共查询到20条相似文献,搜索用时 24 毫秒
1.
J. Blasco J. García M.C. Sánchez J. Campo G. Subías J. Pérez-Cacho 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):469-479
Magnetic measurements have been carried out in different LaNi1-xMnxO
3 + δ
samples with 0.1 ⩽
x
⩽ 0.9. All these samples show two magnetic anomalies, one at relatively high temperature characteristic of a ferromagnetic ordering
and the other at low temperature, typical of magnetic relaxation phenomena. Neutron diffraction patterns indicate that long-range
ferromagnetic ordering is only achieved for x
≥ 0.5. Neutron patterns of LaNi0.5Mn0.5O
3 + δ
samples show an ordered arrangement of Ni and Mn atoms in the perovskite lattice. LaNi0.5Mn0.5O
3 + δ
is then, a double perovskite A2BB'O6 whereas Ni and Mn atoms are randomly distributed for the rest of the samples. X-ray magnetic circular dichroism experiments
confirm the presence of collinear ferromagnetism in LaNi0.5Mn0.5O
3 + δ
. The role of competitive magnetic interactions, structural disorder, magnetic anisotropy and magnetic disaccommodation is
also discussed
Received 19 July 2002 / Received in final form 23 October 2002 Published online 31 December 2002 相似文献
2.
G. Li S.-J. Feng F. Liu Y. Yang R.-K. Zheng T. Qian X.-Y. Guo X.-G. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):5-11
The magnetic transport properties have been measured for La0.67-xYxCa0.33MnO3 ( 0 ⩽
x
⩽ 0.14) system. It was found that the transition temperature T
p
almost linearly moves to higher temperature as H increases. Electron spin resonance confirms that above T
p
, there exist ferromagnetic clusters. From the magnetic polaron point of view, the shift of T
p
vs. H was understood, and it was estimated that the size of the magnetic polaron is of 9.7 ∼ 15.4 ? which is consistent with the magnetic correlation length revealed by the small-angle neutron-scattering technique. The
transport properties at temperatures higher than T
p
conform to the variable-range hopping mechanism.
Received 27 August 2002 / Received in final form 2 December 2002 Published online 14 March 2003 相似文献
3.
Yu. G. Chukalkin A. E. Teplykh A. N. Pirogov D. G. Kellerman 《Physics of the Solid State》2010,52(12):2545-2551
The specific features of the crystal structure and the magnetic state of stoichiometric lithium manganite in the structurally
ordered Li[Mn2]O4 and disordered Li1 − δMnδ[Mn2 − δLiδ]O4 (δ = 1/6) states have been investigated using neutron diffraction, X-ray diffraction, and magnetic methods. The structurally
disordered state of the manganite was achieved under irradiation by fast neutrons (E
eff ≥ 1 MeV) with a fluence of 2 × 1020 cm−2 at a temperature of 340 K. It has been demonstrated that, in the initial sample, the charge ordering of manganese ions of
different valences arises at room temperature, which is accompanied by orthorhombic distortions of the cubic spinel structure,
and the long-range antiferromagnetic order with the wave vector k = 2π/c(0, 0, 0.44) is observed at low temperatures. It has been established that the structural disordering leads to radical changes
in the structural and magnetic states of the LiMn2O4 manganite. The charge ordering is destroyed, and the structure retains the cubic symmetry even at a temperature of 5 K. The
antiferromagnetic type of ordering transforms into ferrimagnetic ordering with local spin deviations in the octahedral sublattice
due to the appearance of intersublattice exchange interactions. 相似文献
4.
The magnetic susceptibility χ of Hg
1−x
Mn
x
S is investigated at temperatures T = 77–300 K for H = 4 kOe by the Faraday method before and after thermal treatment of the
sample in compound vapors. The special features of χ are found to be caused by the presence in the crystals of Mn-S-Mn-S clusters of different sizes in which indirect antiferromagnetic exchange interaction of the Mn atoms occurs through the chalcogen atoms. Thermal treatment of samples in compound vapors causes changes of sizes of clusters
existing in the crystal and even dissipation of the second-phase inclusions.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 59–63, March, 2008. 相似文献
5.
The magnetic and elastic properties of the Bi1-xCaxMnO3 manganites are studied. The phase transformations revealed are ferromagnet-spin glass (x≥0.15) and spin glass-charge-ordered antiferromagnet (x≥0.25). The ferromagnetic state is characterized by ordering of the Mn3+d x 2-y orbitals. It is suggested that thespin glass state originates from local static Jahn-Teller distortions. The antiferromagnetic charge-ordered and the spin-glass disordered phases coexist in samples with 0.25<x<0.32, which may be due to the charge order-disorder phase transformation being martensitic in character. The magnetic phase diagram is constructed. 相似文献
6.
