scholarly journals Аномальное изменение размера спинового полярона в парамагнитной области температур в La-=SUB=-1.2-=/SUB=-Sr-=SUB=-1.8-=/SUB=-Mn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-

2021 ◽  
Vol 63 (12) ◽  
pp. 1978
Author(s):  
С.А. Гудин
Keyword(s):  
Magnetic Field ◽  
Colossal Magnetoresistance ◽  
Double Perovskite ◽  
Peak Height ◽  
Temperature Curve ◽  
Linear Size ◽  
Spin Polaron ◽  
Anomalous Temperature ◽  
Increasing Temperature ◽  
The Magnetic Field

In this work, we continued the study of the magnetic and electrical properties of the double perovskite La1.2Sr1.8Mn2O7, which has a colossal magnetoresistance in excess of 1200 near the Curie temperature. It is shown that the colossal magnetoresistance observed in La1.2Sr1.8Mn2O7 is well described on the basis of the “orientational” and “spin-polaron” conduction mechanisms. It was found in the work that in the absence of a magnetic field, the linear size of the spin polaron decreases with increasing temperature in the ferromagnetic region, and upon the transition of manganite to the paramagnetic state, the linear size begins to increase, reaching a maximum at 180 K. At temperatures exceeding 180 K, an anomalous temperature change the size of the spin polaron disappears. In the absence of a magnetic field, the detected peak on the temperature curve of the change in the size of the spin polaron is maximal; with the inclusion of the magnetic field, the peak height decreases. Mechanisms are proposed to explain this anomalous temperature behavior of the spin polaron size.

scholarly journals Описание колоссального магнитосопротивления La-=SUB=-1.2-=/SUB=-Sr-=SUB=-1.8-=/SUB=-Mn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=- на основе "спин-поляронного" и "ориентационного" механизмов проводимости в парамагнитной области температур

2020 ◽  
Vol 62 (5) ◽  
pp. 669
Author(s):  
С.А. Гудин ◽  
Н.И. Солин
Keyword(s):  
Magnetic Field ◽  
Colossal Magnetoresistance ◽  
Main Role ◽  
Spin Polaron ◽  
Temperature Range ◽  
Conduction Mechanisms ◽  
Theoretical Investigations ◽  
Temperature Dependences ◽  
The Magnetic Field ◽  
Good Agreement

Experimental and theoretical investigations of the resistance of the La1.2Sr1.8Mn2O7 single crystal in magnetic fields from 0 to 90 kOe and in the temperature range from 75 to 300 K has been studied. The magnetoresistance is determined by the “spin-polaron” and “orientation” conduction mechanisms. Using the method of separating contributions to the magnetoresistance from several conduction mechanisms, the observed magnetoresistance of La1.2Sr1.8Mn2O7 manganite in the temperature range of 75-300 K is described, good agreement between the calculated and experimental data is obtained. In a magnetic field of 0 and 90 kOe, the temperature dependences of the size of the spin polaron (in relative units) are calculated for the temperature range 75–300 K. It is shown, that the КМС value is determined by an increase in the linear size of the spin polaron (along the magnetic field), i.e. the main role in the magnitude of the colossal magnetoresistance is made by the change in the size of the magnetic inhomogeneities of the crystal.

MAGHETOTHERMO POWER OF ZnO FILMS

2005 ◽  
Vol 19 (01n03) ◽  
pp. 651-653
Author(s):  
W. L. WANG ◽  
L. LI ◽  
K. J. LIAO ◽  
J. ZHANG ◽  
R. J. ZHANG ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thermoelectric Power ◽  
Substrate Surface ◽  
Zno Films ◽  
X Ray Diffraction ◽  
Electrical Measurements ◽  
X Ray ◽  
Increasing Temperature ◽  
The Magnetic Field ◽  
Orientation Growth

The Magnetothermoelectric and thermoelectric power of nano- ZnO films was investigated. The ZnO films in this study were prepared by DC reactive sputtering using a Zn target (99.99%) containing AL of 1.5%. The films obtained were characterized by SEM, x-ray diffraction, optical and electrical measurements. It was found that the sputtering ZnO films were highly orientation growth with the c-axis perpendicular to the substrate surface. The measurements showed that there was a striking seebeck effect in the ZnO films, and their thermoelectric power was linearly increased with increasing temperature. The experimental results were also demonstrated that the thermoelectric power was degraded under the magnetic field. This finding may ascribe to the magneto resistive effect.

scholarly journals Magnetic Field Measurements during Magnetic Pulse Welding Using CMR-B-Scalar Sensors

