共查询到20条相似文献,搜索用时 15 毫秒
1.
NMR on 55Mn in the single-crystal manganite La0.6Pb0.4Mn0.86Ni0.14O3 (T
C
=242 K), which exhibits metallic conductivity below T
C
, is investigated in the temperature range 61–215 K. At low temperatures, together with a line corresponding to the averaged
hyperfine field at the 55Mn nuclei (the averaging is due to the motion of electronic holes along Mn sites), the NMR spectrum also contains two lines
corresponding to localized states Mn4+ and Mn3+. In the temperature range 100–200 K it is found that the complicated NMR spectrum is transformed into a single line on account
of a delocalization of the holes in the e
g
orbitals of manganese. A comparison of the NMR data with the temperature dependence of the resistivity suggsets that a wide
distribution of charge-carrier mobilities exists in the crystal.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 522–527 (25 October 1999) 相似文献
2.
K. N. Mikhalev S. A. Lekomtsev A. P. Gerashchenko V. E. Arkhipov A. V. Korolev Ya. M. Mukovskii A. A. Arsenov 《JETP Letters》2000,72(12):599-602
Magnetic susceptibility of the La0.9MnO3 single crystal was measured and its (139La, 55Mn) NMR spectra were recorded. The data obtained indicate that the areas with an A-type antiferromagnetic order (T N=140 K) and magnetic moments aligned with the b axis occupy a major part of the sample volume in manganite with a considerable concentration of cationic vacancies; simultaneously, the clusters with a canted magnetic sublattice and ferromagnetic interaction between magnetic moments are formed near the vacancies. Charge distribution in these clusters is materially different from that in the antiferromagnetic areas. Magnetic state and relative concentration of the clusters are discussed. 相似文献
3.
ZHANG Ruili DAI Jianming SONG Wenhai MA Yongqing YANG Jie & SUN Yuping . Key Laboratory of Internal Friction Defects in Solids Institute of Solid State Physics Chinese Academy of Sciences Hefei China . National Laboratory of Solid State Microstructures Nanjing University Nanjing China Correspondence should be addressed to Zhang Ruili 《中国科学G辑(英文版)》2004,47(1)
1IntroductionWiththediscoveryofcolossalmagnetoresistance(CMR)effectinmanganites,hole-dopingperovskitemanganiteswithunusualelectronictransportandmagneticpropertieshaveattractedconsiderableattention.Thesepropertiesresultfromanintrinsicinteractionbetweencharge,spin,orbitalandlatticedegreesoffreedomthatarestronglycoupledtoeachother[1—6].DoubleexchangemodelcombinedwithJohn-Tellereffectwasusedtoexplainthesepropertiespartly[7—9].InordertogetbetterunderstandingofthemechanismofCMReffect,externals… 相似文献
4.
Moussa F Hennion M Wang F Gukasov A Suryanarayanan R Apostu M Revcolevschi A 《Physical review letters》2004,93(10):107202
The bilayer manganite La1.2Sr1.8Mn2O7 exhibits a phase transition from a paramagnetic insulating (PI) to a ferromagnetic metallic (FM) state with a colossal magnetoresistance (CMR) effect. Upon 60% Pr substitution, magnetic order and PI to FM transition are suppressed. Application of a moderate magnetic field restores an FM state with a CMR effect. Neutron scattering by a single crystal of (La0.4Pr0.6)1.2Sr1.8Mn2O7, under a magnetic field of 5 T, has revealed a long-range and homogeneous ferromagnetic order. In the PI phase, under zero field, correlated lattice polarons have been detected. At 28 K, under 5 T, the spin wave dispersion curve determines an in-plane isotropic spin wave stiffness constant of 146 meV A(2). So the magnetic field not only generates a homogeneous ferromagnetic ground state, but also restores a magnetic coupling characteristic of FM CMR manganites. 相似文献
5.