Electron spin resonance (ESR) measurements have been performed on
polycrystalline samples of Pr0.6Ca0.4Mn1-xRuxO3 (x
= 0, 0.1). The substitution of Ru in the Mn-site strengthens ferromagnetic
interactions due to the double exchange between the Mn3+ and Mn4+
species and super-exchange between the Ru5+ and Mn3+ species. The
temperature dependence of the ESR spectra indicates development of magnetic
phase separation in Pr0.6Ca0.4Mn0.9Ru0.1O3 in
contrast with the un-doped sample. 相似文献
7.
The heavy-fermion metal CePd1−x
Rh
x
can be tuned from ferromagnetism at x = 0 to the nonmagnetic state at some critical concentration x
c
. The non-Fermi liquid behavior (NFL) at x ≃ x
c
is recognized by the power-law dependence of the specific heat C(T) given by the electronic contribution susceptibility X(T) and volume expansion coefficient α(T) at low temperatures: C/T ∝ X(T) ∝ α(T)/T∝ 1/ √T. We also demonstrate that the behavior of the normalized effective mass M
N
*
observed in CePd1−x
Rh
x
at x ≃ 0.8 agrees with that of M
N
*
observed in paramagnetic CeRu2Si2 and conclude that these alloys exhibit the universal NFL thermodynamic behavior at their quantum critical points. We show
that the NFL behavior of CePd1−x
Rh
x
can be accounted for within the frameworks of the quasiparticle picture and fermion condensation quantum phase transition,
while this alloy exhibits a universal thermodynamic NFL behavior that is independent of the characteristic features of the
given alloy such as its lattice structure, magnetic ground state, dimension, etc.
The text was submitted by the authors in English. 相似文献
8.
The magnetism in heavily Dy doped La0.7−x
Dy
x
Sr0.3MnO3 (0.40⩽x⩽0.70) system is studied in this paper. The M-T relation seems to be complicated with the increase of x. For sample with x = 0.40, AFM behavior exists at T⩽T
N and M-T curves under zero field cooling (ZFC) and field cooling (FC) exhibit typical behavior of spincluster glass state above T
N. For the sample with x = 0.50, the M-T curve under ZFC exhibits a valley at a low temperature while the M-T curve under FC exhibits the negative magnetization below T
N. For samples with x = 0.60, 0.70, their ZFC M-T curves are similar to that of x = 0.50, but the FC M-T curves do not exhibit negative values any more. All the peculiar phenomena above are well explained by Néel double-lattice
model combined with M-H relation at typical temperatures. The molecular field theory fits well the negative magnetization for x = 0.50.
Supported by the State Key Project of Fundamental Research of China (Grant No. 2007CB925001), the State Key Development Program
for Basic Research of China (Grant No. 001CB610604), the Natural Science Foundation of Anhui Higher Education Institutions
of China (Grant Nos. 2006KJ266B and ZD2007003-1), Anhui Key Laboratory of Spin Electron and Nanomaterials (Cultivating Base) 相似文献
9.
This paper addresses the synthesis structural and electrochemical properties of LiFe0.5Mn0.5PO4 electrode materials for Li-ion batteries. The charge–discharge reaction of Li/LiPF6-EC–DEC/LiFe0.5Mn0.5PO4 cell carried out at the 1-C rate shows a capacity retention of 128 mAh/g. The local structure of the delithiated Li
x
Fe0.5Mn0.5PO4 phases have been studied by Fourier transform infrared spectroscopy and magnetometry. Spectral features indicate that the
structure of the delithiated phase remains in the orthorhombic system. The compositional dependence of the magnetic moment
is found to be in quantitative agreement with the theoretical value predicted for oxidation of M
2+ ions in the high spin state.
Paper presented at the 11th Euro-Conference on Science and Technology of Ionics, Batz-sur-Mer, France, 9–15 Sept. 2007 相似文献
10.
D. Golberg P.S. Dorozhkin Y. Bando Z.-C. Dong C.C. Tang Y. Uemura N. Grobert M. Reyes-Reyes H. Terrones M. Terrones 《Applied Physics A: Materials Science & Processing》2003,76(4):499-507
Transport and field-emission properties of as-synthesized CNx and BNCx (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those
were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron
microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CNx nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas
those made of BNCx nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission
properties with emitting currents per rope reaching ∼4 μA(CNx) and ∼2 μA (BNCx), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CNx or BNCx nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm2 (BNCx) and 5.5 mA/cm2 (CNx) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm2 both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing
the current density to 0.2–0.4 A/cm2, only CNx films continued to emit steadily, while the field emission from BNCx nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating.
Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003
RID="*"
ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp 相似文献
11.
The layered LiNi0.5Mn0.47Al0.03O2 was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The
powders adopted the α-NaFeO2 structure. This substitution of Al for Mn promotes the formation of Li(Ni0.472+Ni0.033+Mn0.474+Al0.033+)O2 structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice
unit cell. The concentration of antisite defects in which Ni2+ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni2+(3a)–Mn4+(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%.
The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with
the combination of Ni2+ (S = 1), Ni3+ (S = 1/2) and Mn4+ (S = 3/2) spin-only values. Delithiation has been made by the use of K2S2O8. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni4+ in the high spin configuration, while Ni2+(3a)–Mn4+(3b) ferromagnetic pairs remain, as the Li+(3b) ions linked to the Ni2+(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn4+ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments. 相似文献
12.
O. Volkova E. Goodilin A. Vasiliev D. Khomskii N. Tristan P. Kerschl Yu. Skourski K. -H. Mueller B. Buechner 《JETP Letters》2005,82(10):642-645
The ferrimagnetic compounds Ca(CuxMn3?x)Mn4O12 of the double distorted perovskites AC3B4O12 family exhibit a rapid increase of the ferromagnetic component in magnetization at partial substitution of square coordinated (Mn3+)C for (Cu2+)C. In the transport properties, this is seen as a change of the semiconducting type of resistivity for the metallic one. The evolution of magnetic properties of Ca(CuxMn3?x)Mn4O12 is driven by strong antiferromagnetic exchange interaction of (Cu2+)C with (Mn3+/Mn4+)B coordinated octahedra. The competing interactions of (Mn3+)C with (Mn3+/Mn4+)B lead to the formation of noncollinear magnetic structures that can be aligned by magnetic fields. 相似文献
13.
Films of Mn1−x
Fe
x
Se (x = 0–0.45) solid solutions were flash-sputtered. We measured the transmission spectra of the films in the wavelength
range 200–1000 nm at room temperature. From these spectra, we calculated the absorption coefficients and determined the fundamental
absorption edge, the position of which is shifted from 2.65 eV in MnSe to 2.30 eV in solid solutions of compositions x = 0.20–0.45.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 136–138, January–February, 2007. 相似文献
14.
A. G. Razumnaya M. F. Kupriyanov Yu. V. Kabirov A. G. Rudskaya N. B. Kofanova 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1143-1145
Spontaneous deformation in the PbTi1 − x
Mn
x
O3 system at room temperature is found to decrease as x increases, indicating a drop in the temperature of the ferroelectric phase transition. 相似文献
15.
L. Seetha Lakshmi K. Dörr K. Nenkov A. Handstein V. S. Sastry K.-H. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):115-121
We report the charge state modification effects at the Mn site on the ground
state properties of colossal magnetoresistive manganites. Ta5+
substitution results in an appreciable increase in the lattice parameters
and unit cell volume due to increased Mn3+ concentration. The
ferromagnetic-metallic ground state modifies to a cluster glass insulator
for
. The reduction in the transition temperatures with
increasing x is ∼39 K/at.%. Besides the modification of majority carrier concentration due to increased Mn3+ concentration and enhanced local structural effects, the local
electrostatic potential of the substituent seems to contribute to the
unusually strong reduction of the transition temperatures of the compounds.
Thermo magnetic irreversibility just below Curie temperature (Tc),
non-saturation of magnetization, two distinct magnetic transitions in ac
susceptibility in an appropriate static field: close to Tc and other at
low temperature (the spin freezing temperature (Tg)) and non-stationary
dynamics with a characteristic maximum in the magnetic viscosity close to
Tg confirm a cluster glass state for
. These results
find additional support from a linear low temperature magnetic specific heat
of x = 0.10 with a characteristic broad maximum close to Tg. 相似文献
16.
