Magnetotransport Properties Of La0 Research Articles

Comparative study on multifunctional behaviour of rare earth manganites with micro and nano grain size

We have investigated electrical and magnetotransport properties of La0.7Sr0.3MnO3 samples with grain size in micro to nanometric regime. The structural parameters obtained by Rietveld refinement of X-ray diffraction data revealed perovskite structure with orthorhombic (Pnma) and rhombohedral (R3C) symmetry for nano and bulk samples respectively. The average particle size was 22 nm and 2 μm for the two representative samples. A metal–insulator transition and substantial increase in electrical resistivity was observed in nanomaterials. An enhanced magnetoresistance observed in nanomaterials samples, makes them more promising for advanced device applications. The magnetization study showed signature of ferromagnetic cluster behavior and higher temperature coefficient of magnetization in nanoparticle samples.

Metastable magnetic state and magnetotransport in disordered manganite thin films

We report on the magnetic, electrical, and magnetotransport properties of La0.7Ca0.3Mn1−XAlXO3 (X = 0, 0.05, 0.15) thin films grown on LaAlO3 (001) substrate. It is observed that the low temperature ferromagnetic phase of La0.7Ca0.3MnO3 transforms into metastable magnetic state in 15 at. % Al doped sample, which has been characterized using long-time relaxation measurement as well as different temperature sweep rates (during cooling and heating) of magnetization measurements. Our results clearly show that the magnetic transition in this film is connected with the kinetics of first order phase transition. The metastable magnetic phase also shows increased magnetoresistance.

Substitutional effects on structural and magnetotransport properties of La0.85−xSmxK0.15MnO3 (x = 0.05, 0.1 and 0.15)

A series of polycrystalline La0.85−xSmxK0.15MnO3 (x=0.05, 0.1 and 0.15) have been synthesized by standard solid state reaction method to study effects of substituting La3+ by Sm3+ ion on the structural, electrical and magnetic properties. The Rietveld refinement of X-ray diffraction data revealed that mixed valence manganites crystallize in rhombohedral structure (space group R3¯C, no. 167). Raman spectra at room temperature reveal gradual change in phonon modes on increased doping. The temperature dependent electrical resistivity is measured by a standard four-probe method between 5 and 300K. The temperature dependent electrical resistivity exhibits metal–insulator transition at temperature TMI and metallic state (T<TMI) signifies importance of electron–electron, electron–phonon and electron–spin fluctuation scattering process. The peak resistivity ρm increases rapidly with Sm and TMI shifts to a lower temperature. The high temperature (T>TMI) conductivity data signifies polaronic nature. Application of magnetic field suppresses resistivity in entire temperature range. Low temperatures resistivity infers a field-dependent minimum and is due to electron–electron interaction and Kondo effects of mixed valence manganites. The ferro to paramagnetic transition temperature (TC) decreases with decreasing ionic radius as well as one-electron bandwidth of the A-site cation.

Nanostructure Induced Metal-Insulator Transition and Enhanced Low-Field Magnetoresistance in La&lt;SUB&gt;0.7&lt;/SUB&gt;Sr&lt;SUB&gt;0.3&lt;/SUB&gt;MnO&lt;SUB&gt;3&lt;/SUB&gt; Systems

We investigated implications of nanostructure formation on structural and magnetotransport properties of La0.7Sr0.3MnO3 compound. The polycrystalline nanomaterials of variable grain sizes were synthesized by using sol-gel method. The structural parameters obtained by Rietveld refinement of the X-ray diffraction data indicated that the samples possess perovskite structure with orthorhombic Pnma symmetry. The X-ray Photoemission Spectra showed chemical shift in the lowest particle size sample due to oxygen deficiency. The average particle size observed through transmission electron microscopy varied from 22 nm to 34 nm. The particle size induced metal-insulator transition and substantial increase in electrical resistivity observed in these nanomaterials are in contrast with the bulk material phase diagram. We also observed temperature and magnetic field dependent colossal magnetoresistance. The low-field magnetoresistance is substantially enhanced in nanomaterials samples, making it more promising for device applications. A divergence in field cooled and zero field cooled magnetization indicated possibility of magnetic spin-glass behavior.

