Enhancement of the CMR Effect Near Room Temperature by Defects and Structural Transitions in La1−x−yCaxSryMnO3

1999 ◽  
Vol 602 ◽  
Author(s):  
S. Kolesnik ◽  
B. Dabrowski ◽  
Z. Bukowski ◽  
J. Mais
Keyword(s):  
Magnetic Field ◽  
Room Temperature ◽  
Structural Phase ◽  
Zero Magnetic Field ◽  
Ferromagnetic Transition ◽  
Spin Lattice ◽  
Preparation Conditions ◽  
Close Proximity ◽  
Selection Of ◽  
Structural Phase Transformations

AbstractWe have studied magnetoresistance of a series of La1−xSrxMnO3 and La1−x−yCaxSryMnO3 samples, for which structural and ferromagnetic transformation temperatures are in close proximity. On cooling in zero magnetic field, we observe a rapid increase of resistivity just above TC for La1−xSrxMnO3 samples with x < 0.1425 and x ≤ 0.1725 due to the O*-O' and R-O* - structural phase transformations, respectively. This increase is followed by a rapid decrease due to the ferromagnetic transition. The applied magnetic field significantly shifts the ferromagnetic transition to higher temperatures and suppresses the structure-related resistivity increase. We show that a combination of structural and ferromagnetic transitions gives rise to an enhancement of the negative magnetoresistance due to strong spin-lattice coupling. By choosing a proper composition, the enhancement can be optimized to appear in relatively low magnetic fields. A proper selection of Sr and Ca contents in La1−x−yCaxSryMnO3 and preparation conditions leads to an enhancement of the magnetoresistance effect at room temperature.

scholarly journals Skyrmion formation in a bulk chiral magnet at zero magnetic field and above room temperature

2017 ◽  
Vol 1 (7) ◽  
Author(s):  
K. Karube ◽  
J. S. White ◽  
D. Morikawa ◽  
M. Bartkowiak ◽  
A. Kikkawa ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Room Temperature ◽  
Zero Magnetic Field

Convergent-beam characterization of some oxides which undergo structural phase transformations

1987 ◽  
Vol 45 ◽  
pp. 20-23
Author(s):  
M. Tanaka
Keyword(s):  
Phase Transformations ◽  
Room Temperature ◽  
Materials Science ◽  
Present Report ◽  
Structural Phase ◽  
Crystal Defects ◽  
Temperature Phase ◽  
Space Group ◽  
Convergent Beam ◽  
Structural Phase Transformations

We have been concerned with the development of convergent-beam electron diffraction (CBED) techniques and their application to materials science. Our effort is now concentrated to identify the nature of crystal defects. Our application has been focussed on materials most of which undergo structural phase transformations: NdNbO4, La2Ti2O7, Sr2(Ta1-xNbx)2O7, Fe3O4, PbZrO3, PbZrO0-7Ti0.3O3, SrTiO3, BaPb1-xBixO3, hex.BaTiO3, Bi2.5Na0.5Nb2O9, MgAl2O4, MnSi, TaS3, NbS3+x, Mo2S3. In the present report, the results on four oxides will be reviewed.a) La2Ti2O7Gasperin determined the space group of the room temperature phase to be P21, but Scheunemann and Miüller-Buschbaum reported its space group to be Pna21. Ishizawa et al. studied the phase transformation between room temperature and 1173 K using X-ray diffraction. They determined the space group of the room temperature phase to be P21 and found the presence of twin domains.

Optically Detected Spin Locking of Zero Field Electronic Triplet States and Cross Relaxation in the Rotating Frame

1975 ◽  
Vol 30 (3) ◽  
pp. 361-371 ◽  
Author(s):  
H. Schuch ◽  
C. B. Harris
Keyword(s):  
Magnetic Field ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Triplet States ◽  
Rotating Frame ◽  
Spin Lattice ◽  
Optically Detected ◽  
Spin Locking

The spin locking method known from NMR is shown to be useful also in ESR for investigating spin lattice relaxation problems and “slow” motions, e. g. questions of energy transfer by triplet states in organic molecular crystals, and probing of nuclear quadrupolar splittings even smaller than the ESR line width at zero magnetic field.Optically detected ESR spin locking experiments for isolated triplet states in zero field are demonstrated. It is shown how the complication of incoming and decaying triplet states and relaxation between all three triplet sublevels has to be handled during spin locking. An application, the study of the cross-relaxation between electronic triplet spin states and deuteron or proton spins is presented. These experiments are possible in spite of the first order quenching of the hyperfine coupling in zero magnetic field. Another application is briefly mentioned, in which the adiabatically demagnetized state in the rotating frame is used to probe the electronic triplet state transfer and nuclear spin lattice relaxation.

scholarly journals Field induced crossover in critical behaviour and direct measurement of the magnetocaloric properties of La0.4Pr0.3Ca0.1Sr0.2MnO3

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Sagar Ghorai ◽  
Ridha Skini ◽  
Daniel Hedlund ◽  
Petter Ström ◽  
Peter Svedlindh
Keyword(s):  
Magnetic Field ◽  
Temperature Change ◽  
Room Temperature ◽  
Ion Beam ◽  
Mean Field ◽  
Critical Behaviour ◽  
Potential Candidate ◽  
Ferromagnetic Transition ◽  
X Ray ◽  
Lattice Distortions

Abstract La0.4Pr0.3Ca0.1Sr0.2MnO3 has been investigated as a potential candidate for room temperature magnetic refrigeration. Results from X-ray powder diffraction reveal an orthorhombic structure with Pnma space group. The electronic and chemical properties have been confirmed by X-ray photoelectron spectroscopy and ion-beam analysis. A second-order paramagnetic to ferromagnetic transition was observed near room temperature (289 K), with a mean-field like critical behaviour at low field and a tricritical mean-field like behaviour at high field. The field induced crossover in critical behaviour is a consequence of the system being close to a first-order magnetic transition in combination with a magnetic field induced suppression of local lattice distortions. The lattice distortions consist of interconnected and weakly distorted pairs of Mn-ions, where each pair shares an electron and a hole, dispersed by large Jahn–Teller distortions at Mn3+ lattice sites. A comparatively high value of the isothermal entropy-change (3.08 J/kg-K at 2 T) is observed and the direct measurements of the adiabatic temperature change reveal a temperature change of 1.5 K for a magnetic field change of 1.9 T.

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