共查询到20条相似文献,搜索用时 31 毫秒
1.
S. Hébert A. Maignan V. Hardy C. Martin M. Hervieu B. Raveau R. Mahendiran P. Schiffer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):419-424
The low temperature magnetic and transport properties of the Pr0.5Ca0.5Mn1-xNixO3 manganites ( 0≤
x
≤0.1) have been investigated. The presence of Ni hinders the charge and orbital ordering observed in Pr0.5Ca0.5MnO3 and favors the creation of ferromagnetic regions, leading to phase separation. The ferromagnetic fractions induced by the
Ni substitution have been estimated from magnetization measurements, they are large and reach 40% for 4% of Ni. Steps are
observed in the M
(
H
) and ρ(
H
) curves of all the samples at T
< 5 K. They are similar to the steps observed in Pr0.5Ca0.5Mn1-xMxO3, where M is a non magnetic cation (Mg2+, Ga3+,...), and for which the ferromagnetic fractions are very small (less than 2%), however, their appearance is restricted to
lower temperatures (T
< 5 K) with Ni dopant than with non magnetic cations. This study shows that steps can be observed in a wide range of phase-separated
systems, even when the ferromagnetic fraction is very large.
Received 5 April 2002 / Received in final form 8 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: antoine.maignan@ismra.fr 相似文献
2.
S. Hébert A. Maignan R. Frésard M. Hervieu R. Retoux C. Martin B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):85-89
The doping of the manganese site by iridium (up to 15%) in the small A cation manganites Pr1-xCaxMnO3 ( 0.4 ?
x
? 0.8), has been investigated as a new method to suppress charge-ordering and induce CMR effects. Ir doping leads to ferromagnetism
and to insulator to metal transitions, with high transition temperatures reaching 180 K and CMR ratio in 7 T as large as 104. The efficiency with which iridium induces ferromagnetism and CMR is compared to previous results obtained with other substitutions
(Ru, Rh, Ni, Cr...). The ionic radius of the foreign cations and their mixed-valencies are found to be the main parameters
governing the ability to collapse the charge-ordered state.
Received 14 May 2001 and Received in final form 2 July 2001 相似文献
3.
E. Bertin P. Bonville J.-P. Bouchaud J.A. Hodges J.P. Sanchez P. Vulliet 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):347-354
Using 155Gd M?ssbauer spectroscopy down to 27 mK, we show that, in the geometrically frustrated pyrochlore Gd2Sn2O7, the Gd3+ hyperfine levels are populated out of equilibrium. From this, we deduce that the hyperfine field, and the correlated Gd3+ moments which produce this field, continue to fluctuate as T
↦ 0. With a model of a spin 1/2 system experiencing a magnetic field which reverses randomly in time, we obtain an analytical
expression for the steady state probability distribution of the level populations. This distribution is a simple function
of the ratio of the nuclear spin relaxation time to the average electronic spin-flip time. In Gd2Sn2O7, we find the two time scales are of the same order of magnitude. We discuss the mechanism giving rise to the nuclear spin
relaxation and the influence of the electronic spin fluctuations on the hyperfine specific heat. The corresponding low temperature
measurements in Gd2Ti2O7 are presented and discussed.
Received 17 October 2001 Published online 6 June 2002 相似文献
4.
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
5.
W. Boujelben A. Cheikh-Rouhou J.C. Joubert 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):419-423
Deficiency effects in the A site upon the structural, magnetic and electrical properties in the lacunar perovskite manganite
oxides Pr0.7Sr0.3-x
xMnO3 ( 0 ?
x
? 0.3) and Pr0.7-x
xSr0.3MnO3 ( 0 ?
