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1.
The influence of Gd doping at La-site on the electrical transport properties and the colossal magnetoresistance of La0.7−x
Gd
x
Sr0.3MnO3 (x=0.00, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, and 0.70) is studied. The experimental results indicate that the transport
properties exhibit abnormal behavior under high doping condition. Forx=0.50, we find that a transition from metal to insulator occurs after the occurrence of insulator-metal transition nearT
c, which seldom occurs in ABO3 structure. For samplesx=0.60 and 0.70, it exhibits insulator behavior far aboveT
c. These abnormal behaviors are attributed to different magnetic background, i.e. the system undergoes a transition from long
range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order. 相似文献
2.
M. M. Markina K. V. Zakharov A. N. Vasil’ev I. Balasz I. Deac E. Burzo 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(2):190-192
The thermodynamic and magnetic properties of the La1 − x
Pb
x
MnO3 (0.24 ≤ x ≤ 0.40) solid solution system were investigated in the temperature range of 4.2–340 K. All objects were ferromagnetics with
Curie temperature T
C
≈ 320–340 K, which slowly increased with x. The M(T) behavior in the magnetic ordering region indicated a nonuniform ground state, due possibly to the competition of ferromagnetic
and antiferromagnetic interactions. The increase in the saturation magnetic moment with x can be described by a simple model of the binary bonds in La1 − x
Pb
x
MnO3. 相似文献
3.
Qian Wan KuiJuan Jin QingQing Li YaQing Feng Can Wang Chen Ge Meng He HuiBin Lu HaiZhong Guo XiaoLong Li YuPing Yang GuoZhen Yang 《中国科学:物理学 力学 天文学(英文版)》2017,60(5):057711
We investigated the effects of oxygen vacancies on the structural, magnetic, and transport properties of La1–x Sr x MnO3 (x=0.1, 0.2, 0.33, 0.4, and 0.5) grown around a critical point (without/with oxygen vacancies) under low oxygen pressure (10 Pa) and high oxygen pressure (40 Pa). We found that all films exhibit ferromagnetic behavior below the magnetic critical temperature, and that the films grown under low oxygen pressures have degraded magnetic properties with lower Curie temperatures and smaller magnetic moments. These results show that in epitaxial La1–x Sr x MnO3 thin films, the magnetic and transport properties are very sensitive to doping concentration and oxygen vacancies. Phase diagrams of the films based on the doping concentration and oxygen vacancies were plotted and discussed. 相似文献
4.
S. V. Trukhanov M. V. Bushinsky I. O. Troyanchuk H. Szymczak 《Journal of Experimental and Theoretical Physics》2004,99(4):756-765
The structural, magnetic, and electrotransport properties of La1?xSrxMnO3? x/2(0≤x≤0.30) manganites with perovskite structure are investigated experimentally as a function of oxygen deficiency. In the solid solutions La1?xSrxMnO3, a change in the type of symmetry of the unit cell is observed at x=0.125. Samples with x≤0.125 are characterized by an O′-orthorhombic unit cell, whereas samples with x>0.125 are characterized by a rhombohedral unit cell. The structural properties of the anion-deficient solid solutions La1?xSrxMnO3?x/2 are analogous to those of the stoichiometric system. It is assumed that, as the oxygen content decreases, La1? xSrxMnO3?x/2 anion-deficient solid solutions experience a series of successive magnetic phase transformations in the ground state: from an A-type (x=0) antiferromagnet to a cluster spin-glass-type inhomogeneous magnetic state (0.175>x≤0.30) through a two-phase (antiferromagnetic and ferromagnetic) state (0>x≤0.175). The anion-deficient solid solution with x=0.175 has the maximal value of the ferromagnetic component. As the oxygen deficiency increases, the resistivity of La1? xSrxMnO3?x/2 samples first decreases (up to a value of x=0.175), acquiring an activation character, and then increases (up to a value of x=0.30). In this case, none of the anion-deficient solid solutions exhibits a metal-semiconductor transition in the whole range of concentrations considered. A peak of magnetoresistance at a temperature below the point of magnetic ordering is observed only in the sample with x=0.175. The results of experiments carried out with a series of La1?xSrxMnO3?x/2 anion-deficient solid solutions are summarized in the concentration diagrams of the spontaneous magnetic moment and the critical temperature of magnetic phase transitions. Hypothetical magnetic phase states are pointed out. The experimental results obtained can be interpreted in terms of the phase-separation model and the competition between ferromagnetic and antiferromagnetic indirect superex-change interactions. It is assumed that Mn3+-O-Mn3+ indirect superexchange interactions in the orbitally disordered phase are positive in the case of octahedral coordination of manganese ions and are negative when the coordination of at least one Mn3+ ion is pentahedral. 相似文献
5.
