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1.
L. S. Ewe I. Hamadneh H. Salama N. A. Hamid S. A. Halim R. Abd-Shukor 《Applied Physics A: Materials Science & Processing》2009,95(2):457-463
The magnetotransport and magnetoresistive (MR) properties of manganese-based La0.67Ca0.33MnO3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature
in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T
IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T
IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T
IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region
and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E
F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The
ρ–T
2 curves are nearly linear in the metallic regime, but the ρ–T
2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data
well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers.
MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling
effect. 相似文献
2.
The transformation of the band structure of LaCoO3 in the applied magnetic field has been theoretically studied. If the field is below its critical value B
C
≈ 65 T, the dielectric band gap decreases with the field, thus giving rise to negative magnetoresistance that is highest
at T ≃ 300–500 K. The critical field is related to the crossover between the low- and high-spin terms of Co3+ ions. The spin crossover results in an insulator-metal transition induced by an increase in the magnetic field. 相似文献
3.
D. P. Kozlenko Z. Jirák N. O. Golosova B. N. Savenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(3):327-334
The crystal and magnetic structure of the perovskite-like, oxygen deficient
cobalt oxide YBaCo2O5.5 has been studied by means of neutron and
X-ray diffraction in the 10–300 K temperature range. The magnetic ground
state is characterized by a coexistence of two distinct antiferromagnetic
phases. In the first one, the ionic moments of high-spin Co3+ ions in
the pyramidal sites are ordered in a spiral arrangement, while octahedral
sites are non-magnetic due to presence of low-spin Co3+ ions. The
arrangement in the second phase is collinear of the G-type, with non-zero
moments both in pyramidal (high-spin Co3+ ions) and octahedral sites
(presumably a mixture of the low- and high-spin states). With increasing
temperature, at 260–300 K, the system develops a gradual structural
transformation, which is associated with appearance of spontaneous magnetic moment.
This process is related to a thermally induced reversion of low- and
high-spin states at the octahedral sites to the intermediate-spin Co3+
states, resulting in an insulator-metal transition at TC ≈
TIM ≈ 295 K. 相似文献
4.
V. Kusigerski D. Markovic V. Spasojevic M. Tadic M. Zentkova M. Mihalik 《Journal of nanoparticle research》2010,12(4):1299-1306
Pressure effects on magnetic properties of two La0.7Ca0.3MnO3 nanoparticle samples with different mean particle sizes were investigated. Both the samples were prepared by the glycine-nitrate
method: sample S—as-prepared (10 nm), and sample S900—subsequently annealed at 900 °C for 2 h (50 nm). Magnetization measurements revealed remarkable differences in magnetic properties
with the applied pressure up to 0.75 GPa: (i) for S sample, both transition temperatures, para-to-ferromagnetic T
C = 120 K and spin-glass-like transition T
f = 102 K, decrease with the pressure with the respective pressure coefficients dT
C/dP = −2.9 K/GPa and dT
f/dP = −4.4 K/GPa; (ii) for S900 sample, para-to-ferromagnetic transition temperature T
C = 261 K increases with pressure with the pressure coefficient dT
C/dP = 14.8 K/GPa. At the same time, saturation magnetization M
S recorded at 10 K decreases/increases with pressure for S/S900 sample, respectively. Explanation of these unusual pressure effects on the magnetism of sample S is proposed within the scenario
of the combined contributions of two types of disorders present in the system: surface disorder introduced by the particle
shell, and structural disorder of the particle core caused by the prominent Jahn–Teller distortion. Both disorders tend to
vanish with the annealing of the system (i.e., with the nanoparticle growth), and so the behavior of the sample S900 is similar to that previously observed for the bulk counterpart. 相似文献
5.
We present the results a study of structure by neutron diffraction and data on the magnetic properties (linear and nonlinear
(second and third order) susceptibilities) of polycrystalline La0.88MnO2.95. This compound exhibits an insulator-metal (IM) phase transition at T
IM
≈ 253 K (above the Curie temperature, T
C
≈ 244 K) and reveals colossal magnetoresistance. The crystal structure is found to be rhombohedral, and the space group is
R3c. Analysis of magnetic properties shows that at T* ≈ 258 K > T
C
, isolated paramagnetic clusters occur in the paramagnetic matrix; their concentration increases upon cooling. We observed
no noticeable differences between the temperature evolution of the clustered state of this manganite with its insulator-metal
transition and in the insulator La0.88MnO2.91. Possible scenarios of the paramagnet-ferromagnet and I-M transitions in a self-organized clustered structure are discussed. 相似文献
6.
