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1.
P. Orgiani C. Aruta G. Balestrino S. Lavanga P.G. Medaglia A. Tebano 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):23-28
Transport properties of SrRuO3 thin films were studied as a function of the epitaxial strain. SrRuO3 films were grown on (100) SrTiO3 substrates by the Pulsed Laser Deposition technique equipped with Reflection High Energy Electrons Diffraction (RHEED). Samples
thickness has been varied from a few unit cells to above 1000 ? while monitoring RHEED intensity oscillations. In thicker
films epitaxial strain was found to be progressively relaxed. SrRuO3 relaxed films (thickness 1000 ?) show metallic behavior for the whole temperature range with a ferromagnetic ordering at about 150 K. For thinner
films, ferromagnetic ordering occurs at progressively lower temperatures, until in films thinner than 400 ? it disappears.
Films thinner than 80 ? show a semiconducting behavior at low temperatures. Our results provide direct evidence of the crucial
role of the strain effect for conducting and magnetic properties of SrRuO3.
Received 16 July 2001 and Received in final form 22 October 2001 相似文献
2.
F. Maury I. Mirebeau M. Nicolas-Francillon F. Bourée 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):459-466
The magnetic structure of tetragonal insulating YBa2Cu3-xLixOy has been studied as a function of x and y. The Néel temperature and the mean ordered magnetic moment on the Cu2 sites were determined by neutron powder diffraction
measurements. The decrease of these two parameters as compared to YBa2Cu3O6 is much stronger for lithium than for zinc substitution. The difference is quantitatively explained by the presence of holes
created in the CuO2 planes. These holes arise from the substitution of plane Cu2+ by Li+. We suggest an explanation why such holes are not seen for the same substitution of plane Cu2+ by Li+ in orthorhombic superconducting YBa2Cu3-xLixO
7 - δ
.
Received 31 October 2001 and Received in final form 6 March 2002 Published online 25 June 2002 相似文献
3.
A.M. Balagurov V.Yu. Pomjakushin D.V. Sheptyakov V.L. Aksenov N.A. Babushkina L.M. Belova O.Yu. Gorbenko A.R. Kaul 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):215-223
The atomic structure of (
La
1 - y
Pr
y
)
0.7
Ca
0.3
MnO
3
compound with 0.5≤
y
≤1 has been systematically studied by neutron powder diffraction in the temperature range from 15 to 293 K. For composition
with y
= 0.75, the structural analysis was performed on two samples, one containing the natural mixture of oxygen isotopes and the other
one 75% enriched by
18
O. The room temperature structural characteristics of the series, including cell volume, average Mn-O bond distance, and average
Mn-O-Mn bond angle, are the linear functions of the <
r
A
>. Temperature dependencies of these parameters are quite smooth, except for the point T
=
T
FM
, where a jump like changes occur. The isotope enriched samples have been found identical in crystal and magnetic structure
down to the temperature of transition of the sample with
16
O into the metallic ferromagnetic phase. It confirms that different transport and magnetic properties of the samples with
16
O and
18
O at low temperature are driven by the different oxygen atoms dynamics solely. Temperature dependencies of the CO and AFM diffraction
peak intensities and of the peak widths for compositions close to the metal-insulator boundary ( y
≈ 0.75) indicate the macroscopically phase separated AFM-dielectric + FM-metallic state below T
FM
.
Received 28 April 2000 相似文献
4.
N. El Khayati R. Cherkaoui El Moursli J. Rodríguez-Carvajal G. André N. Blanchard F. Bourée G. Collin T. Roisnel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):429-442
We have studied in detail the crystal and magnetic structures of the oxyphosphates MFePO5 (M: divalent transition metal) using neutron powder diffraction as a function of temperature. All of them are isomorphic
to the mixed valence compound α-Fe2PO5 with space-group Pnma. No disorder exists between the two metallic sites. The M2+O6 octahedra share edges between them and faces with Fe3+O6 octahedra building zigzag chains running parallel to the b-axis that are connected by PO4 tetrahedra. The topology of this structure gives rise to a complex pattern of super-exchange interactions responsible of
the observed antiferromagnetic order. The magnetic structures are all collinear with the spin directed along the b-axis except for M = Co. The experimental magnetic moments of Cu+2 and Ni2+ correspond to the expected ionic value, on the contrary the magnetic moment of Fe3+ is reduced, probably due to covalence effects, and that of Co2+ is greater than the spin-only value indicating a non negligible orbital contribution. Using numerical calculations we have
established a magnetic phase diagram adapted for this type of crystal structure and determined the constraints to be satisfied
by the values of the exchange interactions in order to obtain the observed magnetic structure as the ground state.