S. A. Lekomtsev K. N. Mikhalev A. Yu. Yakubovskiĭ A. R. Kaul 《Journal of Experimental and Theoretical Physics》2006,102(4):671-676
The spin-lattice and spin-spin relaxation times of 139La are measured in manganite LaMnO3. Analysis of the frequency dependence of the spin-lattice relaxation rate in the paramagnetic temperature range shows that this quantity is determined by magnetic fluctuations. The magnitude of the fluctuating field is estimated. It is shown that the correlation time for spin fluctuations varies with temperature in accordance with the Arrhenius law. The high value of the spin-spin relaxation rate in the paramagnetic region can be due to strong anisotropy of fluctuating magnetic fields at La nuclei. 相似文献
6.
In order to gain insights into the origin of colossal magnetoresistance (CMR) in manganese oxides, we performed a 139La NMR study in the double-layered compound La(1.2)Sr(1.8)Mn2O7. We find that above the Curie temperature T(C) = 126 K, applying a magnetic field induces a long-range ferromagnetic order that persists up to T = 330 K. The critical field at which the induced magnetic moment is saturated coincides with the field at which the CMR effect reaches a maximum. Our results therefore indicate that the CMR observed above T(C) in this compound is due to the field-induced ferromagnetism that produces a metallic state via the double exchange interaction. 相似文献
7.
Ali Osman Ayaş Mustafa Akyol Selda Kılıç Çetin Melike Kaya İlker Dinçer Ahmet Ekicibil 《哲学杂志》2013,93(9):671-682
AbstractIn this work, we have studied on double-layered perovskite (Ruddlesden–Popper) manganite structure in Pr1.75Sr1.25Mn2O7 synthesised by sol–gel method. The crystal structure of the double-layered perovskite is found as tetragonal from the X-ray diffraction analysis with I4/mmm space group. A high Curie temperature, TC = 305 K is observed from the temperature dependence of magnetisation measurement. The isothermal magnetisation curves showed that magnetic phase transition is second order due to the positive slope of the Arrott plots. Maximum magnetic entropy change (ΔSM) and adiabatic temperature change (ΔTad) values are calculated as 3.99 J kg?1 K?1 and 2.1 K under external magnetic field of 70 kOe, respectively. Since our double-layered perovskite manganite sample has desired TC value and relatively high ΔSM, it can be a potential candidate as a magnetocaloric material for room temperature magnetic cooling systems. 相似文献
8.
Kubota M Oohara Y Yoshizawa H Fujioka H Hirota K Moritomo Y Endoh Y 《Physical review letters》2003,91(4):047201
We have observed magnetic diffuse signals of the bilayer manganite La1.1Sr1.9Mn2O7 by neutron scattering. Even at the low temperature, 20 K, there is a diffuse signal, which is much stronger than that observed in the high temperatures, 144 and 288 K. This signal cannot be characterized by a bilayer structure as observed at 144 K nor by a monolayer structure as at 288 K, but by a high degeneracy of a canted spin structure. Thus, an observation of this diffuse signal is the direct evidence for the establishment of the canted spin structure in La1.1Sr1.9Mn2O7. 相似文献
9.
A polycrystalline, double-layered, colossal magnetoresistive manganite La1.2Sr1.8Mn2O7 is synthesized by sol-gel process and its magnetic and ultrasonic properties were investigated in the temperature range 80–300 K. The sample has Curie temperature at 124 K, where the sample exhibits a transition from paramagnetic insulator to ferromagnetic metallic state. The longitudinal sound velocity measurements show a significant hardening of sound velocity below TC, which may be attributed to the coupling between ferromagnetic spins and longitudinal acoustic phonons. The magnetization and ultrasonic studies reveal the presence of secondary transition at ≈ 260 K in this sample. The present sound velocity measurement results confirm the reliability of ultrasonic investigations as an independent tool to probe magnetic transitions in manganites. 相似文献
10.
