Magnetic Properties Of Manganites Research Articles

Critical Behavior and Its Correlation with Magneto-Electrical Properties in La0.47Ln0.2Pb0.33MnO3 (Ln = Y and Eu) Polycrystalline

The relationship between electrical and magnetic properties of manganites has been traced through the analysis of dependence of La0.47Eu0.2Pb0.33MnO3 (LEPMO) and La0.47Y0.2Pb0.33MnO3 (LYPMO) resistivity on temperature. The dependence of electrical resistivity on temperature shows a metal–semiconductor transition at TM-Sc and a decrease in TM-sc with Eu and Y substitution. The critical property of both systems around second order transition was investigated using Fisher–Langer relation and Suezaki–Mori method. The obtained exponents values from resistivity were so close to those predicted by the 3D-Ising model. These results and the analysis of the critical exponents from magnetization measurements were in good agreement. For low temperatures (T < TM-Sc), the electrical conduction process obeys the Scattering model defined by $$\rho (T) = \rho_{0} + \rho_{2} T^{2} + \rho_{5} T^{5}$$ . While for T > TM-Sc, for the two samples, the mechanism of electrical conduction is governed by the thermal activation model defined by $$\rho = \rho_{0} T\exp (E_{\text{a}} /k_{\text{B}} T)$$ . In order to understand the transport mechanism in the whole temperature range, the phenomenological percolation model, based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions, was used in fitting the electrical resistivity. Therefore, it was found that the estimated values of the resistivity are in good agreement with experimental data. Magnetoresistance study showed a peak that has a great value around the transition temperature (TM-Sc).

Correlation between magnetic and electrical properties of La0.6Sr0.4Mn0.9V0.1O3 based on critical behavior

ABSTRACTThe electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic isolant regions. So, we found that the estimated results are in adequate accordance with experimental data. The relationship between electrical and magnetic properties of manganites has been traced through the analysis of temperature dependence of the La0.6Sr0.4Mn0.9V0.1O3 resistivity. The estimated critical exponents are (β = 0.326 ± 0.01; γ=1.237 ± 0.02 and α = 0.112). The values of these exponents obtained from resistivity are very close to them predicted by the 3D-Ising model. These results are in good agreement with the analysis of critical exponents from magnetization measurements. The obtained values of the temperature coefficient of resistance (TCR) for La0.6Sr0.4Mn0.9V0.1O3 sample is comparable with some systems used for infrared sensors.

Giant magnetoresistance and correlation between critical behavior and electrical properties in a new compound La0.6Gd0.1Sr0.3Mn0.8Si0.2O3 manganite

We investigated the influence of silicone (Si) doping on the structural, magnetic and electrical properties of polycrystalline sample La0.6 Gd0.1 Sr0.3 Mn0.8 Si0.2 O3 (LGSMSiO), prepared by sol–gel method. The crystallographic study showed that the sample crystallizes in orthorhombic system with Pnma space group. The relationship between the electrical and magnetic properties of manganites was traced through analyzing the dependence of LGSMSiO resistivity on temperature. The measurement of resistivity versus the temperature ρ(T) showed a transition change from ferromagnetic (FM) to paramagnetic (PM) at Curie temperature (TC), this usually accompanied by a simultaneous metal-semiconductor (M-semiconductor) transition. Resistivity decreased with increasing the applied magnetic field. The values of TM-semiconductor were found to move towards a high temperature side with increasing the magnetic field. The critical properties of electron doped manganite LGSMSiO were investigated on the data of static magnetization measurements around the second order ferromagnetic-paramagnetic transition region TC. The magnetic data analyzed in the critical region using Kouvel-Fisher method yield the critical exponents of γ=1.013±0.02 with TC=270.69±0.22K (from the temperature dependence of inverse initial susceptibility above TC) and β=0.2535±0.0032 with TC=269.89±0.12K (from the temperature dependence of spontaneous magnetization below TC). The critical magnetization isotherm M(TC, μ0H) gives δ = 5.01 ± 0.03. The critical exponents found in this study obeyed the Widom scaling relation: δ = 1+γ/β, implying that the obtained values of γ and β are reliable.The exponents values obtained from resistivity were quite close to those predicted by the tricritical mean-field model. These results were in good agreement with the analysis of the critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of the ferromagnetic metallic regions and the paramagnetic semiconductor regions. So, we found that the estimated results were in accordance with the experimental data. The magnetocaloric value is 5.35 J/kgK, extracted from the M(μ0H) curves.