Received 15 December 2000 and Received in final form 25 June 2001 相似文献
5.
M. Liberati R.V. Chopdekar V. Mehta E. Arenholz 《Journal of magnetism and magnetic materials》2009,321(18):2852-2854
Epitaxial thin films of CaVO3 were synthesized on SrTiO3, LaAlO3 and (La0.27Sr0.73)(Al0.65Ta0.35)O3 substrates by pulsed laser deposition. All CaVO3 films, independent of epitaxial strain, exhibit metallic and Pauli paramagnetic behavior as CaVO3 single crystals. X-ray absorption measurements confirmed the 4+ valence state for Vanadium ions. With prolonged air exposure, an increasing amount of V3+ is detected and is attributed to oxygen loss in the near surface region of the films. 相似文献
6.
F. Fauth E. Suard V. Caignaert B. Domengès I. Mirebeau L. Keller 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):163-174
The oxygen deficient cobaltites LnBaCo2O5 (Ln = Tb, Dy, Ho) exhibit two successive crystallographic transitions at T
N
∼340 K and at T
CO
∼210 K. Whereas the first transition (P4/mmm to Pmmm) is related to the long-range antiferromagnetic ordering of the Co ions
(spin ordering), the second transition (Pmmm to Pmmb) corresponds to the long-range ordering of the Co2+ and Co3+ species (charge ordering) occurring in 1:1 ratio in the structure. The charge ordered (CO) state was directly evidenced by
the observation of additional superstructure peaks using neutron and electron diffraction techniques. The CO state was also
confirmed indirectly from refinement of high resolution neutron diffraction data as well as from resistivity and DSC measurements.
From the refined saturated magnetic moment values only, ∼3.7
and ∼2.7
, the electronic configuration of the Co ions in LnBaCo2O5 remains conjectural. Two pictures, with Co3+ ions either in intermediate spin state ( t
5
2g
e
1
g
) or in high spin state ( t
4
2g
e
2
g
), describe equally well our experimental data. In both cases, the observed magnetic structure can be explained using the
qualitative Goodenough-Kanamori rules for superexchange. Finally, in contrast to the parent Ln = Y compound [Vogt et al. , Phys. Rev. Lett. 84, 2969 (2000)], we do not report any spin transition in LnBaCo2O5 (Ln = Tb, Dy, Ho).
Received 13 December 2000 相似文献
7.
N. N. Loshkareva Yu. P. Sukhorukov E. A. Gan’shina E. V. Mostovshchikova R. Yu. Kumaritova A. S. Moskvin Yu. D. Panov O. Yu. Gorbenko A. R. Kaul’ 《Journal of Experimental and Theoretical Physics》2001,92(3):462-473
A new approach to the study of phase separation in lanthanum manganites is proposed based on the combined investigation of their optical and magnetooptical characteristics providing information about the conducting and ferromagnetic regions, respectively. Effects of the 18O isotope substitution for 16O in the epitaxial films of (La0.5Pr0.5)0.7Ca0.3MnO3 (grown on SrTiO3 or LaAlO3 substrates) upon the IR absorption spectra and the equatorial Kerr effect measured in the 1.5–3.8 eV range were studied. A giant drop in the temperature of maximum resistance of the film grown on SrTiO3 and disappearance of the metal-insulator transition in the film on LaAlO3, observed upon the isotope exchange, are accompanied by a decrease in the contribution of free charge carriers to the absorption spectra, by the appearance of bands due to localized states, and by a decrease in magnitude of the equatorial Kerr effects. Measurements of the Kerr effect and the temperature variation of the optical transmission show evidence of the presence of ferromagnetic metal regions in the 18O-isotope-substituted (La0.5Pr0.5)0.7Ca0.3MnO3/LaAlO3 film at low temperatures, with a general semiconductor character of the resistivity behavior in the entire temperature range studied. Changes observed in the absorption spectra are explained based on a model of the pseudo-Jahn-Teller polar centers and phase separation. The optical and magnetooptical data show evidence of a percolation nature of the giant isotope effect in manganites. 相似文献
8.
