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1.
Physical mechanisms of magnetization reversal of multilayer magnetic nanofilms by laser radiation are examined and the experiments
on the effect of the magnetic field and nanosecond and picosecond laser pulses on the conductivity of the Tb 19Co 5Fe 76/Pr 6O 11/Tb 22Co 5Fe 73 and Co 80Fe 20/Pr 6O 11/Co 30Fe 70 tunnel microcontacts are carried out. It is shown that with the help of such laser pulses, magnetization reversal of magnetic
nanolayers is possible in a zero external magnetic field under the action of the spin current magnetic field, induced by the
photon pressure of laser radiation, or the magnetic field generated by circularly polarized picosecond laser pulses. A relative
change in the resistance upon the laser magnetization reversal of one of the nanolayers in the Co 80Fe 20/Pr 6O 11/Co 30Fe 70 microcontacts reaches a value of Δ R/ R = 0.06 for T = 300 K and Δ R/ R = 0.25 for T = 80 K, in the Tb 19Co 5Fe 76/Pr 6O 11/Tb 22Co 5Fe 73 microcontacts, Δ R/ R = 0.3 for T = 300 K and Δ R/ R = 0.7 for T = 80 K. 相似文献
2.
The crystal structure and Raman spectra of Pr 0.7Ca 0.3MnO 3 manganite at high pressures of up to 30 GPa and the magnetic structure at pressures of up to 1 GPa have been studied. A structural
phase transition from the orthorhombic phase of the Pnma symmetry to the high-pressure orthorhombic phase of the Imma symmetry has been observed at P ∼ 15 GPa and room temperature. Anomalies of the pressure dependences of the bending and stretching vibrational modes have
been observed in the region of the phase transition. A magnetic phase transition from the initial ferromagnetic ground state
( T
C = 120 K) to the A-type antiferromagnetic state ( T
N = 140 K) takes place at a relatively low pressure of P = 1 GPa in the low-temperature region. The structural mechanisms of the change of the character of the magnetic ordering
have been discussed. 相似文献
3.
The crystal and magnetic structures of manganite Pr 0.7Ba 0.3MnO 3 have been studied at high pressures of up to 5.1 GPa and temperatures from 10 to 300 K by means of the neutron diffraction.
At normal pressure and a temperature T
C = 200 K, a ferromagnetic state forms in Pr 0.7Ba 0.3MnO 3. At high pressures P ≥ 1.9 GPa and T < T
N ≈ 153 K, a new antiferromagnetic state of A-type have been observed. Under high pressure, the Curie temperature T
C increases with the characteristic quantity dT
C/ dP ≈ 2.4 K/GPa. A possible reason for the appearance of an A-type antiferromagnetic phase in Pr 0.7Ba 0.3MnO 3 at high pressures may be anisotropic uniaxial compression of oxygen octahedra along the b axis of the orthorhombic structure. 相似文献
4.
The structural and magnetic transitions in Pr 0.5Sr 0.41Ca 0.09MnO 3 have been investigated by neutron diffraction and electron microscopy. Two structural transitions, Imma to I4/mcm and I4/mcm to Pmmn, are observed by decreasing the temperature. Two magnetic transitions, from a paramagnetic insulating to a ferromagnetic metallic and from a ferromagnetic metallic to an antiferromagnetic insulating states at TC=250 K and TN=180 K, respectively, are also observed. The structures of these three forms have been determined from neutron powder diffraction data. The first important result concerns the low temperature antiferromagnetic CE type and charge ordered structure, which has been refined in the Pmmn space group, without any constraint. This structure is completely long range ordered, with two Mn-sites, Mn 3+ in tetragonally elongated octahedra, and Mn 4+, off-centered in nearly regular octahedra. The second important point concerns the abrupt character of the structural transition from the I4/mcm to the Pmmn structure, without any appearance of incommensurability. The magnetic and transport properties of this compound are compared with those of Pr 0.5Sr 0.5MnO 3. 相似文献
5.