Critical scaling and percolation model in La0.57Gd0.1Sr0.33Mn0.9In0.1O3 manganite

We investigated the influence of indium (In) doping on the structural, magnetic and electrical properties of polycrystalline sample La0.57Gd0.1Sr0.33Mn0.9In0.1O3, prepared by sol–gel method. The crystallographic study showed that the sample crystallizes in the rhombohedral system with R3¯c space group. The relationship between the electrical and magnetic properties of manganites was traced through analyzing the dependence of La0.57Gd0.1Sr0.33Mn0.9In0.1O3 resistivity on temperature. The measurement of resistivity versus the temperature ρ(T) of the sample showed that a ferromagnetic (FM) to a paramagnetic (PM) transition at Curie temperature (TC) was usually accompanied by a simultaneous metal-insulator (M-I) transition. Resistivity decreased with increasing the applied magnetic field. The values of TM−Sc were found to move towards a high temperature side with increasing the magnetic field. The estimated critical exponents are (β = 0.272 ± 0.004; γ = 1.067 ± 0.002 and α = 0.453). The values of these exponents obtained from resistivity were very close to those predicted by the tricritical mean-field model. These results were in good agreement with the analysis of the critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of the ferromagnetic metallic regions and the paramagnetic semiconductor regions. So, we found that the estimated results were in accordance with the experimental data.

Correlation between magnetic and electric properties of La0.5Ca0.3Ag0.2MnO3 based on critical behavior of resistivity

The relationship between electrical and magnetic properties of manganites has been traced through the analysis of temperature dependence of the La0.5Ca0.3Ag0.2MnO3 resistivity. The measurement of resistivity versus temperature ρ(T) of the sample shows a paramagnetic semiconductor-ferromagnetic metallic transition at T=TMS. The application of magnetic field increases the TMS value and reduces the resistivity of the compound. The estimated critical exponents are (β=0.273±0.01; γ= 1.074±0.02 and α=0.456). The values of these exponents obtained from resistivity are very close to them predicted by the tri-critical mean-field model. These results are in good agreement with the analysis of critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic semiconductor regions. So, we found that the estimated results are in adequate accordance with experimental data.

Magnetic properties of manganites doped with gallium, iron, and chromium ions

The magnetization and the crystal structure of the La0.7Sr0.3Mn1 − xMxO3 (M = Ga, Fe, Cr; x ≤ 0.3) systems are studied. The substitution of gallium and chromium is shown to cause phase separation into antiferromagnetic and ferromagnetic phases, whereas the substitution of iron for manganese stabilizes a spinglass state. The ferromagnetic phase in the chromium-substituted compositions is much more stable than that in the case of substitution by iron ions or diamagnetic gallium ions. The magnetic properties are explained in terms of the model of superexchange interactions and the localization of most eg electrons of manganese. The stabilization of ferromagnetism in the chromium-substituted compositions can be caused by the fact that the positive and negative contributions to the superexchange interaction between Mn3+ and Cr3+ ions are close to each other but the antiferromagnetic part of the exchange is predominant. Moreover, some chromium ions are in the tetravalent state, which maintains the optimum doping conditions.

Influence of heat treatment on the vacancy content at the B‐site in the ABO3 manganites La0.6Sr0.1MnO3−δ

AbstractThe effects of heat‐treatment temperature, THT, and heat‐treatment time, tHT, on the structural and magnetic properties of manganites with a nominal composition La0.6Sr0.1MnO3−δ, prepared by the sol–gel method, were investigated. The XRD spectra indicate that the samples have two phases with the $R\overline {3} c$ perovskite being the dominant phase and Mn3O4 being the second phase. It was found that the Curie temperature of the samples varies as THT and tHT are changed. Calculation of the ion content ratios at the A, B, and O sites in the ABO3 perovskite phase on the basis of the thermal equilibrium theory of crystal defects, and Rietveld fitting of X‐ray powder diffraction data lead us to believe that the origin of this variation is due to the fact that the vacancy content, z, at B‐sites in the ABO3 perovskite phase increases as THT and tHT increase. The calculations also show that the samples are double‐phase compositions of La0.6Sr0.1Mn1−yO1.5(1.7‐y+z)/(Mn3O4)y/3.

