Effect of the magnetic impurity on the charge diffusion in highly dilute Ce doped LaMnO3 (original) (raw)
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We performed a perturbed angular correlation (PAC) study on the prototypical LaMnO 3þd system that presents a rich variety of structural and magnetic phase transitions as a function of the oxygen content ðdÞ or as a function of temperature ðTÞ: The PAC signal at room temperature allowed the determination of the electrical field gradient parameters in the orthorhombic (O 0 or O Ã ) or rhombohedral (R) phases, which show a drastic changes in the O Ã -R transition. r
Studies of transport and magnetic properties of Ce-doped LaMnO3
Journal of Alloys and Compounds, 2004
The X-ray diffraction, electrical resistivity (ρ), piezoresistance, thermoelectric power (TEP, S) and magnetisation experiments have been performed on polycrystalline La 1 − x Ce x MnO 3 (x = 0-0.6) samples over a temperature range (20-320 K). All the compounds except x = 0.1 display a metal-insulator (MI) transition at T MI . From the analysis of the resistivity data we find that the double peaks observed in the ρ(T) data of ceramic samples are originating from the grain boundary effects. Moreover, the charge conduction at higher temperature occurs by means of a thermally activated polaron hopping mechanism. The application of pressure suppresses the resistivity and enhances the resistive transition temperature (T MI ) and hence the Curie temperature (T C ). The thermopower (TEP, S) of all the samples is positive and above T C , both the ρ(T) and S(T) curves show that charge conduction at high temperatures takes place according to Emin and Holstein's theory of adiabatic polaron hopping. At low temperatures, thermal variation of the magnetization (M) can be explained considering the conventional spin wave theory containing T 3/2 and T 2 terms. In the paramagnetic region, the M(T) data fits well with the Curie-Weiss law.
Physical review. B, Condensed matter, 1996
Using perturbed-angular-correlation ͑PAC͒ spectroscopy, via the 181 Hf→ 181 Ta probe, we have measured Mn-site electric-field gradients ͑EFG's͒ at Ta nuclei in ceramic samples of LaMnO 3 . Two crystallographic phases coexist over a temperature interval of Ϸ16 K near the orthorhombic-to-rhombohedral transition at Ϸ724 K, which shows a thermal hysteresis of Ϸ1.7Ϯ0.2 K. Concurrently, in the two phases, we determined the temperature dependence of the EFG parameters, V zz , , and ␦, and the ratio of the probe concentrations A 1 /A 2 . To explain the apparent coexistence of two phases in this weakly first-order transition, we present a model that assumes a spatial distribution of T c values. This distribution could arise from a spatially nonuniform distribution of Mn 4ϩ ions. We show the PAC technique to be a uniquely powerful probe of local symmetries that reflect the effects of a local distribution of valences, which drive the phase transition.
Tailoring the magnetic landscape in Al-doped LaMnO3: An experimental and computational perspective
Cornell University - arXiv, 2022
We have presented the synthesis, structural and the magnetic properties from the experimental point of view. Then we verified our experimental observation by studying the electronic and the magnetic properties of Al-doped LaMnO 3 from the first principle density functional theory (DFT) and Monte-Carlo simulation. We have synthesized the LaAl x Mn 1−x O 3 (x= 0.05, 0.15, 0.25) and performed the Rietveld refinement of XRD data to determine the lattice parameters. To see the mixed valance of Mn-ion, we have performed the XPS of 25% Al doped material. The magnetic study shows the ferromagnetic transition of these materials. Using xrd refinement values, we have performed the DFT calculations. The Monte Carlo simulation has been done through the anisotropic Ising model to analyze the origin of magnetic transition. We have determined the anisotropy and the interaction constants from the DFT calculations.
Evidence of a canted magnetic state in self-doped LaMnO 3+δ (δ = 0.04): a magnetocaloric study
Journal of Physics: Condensed Matter, 2012
We report a detailed investigation of the magnetocaloric properties of self-doped polycrystalline LaMnO 3+δ with δ = 0.04. Due to the self-doping effect, the system exhibits a magnetic transition from a paramagnetic to ferromagnetic-like canted magnetic state (CMS) at ∼120 K, which is associated with an appreciably large magnetocaloric effect (MCE). The CMS is an inhomogeneous magnetic phase developing due to a steady growth of antiferromagnetic correlation in its predominant ferromagnetic state below ∼120 K. The stabilization of CMS in this material is concluded from a comprehensive analysis of magnetocaloric data using Landau theory, which is in excellent agreement with our neutron diffraction study. The magnetic entropy change versus temperature curves for different applied fields collapse into a single curve, revealing a universal behavior of MCE. Our studies suggest that investigation of MCE is an effective technique to acquire fundamental understanding about the basic magnetic structure of a system with complex competing interactions.