La2NiO4+δ体系额外氧δ=0.071,0.110,0.135,0.140样品中存在着 一个间隙氧弛豫运动引起的低频内耗峰,其内耗峰峰位置随额外氧的增多向高温移动.而额外氧处于其间位 置δ=0.087样品中则出现了两个弛豫型内耗峰,分析认为它们源于体系相分离后形成的不同一维有序结构中间隙氧的跳跃. 此外,额外氧δ=0.038样品中也观察到两个弛豫型内耗峰,其中低温峰性质与上相同,而高温内耗峰则可能对应于体系相分离后形成的低温四方相中氧原子的跳跃弛豫.
关键词:
La2NiO4
内耗
相分离 相似文献
11.
12.
Kamenev KV Lees MR Balakrishnan G Paul DM Marshall WG Tissen VG Nefedova MV 《Physical review letters》2000,84(12):2710-2713
The effect of pressure of up to 9 GPa on the magnetic and structural properties of layered (La0.6Nd0.4)1.2Sr1.8Mn2O7 manganite has been investigated. Pressure shifts the Mn atoms from the center of each bilayer towards the adjacent bilayer. The observed shift of the Mn atoms involves mainly a charge redistribution within the d(3z(2)-r(2)) axial orbital. The decrease in the interbilayer spacing and the shift of the Mn atoms away from the center of each bilayer result in increased magnetic and electronic coupling between the adjacent bilayers along the c axis. 相似文献
13.
《Journal of magnetism and magnetic materials》1995,146(3):L241-L246
55Mn nuclear magnetic resonance has been measured for both cubic C15 and hexagonal C14 HoMn2. In the ordered state, we found a high-frequency signal, which can be assigned to magnetic Mn atoms, for both C15 and C14 phases together with a low-frequency signal from non-magnetic Mn atoms. The results of the spin-spin relaxation time T2 in the ordered state and the NMR spectra in the paramagnetic state are also given to discuss the magnetic instability and the magnetic structure. 相似文献
14.
Herein we investigated the electronic properties of layered transition-metal oxides Na2Ti2Sb2O by23Na nuclear magnetic resonance(NMR)measurement.The resistivity,susceptibility and specific heat measurements show a phase transition at approximately 114 K(TA).No splitting or broadening in the central line of23Na NMR spectra is observed below and above the transition temperature indicating no internal field being detected.The spin-lattice relaxation rate divided by T(1/T1T)shows a sharp drop at about 110 K which suggests a gap opening behavior.Below the phase transition temperature zone,1/T1T shows Fermi liquid behavior but with much smaller value indicating the loss of large part of electronic density of states(DOS)because of the gap.No signature of the enhancement of spin fluctuations or magnetic order is found with the decreasing temperature.These results suggest a commensurate charge-density-wave(CDW)phase transition occurring. 相似文献
15.
The dielectric and conductive characteristics of La2NiMnO6 double perovskite ceramics were investigated together with the crystal structure. La2NiMnO6 ceramics crystallized in the monoclinic P21/n structure in which the Ni2+ and Mn4+ ions ordered periodically. Relaxor-like dielectric behavior combined with a giant dielectric constant step was observed in the present ceramics, and these unique dielectric characteristics should be attributed to the charge ordering of Ni2+ and Mn4+. The dielectric relaxation was well fitted by the modified Debye equation and Arrhenius law with the activation energy of 0.17 eV. The dc conductivity of La2NiMnO6 could be well fitted using a variable-range hopping mechanism instead of a band conduction mechanism. 相似文献
16.