Manganese-doped ZnSiAs<Subscript>2</Subscript> chalcopyrite: A new advanced material for spintronics
L.?I.?Koroleva D.?M.?Zashchirinski? T.?M.?Khapaeva S.?F.?Marenkin I.?V.?Fedorchenko R.?Szymczak B.?Krzumanska V.?Dobrovol’ski? L.?Kilanski? 《Physics of the Solid State》2009,51(2):303-308
A new spintronics material with the Curie temperature above room temperature, the ZnSiAs2 chalcopyrite doped with 1 and 2 wt % Mn, is synthesized. The magnetization, electrical resistivity, magnetoresistance, and
the Hall effect of these compositions are studied. The temperature dependence of the electrical resistivity follows a semiconducting
pattern with an activation energy of 0.12–0.38 eV (in the temperature range 124 K ≤ T ≤ 263 K for both compositions). The hole mobility and concentration are 1.33, 2.13 cm2/V s and 2.2 × 1016, 8 × 1016 cm−3 at T = 293 K for the 1 and 2 wt % Mn compositions, respectively. The magnetoresistance of both compositions, including the region
of the Curie point, does not exceed 0.4%. The temperature dependence of the magnetization M(T) of both compositions exhibits a complicated character; indeed, for T ≤ 15 K, it is characteristic of superparamagnets, while for T > 15 K, spontaneous magnetization appears which correspond to a decreased magnetic moment per formula unit as compared to
that which would be observed upon complete ferromagnetic ordering of Mn2+ spins or antiferromagnetic ordering of spins of the Mn2+ and Mn3+ ions. Thus, for T > 15 K, it is a frustrated ferro- or ferrimagnet. It is found that, unlike the conventional superparamagnets, the cluster
moment μ
c
in these compositions depends on the magnetic field: ∼12000–20000μB for H = 0.1 kOe, ∼52–55μB for H = 11 kOe, and ∼8.6–11.0μB at H = 50 kOe for the compositions with 1 and 2 wt % Mn, respectively. The specific features of the magnetic properties are explained
by the competition between the carrier-mediated exchange and superexchange interactions. 相似文献
7.
Karen B. Paul 《Central European Journal of Physics》2005,3(1):115-126
A monocrystal ofFe
3
O
4 is characterized by resistance, magnetoresistance and magnetic measurements in a temperature range from 4.2 K to 350 K and
magnetic field-cycling from −9 T to 9 T. The resistance measurements revealed a metal-insulator Verwey transition (VT) atT
v
=123.76 K with activation energy E=92.5 meV at T >T
v
and temperature-substitute for the activation energy below the VT,T
0=E/k
B
≈3800 K within 70 K–110K. The magnetotransport results independently verified the VT at 123.70 K, with discontinuous change
in the magnetic moment ΔM≈0.21 ΔM≈0.21μ
B
and resistance hysteresis, dependent on the magnetic field in a narrow temperature range of 0.4° around theT
v
. The magnetic characterization established self consistentlyT
v
as ≈123.67 K, the jump in the magnetization at the VT≈0.25μ
B
and confirmed, that the magnetocrystalline anisotropy is the main microscopic mechanism responsible for the magnetization
of the monocrystal (88%) with additional natural and imposed defects contributing as 12%. 相似文献
8.
S. V. Trukhanov A. V. Trukhanov A. N. Vasiliev H. Szymczak 《Journal of Experimental and Theoretical Physics》2010,111(2):209-214
The magnetic and thermal properties of the anion-deficient La0.70Sr0.30MnO2.85 manganite are investigated in wide temperature (4–350 K) range, including under hydrostatic pressure (0–1.1 GPa). Throughout
the pressure range investigated, the sample is spin glass with diffused phase transition into paramagnetic state. It is established,
that spin glass state is a consequence of exchange interaction frustration of the ferromagnetic clusters embeded into antiferromagnetic
clusters. The magnetic moment freezing temperature T
f
of ferromagnetic clusters increases under pressure, freezing temperature dependence on pressure is characterized by derivative
value ∼4.5 K/GPa, while the magnetic ordering T
MO temperature dependence is characterized by derivative value ∼13 K/GPa. The volume fraction of sample having ferromagnetic
state is V
fer ∼ 13% and it increases under a pressure of 1.1 GPa by ΔV
fer ≈ 6%. Intensification of ferromagnetic properties of the anion-deficient La0.70Sr0.30MnO2.85 manganite under hydrostatic pressure is a consequence of oxygen vacancies redistribution and unit cell parameters decrease.