A systematic study of the structural, magnetic and electrical properties of the manganites Pr 1-x Sr x MnO 3(0≤ x ≤ 0.5) has been carried out. X-ray diffraction investigation shows a structural change with composition, from orthorhombic (0 ≤ x ≤ 0.2) to rhombohedral (0.25 ≤ x ≤ 0.5). The magnetic properties of Pr 1-x Sr x MnO 3 samples could be explained on the basis of a double exchange mechanism between pairs of Mn 3+ and Mn 4+ ions. These properties are strongly dependent on the ratio of Mn 3+/Mn 4+. The maximum of the ferromagnetic transition temperature Tc is reached at x ≈ 0.35 corresponding to a value 1.85 of this ratio. The investigation of the electrical properties shows a semiconductor to metal transition as a function of temperature (0.25≤ x≤0.4) with a metallic-like behaviour above a critical temperature Tp . A semiconducting-like one is observed for all the range of temperature (50–300 K) for (0 ≤ x ≤ 0.2 and x = 0.5). The evolution of activated energies with the carrier concentration has been investigated. 相似文献
6.
The heat capacity and the magnetocaloric effect of Pr0.6Sr0.4Mn1–xFexO3(x = 0 and 0.1) manganite have been studied in the temperature range 80–350 K and magnetic fields to 18 kOe. The magnetocaloric effect is estimated using two independent methods: the method of magnetic field modulation (direct method) and from the data on the heat capacity in magnetic field and without magnetic field (indirect method). The substitution of Fe atoms for Mn atoms (x = 0.1) shifts T
C by 167 K to lower temperatures; in this case, the magnetocaloric effect (MCE) is changed insignificantly in magnetic field 18 kOe with ΔS
M = 2.05 and 2.31 J/kg K for x = 0 and 0.10, respectively. 相似文献
7.
The crystal and magnetic structure and the Raman spectra in Pr 0.7Ba 0.3MnO 3 manganite have been studied by the neutron diffraction technique at pressures up to 5 GPa as well as by the X-ray diffraction
and Raman spectroscopy at pressures up to 30 GPa. The pressure dependence is determined for the lattice parameters, unit cell
volume, Mn-O bond lengths in the orthorhombic structure of the Imma symmetry, and bending and stretching vibration modes for oxygen octahedra. In the low-temperature range at pressure P = 1.9 GPa, the magnetic transition from the initial ferromagnetic (FM) ground state ( T
C = 197 K) to the A-type antiferromagnetic (AFM) state ( T
N = 153 K) has been revealed. The FM and AFM phases coexist at pressures up to 5.1 GPa and exhibit negative and positive values
of the pressure coefficient for the Curie and Néel temperature, respectively ( dT
C/ dP = −2.3 K/GPa and dT
N/ dP = 8 K/GPa). The pressure dependence of the Curie temperature in Pr 0.7Ba 0.3MnO 3 differs drastically from that observed in other manganites of nearly the same composition with the orthorhombic Pnma and rhombohedral R[`3] cR\bar 3c structures, where the FM phase is characterized by the positive values of dT
C/ dP. The structural mechanisms of these phenomena are discussed. 相似文献
8.
A crystal and magnetic structure of manganites Pr 0.7Ca 0.3Mn 1?y Fe y O 3 ( y = 0, 0.1) has been studied by means of powder neutron diffraction at pressures up to 4 GPa in the temperature range 15-300 K. Under high pressure, an appearance of A-type antiferromagnetic state in both systems was observed. Both compounds exhibit anisotropic compression of the lattice which leads to the apical compression of MnO 6 octahedra along the crystallographic b-axis. The calculated from obtained structural data pressure dependence of the charge-carrier bandwidth is in a qualitative agreement with observed pressure behavior of insulator-metal transition temperature within the framework of the double-exchange model. 相似文献
9.