Effects of conjugated polymer on the magnetotransport properties in La0.7Sr0.3MnO3 ferromagnetic electrodes

Magnetotransport of La0.7Sr0.3MnO3 (LSMO)/regioregular poly3-hexylthiophene (rr-P3HT) interfaces were studied at 5–300 K to gain insight of spin transport in polymer coated LSMO. LSMO films on SrTiO3 (STO), MgO, and quartz substrates were characterized in pristine state, after depositing rr-P3HT and after removing rr-P3HT. Application and removal of rr-P3HT caused the disappearance of colossal magneto resistance and the emerging of low-field magnetoresistance (LFMR) in STO/LSMO, while the same treatment on MgO and quartz showed only a large LMFR signal with no significant changes during application and removal of rr-P3HT. This result signifies that epitaxial thin films of LSMO do not maintain their transport characteristics when coated with organic semiconductors, posing a limitation for efficient spin polarized injection at such interfaces.

The effect of MgO doping on the structural, magnetic, and magnetotransport properties of La0.8Sr0.2MnO3 manganite

Abstract The effect of MgO doping on the structural, magnetic, and magnetotransport properties of La0.8Sr0.2MnO3 (LSMO)/x MgO has been investigated. All samples were prepared by a solid-state reaction method. Alternating current susceptibility measurements for LSMO/x MgO samples show that the Curie transition temperature (T c) and magnetization decrease with the increase of MgO concentration. The rate of the decrease of T c at higher doping level is very fast. Also, samples with low doping level (x ≤ 2) show insulator-metal transition, but the transition temperature decreases and resistivity increases with the amount of MgO. It is observed that there is no insulator-metal transition at higher MgO doping level (x ≥ 3). Also, the results show that the value of low-field magnetoresistance decreases with the increase of MgO doping level. It seems that due to the higher sintering temperature and almost the same ionic radii of Mg2+ and Mn3+, Mg2+ mostly replaced Mn3+ and weakened the double-exchange interaction, and consequently, T c and magnetoresistance decrease and resistivity increases with MgO doping.

Structural, Electrical and Magnetotransport properties of La0.7Ca0.2Sr0.1MnO3 by self propagating high temperature synthesis.

Structural, Electrical and Magnetotransport properties of La0.7Ca0.2Sr0.1MnO3 by self propagating high temperature synthesis.

Giant Positive Magnetoresistance in Ferromagnetic Manganites/Silicon Nanotips Diode

The current–voltage relations and magnetotransport properties of La0.7Sr0.3MnO3/Si-nanotips and La0.7Sr0.3MnO3/Si-film junctions are studied, revealing that their transport properties are dominated by various mechanisms depending on temperature and bias voltage. A giant positive magnetoresistance (PMR) of ∼200% is observed at 40 K in La0.7Sr0.3MnO3/Si-nanotips junction. The temperature dependence of resistance in the presence of magnetic field suggests the origin of giant PMR to be the strong electron–electron interaction and electron–magnon scattering. Interestingly, such behavior is not observed in regular La0.7Sr0.3MnO3/Si-film junction, implying that the coupling between spin and charge could be greatly enhanced at the interface of La0.7Sr0.3MnO3 and Si nanotips.

Effect of inhomogeneity on magnetic, magnetocaloric, and magnetotransport properties of La0.6Pr0.1Ca0.3MnO3 single crystal

The effect of magnetic inhomogeneity on magnetic, magnetocaloric, and transport properties of the colossal magnetoresistance manganites with first order ferromagnetic-to-paramagnetic phase transition is studied. The experiments were performed on the single-crystalline samples of La0.6Pr0.1Ca0.3MnO3. The inhomogeneity is described by the Curie temperature distribution function, which is found from the magnetization data. The temperature dependence of the magnetic field induced change in the entropy is shown to be determined by the distribution function and the shift of the transition temperature in a magnetic field. Similarly, magnetoresistance in the transition region is determined by the resistivity at H=0 and the shift of the transition temperature. The maximum entropy change as well as maximum magnetoresistance can be achieved in the magnetic field of order δTC/BM where δTC is the transition width and BM is the rate of change of the Curie temperature with magnetic field.Our approach to analysis of the effects of inhomogeneity is general and therefore can be used for all compounds with the first order magnetic phase transition.