The most likely mechanism of frustrated exchange interactions formation is discussed. 相似文献
9.
Kh. G. Bogdanova A. R. Bulatov V. A. Golenishchev-Kutuzov L. V. Elokhina A. V. Kapralov A. V. Korolev É. A. Neifel’d M. M. Shakirzyanov 《Physics of the Solid State》2003,45(2):298-303
This paper reports on measurements of the acoustic, magnetic, and electrical properties and on an x-ray microprobe analysis of a La0.825Sr0.175MnO3 single-crystal sample. The acoustic studies were made with a pulsed acoustic spectrometer operating on a 770-MHz carrier. The studies revealed anomalies in the damping coefficients and sound velocity near 300, 200 K, and the Curie temperature TC (283 K) where the colossal magnetoresistance occurs. The effect of a magnetic field on the magnetic texture of lanthanum manganites cooled below TC, observed earlier in samples of other composition, is confirmed. In addition, a region was found wherein the magnetic susceptibility of an unclamped sample behaves anomalously. The electrical resistivity was observed to decrease substantially below TC; this effect exhibits a hysteretic pattern in the interval 200–180 K. 相似文献
10.
A. Kh. Matiev A. N. Georgobiani V. V. Kodin M. A. Matiev 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(9):1326-1328
The electrical conductivity and magnetoresistance effect of n and p types of CuInSe2 single crystals were studied within the temperature range of 4.2–300 K and within magnetic fields of up to 6 T. It was found
that the hopping mechanism of conductivity dominates in the temperature range of 4.2–100 K. A peculiarity of electrical conductivity
behavior, accompanied by a change in the magnetoresistance sign in the vicinity of T ≈ 60 K, was revealed. 相似文献
11.
Wang P. Li J. Lang P. L. Li S. L. Chu H. F. Xie T. Y. Zheng D. N. 《Applied Physics A: Materials Science & Processing》2011,102(2):449-455
High quality La2/3Ca1/3MnO4(LCMO) thin films have been deposited on silicon-on-insulator (SOI) substrates only buffered by yt tria-stabilized zirconia
(YSZ) by using the pulsed laser deposition (PLD) technique. The results obtained from X-ray diffraction (XRD), reflection
high energy electron diffraction (RHEED), scanning electron microscopy (SEM) and magnetization investigations indicate that
the LCMO films are highly oriented both in-plane and out-of-plane. The Curie temperature T
c is close to 260 K and the insulator–metal (I–M) transition appears around 220 K. The conducting mechanism at low temperatures
is dominated by the electron–magnon scattering. A tensile stress from the film–substrate lattice mismatch results in magnetic
‘easy axes’ in the film plane and the magnetic anisotropy energy increases with cooling. A maximum magnetoresistance (MR) is observed near 190 K, with the external magnetic field either parallel or vertical to the LCMO film plane. Moreover, the
large intrinsic high-field magnetoresistance (HFMR) and the very small extrinsic low-field magnetoresistance (LFMR) again
reveal that the LCMO films on SOI substrates are highly oriented thin films of good crystallinity. 相似文献
12.
D. M. Zashchirinskii L. I. Koroleva A. S. Morozov Yu. V. Dolzhenkova 《Physics of the Solid State》2011,53(2):316-319
The magnetocaloric effect ΔT has been studied by a direct method in two samples of the manganite Sm0.55Sr0.45MnO3, namely, a single crystal (sample A) and a ceramic sample (sample C). The temperature dependences of the ΔT effect of both samples exhibit a maximum at T
max = 143.3 K for the sample A and T
max = 143 K for the sample C. In these maxima, the values of the ΔT effect are 0.8 and 0.4 K in the magnetic field H = 14.2 kOe for the samples A and C, respectively. In addition, the ΔT(T) curve of the sample A has a minimum at T
min = 120 K, in which ΔT = −0.1 K. The maximum value of the ΔT effect increases with an increase in the magnetic field H in the range of magnetic fields up to 14.2 kOe, and the rate of this increase at H > 8 kOe is higher than that at H < 8 kOe. These features of the ΔT effect are explained by the presence of ferromagnetic and antiferromagnetic A- and CE-type clusters in the samples. 相似文献
13.