The influence of Ga or Si substitution for Co on the structural and magnetic properties of Pr 2Co 17 compounds is investigated. All samples studied here are single phase and have the rhombohedral Th 2Zn 17-type structure. The unit-cell volume is found to increase linearly by the substitution of Ga for Co,but reduce by the substitution of Si for Co in Pr 2Co 17 compounds. In Pr 2Co 17-x M x, the Curie temperature decreases monoto nically with increasing at an approximate rate of 153K per Ga atom and 175K per Si atom. The saturation magnetic moment of Pr 2Co 17-x M x ( M=Ga,Si) decreases with increasing x. The rates of the decrease are larger than that expected as a simple dilution. For Pr 2Co 17-xSi x ,the spin reorientation transition is observed above room temperature. The spin-reorientation temperature Tsrfirst decreases with increasing Si content and then increases at higher x values (x>2). The spin reorientat ion behavior is interpreted by the competition between the Pr and Co sublattice anisotropies. The easy magnetization direction in Pr 2Co 17-xGa x compounds is perpendicular to the c-axis, and no spin reorientation transition is observed. 相似文献
10.
Studies of the structural, magnetic and magnetocaloric properties of polycrystalline Pr 0.6−xEu xSr 0.4MnO 3 (0≤x≤0.15) perovskite manganites were carried out. Substitution for praseodymium with europium, with smaller ionic radius, induces local distortion in the 〈Mn–O–Mn〉 bonds and consequently causes a random distribution in the magnetic exchange interactions. The competition between magnetic interactions leads to the appearance of an inhomogeneous magnetic state in our samples. Pr 0.6−xEu xSr 0.4MnO 3 ( x=0, 0.05, 0.1 and 0.15) polycrystalline samples were prepared using the solid–solid reaction method at high temperature. The compounds yielded are single phase and crystallize in the orthorhombic system with the Pnma space group. The substitution of Eu for Pr leads to a decrease of the Curie temperature TC from 303 K for x=0.00 to 260 K for x=0.15. All of our compounds exhibit a large magnetic entropy change with a maximum around 2.2 J/kg K under a magnetic applied field change of 2 T for all compounds. 相似文献
11.
A novel class of Co-substituted 3 : 29 materials, Pr 3(Fe 1−xCo x) 27.5Ti 1.5 ( x=0, 0.1, 0.2, 0.3) have been synthesized. Rietveld analysis of X-ray powder diffraction patterns for the x=0, 0.1 and 0.2 compositions showed that nearly all of the compounds are formed in monoclinic symmetry, with A2/m space group with traces of α-Fe, whereas, in x=0.3, additional traces of a (Co/Fe)–Ti (1 : 12) phase are also seen. The saturation magnetization increases with Co concentration both at 5 and 300 K and is explained on the basis of a rigid band model. A magnetic transition is observed for x=0.1 near 240 K. A large increase in Curie temperature, of about 180 K for x=0.1 and about 110 K for the other concentrations, is discussed on the basis of the strengthening of TM–TM exchange by the preferential occupation of Co in some of the Fe sites originally participating in antiferromagnetic bonds. 相似文献
12.
The magnetic and magnetotransport properties of Pr 0.5Sr 0.5Mn 1 − x
Co
x
O 3 ( x ≤ 0.5) solid solutions have been investigated using neutron diffraction methods. The magnetization and electrical conductivity
have been measured in magnetic fields up to 140 kOe. It has been established that, during cooling in the temperature range
from 160 to 110 K, the compounds of compositions with a cobalt content x ≤ 0.07 undergo a structural phase transition from the high-temperature ferromagnetic phase to the antiferromagnetic phase.
A further substitution of cobalt for manganese leads to a stabilization of the inhomogeneous dielectric ferromagnetic state,
whereas a state of the cluster spin-glass type has been revealed in compositions with x = 0.15 and 0.20. At x ≥ 0.25, a new magnetic phase with a Curie temperature up to 210 K is formed as a result of the magnetic interaction between
manganese and cobalt ions. A magnetic phase diagram of the system under investigation has been constructed. 相似文献
13.