Magneto-transport Properties of La0.80Sr0.20Mn1?xCuxO3 Thin Films Fabricated by Using Spray Pyrolysis

Magneto-transport Properties of La0.80Sr0.20Mn1?xCuxO3 Thin Films Fabricated by Using Spray Pyrolysis

Strain engineering to control the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films

Strain engineering can be used to tailor the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films by varying the tetragonal distortion (c/a ratio) between a compressive strain of 1.005 and a tensile strain of 0.962 through the choice of the substrate type and the presence of a buffer layer. We find that increasing the tensile tetragonal distortion of the La0.67Sr0.33MnO3 thin film decreases the saturation magnetization, changes the temperature dependence of the resistivity and magnetoresistance, and increases the resistivity by several orders of magnitude.

The incongruous observation of magnetic phase separation in La0.85Sr0.15CoO3 spin glass system

Phase separation (PS) in hole-doped cobaltites (La1−xSrxCoxO3) is drawing renewed interest recently. In particular, the magnetic behavior of La0.85Sr0.15CoO3 has been subjected to a controversial debate for the past several years; while some groups show evidence for magnetic PS, others show spin glass (SG) behavior. Here, an attempt is made to resolve the controversy related to “PS versus SG” behavior in this compound. We present the results of a comprehensive investigation of the dc magnetization, ac susceptibility, and the magnetotransport properties of La0.85Sr0.15CoO3 samples. We contemplate that the magnetic PS in La0.85Sr0.15CoO3 is neither intrinsic nor inherent, but it is a consequence of the preparation conditions. It is realized that a low temperature annealed (LTA) sample shows PS whereas the high temperature annealed (HTA) sample shows SG behavior. The Brillouin-like behavior of field cooled dc magnetization and apparently no frequency dependent peak shift in ac susceptibility for the LTA sample characterize it to be of ferromagneticlike whereas a kink in field cooled dc magnetization and a considerable amount (∼3 K) of frequency dependent peak shift in the ac susceptibility for the HTA sample characterize it to be of SG state. The magnetotransport properties show that the HTA sample is more semiconducting as compared to the LTA sample. This is interpreted in terms of the presence of isolated as well as coalescing metallic ferromagnetic clusters in the case of LTA sample. The magnetoresistance (MR) at 10 K for the HTA sample exhibits a huge value (∼65%) as compared to the LTA sample, and it monotonically decreases with the rise in temperature. Such a high value of MR in the case of HTA sample is strongly believed to be due to the spin dependent part of random potential distribution. Further, the slow decay of remnant magnetization with progress of time and the existence of hysteresis at higher temperatures (up to 200 K) in the case of LTA sample as compared to the HTA sample clearly unveil different magnetic states associated with them.

Effect of Co doping on the magnetotransport properties of La0.45Sr0.55MnO3 perovskite

We investigated the magnetotransport properties of polycrystalline La0.45Sr0.55Mn1−xCoxO3 (0≤x≤0.15). Ferromagnetism is enhanced with the doping of Co ions in La0.45Sr0.55MnO3, but the antiferromagnetism is nearly destroyed in the low-temperature region. The Mn3+–Mn4+ double-exchange (DE) and Co2+–Mn4+ ferromagnetic (FM) superexchange interactions are mainly responsible for the magnetic properties of the doped system. With increased Co doping, the insulating properties and the magnetoresistance (MR) effect are simultaneously enhanced. This indicates that the Co doping strengthens both the Mn3+–Mn4+ DE and Co2+–Mn4+ FM superexchange interactions. The Co doping increases the disorder in the system, causing the MR effect to increase with decreasing temperature.

Magneto- and electroresistance of La0.7Sr0.3MnO3/Nb(1.0%):SrTiO3 junctions

The current-voltage characteristics and magnetotransport properties of La0.7Sr0.3MnO3/Nb(1.0%):SrTiO3 junctions under various currents ranging from 10−6 to 10−3 A and different temperatures ranging from 10 to 300 K were investigated. The current-voltage curves exhibit rectifying behavior. The resistance, magnetoresistance, and electroresistance of the junctions are strongly dependent on bias-current direction, current, temperature, and magnetic field. A detailed analysis of the conductance-voltage curves showed that quantum mechanical tunneling was the dominating transport mechanism.