A. M. Aliev A. G. Gamzatov A. B. Batdalov A. S. Mankevich I. E. Korsakov 《Journal of Experimental and Theoretical Physics》2011,112(3):460-468
A technology for obtaining single-phase ceramic samples of La1 − x
K
x
MnO3 manganites, as well as the dependence of their structure parameters on the potassium content, is described. The magnetocaloric
effect in the samples has been measured by two direct methods, the classical method and the magnetic field modulation method,
and has been calculated from the specific heat data. The values of the magnetocaloric effect obtained by these methods are
significantly different. The observed discrepancies have been explained. Correlation between the doping level and the value
of the effect has been found. It has been shown that the magnetic-field dependence of variation of the magnetic entropy near
T
C in weak fields corresponds to theoretical calculations and that the value of the magnetocaloric effect in high magnetic fields
can be predicted using this dependence. 相似文献
6.
Mitsuo Kataoka 《Czechoslovak Journal of Physics》1996,46(4):1857-1858
To clarify the origin of the giant magnetoresistance (GMR) observed in La1?x A x MnO3 (A2+=Sr2+, Pb2+, Ba2+ and Ca2+), we have investigated theoretically the electrical resistivity ρ of carriers in the background of Mn spins which interact with each other through the double exchange interaction. It has been found that extraordinarily large pin fluctuations caused by the instability of the ferromagnetic state are responsible for the transport anomalies including the GMR. 相似文献
7.
YingTang Zhang ChunChang Wang WeiBin Liu Zhong Wang HuiBin Lu ZiYu Chen 《中国科学G辑(英文版)》2009,52(12):1893-1897
A series of samples of La1−x
Tb
x
MnO3 (0⩽x⩽0.15) are prepared. The static and dynamic magnetizations of La1−x
Tb
x
MnO3 have been investigated. The results indicate that the spins with the short-range order are frozen into random direction at
low enough temperatures which leads to the samples exhibiting the spin-glass like behavior. It is considered that the spin-glass
like behavior originates from the competition between ferromagnetic double exchange among Mn3+ and Mn2+ and antiferromagnetic superexchange among Mn3+ and Mn3+, as well as Tb3+ and Tb3+. 相似文献
8.
I. O. Troyanchuk D. V. Karpinskii V. M. Dobryanskii Yu. A. Fedotova H. Szymczak 《Journal of Experimental and Theoretical Physics》2005,100(6):1121-1126
The preparation conditions and magnetic properties of the La(Co1?xFex)O3?d system of solid solutions were studied. Irrespective of synthesis conditions, the samples with x ≤ 0.15 were rhombohedral (space group \(R\bar 3c\)), and those with x ≥ 0.7, orthorhombic (space group Pnma). In the intermediate region of 0.15 < x < 0.7, the samples could be mixtures of rhombohedral and orthorhombic phases. Structural heterogeneity considerably decreased as the temperature of the synthesis increased or after annealing in a reducing medium. The samples containing more than 40% iron exhibited weak spontaneous magnetization, as is characteristic of weak ferromagnets. The magnetic properties and structure depend on the content of oxygen. A decrease in the concentration of oxygen sharply increases magnetic anisotropy; the coercive force is then close to 10 kOe, which is more than that known for other oxide systems. The magnetic properties are explained in terms of the model according to which Co3+ ions are in the low-spin state. 相似文献
9.
L. Liu J. J. Zheng S. L. Yuan Z. M. Tian C. H. Wang 《Journal of nanoparticle research》2011,13(6):2305-2310
Magnetic properties of La1−x
Ca
x
MnO3 (0.5 ≤ x ≤ 0.8) samples with an equivalent average particle size ~50 nm prepared by a sol–gel method were investigated. The charge
ordering (CO) transition that is observed in the bulks disappears and the ferromagnetic (FM) transition occurs in all the
prepared samples. For all the samples, the spontaneous magnetization (M
S) value is much lower than the corresponding theoretic value, which shows that the majority of the sample is antiferromagnetic
(AFM). However, the M
S value is much larger than the corresponding value reported by some other groups. The invisible of CO transition and the large
M
S value can be attributed to the good connection among the adjacent particles. Moreover, the exchange bias (EB) phenomenon
is observed except the x = 0.5 sample. With x increasing, the M
S value decreases and the EB field increases, which can be understood by considering the coexistence of FM phase with Mn3+–Mn4+ spin clusters in the shell and the AFM phase in the core of the nanoparticles. 相似文献
10.
