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Title: Detailed magnetic and structural properties of exchange-biased La{sub 1-x}Ca{sub x}MnO{sub 3}.

Abstract

We measured structural, magnetic and, magneto-transport properties of heterostructures consisting of La{sub 1-x} Ca{sub x} MnO{sub 3} ferromagnetic (FM) layers (x = 0.33) and antiferromagnetic (AF) layers (x = 0.67). We grew FM/AF superlattices via a high-pressure sputtering technique on (001) oriented SrTiO{sub 3} substrates. We systematically varied the thickness of the ferromagnetic layers, while maintaining a fixed thickness of the antiferromagnetic layers. Alternatively, we also varied the thickness of the antiferromagnetic layers, keeping a fixed ferromagnetic layer thickness. The total superlattice thickness was kept approximately constant. XRD analysis confirms the existence of the superlattice structure by the observation of multiple satellite peaks around the (00l) manganite Bragg reflections. We extracted the average lattice parameter of the superlattice and its dependence on the thicknesses of the ferro- and antiferromagnetic layers. We conducted field cooling (FC) and zero field cooling (ZFC), magneto-thermal, and magneto-resistance measurements. The existence of an exchange bias effect at temperatures below the Neel temperature of the AF layer was revealed by magnetization loops measured after FC. We studied the dependence of magnetic parameters on the thicknesses of the ferro- and antiferromagnetic layers. We found that the structural, magnetization, and magneto transport properties as functions of F-layer thicknessmore » are all correlated.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); COLCIENCIAS
OSTI Identifier:
940953
Report Number(s):
ANL/MSD/JA-62861
Journal ID: ISSN 1610-1634; TRN: US200824%%315
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys. Stat. Sol. C; Journal Volume: 4; Journal Issue: 11 ; 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; BRAGG REFLECTION; LATTICE PARAMETERS; MAGNETIZATION; NEEL TEMPERATURE; SUPERLATTICES; THICKNESS; LANTHANUM OXIDES; CALCIUM OXIDES; MANGANESE OXIDES; MAGNETORESISTANCE