x
? 0.23) have been investigated. This study focuses on the different parameters which govern the magnetic and electrical properties
in such samples. The powder X-ray diffraction patterns for all samples could be indexed either with a rhombohedral perovskite
structure and R
c space group for x
? 0.2 in strontium deficient samples and for x
? 0.1 for praseodymium deficient ones. For other values of x the samples could be indexed in the orthorhombic structure with Pbnm space group. Magnetic and electrical investigations
show that praseodymium and strontium vacancies do not have similar effects on the lacunar compounds. Magnetization measurements
versus temperature show that all our samples exhibit a magnetic transition when the temperature decreases. All the praseodymium
deficient samples exhibit a paramagnetic-ferromagnetic transition when the temperature decreases while the strontium deficient
ones exhibit this transition only for low x values. The magnetic transition temperature shifts to lower values as the strontium deficiency increases (from 265 K for
x
= 0 to 90 K for x
= 0.3) and to higher values with the praseodymium deficiency increase (from 265 K for x
= 0 to 315 for x
= 0.23). Resistivity measurements as a function of temperature show a semiconducting-metallic transition for all x values in the praseodymium lacunar samples and only for low x values ( 0 ?
x
? 0.1) in the strontium lacunar ones when the temperature decreases.
Received 12 April 2000 and Received in final form 8 January 2001 相似文献
6.
N.A. Babushkina L.M. Belova E.A. Chistotina O.Yu. Gorbenko A.R. Kaul B. Güttler K.I. Kugel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):409-415
The effect of
16
O
→
18
O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La0.35Pr0.35Ca0.3MnO3 epitaxial thin films deposited onto LaAlO3 and SrTiO3 substrates. For the films on LaAlO3, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic
field ( H
≥ 2
T) transformed the sample with 18O back to the metallic state. The films on SrTiO3 remained metallic at low temperatures for both 16O and 18O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after
16
O
→
18
O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis,
especially pronounced in the case of the films on LaAlO3. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and
charge ordering.
Received 11 February 2000 and Received in final form 13 September 2000 相似文献
7.
Y. Piskunov D. Jérome P. Auban-Senzier P. Wzietek C. Bourbonnais U. Ammerhal G. Dhalenne A. Revcolevschi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):443-456
63Cu-NMR measurements have been performed on two-leg hole-doped spin ladders Sr14-xCaxCu24O41 single crystals 0 ?
x
? 12 at several pressures up to the pressure domain where the stabilization of a superconducting ground state can be achieved.
The data reveal a marked decrease of the spin gap derived from Knight shift measurements upon Ca substitution and also under
pressure and confirm the onset of low lying spin excitations around P
c
as previously reported. The spin gap in Sr
2
Ca
12
Cu
24
O
41
is strongly reduced above 20 kbar. However, the data of an experiment performed at P
= 36 kbar where superconductivity has been detected at 6.7 K by an inductive technique have shown that a significant amount of
spin excitations remains gapped at 80 K when superconductivity sets in. The standard relaxation model with two and three-magnon
modes explains fairly well the activated relaxation data in the intermediate temperature regime corresponding to gapped spin
excitations using the spin gap data derived from Knight shift experiments. The data of Gaussian relaxation rates of heavily
doped samples support the limitation of the coherence length at low temperature by the average distance between doped holes.
We discuss the interplay between superconductivity and the spin gap and suggest that these new results support the exciting
prospect of superconductivity induced by the interladder tunneling of preformed pairs as long as the pressure remains lower
than the pressure corresponding to the maximum of the superconducting critical temperature.
Received 8 March 2001 and Received in final form 27 July 2001 相似文献
8.
J. Sichelschmidt M. Paraskevopoulos M. Brando R. Wehn D. Ivannikov F. Mayr K. Pucher J. Hemberger A. Pimenov H.-A. Krug von Nidda P. Lunkenheimer V.Yu. Ivanov A.A. Mukhin A.M. Balbashov A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):7-17
The charge-ordered perovskite Pr0.65Ca0.28Sr0.07MnO3 was investigated by means of magnetic susceptibility, specific heat, dielectric and optical spectroscopy and electron-spin
resonance techniques. Under moderate magnetic fields, the charge order melts yielding colossal magnetoresistance effects with
changes of the resistivity over eleven orders of magnitude. The optical conductivity is studied from audio frequencies far
into the visible spectral regime. Below the phonon modes hopping conductivity is detected. Beyond the phonon modes the optical
conductivity is explained by polaronic excitations out of a bound state. ESR techniques yield detailed informations on the
(H,T ) phase diagram and reveal a broadening of the linewidth which can be modeled in terms of activated polaron hopping.