Sensors ◽  
2020 ◽  
Vol 20 (20) ◽  
pp. 5925
Author(s):  
Voitech Stankevic ◽  
Joern Lueg-Althoff ◽  
Marlon Hahn ◽  
A. Erman Tekkaya ◽  
Nerija Zurauskiene ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Colossal Magnetoresistance ◽  
Welding Process ◽  
Nondestructive Method ◽  
Magnetic Field Measurement ◽  
Magnetic Pulse ◽  
Magnetic Pulse Welding ◽  
Pulse Welding ◽  
The Magnetic Field

The possibility of applying CMR-B-scalar sensors made from thin manganite films exhibiting the colossal magnetoresistance effect as a fast-nondestructive method for the evaluation of the quality of the magnetic pulse welding (MPW) process is investigated in this paper. This method based on magnetic field magnitude measurements in the vicinity of the tools and joining parts was tested during the electromagnetic compression and MPW of an aluminum flyer tube with a steel parent. The testing setup used for the investigation allowed the simultaneous measurement of the flyer displacement, its velocity, and the magnitude of the magnetic field close to the flyer. The experimental results and simulations showed that, during the welding of the aluminum tube with the steel parent, the maximum magnetic field in the gap between the field shaper and the flyer is achieved much earlier than the maximum of the current pulse of the coil and that the first half-wave pulse of the magnetic field has two peaks. It was also found that the time instant of the minimum between these peaks depends on the charging energy of the capacitors and is associated with the collision of the flyer with the parent. Together with the first peak maximum and its time-position, this characteristic could be an indication of the welding quality. These results were confirmed by simultaneous measurements of the flyer displacement and velocity, as well as a numerical simulation of the magnetic field dynamics. The relationship between the peculiarities of the magnetic field pulse and the quality of the welding process is discussed. It was demonstrated that the proposed method of magnetic field measurement during magnetic pulse welding in combination with subsequent peel testing could be used as a nondestructive method for the monitoring of the quality of the welding process.

Phonon properties of delafossite multiferroic compound CuFeO2. Comparison with CuCrO2

2019 ◽  
Vol 33 (12) ◽  
pp. 1950141
Author(s):  
A. T. Apostolov ◽  
I. N. Apostolova ◽  
J. M. Wesselinowa
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Phase Transition ◽  
Dopant Concentration ◽  
Phonon Energy ◽  
Function Technique ◽  
Ion Doping ◽  
Increasing Temperature ◽  
The Magnetic Field ◽  
Phonon Properties

The temperature, magnetic field and ion doping dependence of the phonon properties of CuFeO2 are studied on the basis of a microscopic model and using Green’s function technique. The phonon energy decreases with increasing temperature, whereas the phonon damping increases. There is a kink at the phase transition temperature [Formula: see text] which shows the influence of the magnetic field on the phonon properties. The kinks vanish by applying an external magnetic field. By doping of ions with different radius compared to the Fe ion, the phonon energy in CuFeO2 can increase (Ga) or decrease (Sc) with increasing dopant concentration, whereas the damping is always enhanced. The results are compared with those of CuCrO2. Some discrepancies in the literature are discussed. The observed results are in qualitative agreement with the experimental data.

Electron Phase Microscopy of Magnetic Fields in Ferromagnets and Superconductors

2011 ◽  
Vol 1318 ◽  
Author(s):  
Akira Tonomura
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Colossal Magnetoresistance ◽  
Layer Plane ◽  
Perpendicular Recording ◽  
High Tc ◽  
Phase Microscopy ◽  
Highly Sensitive ◽  
Aharonov Bohm ◽  
The Magnetic Field

ABSTRACTHighly sensitive electron phase microscopy based on the Aharonov-Bohm (AB) effect principle has been used to observe microscopic distributions of magnetic fields in ferromagnets and superconductors. The observation examples include the unconventional behaviors of interlayer Josephson vortices in anisotropic layered high-Tc superconducting YBa2Cu3O7-δ (YBCO) thin films, which are produced when the applied magnetic field is greatly tilted to the layer plane, and the magnetic-field distributions of tiny magnetic heads for perpendicular recording and of colossal magnetoresistance (CMR) materials.

