnetron sputtering was used to deposit the single crystalline films (30 and 100 nm in thickness) on single crystal (0 0 1) LaAlO3 (LAO) and polycrystalline films (100 nm) on (1 0 0) Yttrium-stabilized ZrO2 (YSZ) substrates. The in-plane and out-of-plane magnetotransport properties of these films differ significantly. A large low field AMR is observed in all the films. AMR shows a peak below the insulator-metal transition temperature in the single crystalline films, while the same increases monotonically in the polycrystalline film. Relatively larger low field AMR (∼20% at T=78 K and H=1.7 kOe) in the polycrystalline films suggests the dominance of the shape anisotropy. 相似文献
6.
We have performed magnetization measurements and electron spin resonance (ESR) on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 (x = 0.1). Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K (~ Tc) and 185 K (~ TN), the system coexists of the paramagnetic phase and the ferromagnetic (FM) phase. Between 185 K and 140 K, the system coexists of the FM phase and the antiferromagnetic (AFM) phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba^2+ ions for the smaller Sr^2+ ions. 相似文献
7.
The transport properties and magnetic phase transitions of charge ordering manganites Nd0.5Sr0.5MnO3 have been investigated. From resistivity measurements, a continuous increase of resistivity upon the thermal cycling occurs at , and shows an instable behavior in the system. The experimental results of magnetization and electron-spin-resonance spectra indicate that the ferromagnetic phase and antiferromagnetic phase coexist in a broad temperature region. We think that the origin of the instability stems from an inhomogeneous strain yielded in the ferromagnetic interface, due to the competition among different phases. 相似文献
8.
M. P?ka?a K. P?ka?a J.F. Fagnard 《Journal of magnetism and magnetic materials》2010,322(21):3460-3463
The polycrystalline manganite La0.75Sr0.25MnO3 prepared by an alternative carbonate precipitation route reveals the rhombohedral perovskite structure. Magnetization isotherms measured up to 2 T are used to determine Curie temperature of 332 K by means of Arrott plot. Maximum of magnetic entropy change is found at Curie temperature. The relative cooling power equal to 64 J/kg for 1.5 T magnetic field, is superior as compared to the manganite with the same chemical composition from the sol-gel method. 相似文献
9.
The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La0.5Ca0.3Sr0.2MnO3 have been studied. The La0.5Ca0.3Sr0.2MnO3 can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔSM for the as-prepared sample is 0.88 J kg−1 K−1 at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg−1 K−1, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application. 相似文献
10.
Jiyu Fan Bo Hong Yangguang Shi Langsheng Ling Yuheng Zhang 《Journal of magnetism and magnetic materials》2010,322(22):3692-3695
The magnetic behavior and electronic transport in the half-doped manganite Nd0.5Ca0.25Sr0.25MnO3 have been investigated. The critical exponents are studied by using isothermal magnetization methods. The results show that the paramagnetic-ferromagnetic transition is second order and the magnetic interaction is satisfied with the prediction of three-dimensional Heisenberg model. The electronic transport belongs to the percolation mechanism. These findings demonstrate that the critical behavior of the magnetic transition and conductivity for manganites are related to Mn-site ordering degree. 相似文献
11.
M. Koubaa W. Cheikh-Rouhou Koubaa A. Cheikhrouhou 《Journal of magnetism and magnetic materials》2009,321(21):3578-3584
The effects of monovalent doping on the crystallographic, magnetic and magnetocaloric properties of La0.65Ba0.3M0.05MnO3 (M=Na, Ag, K) powder samples, elaborated using the solid state reaction method at high temperature, have been investigated. In our three samples the Mn4+ amount remains constant equal to 40%. The Rietveld refinement of the X-ray powder diffraction shows that all our synthesized samples are single phase and crystallize in the distorted rhombohedral system with R3¯c space group. All our studied samples undergo a paramagnetic–ferromagnetic transition with decreasing temperature. Using the Arrott plot, the second-order transition Curie temperature TC for M=Na, Ag and K is found to be 310, 300 and 290 K, respectively. The magnetic entropy change, deduced from isothermal magnetization curves, exhibits a maximum |ΔSMMax| of about 2.65, 2.82 and 2.66 J/kg K for M=Na, Ag and K, respectively, in a magnetic applied field change of 5 T. Although these values are modest, the magnetocaloric effect extends over a large temperature range leading to an important value of the relative cooling power (RCP). The RCP values exhibit a nearly linear dependence with the magnetic applied field. The refrigeration capacity in a magnetic applied field of 1 T is found to be 28.8, 27.8 and 25.6 J/kg for M=Na, Ag and K compounds. 相似文献
12.