M. Abbate J.A. Guevara S.L. Cuffini Y.P. Mascarenhas E. Morikawa 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):203-208
We studied the changes in the electronic structure of SrTi1-xRuxO3 across the metal-insulator transition. The parent compound, SrTiO3, is a well known diamagnetic insulator; whereas the doped compound, SrTi1-xRuxO3, becomes a ferromagnetic metal above x
C
= 0.35. The techniques used in the study were photoemission (PES) and O 1
s X-ray absorption (XAS) spectroscopy. The experimental spectra were analyzed in terms of band structure and Hubbard model
calculations. The PES and XAS spectra of SrTi1-xRuxO3 show the Ru 4
d bands growing in the band gap of SrTiO3 . The analysis in terms of the Hubbard model indicates that the Ti 3
d and Ru 4
d bands are mostly decoupled. This suggests that the metal-insulator transition is a percolation transition like that of metals
embedded in a rare gas matrix. Electron correlation effects are present in this system, but they do not seem to play a major
role in the transition.
Received 10 September 2001 相似文献
9.
D. Rubio Temprano J. Mesot S. Janssen K. Conder A. Furrer A. Sokolov V. Trounov S.M. Kazakov J. Karpinski K.A. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):5-8
The copper isotope effect (63Cu vs.
65Cu) on the relaxation rate of crystal-field excitations in the slightly underdoped high-temperature superconductor HoBa2Cu4O8 has been investigated by inelastic neutron scattering. For the 63Cu compound there is clear evidence for the opening of an electronic gap in the normal state at T
*
≈ 160 K far above T
c
= 79.0 K. Upon substitution of 63Cu by 65Cu, T
c
decreases marginally to 78.6 K, whereas T
*
is increased to about 185 K. This large copper isotope shift Δ
T
*
(
Cu
) =
T
*
(
65
Cu
) -
T
*
(
63
Cu
) ≈ 25 K - together with the corresponding oxygen isotope shift Δ
T
*
(
O
) =
T
*
(
18
O
) -
T
*
(
16
O
) ≈ 50 K found in an earlier investigation - suggests that phonons or lattice fluctuations involving both the copper and the oxygen
ions are important for the pairing mechanism in high-T
c
materials.
Received 13 October 2000 相似文献
10.
A. Wahl V. Hardy C. Martin Ch. Simon 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):135-140
The Pr
1-x
CaxMnO3 system exhibits a ferromagnetic insulating state for the composition range x
? 0.25. A metallic ferromagnetic state is never realized because of the low hole concentration and the very small averaged A-site
cation radius. In the present study, the nature of the magnetic excitations at low temperature has been investigated by specific
heat measurements on a Pr
0.8
Ca0.2MnO3 single crystal. The decrease of the specific heat under magnetic field is qualitatively consistent with a suppression of
ferromagnetic spin waves in a magnetic field. However, at low temperature, the qualitative agreement with the ferromagnetic
spin waves picture is poor. It appears that the large reduction of the specific heat due to the spin waves is compensated
by a Schottky-like contribution possibly arising from a Zeeman splitting of the ground state multiplet of the Pr3+ ions.
Received 21 May 2001 and Received in final form 14 December 2001 相似文献
11.
F. Giubileo A. Jossa F. Bobba A.I. Akimenko A.M. Cucolo 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):305-308
We have applied the break-junction technique to highly biepitaxial c-axis oriented YBa2Cu3O7 thin films with T
C
(ρ=0) = 91 K. Mechanically adjustable junctions with a good stability and tunneling current favored along the ab-planes have been realized. The conductance characteristics of these junctions show the presence of gap related maxima that
move towards zero bias for increasing temperatures. Considering the misorientation angle α≈ 45
°
± 5
°
of the junction, a maximum gap value at the Fermi level Δ
≈ 22 meV is inferred at T
= 13 K. The temperature dependence of the gap related structures, shows a quasilinear behavior for T
> 0.4
T
C
similar to that observed in c-axis oriented, S-I-N type YBa2Cu3O7 planar junctions.
Received 20 July 2001 相似文献
12.