Citation Formats

Gomez, M. E., Campillo, G., Ramirez, J.-G., Hoffmann, A., Guimpel, J., Univ. del Valle, and Inst. Balseiro. Detailed magnetic and structural properties of exchange-biased La{sub 1-x}Ca{sub x}MnO{sub 3}.. United States: N. p., 2007. Web. doi:10.1002/pssc.200675906.
Gomez, M. E., Campillo, G., Ramirez, J.-G., Hoffmann, A., Guimpel, J., Univ. del Valle, & Inst. Balseiro. Detailed magnetic and structural properties of exchange-biased La{sub 1-x}Ca{sub x}MnO{sub 3}.. United States. doi:10.1002/pssc.200675906.
Gomez, M. E., Campillo, G., Ramirez, J.-G., Hoffmann, A., Guimpel, J., Univ. del Valle, and Inst. Balseiro. Mon . "Detailed magnetic and structural properties of exchange-biased La{sub 1-x}Ca{sub x}MnO{sub 3}.". United States. doi:10.1002/pssc.200675906.
@article{osti_940953,
title = {Detailed magnetic and structural properties of exchange-biased La{sub 1-x}Ca{sub x}MnO{sub 3}.},
author = {Gomez, M. E. and Campillo, G. and Ramirez, J.-G. and Hoffmann, A. and Guimpel, J. and Univ. del Valle and Inst. Balseiro},
abstractNote = {We measured structural, magnetic and, magneto-transport properties of heterostructures consisting of La{sub 1-x} Ca{sub x} MnO{sub 3} ferromagnetic (FM) layers (x = 0.33) and antiferromagnetic (AF) layers (x = 0.67). We grew FM/AF superlattices via a high-pressure sputtering technique on (001) oriented SrTiO{sub 3} substrates. We systematically varied the thickness of the ferromagnetic layers, while maintaining a fixed thickness of the antiferromagnetic layers. Alternatively, we also varied the thickness of the antiferromagnetic layers, keeping a fixed ferromagnetic layer thickness. The total superlattice thickness was kept approximately constant. XRD analysis confirms the existence of the superlattice structure by the observation of multiple satellite peaks around the (00l) manganite Bragg reflections. We extracted the average lattice parameter of the superlattice and its dependence on the thicknesses of the ferro- and antiferromagnetic layers. We conducted field cooling (FC) and zero field cooling (ZFC), magneto-thermal, and magneto-resistance measurements. The existence of an exchange bias effect at temperatures below the Neel temperature of the AF layer was revealed by magnetization loops measured after FC. We studied the dependence of magnetic parameters on the thicknesses of the ferro- and antiferromagnetic layers. We found that the structural, magnetization, and magneto transport properties as functions of F-layer thickness are all correlated.},
doi = {10.1002/pssc.200675906},
journal = {Phys. Stat. Sol. C},
number = 11 ; 2007,
volume = 4,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Recent magnetometry measurements in modulation-doped La{sub 1-x}Ca{sub x}MnO{sub 3} suggested that a net magnetization extends from the ferromagnetic layers into the adjacent antiferromagnet layers. Here we test this hypothesis by polarized neutron reflectometry, which allows us to determine the depth resolved magnetization profile. From fits to the reflectivity data we find that the additional magnetization does not occur at the ferromagnetic/antiferromagnetic interfaces, but rather in a thin region of the first antiferromagnetic layer adjacent to the interface with the substrate.
  • Neutron scattering has been used to study the magnetic order, spin dynamics, and structural properties of La{sub 1{minus}x}Ca{sub x}MnO{sub 3} in the ferromagnetic regime (0{lt}x{lt}(1)/(2)). For x=(1)/(3)(T{sub C}=250 K) where the magnetoresistance effects are largest the system behaves as an ideal isotropic ferromagnet at low T, with a gapless ({lt}0.04 meV) dispersion relation E=Dq{sup 2} and D{sub T=0}{approx}155 meV{Angstrom}{sup 2}. However, an anomalous diffusive component develops above {approximately}200 K and dominates the fluctuation spectrum as T{r_arrow}T{sub C}. A magnetic field strongly reduces this quasielastic scattering, shifting the spectral weight into the spin wave component of the fluctuation spectrum. {copyright} {italmore » 1997 American Institute of Physics.}« less
  • Complementary x-ray synchrotron radiation diffraction (XRD) and resonant scattering (RXS) measurements were performed at the Mn K-edge between 10 and 300 K in order to analyze the effect of epitaxial strain and tetragonal lattice distortions on the exchange bias (EB) mechanism observed in [La{sub 2/3}Ca{sub 1/3}MnO{sub 3}(FM)/La{sub 1/3}Ca{sub 2/3}MnO{sub 3}(AF)]{sub 15} multilayers below a blocking temperature, T{sub B}, of 80 K. XRD measurements showed that the c/a axial ratio, an indication of the tetragonal lattice distortion in pseudocubic lattice settings, reaches its maximum at the onset of the EB effect and the corresponding structural correlation length varies substantially at themore » onset of T{sub B}. The in-plane lattice parameter a at T{sub B} is close to the bulk lattice parameters of the antiferromagnetic (AF) layers, thus indicating that the EB effect is related with the accommodation of strain inside the ferromagnetic (FM) and AF layers. RXS measurements revealed a ferrodistortive (FD) state. The RXS intensity difference signal exhibits a main-edge feature and a postedge feature at {approx}6.57 keV that scales linearly with temperature and the c/a ratio up to 80 K. The disappearance of the postedge feature above 80 K(=T{sub B}) may signify a rearrangement of Mn-O-Mn bonding angles due to strain-driven effects at the FM/AF interfaces, inducing disorder in FD octahedral tilt ordering which may pin the local distortions below the T{sub B}.« less
  • Using time-of-flight and triple-axis inelastic neutron spectroscopy, we determine spin-wave excitations throughout the Brillouin zone for ferromagnetic manganites La1−xCaxMnO3 (x=0.25, 0.3) in their lowtemperature metallic states. While spin-wave excitations in the long-wavelength limit spin stiffness D have similar values for both compounds, the excitations near the Brillouin-zone boundary of La0.7Ca0.3MnO3 are considerably softened in all symmetry directions compared to that of La0.75Ca0.25MnO3. A Heisenberg model with the nearest neighbor and the fourth neighbor exchange interactions can describe the overall dispersion curves fairly well. We compare the data with various theoretical models describing the spin excitations of ferromagnetic manganites.
  • In this work, we report the effect of Na doping on the structural, magnetic and magnetocaloric properties in La{sub 0.8}Ca{sub 0.2−x}Na{sub x}MnO{sub 3} powder samples. Our polycristalline samples have been synthesized using the solid-state reaction method at high temperatures. The parent compound La{sub 0.8}Ca{sub 0.2}MnO{sub 3} crystallizes in the orthorhombic system with Pbnm space group. Na doping induces a structural transition from orthorhombic (Pbnm space group) to rhombohedral (R-3C space group) symmetry. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperaturemore » T{sub C} increases with Na content from 240 K for x=0 to 330 K for x=0.2. A large magnetocaloric effect has been observed in all samples, the maximum entropy change, |∆S{sub M}|{sub max}, shifts to smaller values with increasing Na content, from4.56 J/kg K (x=0.05) to 2.3 J/kg K (x=0.2) under a magnetic field change ∆µ{sub 0}H of 2 T. For the same applied magnetic field of 2 T, the Relative Cooling Power (RCP) values are found to be constant around 91 J/kg. - Graphical abstract: Sodium doping induces an increase of T{sub C} from 240 K for x=0 to 330 K for x=0.2. - Highlights: • La{sub 0.8}Ca{sub 0.2−x}Na{sub x}MnO{sub 3} are synthesized using the ceramic method at high temperatures. • Na doping induces a structural transition from Pbnm to R-3C space group. • T{sub C} increases with Na content from 240 K for x=0 to 330 K for x=0.2. • RCP is constant around 91 J/kg for all compounds under 2 T.« less