Optical spectroscopy was used to obtain information on the energy and symmetry of the crystal-field (CF) levels within the
4 f
2 configuration of Pr 3+ in PrFe 3(BO 3) 4, along with changes in the frequencies and intensities of the f- f transition lines upon magnetic ordering ( T
N
= 32K). Analysis of the experimental data yielded the values of the parameters for the CF and the anisotropic Pr 3+-Fe 3+ exchange-interaction Hamiltonians. 相似文献
14.
采用固相烧结方法制备了Pr1-xCaxMnO3(x=0.3)钙态矿结构锰氧化物陶瓷样品,对其在磁场和电场下的直、交流输运性质做了系统研究.通过测量加磁场和零场下的Ⅰ-Ⅴ曲线,得到其居里温度为150K,与VSM测试结果一致.通过测量加磁场与零场下交流的阻抗频谱,发现加磁场后样品的晶界电阻明显减小,而晶粒电阻几乎保持不变,表明Pr1-xCaxMnO3陶瓷多晶样品的CMR效应源于样品的晶界.为确定晶界处的势垒高度,测量了样品在不同频率下的阻抗温谱,根据Arrhenius定律拟合得出势垒高度为117 meV,与用直流R-T数据拟合得出的激活能一致. 相似文献
15.
研究了Pr xFe 82-x-yTi yCo 10B 4C 4 ( x=9—10.5; y=0, 2)纳米晶薄带的结构与磁性. 结果表明,所有薄带皆主要由2∶14∶1, 2∶17和α-(Fe, Co)三相组成. 对于 y=0的合金,其内禀矫顽力随Pr含量 x的增加而增加,剩磁随Pr含量 x的增加而减小. 以Ti置换部分Fe ( y=2),合金的磁性能得到显著提高,表现为:添加Ti后,合金的剩磁 Br基本不降低, x=10.5时合金的 Br值甚至有较明显的提高;同时添加Ti后,合金的内禀矫顽力及退磁曲线的方形度都明显改善. 当 x=10.5,y=2时,合金薄带的磁性能达到最佳值为: Br=9.6 kGs(1 Gs=10 -4 T), iHc =10.2 kOe(1 Oe=79.5775 A/m)和( BH) max=17.4 MGOe. 随着Pr含量的提高,合金中的硬磁相2 ∶14 ∶1的含量相对增加,内禀矫顽力提高;而Ti置换Fe抑制了软磁相α-(Fe, Co)在快淬和热处理过程中的优先长大,使合金中软磁相和硬磁相的晶粒尺寸及比例趋向最佳组合,交换耦合作用明显增强.
关键词:
纳米晶永磁材料
2Fe 14(C')" href="#">Pr 2Fe 14(C
B)
Ti添加
交换耦合 相似文献
16.
The magnetocaloric effect in alternating magnetic fields has been investigated in Pr 1 − x
Ag
x
MnO 3 manganites with x = 0.05−0.25. The stepwise reversal of the sign of the magnetocaloric effect has been revealed in a weakly doped sample ( x = 0.05) at low temperatures (∼80 K). This reversal is attributed to the coexistence of the ferromagnetic and canted antiferromagnetic
phases with different critical temperatures. 相似文献
17.
The magnetocaloric effect in polycrystalline of Pr 1-xSr xMnO 3 (x=0.33, 0.43, 0.50) has been investigated. A large magnetic entropy change (7.1J/kgK) was discovered in Pr 0.5Sr 0.5MnO 3 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
18.