Influence of non-magnetic Ti4+ ion doping at Mn site on structural and magnetic properties of La0.67Ba0.33MnO3

We have investigated the effect of titanium substitution on the structure and the magnetic properties of manganites with La0.67Ba0.33Mn1−xTixO3 (0 ⩽ x ⩽ 0.3) nominal composition. The polycrystalline samples have been produced by the conventional ceramic method at 1523 K. The morphology, grain size and phase identification studies were carried out by scanning electron microscopy, diffraction techniques (neutron and x-ray) and the chemical compositions were precisely determined by the inductively coupled plasma atomic emission spectroscopy technique. The structural refinement at room temperature by the Rietveld method revealed that for x ⩾ 0.1 the compounds are almost a single phase manganite crystallizing in a rhombohedral perovskite structure (LaAlO3 type). The more salient structural feature is an increase in cell parameter and inter-ionic distances with increasing Ti content. For x = 0 and x = 0.05 the samples exhibit two manganite phases with orthorhombic (Imma) and rhombohedral space groups. Compounds with x ⩽ 0.1 are ferromagnetic with a Curie temperature decreasing with increasing x. More complicated magnetic behaviour is observed for larger Ti content.

Rietveld fitting of x-ray diffraction spectra for the double phase composites La0.7−xSr0.3Mn1−yO3−1.5(x+y)/(Mn3O4)y/3

The effects of lanthanum deficiency on the structural and magnetic properties of manganites with normal composition La0.7−xSr0.3MnO3 prepared by the sol-gel method with the highest heat treatment temperature at 800 °C have been investigated. X-ray diffraction (XRD) spectra indicate that the materials possess a single phase with the R3¯c perovskite structure for x≤0.05, and that they possess two phases with the R3¯c perovskite being the dominant phase and Mn3O4 being the second phase for x≥0.10. Using XRD analysis, these materials can be expressed as La0.7−xSr0.3Mn1−yO3−1.5(x+y)/(Mn3O4)y/3. On the basis of the thermal equilibrium theory of crystal defects, the ion ratios at the A, B, and O sites in the ABO3 perovskite phase were calculated. Those ion ratios were used in Rietveld fitting of the XRD spectra. It was found that the dependence of the Curie temperature TC on the content ratio RM4 of Mn4+ ions at B site is similar to that of the typical perovskite La1−xSrxMnO3.

La 0.7Sr 0.3MnO 3 thin films on Bi 4Ti 3O 12/CeO 2/yttria-stabilised-zirconia buffered Si(0 0 1) substrates: Electrical, magnetic and 1/f noise properties

The remarkable electronic and magnetic properties of manganites have raised lot of interests for applications. Together with room temperature operation, depositing epitaxial films onto Si substrates is one of the main concerns for their future breakthrough. This paper presents the structural, magnetic and electrical properties of La 0.7Sr 0.3MnO 3 (LSMO) thin films deposited on Bi 4Ti 3O 12 (BTO)/CeO 2/yttria-stabilised-zirconia (YSZ) buffered Si(0 0 1) substrates. A comprehensive X-ray diffraction study was performed in order to investigate the epitaxial quality. The temperature of maximum resistance and the Curie temperature was 390 and 350 K, respectively, for the 50 nm thick films. Preliminary low frequency noise measurements were performed. The normalized Hooge parameter was in the range 10 −27 to 10 −28 m 3, which make these films already competitive for uncooled bolometer applications, even if the noise is about one or two orders of magnitude higher than what we typically measured in the best LSMO films deposited on (0 0 1) SrTiO 3 substrates. LSMO films deposited on BTO/CeO 2/YSZ buffered silicon substrates were of overall good quality and suitable for use in device fabrication.

Disorder-induced first order transition and Curie temperature lowering in ferromagnetic manganites

We study the effect that size disorder in the cations surrounding manganese ions has on the magnetic properties of manganites. This disorder is mimic with a proper distribution of spatially disordered manganese energies. Both, the Curie temperature and the order of the transition are strongly affected by disorder. For moderate disorder the Curie temperature decreases linearly with the variance of the distribution of manganese site energies, and for a disorder comparable to that present in real materials the transition becomes first order. Our results provide a theoretical framework to understand disorder effects on the magnetic behavior of manganites.

Influence of the four-spin exchange interaction on the magnetic properties ofmanganites

It is shown that non-Heisenberg exchange interaction should betaken into account to reproduce the magnetic phase diagram ofLa1−xAxMnO3 (A = Ca,Sr) using only effective exchange parameters and spins. The formation of the four-spinexchange arises from carrier hopping and coincides with the critical concentrationmetal–dielectric transition. The two- and four-spin exchange parameters are determined byMonte Carlo simulations.