Importance of anisotropic Coulomb interaction in LaMnO 3
Physical Review B, 2015
In low-temperature anti-ferromagnetic LaMnO3, strong and localized electronic interactions among Mn 3d electrons prevent a satisfactory description from standard local density and generalized gradient approximations in density functional theory calculations. Here we show that the strong on-site electronic interactions are described well only by using direct and exchange corrections to the intra-orbital Coulomb potential. Only DFT+U calculations with explicit exchange corrections produce a balanced picture of electronic, magnetic and structural observables in agreement with experiment. To understand the reason, a rewriting of the functional form of the +U corrections is presented that leads to a more physical and transparent understanding of the effect of these correction terms. The approach highlights the importance of Hund's coupling (intra-orbital exchange) in providing anisotropy across the occupation and energy eigenvalues of the Mn d states. This intra-orbital exchange is the key to reproducing experimental Jahn-Teller distortion, band gap and magnetic ground state in LaMnO3. PACS numbers: 71.15.Mb, 71.20.-b, 75.30.Et, 75.25.Dk arXiv:1503.08871v1 [cond-mat.mtrl-sci]
Study of the local magnetic environment in LaMnO3 perovskite by measuring hyperfine interactions
Journal of Magnetism …, 2004
TDPAC technique has been used to investigate the hyperfine interactions in the LaMnO 3 perovskite using 140 La( 140 Ce) as probe nuclei. Temperature dependence of the magnetic hyperfine field (MHF) at La sites shows an antiferromagnetic behavior with N! eel temperature around 142 K. For temperatures below 80 K, however, the values of MHF decrease and deviate from the expected regular behavior. r
Physica B: Condensed Matter, 2018
We have investigated the effect of cation deficiency on the electric and magnetic properties of LaMnO3 in terms of both substitution of La by a divalent ion (Sr 2+) and creating La-deficiency. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are to be found in rhombohedral structure. The excess oxygen in all compounds was detected through iodometric titration. The metal to semiconducting transition and the paramagnetic to ferromagnetic transition is found to decrease with Mn 4+ for all samples. The occurrence of magnetoresistance (MR) at low temperature and low field for La-deficient compounds is suggested due to the tunneling of electron through the grain boundary (GB). The nonlinear current-voltage (I − V) characteristic for La-deficient compounds indicates inelastic tunneling via localized states dominate the transport mechanism.
Structural and magnetic behavior of LaMnO3+δ and LaMn0.9Cr0.1O3+δ at the same “hole concentration”
Journal of Alloys and Compounds, 2004
We report a comparative magnetic and a neutron powder diffraction (NPD) study of un-doped LaMnO 3+δ (δ = 0.05 and 0.09) and Cr doped LaMn 0.9 Cr 0.1 O 3+δ (δ = 0.00 and 0.04) with the same "hole concentration". Samples with controlled oxygen contents were prepared by annealing at different temperatures and p(O 2) values. The refinement of the neutron powder diffraction data at 2 K shows that the AFM components for the Cr doped samples are higher than those of the un-doped ones for the same "hole concentration". The FC and ZFC dc magnetization measurements versus T under 100 Oe also reveal a strong AFM character for the Cr-doped samples. These results clearly show a different role in the magnetic interactions for samples doped with Cr 3+ and Mn 4+ ions.
Physical Review B, 2007
We observe a distinct anomaly in dielectric permittivity (ε') as well as relaxation time (τ 0 ) versus temperature (T) pattern at the antiferromagnetic transition point T N in single crystal of LaMnO 3 . The equivalent circuit analysis of the impedance spectra across T N reveals clear anomaly in the capacitive component C 0 at T N . Since no structural transition takes place across T N , the anomaly in τ 0 and C 0 at T N possibly signifies multiferroicity stemming from coupling between orbital and spin order in LaMnO 3 .