V. V. Mashkautsan R. I. Zainullina N. G. Bebenin V. V. Ustinov Ya. M. Mukovskii 《Physics of the Solid State》2003,45(3):494-498
A study of the temperature dependences of the ordinary and anomalous Hall coefficients and of the Hall mobility of carriers in single crystals of the ferromagnetic manganites La1?xSrxMnO3 (x=0.15, 0.20, 0.25) was carried out in the temperature interval from 85 to 400 K. The nature of the carriers and the conduction mechanisms in these compounds are discussed. 相似文献
11.
I. K. Kamilov A. G. Gamzatov A. B. Batdalov A. S. Mankevich I. E. Korsakov 《Physics of the Solid State》2010,52(4):789-793
The magnetocaloric effect and the heat capacity of La1 − x
K
x
MnO3 (x = 0.1, 0.15, 0.175) ceramic samples have been studied at temperatures in the range 77–350 K and in magnetic fields of up
to 27 kOe. The technique for preparing the samples has been described. The heat capacity anomalies related to the ferromagnetic-paramagnetic
magnetic phase transition have been revealed and interpreted. It has been demonstrated that the change in the magnetic entropy
ΔS calculated from the data on the heat capacity C
p
and direct measurements of the magnetocaloric effect ΔT reaches values that are of practical interest. 相似文献
12.
A generalized expression relating the magnetoresistance of manganites La1 − x
Ag
x
MnO3 with the change in the magnetic entropy has been proposed. The correct inclusion of the acting mechanisms of appearance of
the magnetoresistance is shown to lead to adequate agreement between the experimental and calculated values of ΔS
M
. 相似文献
13.
A. G. Gamzatov Sh. B. Abdulvagidov A. M. Aliev A. B. Batdalov O. V. Mel’nikov O. Yu. Gorbenko 《JETP Letters》2007,86(5):340-343
The heat capacity of La1?x Ag x MnO3 manganites with x = 0.1, 0.15, and 0.2 is measured in the temperature range 77–350 K. An analogy between the effect of doping and the effect of a magnetic field on the temperature dependence of heat capacity of the La1?x Ag x MnO3 system is revealed. As lanthanum is replaced by silver, the volume fraction of the ferromagnetic phase increases, while, in the paramagnetic state, the Jahn-Teller distortions are eliminated. The results of the aforementioned measurements suggest that the phase transition near the Curie point is caused by the competition between the Coulomb and exchange electrostatic interactions. The comparison of the concentration dependences of T C for La1?x Sr x MnO3 and La1?x Ag x MnO3 points to good potentialities of the latter system from the viewpoint of applications. 相似文献
14.
N. I. Solin S. V. Naumov N. M. Chebotaev A. V. Korolev 《Physics of the Solid State》2010,52(2):289-297
The effect of an oxygen excess δ on the magnetic and electrical properties of La1−x
Ca
x
MnO3+δ (x=0.10–0.15) has been studied over wide ranges of temperatures and magnetic fields. As δ increases, the magnetic ordering temperature
Tcdecreases by 70–90 K, the magnetoresistance increases (the electrical resistivity decreases by a factor of up to 104 in a field of 9 T), and the effective moment μeff of the paramagnetic susceptibility substantially exceeds the theoretical value at temperatures two to four times higher than
T
c and undergoes a jump, just as the activation energy of electrical resistivity, at T∼270 K. These results are attributed to
the formation of cation vacancies, the localization of electrons in their vicinity with the subsequent formation of magnetic
clusters, tunneling (or hopping) of carriers among them, changes in the sizes of clusters with variations in the temperature
and magnetic field strength, the onset of frustrations initiated by the competition among different types of exchange interaction,
and the dependence of the cluster parameters on the annealing conditions. Annealing of the oxygen-excess samples at high temperatures
in vacuum (above 1100°C) restores the samples to a nearly initial state with the magnetic and magnetotransport properties
characteristic of weakly doped manganites, as a result of the removal of cation vacancies. 相似文献
15.