J. Cederkäll M. Lipoglavšek M. Palacz J. Persson J. Blomqvist A. Ataċ C. Fahlander H. Grawe A. Johnson W. Klamra J. Kownacki A. Likar L.–O. Norlin J. Nyberg R. Schubart D. Seweryniak G. de Angelis P. Bednarczyk Z. Dombrádi D. Foltescu M. Górska D. Jerrestam S. Juutinen E. Mäkelä B. M. G. Perez M. de Poli H. A. T. Shizuma Ö. Skeppstedt G. Sletten S. Törmänen 《The European Physical Journal A - Hadrons and Nuclei》1998,1(1):7-9
New excited states have been observed in the neutron deficient isotope 98Ag following the 58Ni+50Cr →108Te* heavy–ion reaction. One of these states may be interpreted as a maximum spin aligned state of the πg9/2
−3νg7/2 configuration. Other possible interpretations within the nuclear shell model are discussed as well.
Received: 24 October 1997 相似文献
13.
W. Zhong W. Chen H.Y. Jiang X.S. Liu C.T. Au Y.W. Du 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):331-337
Polycrystalline two-layered perovskite La2.5-xK0.5+xMn2O
7 + δ
(0 <
x
< 0.5) samples have been prepared by a modified sol-gel method and their magnetoresistance and magnetocaloric effects have been
studied. A large deviation between the metal-insulator (MI) transition temperature (T
ρ
) and the magnetic transition temperature (TC) is observed. Large magnetoresistance (MR) effects with Δρ/ρ
of ∼40% at 12 kOe are obtained in wide temperature ranges. The maximum of the magnetic entropy change peaks at its Curie temperature
(TC), far above its MI transition temperature (T
ρ
). The large magnetic entropy change (∼1.4 J/kg.K) is obtained in the sample La2.5-xK0.5+xMn2O
7 + δ
(x
= 0.35) upon 10 kOe applied magnetic field.
Received 2 May 2002 / Received in final form 1st October 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: wzhong@ufp.nju.edu.cn 相似文献
14.
L. Käubler H. Schnare R. Schwengner P. von Brentano F. Dönau J. Eberth J. Enders A. Fitzler C. Fransen M. Grinberg E. Grosse R.-D. Herzberg H. Kaiser P. von Neumann-Cosel N. Pietralla H. Prade A. Richter S. Skoda Ch. Stoyanov H.-G. Thomas H. Tiesler D. Weisshaar I. Wiedenhöver 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):15-18
A nuclear resonance fluorescence experiment on 88Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with
a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742
MeV in 88Sr, in contrast to the previous interpretation as a 1− two-phonon (2+
1⊗ 3−
1) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1+ state at 3.486 MeV may be considered as the 1+
1 one-phonon state and the very strong 1+
1→ 0+
1 deexcitation as proton spin-flip 2p1/2→ 2p3/2 transition.
Received: 3 November 1999 相似文献
15.
E. Popova N. Keller F. Jomard L. Thomas M.-C. Brianso F. Gendron M. Guyot M. Tessier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):69-74
Magnetic exchange coupling has been observed for ultrathin films of yttrium iron garnet (Y3Fe5O12 or YIG). Single-crystalline YIG films were prepared on yttrium aluminium garnet (Y3Al5O12 or YAG) substrates by pulsed laser deposition. (111) and (110) oriented substrates were used. Film thicknesses were varied
from 180 ? to 4600 ?. Epitaxial growth of YIG on YAG was obtained in spite of the lattice mismatch of 3%. Magnetic hysteresis
loops recorded for ultrathin YIG films have a “bee-waist” shape and show a coupling between two different magnetic phases.
The first phase is magnetically soft YIG. A composition study by secondary ion mass spectroscopy shows the second phase to
be Y3Fe5-xAlxO12 due to the interdiffusion of Fe and Al at the film/substrate interface. This compound is known to be magnetically harder
and to have weaker magnetization than YIG. The coupling of the two phases leads to a hysteresis loop displacement at low temperatures.
This displacement varies differently with film thickness for two substrate orientations. Assuming an interfacial coupling,
the maximal interaction energy is estimated to be about 0.17 erg/cm2 at 5 K for (111) oriented sample.
Received 3 June 2002 / Received in final form 7 October 2002 Published online 27 January 2003
RID="a"
ID="a"Presently at LPM, Université H. Poincaré, BP 239, 54506 Vandœuvre-lès-Nancy e-mail: popova@lpm.u-nancy.fr 相似文献
16.