V. P.S. Awana A. Vajpayee M. Mudgel V. Ganesan A. M. Awasthi G. L. Bhalla H. Kishan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(3):281-294
We report synthesis, structure/micro-structure, resistivity under magnetic
field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity
κ(T), and magnetization of ambient pressure argon annealed
polycrystalline bulk samples of MgB2, processed under identical
conditions. The compound crystallizes in hexagonal structure with space
group P6/mmm. Transmission electron microscopy (TEM) reveals electron micrographs
showing various types of defect features along with the presence of 3–4 nm
thick amorphous layers forming the grain boundaries of otherwise crystalline
MgB2. Raman spectra of the compound at room temperature exhibited
characteristic phonon peak at 600 cm-1. Superconductivity is observed
at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power
S(T), and thermal conductivity κ(T) measurements. The power law fitting
of ρ(T) give rise to Debye temperature (ΘD) at 1400 K which is
found consistent with the theoretical fitting of S(T), exhibiting Θ
D of 1410 K and carrier density of 3.81 × 1028/m3. Thermal
conductivity κ(T) shows a jump at 38 K, i.e., at Tc, which was
missing in some earlier reports. Critical current density (Jc) of up to
105 A/cm2 in 1–2 T (Tesla) fields at temperatures (T) of up to 10 K
is seen from magnetization measurements. The irreversibility field, defined
as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe
at 4, 10 and 20 K respectively. The superconducting performance parameters
viz. irreversibility field (Hirr) and critical current density
Jc(H) of the studied MgB2 are improved profoundly with addition of
nano-SiC and nano-diamond. The physical property parameters measured for
polycrystalline MgB2 are compared with earlier reports and a
consolidated insight of various physical properties is presented. 相似文献
14.
O. Kaman P. Veverka Z. Jirák M. Maryško K. Knížek M. Veverka P. Kašpar M. Burian V. Šepelák E. Pollert 《Journal of nanoparticle research》2011,13(3):1237-1252
The magnetic nanoparticles of La0.75Sr0.25MnO3 perovskite manganite with a controlled size were prepared via sol–gel procedure, followed by thermal treatment and subsequent
mechanical processing of the resulting raw product. The prepared materials were structurally studied by the XRD and TEM methods
and probed by DC magnetic measurements. The nanoparticles of the mean crystallite sizes 11–40 nm exhibit T
C in the range of ≈310–347 K and the sample possessing 20-nm crystallites was identified as the most suitable for hyperthermia
experiments. In order to obtain a colloidally stable suspension and prevent toxic effects, the selected magnetic cores were
further encapsulated into silica shell using tetraethoxysilane. The detailed magnetic studies were focused on the comparison
of the raw product, the bare nanoparticles after mechanical processing and the silica-coated nanoparticles, dealing also with
effects of size distribution and magnetic interactions. The heating experiments were carried out in an AC field of frequencies
100 kHz–1 MHz and amplitude 3.0–8.9 kA m−1 on water dispersions of the samples, and the generated heat was deduced from their warming rate taking into account experimentally
determined thermal losses into surroundings. The experiments demonstrate that the heating efficiency of the coated nanoparticles
is generally higher than that of the bare magnetic cores. It is also shown that the aggregation of the bare nanoparticles
increases heating efficiency at least in a certain concentration range. 相似文献
15.
D. P. Kozlenko N. T. Dang Z. Jirák S. E. Kichanov E. V. Lukin B. N. Savenko L. S. Dubrovinsky C. Lathe C. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):407-411
The crystal and magnetic structures of Pr0.15Sr0.85MnO3
manganite have been studied by means of powder X-ray and neutron diffraction
in the temperature range 10–400 K at high external pressures up to 55 and 4 GPa, respectively. A structural phase transition
from cubic to tetragonal
phase upon compression was observed, with large positive pressure
coefficient of transition temperature dT
ct
/dP = 28(2) K/GPa. The C-type
antiferromagnetic (AFM) ground state is formed below T
N
≈ 260 K
at ambient pressure. While at ambient pressure the structural and magnetic
transition temperatures are close, T
ct
~ T
N
, upon compression
they become decoupled with T
N
≪ T
ct
due to much weaker
T
N
pressure dependence with coefficient dT
N
/dP = 3.8(1) K/GPa. 相似文献
16.