A. G. Gamzatov A. M. Aliev I. K. Kamilov A. R. Kaul’ 《Physics of the Solid State》2016,58(7):1346-1349
This paper reports on the results of the investigation into the magnetocaloric properties of sandwich structures of La1–xKxMnO3 manganites with x = 0.11 (LKM11), 0.13 (LKM13), and 0.15 (LKM15) in magnetic fields of up to 18 kOe. The results of the analysis of the field and temperature dependences of the magnetocaloric effect in the structures LKM11 + LKM13 and LKM13 + LKM15 have demonstrated that the use of sandwich structures increases the efficiency of magnetic cooling in a magnetic field of 18 kOe by 45%. 相似文献
16.
The voltage-current characteristics (VCC) of Sm1?xSrx MnO3 samples with x=0.425 and x=0.450 were experimentally studied at a temperature of 77 K in pulsed and constant electric (E) and magnetic (H) fields up to 10 kOe for the H‖E and H⊥E orientations. N-shaped VCCs and high-frequency (up to 3 MHz) current oscillations were observed. It was found that the effect of colossal magnetoresistance had a threshold character and was smoothly reduced to zero with E→0. 相似文献
17.
18.
S. P. Baranov A. V. Lipatov N. P. Zotov 《The European Physical Journal C - Particles and Fields》2011,71(4):1631
We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k
T
-factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix
elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon
contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS
collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics. 相似文献
19.
Yu. P. Sukhorukov E. A. Gan’shina N. N. Loshkareva A. R. Kaul O. Yu. Gorbenko A. V. Telegin S. N. Tugushev O. V. Mel’nikov A. N. Vinogradov 《Journal of Experimental and Theoretical Physics》2007,104(4):569-576
Evolution of optical, magnetooptical, and transport properties of La1?x Ag x MnO3/SrTiO3 epitaxial films depending on the silver concentration (x = 0.05, 0.10, 0.15, and 0.25) is studied. The highest values of the Curie temperature (T C ≈ 317 K), magnetoresistance (~16%), magnetotransmission (~8%), and transverse Kerr effect (δ ~ 20 × 10?3) are attained for a concentration x = 0.10 of Ag+ ions. Comparison of the temperature dependences of the transmission of IR radiation, resistivity, magnetotransmission, magnetoresistance, and Kerr effect indicates electronic and magnetic inhomogeneity of the films in spite of saturation of films with silver. This feature of the film state is explained using the concepts of epitaxial stresses and metastable point defects. 相似文献
20.
H.-F. Li Y. Su Y. G. Xiao J. Persson P. Meuffels Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):149-157
A neutron powder diffraction (NPD) study on the crystal and magnetic structure of a crushed La1-xSrxMnO3 (x ≈ 1/8) single crystal has been performed. The sample belongs to orthorhombic (Pnma, O) above the Jahn-Teller (JT) transition temperature (TJT) and monoclinic (P121/c1, M′) in the JT regime. We have also refined the NPD data below the charge/orbital ordering (CO/OO) temperature (TCO/OO) with a monoclinic (P121/c1, M′′) model because the experimental resolution was insufficient to clearly identify a triclinic structure. The refined lattice parameters show an obvious breathing-mode distortion between TCO/OO and TJT, accompanied by a large deviation of the monoclinic angle β from 90°, signifying a very strong cooperative JT distortion.
A ferromagnetic (FM) moment of 3.43(5)μ
B/Mn besides an A-type antiferromagnetic (A-AFM) moment of 0.54(2) μ
B/Mn is directed mainly along the b axis in P121/c1 symmetry at 5 K. With increasing temperature, the A-AFM domains transform into FM ones above ~100 K and the FM spin orientation
turns from the b to the c axis in crystallographic b-c plane below Tc = 187(1) K. The magnetization measurements show typical anomalies around TCO/OO and TJT. The measured saturation moment of 3.9(1)μ
B/Mn at 70 kOe and 5 K is well consistent with the sum 3.97(5)μ
B/Mn of the refined FM and A-AFM moments at 5 K, implying the A-AFM spins are aligned in field direction at 70 kOe. The applied
magnetic field can affect the paramagnetic insulating (PMI) state in the range of magnetic polarons. Based on the size of
JT distortion and the bond-valence sums (BVS’s), the CO/OO phenomenon is being discussed. 相似文献