Effect of rare-earth-site cations on the physical properties ofLa0.7−yNdyPb0.3MnO3single crystals

Single crystals of $La_{0.7–-y}Nd_yPb_{0.3}MnO_3$ with different y are grown by flux growth technique. The influence of change in average cationic radius $(\langle r_A\rangle)$ and cation size disorder $(\sigma^2)$ on the transport and magnetic properties of these crystals due to the presence of different cations (La and Nd) on the rare-earth sRd site is studied. Curie temperature $T_C$ and metal-insulator transition temperature $T_M_I$ are sensitive to the R site occupation. The temperature dependence of magnetization of $La_{0.7}Nd_yPb_{0.3}MnO_3$ is consistent with spin wave excitations according to the Bloch $T^{3/2}$ law at zero magnetic field limit. The Nd-based systems follow $T^{3/2}$ law only in a certain range of temperature and deviate at low temperatures, which is ascribed to a probably canted ordering of Nd and Mn moments with an antiferromagnetic component at very low temperatures. The values of spin stiffness constants and saturation magnetization vary systematically with changing occupation on the R site. Specific heat measurements of Nd containing samples show a Schottky-like anomaly at low temperature (below 15 K), which increases with the concentration of Nd ions in the lattice. It is concluded that the magnetic properties of manganites with Nd are affected by a tendency for magnetic ordering of the Nd ions.

Interplay between static cooperative Jahn–Teller distortion and magnetic properties ofoptimally doped manganites

An effect of the static long range cooperative Jahn–Teller (JT) distortion on themagnetic properties of (A = La, Pr, Nd; , Sr) manganites with the orthorhombic structure ofPnma symmetry is studied on the basis of structural, magnetic and transport properties data. Adirect relationship between the static JT distortion parameter and the Curie temperaturewas found. The relationship between the static long range cooperative JT distortion,strength of electron–phonon coupling effects and magnetic properties of manganites is discussed.

Jahn‐Teller distortion ordering in single‐crystal Nd 1/2 Sr 1/2 MnO 3

Charge, spin and orbital degrees of freedom play important roles in the electrical and magnetic properties of manganites. Nd0.5Sr0.5MnO3 is a paramagnetic insulator with Imma orthorhombic symmetry at room temperature. Upon cooling it becomes a ferromagnetic metal below 240 K and at 160 K undergoes a first-order phase transition. Below this temperature it is a CE-type antiferromagnetic insulator. In this paper we report synchrotron X-ray scattering investigations of superlattice reflections observed in the low temperature phase of Nd0.5Sr0.5MnO3. Upon cooling below 160 K we observed additional peaks occurring at non-integer positions in reciprocal space. These reflections had a wavevector (1/2, 0, 0) and are due to the structural modulation arising from the Jahn-Teller distortion associated with charge ordering of Mn3+ and Mn4+ ions and orbital ordering in the sample. The peaks observed below 160 K have an intensity of approximately 10−3 that of the Bragg reflections. The intensity profiles of these reflections show that the transition into the ordered phase is strongly first-order. The structural phase transition was observed to display a hysteresis width of 10 K. The measured widths of these peaks show that the charge modulation is correlated primarily in the ac plane rather than the K-direction (long-axis). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic phase diagram for a nonextensive system: Experimental connection with manganites

In the present paper we make a thorough analysis of a classical spin system, within the framework of Tsallis nonextensive statistics. From the analysis of the generalized Gibbs free energy, within the mean-field approximation, a para-ferromagnetic phase diagram, which exhibits first and second order phase transitions, is built. The features of the generalized, and classical, magnetic moment are mainly determined by the values of $q$, the non-extensive parameter. The model is successfully applied to the case of La$_{0.60}$Y$_{0.07}$Ca$_{0.33}$MnO$_3$ manganite. The temperature and magnetic field dependence of the experimental magnetization on this manganite are faithfully reproduced. The agreement between rather "exotic" magnetic properties of manganites and the predictions of the $q$-statistics, comes to support our early claim that these materials are magnetically nonextensive objects.

Variational mean-field approach to the double-exchange model

It has been recently shown that the double exchange Hamiltonian, with weak antiferromagnetic interactions, has a richer variety of first and second order transitions than previously anticipated, and that such transitions are consistent with the magnetic properties of manganites. Here we present a thorough discussion of the variational Mean Field approach that leads to the these results. We also show that the effect of the Berry phase turns out to be crucial to produce first order Paramagnetic-Ferromagnetic transitions near half filling with transition temperatures compatible with the experimental situation. The computation relies on two crucial facts: the use of a Mean Field ansatz that retains the complexity of a system of electrons with off-diagonal disorder, not fully taken into account by the Mean Field techniques, and the small but significant antiferromagnetic superexchange interaction between the localized spins.