M. Reehuis C. Ulrich P. Pattison M. Miyasaka Y. Tokura B. Keimer 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):27-34
The crystal structure and the magnetic ordering pattern of the electrically insulating perovskite CeVO3 was investigated by high-resolution powder X-ray diffraction and single-crystal neutron diffraction. A structural phase transition
from an orthorhombic to a monoclinic structure (with space groups Pbnm and P21/b, respectively) was observed upon cooling below T
s = 136 K. This transition is associated with a strong distortion of the VO6-octahedra and can be attributed to orbital ordering. A magnetic ordering transition driven by exchange interactions between
vanadium moments is observed at T
N = 124 K, and antiferromagnetic interactions between magnetic moments on vanadium and cerium ions induce a progressive magnetic
polarization of the cerium sublattice at lower temperatures. The full magnetic structure is described by a superposition of
the modes (C
x
, F
y
, −) and (F
x
, C
y
, −). The unit cell volume and the tilt angles of the VO6-octahedra in the CeVO3-crystal structure are anomalous compared to those of other members of the series RVO3 (R = lanthanide atom), and the ordered magnetic moments on both vanadium and cerium sublattices at low temperatures are considerably
smaller than the free-ion values of V3+ and Ce3+. Possible origins of this behavior are discussed. 相似文献
17.
A. A. Sinchenko Yu. I. Latyshev A. P. Orlov A. A. Ivanov P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):199-204
We have measured the Hall effect and the transverse
magnetoresistance in NbSe3 single crystals. In the liquid helium
temperature range we observed an absolute negative magnetoresistance
(NMR) — the value of the resistance under magnetic field being much
lower than that at zero field — in NbSe3 single crystals with a
thickness less than 5 μm with the magnetic field oriented in the
(b, c) plane. We show that this NMR effect is observed in the
magnetic field range in which the Hall constant changes its sign.
The results are qualitatively explained by the change of the surface
scattering contribution to the magnetoconductance in the magnetic
field range near the Hall voltage zero crossing. 相似文献
18.
A. Bhattacharjee P.J. van Koningsbruggen Joel S. Miller 《Journal of Physics and Chemistry of Solids》2008,69(11):2713-2718
The 57Fe Mössbauer spectroscopy of mononuclear [Fe(II)(isoxazole)6](ClO4)2 has been studied to reveal the thermal spin crossover of Fe(II) between low-spin (S=0) and high-spin (S=2) states. Temperature-dependent spin transition curves have been constructed with the least-square fitted data obtained from the Mössbauer spectra measured at various temperatures between 84 and 270 K during a cooling and heating cycle. This compound exhibits an unusual temperature-dependent spin transition behaviour with TC(↓)=223 and TC(↑)=213 K occurring in the reverse order in comparison to those observed in SQUID observation and many other spin transition compounds. The compound has three high-spin Fe(II) sites at the highest temperature of study of which two undergo spin transitions. The compound seems to undergo a structural phase transition around the spin transition temperature, which plays a significant role in the spin crossover behaviour as well as the magnetic properties of the compound at temperatures below TC. The present study reveals an increase in high-spin fraction upon heating in the temperature range below TC, and an explanation is provided. 相似文献
19.
High-energy ball milling has been shown to be a promising method for the fabrication of rare earth—transition metal nanopowders.
In this work, NdCo5 nanoflakes and nanoparticles have been produced by a two-stage high-energy ball milling (HEBM), by first using wet HEBM to
prepare precursor nanocrystalline powders followed by surfactant-assisted HEBM. NdCo5 flakes have a thickness below 150 nm and an aspect ratio as high as 102–103; the nanoparticles have an average size of 7 nm. Both the nanoparticles and nano-flakes exhibited high coercivities at low
temperatures, with values at 50 K of 3 and 3.7 kOe, respectively. The high values of coercivity can be attributed to the large
surface anisotropy of nanoparticles that leads to an effective uniaxial-type of behavior in contrast to the planar anisotropy
of the bulk samples. Angle-dependent magnetization measurements at different temperatures were used to determine the spin
reorientation transitions in the nanopowders and nanoparticles. The nanoparticles showed spin reorientation temperatures,
T
SR1 = 276 and T
SR2 = 237 K which are lower when compared with the values of 290 and 245 K, respectively for bulk. 相似文献
20.
A. V. Malakhovskii S. L. Gnatchenko I. S. Kachur V. G. Piryatinskaya A. L. Sukhachev V. L. Temerov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(5):721-723
Optical absorption spectra of the trigonal crystal of TbFe3(BO3)4 in the vicinity of the 7F6 → 5D4 transition in a Tb3+ ion were studied as a function of temperature (2–70 K) and magnetic field strength (0–60 kOe) at 2 K. The splitting of the
excited states of Tb3+ due to both the magnetic ordering of iron and an external magnetic field was determined. Abrupt splitting of the absorption
lines of Tb3+ at temperature TN of the magnetic ordering of the subsystem of iron was revealed, suggesting that the nature of such splitting is not entirely
magnetic. 相似文献