Features Of Magnetoresistance In The Bilayer Single Crystal Manganite LA1.4SR1.6MN2O7

2015 ◽  
Vol 10 (1) ◽  
pp. 63-66
Author(s):  
Stanislav Nikitin ◽  
Sergey Popkov ◽  
Mikhail Petrov ◽  
Konstantin Terent’ev ◽  
Sergey Semenov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Crystal ◽  
Colossal Magnetoresistance ◽  
Transport Current ◽  
Lanthanum Manganite ◽  
Magnetoresistance Effect ◽  
Positive Magnetoresistance ◽  
Lanthanum Manganites ◽  
Colossal Magnetoresistance Effect ◽  
The Magnetic Field

We investigate magnetoresistance of single-crystal bilayer lanthanum manganite La1.4Sr1.6Mn2O7 at a transport current flowing along the crystal c axis and in external magnetic fields applied parallel to the crystal c axis or ab plane. It is demonstrated that the La1.4Sr1.6Mn2O7 manganite exhibits the positive magnetoresistance effect in the magnetic field applied in the ab plane of the sample at the temperatures T < 60 K. The mechanism of this effect is shown to be fundamentally different from the colossal magnetoresistance effect typical of lanthanum manganites. The positive magnetoresistance originates from spin-dependent tunneling of carriers between the manganese-oxygen bilayers and can be explained by features of the magnetic structure of the investigated compounds.

INVESTIGATION OF THE HALL EFFECT IN RECTANGULAR QUANTUM WELLS WITH A PERPENDICULAR MAGNETIC FIELD IN THE PRESENCE OF A HIGH-FREQUENCY ELECTROMAGNETIC WAVE

2014 ◽  
Vol 28 (03) ◽  
pp. 1450001 ◽  
Author(s):  
NGUYEN QUANG BAU ◽  
BUI DINH HOI
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Wave ◽  
Quantum Wells ◽  
Hall Effect ◽  
High Frequency ◽  
Recent Experimental Data ◽  
Electron Systems ◽  
Dc Electric Field ◽  
Increasing Temperature ◽  
The Magnetic Field

The Hall effect is theoretically studied in a rectangular quantum well (RQW) with infinite barriers subjected to a crossed dc electric field and magnetic field (the magnetic field is oriented perpendicularly to the barriers) in the presence of a high-frequency electromagnetic wave (EMW). By using the quantum kinetic equation for electrons interacting with acoustic phonons at low temperatures, we obtain analytical expressions for the conductivity tensor as well as the Hall coefficient (HC). Numerical results for the AlGaN/GaN RQW show the Shubnikov–de Haas (SdH) oscillations in the magnetoresistance (MR) whose period does not depend on the temperature and amplitude decreases with increasing temperature. In the presence of the EMW, the MR shows maxima at Ω/ω c = 1, 2, 3, … and minima at Ω/ω c = 3/2, 5/2, 7/2, … (Ω and ω c are the EMW and the cyclotron frequencies, respectively), and with increasing of the EMW amplitude the MR approaches zero. Obtained results are in accordance with recent experimental data and in good agreement with other theories in two-dimensional (2D) electron systems. The results for the HC show a saturation of the HC as the magnetic field or the EMW frequency increases. Furthermore, in the region of large magnetic field the HC depends weakly on the well-width.

DYNAMICS AND LOCAL STRUCTURE OF COLOSSAL MAGNETORESISTANCE MANGANITES

2000 ◽  
Vol 14 (25n27) ◽  
pp. 2725-2730 ◽  
Author(s):  
C. CASTELLANO ◽  
F. CORDERO ◽  
R. CANTELLI ◽  
C. MENEGHINI ◽  
S. MOBILIO ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Wide Temperature Range ◽  
Colossal Magnetoresistance ◽  
Insulator Transition ◽  
Metal Insulator Transition ◽  
Double Peak ◽  
Metal Insulator ◽  
Temperature Range ◽  
The Magnetic Field

We report Extended X-ray Absorption Fine Structure and anelastic spectroscopy measurements on hole doped manganese oxides La 1-x Ca x MnO 3 which present the colossal magnetoresistance effect. EXAFS measurements were realized both in the absence and presence of an applied magnetic field of 1.1 Tesla, in a wide temperature range (between 330 and 77 K) and at various dopings (x = 0.25 and x = 0.33). The magnetic field orders the magnetic moments so favouring the electron mobility and the reduction of Mn-O octahedra distortions. We observe the presence of four short and two long Mn-O distances (1.93 and 2.05Å respectively) above and also below the metal-insulator phase transition. The overall distortion decreases but does not completely disappear in the metallic phase suggesting the possible coexistence of metallic and insulating regions at low temperatures. The magnetic field reduces the lattice distortions showing evidence of a microscopic counterpart of the macroscopic colossal magnetoresistance. We also present preliminary anelastic relaxation spectra in a wide temperature range from 900 K to 1 K on a sample with x = 0.40, in order to study the structural phase transitions and the lattice dynamics. A double peak has been observed at the metal-insulator transition in the imaginary part of Young's modulus. This double peak indicates that the metal-insulator transition could be a more complex phenomenon than a simple second order phase transition. In particular the peak at lower temperatures can be connected with the possible presence of inhomogeneous phase structures. Another intense dissipation peak has been observed corresponding to the structural orthorhombic-trigonal transition around 750 K.

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