通过室温下的中子衍射和磁性测量对多晶样品Nd0.5Sr0.4Pb0 .1MnO3 的结构和磁性进行了实验研究.中子衍射结果表明,该样品具有正交的钙钛矿结构,空间群 是Pnma,即结构发生了晶场畸变.由M-T和R-T曲线可知,居里温度TC=273 K ,其特征是随着温度的增加样品经历了从铁磁金属态转变到顺磁半导态,且转变温度T p=225 K;用锰氧化物晶场和双交换作用的竞争解
关键词:
结构
磁性
中子衍射
晶场畸变
p')" href="#">转变温度Tp
双交换作用 相似文献
13.
V.A. Ryzhov A.V. Lazuta P.L. Molkanov V.P. Khavronin A.I. Kurbakov V.V. Runov Ya.M. Mukovskii A.E. Pestun R.V. Privezentsev 《Journal of magnetism and magnetic materials》2012
The magnetic, transport and structural properties are studied for La0.83Sr0.17MnO3 and La0.82Sr0.18CoO3 single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т?>TC in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator–metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn3+ and Co3+ ions. 相似文献
14.
S. Kundu 《Journal of magnetism and magnetic materials》2010,322(16):2408-2414
We have thoroughly investigated the entire magnetic states of under-doped ferromagnetic-insulating manganite Nd0.8Sr0.2MnO3 through temperature-dependent linear and non-linear complex ac magnetic susceptibility measurements. This ferromagnetic-insulating manganite is found to have frequency-independent ferromagnetic to paramagnetic transition temperature at around 140 K. At around 90 K (≈T?) the sample shows a second frequency-dependent re-entrant magnetic transition as explored through complex ac susceptibility measurements. Non-linear ac susceptibility measurements (higher harmonics of ac susceptibility) have also been performed (with and without the superposition of a dc magnetic field) to further investigate the origin of this frequency dependence (dynamic behavior at this re-entrant magnetic transition). Divergence of 3rd harmonic of ac susceptibility in the limit of zero exciting field indicates a spin-glass-like freezing phenomena. However, large value of spin-relaxation time (τ0=10−8 s) and small value of coercivity (∼22 Oe) obtained at low temperature (below T?) from critical slowing down model and dc magnetic measurements, respectively, are in contrast with what generally observed in a canonical spin glass (τ0=10−12-10−14 s and very large value of coercivity below freezing temperature). We have attributed our observation to the formation of finite size ferromagnetic clusters which are formed as consequence of intrinsic phase separation and undergo cluster glass-like freezing below certain temperature in this under-doped manganite. The results are supported by the electronic- and magneto-transport data. 相似文献
15.
A. Rostamnejadi M. VenkatesanP. Kameli H. SalamatiJ.M.D. Coey 《Journal of magnetism and magnetic materials》2011,323(16):2214-2218
The La0.67Sr0.33MnO3 composition prepared by sol-gel synthesis was studied by dc magnetization measurements. A large magnetocaloric effect was inferred over a wide range of temperature around the second-order paramagnetic-ferromagnetic transition. The change of magnetic entropy increases monotonically with increasing magnetic field and reaches the value of 5.15 J/kg K at 370 K for Δμ0H=5 T. The corresponding adiabatic temperature change is 3.3 K. The changes in magnetic entropy and the adiabatic temperature are also significant at moderate magnetic fields. The magnetic field induced change of the specific heat varies with temperature and has maximum variation near the paramagnetic-ferromagnetic transition. The obtained results show that La0.67Sr0.33MnO3 could be considered as a potential candidate for magnetic refrigeration applications above room temperature. 相似文献
16.