V.P. Dyakonov M.T. Borowiec A. Jedrzejczak M. Górska N.A. Doroshenko E. Zubov Yu. Bukhantsev T. Zayarnyuk H. Szymczak 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):9-14
Magnetic phase transition in the CsDyW2O8 magnet has been studied by means of low temperature specific heat C
(
T
) measurements. The magnetic ordering temperature of the Dy3+ sublattice was established to be 1.34 K. The experimental results indicate on the antiferromagnetic character of interactions
between Dy3+ ions. The behavior of the C
(
T
) dependencies above and below T
N
is discussed in frames of different theoretical models. The measurements data on temperature and field dependencies of magnetization
are used to calculate the exchange and dipole-dipole interactions energy and to determine the possible magnetic structure
of the ground state.
Received 7 January 2002 / Received in final form 15 May 2002 Published online 7 September 2002 相似文献
17.
Ch. Kegler N. Büttgen H.-A. Krug von Nidda A. Krimmel L. Svistov B.I. Kochelaev A. Loidl A. Prokofiev W. Aßmus 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):321-326
EPR and 7Li NMR measurements were performed in the distorted inverse spinel V(LiCu)O4 down to 1.5 K. Anisotropy effects on magnetic resonance spectra due to the Jahn-Teller distortion of the oxygen octahedra
surrounding the copper ions are discussed. The estimation of the spin-spin interactions deduced from the EPR-relaxation rate
Δ
H reveals a situation comparable to the prototypical one-dimensional S
= 1/2 Heisenberg antiferromagnet CuGeO3. Approaching three-dimensional antiferromagnetic order ( T
N
≈ 2 K) from above, both magnetic relaxation rates, Δ
H
EPR
and
7
(1/
T
1
), respectively, exhibit nearly the same critical divergence reminding to the onset of three-dimensional order in two-dimensional
layered systems.
Received 22 January 2001 and Received in final form 6 May 2001 相似文献
18.
M. Putti E. Galleani d'Agliano D. Marrè F. Napoli M. Tassisto P. Manfrinetti A. Palenzona C. Rizzuto S. Massidda 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):439-443
We report measurements of the resistivity, ρ, and the Seebeck coefficient, S
, of a MgB2 sintered sample, and compare S with theoretical calculations based on precise electronic structure calculations. ρ is fitted well by a generalized Bloch-Grüneisen equation with a Debye temperature Θ
R
of 1050 K. S is given by the sum of a diffusive and a phonon drag term and the behavior in the temperature region T
c
<
T
< 0.1Θ
R
follows the relationship AT+BT3. The phonon drag term indicates a strong electron-phonon interaction. The diffusive term, compared with calculations, suggests
that σ bands give the main contribution to the Seebeck effect.
Received 16 November 2001 and Received in final form 21 December 2001 相似文献
19.
Z.-C. Yan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):15-18
The fully correlated calculations of the Zeeman gJ factors for the first three quartet S states of lithium are presented, including relativistic and radiative corrections of
orders α2, α2
m/M, and α3. The isotope shifts in gJ are predicted precisely for various isotopes of lithium.
Received 4 December 2000 and Received in final form 26 September 2001 相似文献
20.
F. Le Blanc L. Cabaret J.E. Crawford S. Essabaa V. Fedoseyev W. Geithner J. Genevey M. Girod R. Horn G. Huber S. Kappertz J. Lassen J.K.P. Lee G. Le Scornet V. Mishin R. Neugart J. Obert J. Oms A. Ouchrif S. Peru J. Pinard H. Ravn B. Roussière J. Sauvage D. Verney 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):49-51
Laser spectroscopy measurements have been carried out on the very neutron-rich tin isotopes with the COMPLIS experimental
setup. Using the 5s
25p
23
P
0 → 5s
25p6s
3
P
1 optical transition, hyperfine spectra of 126-132Sn and 125m, 127m, 129m-131mSn where recorded for the first time. The variation of the mean-square charge radius ( δ〈r
2〉) between these nuclei and nuclear moments of the isomers and the odd isotopes were thus measured. An odd-even staggering
which inverts at A = 130 is clearly observed. This indicates a small appearance of a plateau on the δ〈r
2〉 which has to be confirmed by measuring the isotope shift beyond A = 132.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: leblanc@ipno.in2p3.fr 相似文献