Matsukawa M Yamato Y Kumagai T Tamura A Suryanarayanan R Nimori S Apostu M Revcolevschi A Koyama K Kobayashi N 《Physical review letters》2007,98(26):267204
We report a steplike lattice transformation of single crystalline (La0.4Pr0.6)1.2Sr1.8Mn2O7 bilayered manganite accompanied by both magnetization and magnetoresistive jumps, and examine the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator to a ferromagnetic metal phase accompanied by a huge decrease in resistance. Our findings support that the abrupt magnetostriction is closely related to an orbital frustration existing in the inhomogeneous paramagnetic insulating phase rather than a martensitic scenario between competing two phases. 相似文献
17.
A. S. Borovik-Romanov S. V. Petrov A. M. Tikhonov B. S. Dumesh 《Journal of Experimental and Theoretical Physics》1998,86(1):197-205
The NMR spectrum of the quasi-one-dimensional easy-plane antiferromagnetic CsMnBr3, which has trigonal spin lattice, is investigated in detail. The measurements were performed on a wide-band NMR decimeter
microwave-band spectrometer over a wide range of magnetic fields at temperatures 1.3–4.2 K. All three branches of the NMR
spectrum previously found by us [JETP Lett. 64, 225 (1996)] are severely distorted because of the dynamic interaction with the Goldstone mode in the antiferromagnetic resonance
spectrum. The experimental results in fields up to 40 kOe are described satisfactorily by an equation obtained by Zaliznyak
et al. [JETP Lett. 64, 473 (1996)]. Formulas are obtained in our work that agree very well with experiment at all fields up to the “collapse” field
H
c
of all sublattices. The unbiased NMR frequency in CsMnBr3 is determined to be v
n0=416 MHz (T=1.3 K) in zero external magnetic field, and in this way the reduction in the spontaneous moment due to the quasi-one-dimensional
nature of the system of Mn2+ spins, which according to our data amounts to 28%, is determined more accurately. The field dependences of the directions
of the magnetic sublattices with respect to the magnetic field are obtained from the NMR spectra, confirming the equations
of Chubukov [J. Phys. Condens. Matter 21, 441 (1988)]. The results on the field dependence of the width and intensities of the NMR lines are discussed, along with
three observed anomalies: 1) a strong increase in the NMR frequency for nuclei in sublattices that are perpendicular to the
magnetic field; 2) the nonmonotonic temperature dependence of the resonance field for the lower branch of the spectrum; 3)
the presence of two branches of the NMR spectrum in large H
c
fields, in which the CsMnBr3 must be a quasi-one-dimensional antiferromagnetic.
Zh. éksp. Teor. Fiz. 113, 352–368 (January 1998)
Deceased. 相似文献
18.
Papavassiliou G Fardis M Belesi M Maris TG Kallias G Pissas M Niarchos D Dimitropoulos C Dolinsek J 《Physical review letters》2000,84(4):761-764
55Mn NMR line shape measurements in La1-xCaxMnO3 for 0.20< or =x< or =0.50 provide experimental evidence about the existence of two distinct regions in the T-x magnetic phase diagram, where the homogeneous ferromagnetic (FM) metallic state is separated into FM metallic and FM insulating regions. These results are in agreement with recent theoretical predictions, which reveal a novel electronic phase separation in two FM states, providing orbital ordering and Jahn-Teller phonons are taken into consideration. 相似文献
19.
《Journal of magnetism and magnetic materials》2005,295(2):168-173
The magnetic and electronic ground states of the polycrystalline perovskite compound La0.7Sr0.3Co0.9Mn0.1O3 have been studied using AC susceptibility, resistivity and neutron depolarization techniques. Results of neutron depolarization study establish the existence of ferromagnetic domains of ∼3 μm size below 180 K. The substitution of 10 at% Mn ions at the Co site in the compound La0.7Sr0.3CoO3 reduces the effective eg electron transfer and suppresses the double exchange interaction. The competition between the reduced ferromagnetic double exchange interaction and the coexisting antiferromagnetic interaction along with the random nature of substitution leads to a randomly canted ferromagnetic ground state for the substituted compound. Resistivity study confirms that the randomly canted ferromagnetic ground state is insulating. 相似文献