E. Govea-Alcaide I. García-Fornaris P. Muné R. F. Jardim 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):373-378
Measurements of the electrical resistivity as a function
of temperature, ρ(T), for different values of applied
magnetic field, Ba (0 ≤ Ba ≤ 50 mT), were performed in
polycrystalline samples of Bi1.65Pb0.35Sr2Ca2
Cu3O10+δ subjected to different uniaxial compacting
pressure (UCP). We have found appreciable differences in the grain
orientation between samples by using X-ray diffractometry. From
the X-ray diffraction patterns performed, in powder and pellet
samples, we have estimated the Lotgering factor along the (00l)
direction, F(00l). The results indicate that F(00l)
increases ~23% with increasing UCP suggesting that grains
of these samples are preferentially aligned along the c-axis,
which is parallel to the compacting direction. The resistive
transition of the samples have been interpreted in terms of the
thermally activated flux-creep model. In addition, the effective
intergranular pinning energy, U0, have been determined for
different applied magnetic field. The magnetic field dependence of
U0, for Ba > 8 mT, was found to follow a H- α
dependence with α = 0.5 for all samples. The analysis of the
experimental data strongly suggested that increasing UCP results
in appreciable changes in both the grain alignment and the grain
connectivity of the samples. We have successfully interpreted the
data by considering the existence of three different
superconducting levels within the samples: the superconducting
grains, the weak-links, and the superconducting clusters. 相似文献
17.
V. R. Galakhov M. Neumann D. G. Kellerman 《Applied Physics A: Materials Science & Processing》2009,94(3):497-500
X-ray absorption, resonant X-ray emission, and X-ray photoelectron spectroscopical methods have been applied for the study
of the electronic structure of defective lithium cobaltites Li
x
CoO2 (0.6≤x≤1.0). Resonant O K
α X-ray emission spectra of LiCoO2 showed localized excitonic states due to a dd transition between occupied and unoccupied Co 3d states. On the base of measurements of Co 3s X-ray photoelectron, Co 2p, and O 1s X-ray absorption spectra, it was established that in defective cobaltites the electronic holes are localized mainly in O
2p states. An evidence of phase separation in Li
x
CoO2 has been found. It was shown that the semiconductor-to-metal transition in Li
x
CoO2 (x<0.76) at about 160 K is not accompanied by changes in the Co 3d electronic configuration which remains 3d
6. 相似文献
18.
B. Schmidt V. Yushankhai L. Siurakshina P. Thalmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):43-47
A pronounced Curie-like upturn of the magnetic susceptibility χ(
T
) of the quasi one-dimensional spin chain compound Ba2V3O9 has been found recently [#!kaul:02!#]. Frequently this is taken as a signature for a staggered field mechanism due to the
presence of g-factor anisotropy and Dzyaloshinskii-Moriya interaction. We calculate this contribution within a realistic structure of vanadium
3
d- and oxygen 2
p-orbitals and conclude that this mechanism is far too small to explain experimental results. We propose that the Curie term
is rather due to a segmentation of spin chains caused by broken magnetic bonds which leads to uncompensated S
= ? spins of segments with odd numbers of spins. Using the finite-temperature Lanczos method we calculate their effective moment
and show that ∼ 1% of broken magnetic bonds is sufficient to reproduce the anomalous low-T behavior of χ(
T
) in Ba2V3O9.
Received 19 December 2002 / Received in final form 29 January 2003 Published online 14 March 2003 相似文献
19.
A. Yu. Mollaev I. K. Kamilov R. K. Arslanov T. R. Arslanov U. Z. Zalibekov V. M. Novotortsev S. F. Marenkin 《JETP Letters》2010,91(9):478-480
The magnetic susceptibility χ/χ0 and the longitudinal Δρ
zz
/ρ0 and transverse Δρ
xx
/ρ0 magnetoresistances have been measured as functions of the hydrostatic pressure P ≤ 7 GPa at room temperature in the high-temperature ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 with a chalcopyrite structure and the Curie temperature T
c = 355 K. A pressure-induced metamagnetic transition from the low-magnetization state to the high-magnetization state has
been observed in Cd0.7Mn0.3GeAs2 near the magnetic ordering temperature. This transition is accompanied by the hysteresis of the magnetic susceptibility and
magnetoresistance. 相似文献
20.
Magnetic and kinetic properties as well as transmission and absorption spectra of Hg
1−x−y
Mn
x
Fe
ySe (0.09 ≤ x ≤ 0.099 and 0.001 ≤ y ≤ 0.01) crystals are investigated at H ≈ 0.5–6 kOe in the temperature range T = 77–300
K. The band parameters are determined on the basis of experimental data. It is found that in the crystals under study at T
≈ 300 K, electron scattering by polar optical phonons dominates, direct optical band-to-band transitions occur, and replacement
of a part of Mn atoms by Fe for x + y = 0.1 results in an increase in Eg
op with Fe content.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 35–39, March, 2007. 相似文献