Received 9 August 2000 相似文献
9.
We report measurements of non-linear charge transport in epitaxial (La1−x
Pr
x
)0.7Ca0.3MnO3 thin films fabricated on (100) oriented SrTiO3 single crystals by pulsed laser deposition. The end members of this series, namely Pr0.7Ca0.3MnO3 and La0.7Ca0.3MnO3 are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr0.7Ca0.3MnO3 is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×105 V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the
highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage
characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven
charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters
dispersed in a CO background. 相似文献
10.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
11.
A. Maignan Ch. Simon V. Caignaert B. Raveau 《Zeitschrift für Physik B Condensed Matter》1995,99(1):305-310
The exploration of the magnetic and transport properties of four series of manganese perovskites, Pr0.7Ca0.34−xAxMnO3−δ (A=Sr, Ba), Pr0.7−xLaxCa0.3 MnO3−δ and Pr0.66Ca0.34−x
SrxMnO3−δ has allowed four phases with colossal magnetoresistive (CMR) properties to be isolated: Pr0.7Ca0.25Sr0.025MnO3−δ and Pr0.66Ca0.26Sr0.08MnO3−δ that exhibit a variation of resistance of 2.5. 107% and 109% at μ0 H=5 T for T=88 K and 50 K respectively, Pr0.58La0.12Ca0.3 MnO3−δ that exhibits a variation of 6.106% for μ0 H=5 T at T=80 K and Pr0.7Ba0.025Ca0.275MnO3−δ for which a resistance variation of 5.109%, at T=50 K, for μ0 H=5 T is evidenced. for each compound of this series except the barium phase, one observes that the temperature Tmax, which corresponds to the resistance maximum on the R(T) curves in zero magnetic field, increases dramatically as the mean
size of the interpolated cations increases, and that the CMR effect correlatively decreases dramatically. The comparison of
the two series Pr0.7Ca0.3−xSrxMnO3−δ and Pr0.66Ca0.34−xSrxMnO3−δ shows also the crucial role of the hole carrier density: for a same mean ionic radius of the interpolated cation Tmax is decreased of about 50 K by introducing 0.034 hole per Mn mole. 相似文献
12.
J.P. Hill C.S. Nelson M. v. Zimmermann Y.-J. Kim D. Gibbs D. Casa B. Keimer Y. Murakami C. Venkataraman T. Gog Y. Tomioka Y. Tokura V. Kiryukhin T.Y. Koo S.-W. Cheong 《Applied Physics A: Materials Science & Processing》2001,73(6):723-730
We review our recent X-ray scattering studies of charge and orbital order in doped manganites, with specific emphasis on the
role of orbital correlations in Pr1-xCaxMnO3. For x=0.25, we find an orbital structure indistinguishable from the undoped structure and long-range orbital order at low
temperatures. For dopings 0.3≤x≤0.5, we find scattering consistent with a charge and orbitally ordered CE-type structure.
While in each case the charge order peaks are resolution limited, the orbital order exhibits only short-range correlations.
We report the doping dependence of the correlation length and discuss the connection between the orbital correlations and
the finite magnetic correlation length observed on the Mn3+ sublattice with neutron-scattering techniques. The physical origin of these domains, which appear to be isotropic, remains
unclear. We find that weak orbital correlations persist well above the phase transition, with a correlation length of 1–2
lattice constants at high temperatures. Significantly, we observe similar correlations at high temperatures in La0.7Ca0.3MnO3, which does not have an orbitally ordered ground state, and we conclude that such correlations are robust to variations in
the relative strength of the electron–phonon coupling.
Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001 相似文献
13.