Md.Motin Seikh Chandrabhas NarayanaSachin Parashar A.K. Sood 《Solid State Communications》2003,127(3):209-214
Brillouin scattering experiments are carried out to study the surface acoustic waves in Nd0.5Sr0.5MnO3 as a function of temperature in the range of 40-300 K covering the metal-insulator and charge-ordering phase transitions. The surface modes include surface Rayleigh wave, pseudo-surface acoustic wave (PSAW) and high velocity PSAW. The observed softening of the sound velocities for the surface modes below paramagnetic to ferromagnetic transition, Tc is related to the softening of the C44 elastic constant. The subsequent hardening of the sound velocity below the charge ordering transition temperature Tco is attributed to the coupling of the acoustic phonon to the charge ordered state via long range ordering of the strong Jahn-Teller (JT) distortion. 相似文献
17.
The structure and magnetic properties of Nd_{0.5}Pb_{0.5-x}Sr_xMnO_3 (0≤x≤0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state. Curie temperature T_C and the MI transition temperature T_p increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn-Teller electron-phonon coupling. 相似文献
18.
I. Bergenti V. Dediu E. Arisi M. Cavallini F. Biscarini C. Taliani M.P. de Jong C.L. Dennis J.F. Gregg M. Solzi M. Natali 《Journal of magnetism and magnetic materials》2007
La0.7Sr0.3MnO3 polycrystalline manganite thin films were grown on silicon (Si) substrates covered by SiOx amorphous native oxide. Curie temperatures of about 325 K were achieved for 70-nm-thick films. Strong room temperature XMCD signal was detected indicating high spin polarization at the surface. Cross-sectional TEM images show sharp interface between SiOx and manganite without signature of chemical reaction at the interface. Unusual sharp splitting of the manganite film was observed: on the top of a transition layer characterized by low crystalline order, a magnetically robust layer is formed. 相似文献
19.
Liping Chen Yuansha ChenYubin Ma Guijun LianYan Zhang Guangcheng Xiong 《Journal of magnetism and magnetic materials》2012,324(6):1189-1192
A series of Pr0.5Sr0.5MnO3 (PSMO) films with various thickness were epitaxially grown on substrates of (0 0 1)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT), LaAlO3 (LAO) and SrTiO3 (STO), and (0 1 1)-oriented STO using pulse laser deposition. Influence of epitaxial growth on phase competition was investigated. A ferromagnetic metal to antiferromagnetic insulator (FMM-AFI) transition upon cooling is present in both largely compressed situations deposited on LAO (0 0 1) and tensile cases deposited on STO (0 0 1) but absent in little strained films grown on LSAT (0 0 1), indicating that the antiferromagnetic insulating state is favored by strains. On the other hand, the 400 nm films deposited on (0 1 1)-oriented STO as well as LAO substrates show FMM-AFI transition. These results reveal that both the orientation of epitaxial growth and substrate-induced strain affect the FMM-AFI transition. 相似文献
20.
F. Genet S. Loridant C. Ritter G. Lucazeau 《Journal of Physics and Chemistry of Solids》1999,60(12):6521-2021
Polycrystalline samples and small single crystals of the perovskite BaCeO3 were studied by neutron diffraction and Raman spectrometry between 300 and 1200 K. The controversy about the phase transitions originally deduced from our previous Raman study and those observed since by neutron diffraction by Knight has stimulated this work. Pretransitional effects which are detected by Raman much before long-range ordering takes place can partly explain the above disagreement. A continuous monitoring of the structural changes by neutron diffraction and by Raman spectroscopy including polarization analysis has allowed discussion of the transition mechanisms: The first transition Pnma–Imma takes place at 573 K and is of second order. Although some modes soften when the temperature is raised as in many of these perovskite compounds the transition is likely partly displacive partly order–disorder. The Raman modes which disappear transform in modes at the X point of the Brillouin zone of the Imma phase. The second transition Imma–R
c takes place at 673 K and is first order. The last transition R
c–Pm3m occurs above 1200 K and the transition temperature which can be deduced by extrapolation to zero Raman intensity is in good agreement with neutron results. This second order transition is progressive and begins at about 400 K, the intermediate R
c structure appearing as an attempt for slowing down the structural evolution toward the cubic perovskite form. 相似文献