We have compared the electrical and magnetic properties of Ru(Gd 1.5−x
Pr
x
)Ce 0.5Sr 2Cu 2O 10−δ
(Pr/Gd samples) with x = 0.0, 0.01, 0.03, 0.033, 0.035, 0.04, 0.05, 0.06, 0.1 and RuGd 1.5(Ce 0.5−x
Pr
x
) Sr 2 Cu 2O 10−δ
(Pr/Ce samples) with x = 0.0, 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2 prepared by the standard solid-state reaction technique. We obtained the XRD
patterns for different samples with various x. The lattice parameters versus x for different substitutions have been obtained from Rietveld analysis. To determine how the magnetic and superconducting
properties of these layered cuprate systems can be affected by Pr substitution, the resistivity, and magnetoresistivity, with
H
ext
varying from 0.0 to 15 kOe, have been measured at various temperatures. Superconducting transition temperature T
c
and magnetic transition T
irr
, have been obtained through resistivity and ac susceptibility measurements. The T
c
suppression due to Pr/Gd and Pr/Ce substitutions show competition between pair breaking by magnetic impurities, hole doping
due to different valances of ions, difference in ionic radii, and oxygen stoichiometry. Pr/Gd substitution suppresses superconductivity
more rapidly than for Pr/Ce, showing that the effect of hole doping and magnetic impurity pair breaking is stronger than the
difference in ionic radii. In Pr/Gd substitution, the small difference between the ionic radii of Pr 3+,4+ and Gd 3+, and absorption of more oxygen due to the higher valence of Pr with respect to Gd, decreases the mean Ru-Ru distance, and
as a result, the magnetic exchange interaction becomes stronger with the increase of x. However, Pr/Ce substitution has the opposite effect. The magnetic parameters such as H
c
, obtained through magnetization measurements versus applied magnetic field isotherm at 77 K and room temperatures, become
stronger with x in Pr/Gd and weaker with x in Pr/Ce substitution. 相似文献
19.
The structural, magnetic, and magnetotransport properties of Pr 0.5Sr 0.5Co 1 − x
Mn
x
O 3 ( x < 0.65) perovskites are studied by magnetization and electrical conductivity measurements in magnetic fields up to 14 T and
by neutron diffraction. In the manganese concentration range x < 0.5 and T = 300 K, the crystal structure is described by monoclinic space group I2/ a; at x > 0.5, it is described by orthorhombic space group Imma. When the temperature decreases, a structural transformation without changing the symmetry takes place in all compounds.
This transformation is caused by an active role of the inner shells of the praseodymium ion in chemical bond formation. The
substitution of manganese for cobalt breaks a long-range ferromagnetic order near x ≈ 0.25, and a metal-dielectric transition occurs at x ≈ 0.15. The negative magnetoresistance is found to be maximal near a critical manganese concentration, where a long-range
magnetic order is broken; it reaches 95% in a field of 14 T at T = 10 K for x = 0.2. An unusual dielectric magnetic state with a small spontaneous magnetic moment and a sharp transition into a paramagnetic
state at T > 200 K is revealed in the concentration range 0.30 ≤ x ≤ 0.65 in spite of the absence of coherent magnetic neutron scattering. A model is proposed to explain the behavior of the
magnetic properties in this phase. 相似文献
20.
139La nuclear magnetic resonance spectra have been recorded and the spin-spin relaxation times in the paramagnetic region in
external magnetic fields of 5 and 9.4 T have been measured for two types of manganites: initial (La 0.25Pr 0.75) 0.7Ca 0.3Mn 16O 3 and enriched with the 18O isotope ((La 0.25Pr 0.75) 0.7Ca 0.3Mn 18O 3). The manganite enriched with the heavier oxygen isotope exhibits disappearance of a signal in the charge-ordering region
( T < T
co) in an external field of 5 T. This effect is related to the anomalous increase in the spin-spin relaxation rate. With an
increase in the external magnetic field to 9.4 T, the difference in the behavior of the relaxation rate for the two samples
in the charge-ordering region remains pronounced, although the magnitude of this effect becomes much smaller. The observed
giant isotope effect is a bright evidence of the important role of oxygen motion in the formation of long-range magnetic order
in the manganites under consideration.
Original Russian Text ? K.N. Mikhalev, I.E. Litvinov, Z.N. Nigamat’yanova, A.Yu. Yakubovskii, A.R. Kaul’, O.Yu. Gorbenko,
K. Kumagai, Y. Furukawa, 2007, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2007, Vol. 71, No. 5,
pp. 726–729. 相似文献
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