Govind A. Pratap Ajay R.S. Tripathi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):153-158
In the present paper, we study the magnetic properties of bilayer cuprate antiferromagnets. In order to evaluate the expressions
for spin-wave dispersion, sublattice magnetization, Néel temperature and the magnetic contribution to the specific heat, the
double time Green's function technique has been employed in the random phase approximation (RPA). The spin wave dispersion
curve for a bilayer antiferromagnetic system is found to consist of one acoustic and one optic branch. The “optical magnon
gap” has been attributed solely to the intra-bilayer exchange coupling (J
⊥
) as its magnitude does not change significantly with the inter-bilayer exchange coupling (Jz). However Jz is essential to obtain the acoustic mode contribution to the magnetization. The numerical calculations show that the Néel
temperature (T
N
) of the bilayer antiferromagnetic system increases with the Jz and a small change in Jz gives rise to a large change in the Néel temperature of the system. The magnetic specific heat of the system follows a T2 behaviour but in the presence of Jz it varies faster than T2.
Received 13 July 2000 and Received in final form 14 May 2001 相似文献
14.
A. Bombardi N. Kernavanois P. Dalmas de Réotier G.H. Lander J.P. Sanchez A. Yaouanc P. Burlet E. Lelièvre-Berna A. Rogalev O. Vogt K. Mattenberger 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):547-552
In the UxLa1-xS system there is an abrupt loss of the long-range ferromagnetic ordering found in pure US at a critical concentration x
c
∼ 0.57, which is far above the percolation limit. As the magnetic ground state in such a system can be strongly affected by small
variations of the 5f localization, we have investigated a set of samples with different x by polarized neutron diffraction and X-ray magnetic circular dichroism (XMCD). The neutron results are consistent with early
measurements performed on pure US. Even at the lowest U content (x
= 0.15, below x
c
) the shape of the induced form factor (f
(
Q
)) is comparable with that found for x
= 1 and is well reproduced by either a U4+ or a U3+ state. The ratio between the orbital and the effective spin moments in the XMCD measurements confirms this result, but the
evolution of the shape at the M5 edge suggests an abrupt change in the distribution of the electrons (holes) in the 5
f density of states around x
c
.
Received 31 January 2001 相似文献
15.
D. Maurer R. Heichele N. Lingg V. Müller A.M. Balbashov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):425-431
The magneto-elastic properties of single-crystalline La0.95Sr0.05MnO3 have been studied ultrasonically. Our investigations focussed on the temperature interval where magnetic ordering starts
to evolve and results in a spin canted antiferromagnetic ground state. In detail the experiments revealed that the magnetic
order parameter in low-doped manganite is only weakly coupled to lattice strains. Furthermore, the anomalous temperature dependence
of the order parameter as found resembles highly that in stoichiometric LaMnO3. However, the main and most surprising finding is that external magnetic fields favor the spin canted phase in La0.95Sr0.05MnO3. It is unclear at present how the exchange interaction can be tuned by magnetic fields in the way observed and we are not
aware of existing theoretical concepts which might give a plausible explanation for the unexpected field dependent behavior
of the critical temperature. We believe, however, that this behavior primarily results from the fact that the exchange interaction
depends sensitively on the orbital configuration of the manganese d electrons.
Received 27 March 2000 相似文献
16.
H.D. Yang I.P. HongF.H. Hsu H.H. LiS.Y. Tu H.L. HuangS. Chatterjee S. MollahY.-K. Kuo T.I. HsuH.C. Ku W.-H. Li 《Solid State Communications》2003,127(3):229-232
The specific heat (C) of bi-layered manganites La2−2xSr1+2xMn2O7 (x=0.3 and 0.5) is investigated for the ground state of low temperature excitations. A T3/2 dependent term in the low temperature specific heat (LTSH) is identified at zero magnetic field and suppressed by magnetic fields for x=0.3 sample, which is consistent with a ferromagnetic metallic ground state. For x=0.5 sample, a T2 term is observed and is consistent with a two-dimensional (2D) antiferromagnetic insulator. However, it is almost independent of magnetic field within the range of measured temperature (0.6-10 K) and magnetic field (6 T). 相似文献
17.
A. Maignan Ch. Simon V. Caignaert B. Raveau 《Zeitschrift für Physik B Condensed Matter》1995,99(3):305-310
The exploration of the magnetic and transport properties of four series of manganese perovskites, Pr0.7Ca0.34?xAxMnO3?δ (A=Sr, Ba), Pr0.7?xLaxCa0.3 MnO3?δ and Pr0.66Ca0.34?x SrxMnO3?δ has allowed four phases with colossal magnetoresistive (CMR) properties to be isolated: Pr0.7Ca0.25Sr0.025MnO3?δ and Pr0.66Ca0.26Sr0.08MnO3?δ that exhibit a variation of resistance of 2.5. 107% and 109% at μ0 H=5 T for T=88 K and 50 K respectively, Pr0.58La0.12Ca0.3 MnO3?δ that exhibits a variation of 6.106% for μ0 H=5 T at T=80 K and Pr0.7Ba0.025Ca0.275MnO3?δ for which a resistance variation of 5.109%, at T=50 K, for μ0 H=5 T is evidenced. for each compound of this series except the barium phase, one observes that the temperature Tmax, which corresponds to the resistance maximum on the R(T) curves in zero magnetic field, increases dramatically as the mean size of the interpolated cations increases, and that the CMR effect correlatively decreases dramatically. The comparison of the two series Pr0.7Ca0.3?xSrxMnO3?δ and Pr0.66Ca0.34?xSrxMnO3?δ shows also the crucial role of the hole carrier density: for a same mean ionic radius of the interpolated cation Tmax is decreased of about 50 K by introducing 0.034 hole per Mn mole. 相似文献
18.
T. Sommer M. Vojta K.W. Becker 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):329-339
The two-layer square lattice quantum antiferromagnet with spins 12 shows a zero-field magnetic order-disorder transition at a critical ratio of the inter-plane to intra-plane couplings. Adding
a uniform magnetic field tunes the system to canted antiferromagnetism and eventually to a fully polarized state; similar
behavior occurs for ferromagnetic intra-plane coupling. Based on a bond operator spin representation, we propose an approximate
ground state wavefunction which consistently covers all phases by means of a unitary transformation. The excitations can be
efficiently described as independent bosons; in the antiferromagnetic phase these reduce to the well-known spin waves, whereas
they describe gapped spin-1 excitations in the singlet phase. We compute the spectra of these excitations as well as the magnetizations
throughout the whole phase diagram.
Received 23 April 2001 相似文献
19.
Dong-Wook Kim 《Solid State Communications》2006,137(10):545-548
A pulsed laser deposition technique was used to grow ferromagnetic La0.7Sr0.3MnO3 (LSMO) films on antiferromagnetic La0.33Ca0.67MnO3 (LCMO) and Pr0.7Ca0.3MnO3 (PCMO) films in bilayer forms. The LSMO film on the PCMO layer had a more elongated out-of-plane lattice than that on the LCMO layer. The former had a lower ferromagnetic transition temperature (320 K) than the latter (350 K). The enhanced low-temperature magnetoresistance of the LSMO/PCMO bilayer suggests that the spin frustration is stronger at this bilayer than in the LSMO/LCMO bilayer. These differences indicate that strain state and defect concentration play important roles in governing interfacial spin interactions. 相似文献
20.
LARGE MAGNETIC ENTROPY CHANGE NEAR CHARGE-ORDERED TRANSITION TEMPERATURE IN PEROVSKITE-TYPE MANGANITE 下载免费PDF全文
The magnetocaloric effect in polycrystalline of Pr1-xSrxMnO3 (x=0.33, 0.43, 0.50) has been investigated. A large magnetic entropy change (7.1J/kgK) was discovered in Pr0.5Sr0.5MnO3 under a low magnetic field of 1T at charge-ordered state transition temperature (161K). The physical mechanism is related to a drastic magnetization change at a temperature where the field-induced magnetic, electron and structural phase transitions occur (from the antiferromagnetic charge-ordered state to the ferromagnetic charge-disordered state). 相似文献