Magnetotransport properties of La0.67Ca0.33MnO3 with different grain sizes

The magnetotransport and magnetoresistive (MR) properties of manganese-based La0.67Ca0.33MnO3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The ρ–T 2 curves are nearly linear in the metallic regime, but the ρ–T 2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers. MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling effect.

Random existence of charge ordered stripes and its influence on the magnetotransport properties of La0.6Sr0.4MnO3 perovskite substituted with diamagnetic ions at Mn sublattice

Phase-singular solid solutions of La0.6Sr0.4Mn1−yMeyO3 (0⩽y⩽0.3) [Me=Li1+, Mg2+, Al3+, Ti4+, Nb5+, Mo6+ or W6+] [LSMey] perovskite of rhombohedral symmetry (space group: R3¯c) have been prepared wherein the valence of the diamagnetic substituent at Mn site ranged from 1 to 6. With increasing y-content in LSMey, the metal-insulator (TM-I) transition in resistivity-temperature ρ(T) curves shifted to low temperatures. The magnetization studies M(H) as well as the M(T) indicated two groups for LSMey. (1) Group A with Me=Mg, Al, Ti, or Nb which are paramagnetic insulators (PIs) at room temperature with low values of M (&amp;lt;0.5μB∕Mn); the magnetic transition [ferromagnetic insulator (FMI)-PI] temperature (TC) shifts to low temperatures and nearly coincides with that of TM-I and the maximum magnetoresistance (MR) of ∼50% prevails near TC (≈TM-I). (2) Group-B samples with Me=Li, Mo, or W which are FMIs with Ms=3.3–3.58μB∕Mn and marginal reduction in TC∼350K as compared to the undoped LSMO (TC∼378K). The latter samples show large temperature differences ΔT=Tc-TM-I, reaching up to ∼288K. The maximum MR (∼60%) prevails at low temperatures corresponding to the M-I transition TM-I rather than around TC. High resolution lattice images as well as microscopy analysis revealed the prevalence of inhomogeneous phase mixtures of randomly distributed charge ordered-insulating (COI) bistripes (∼3–5nm width) within FMI charge-disordered regions, yet maintaining crystallographically single phase with no secondary precipitate formation. The averaged ionic radius ⟨rB⟩, valency, or charge/radius ratio ⟨CRR⟩ cannot be correlated with that of large ΔT; hence cannot be used to parametrize the discrepancy between TC and TM-I. The M-I transition is controlled by the charge conduction within the electronically heterogeneous mixtures (COI bistripes+FMI charge disordered); large MR at TM-I suggests that the spin-ordered FM-insulating regions assist the charge transport, whereas the TC is associated with the bulk spin ordered regions corresponding to the FMI phase of higher volume fraction of which anchors the TC to higher temperatures. The present analysis showed that the double-exchange model alone cannot account for the wide bifurcation of the magnetic and electric transitions, contributions from the charge as well as lattice degrees of freedom to be separated from spin/orbital ordering. The heterogeneous phase mixtures (COI+FMI) cannot be treated as of granular composite behavior

Control of the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films through epitaxial strain

The influence of epitaxial strain, in the form of tetragonal distortions, on the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films was studied. The tetragonal distortion (c∕a ratio) was modulated through the choice of the substrate, ranging from c∕a=1.007 on (001)-oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates to 0.952 on (110)-oriented GdScO3 substrates. In agreement with previous theoretical predictions, these large values of tensile strain cause the Curie temperature and the saturation magnetization to decrease, alter the temperature dependence of the resistivity and magnetoresistance, and increase the resistivity by several orders of magnitude.

Strain-dependent magnetotransport properties of La0.9Sr0.1MnO3 epitaxial films on SrTiO3 and LaAlO3 substrates

The strain effect on the magnetotransport properties in La0.9Sr0.1MnO3 films epitaxially deposited on SrTiO3 (STO) and LaAlO3 (LAO) substrates, is demonstrated. Large compressive strain is formed in the films on the LAO substrate; however, that on the STO is subject to a small tensile strain. Strain relaxation of films grown on both substrates results in the formation of a spin-canted antiferromagnetic (AFM) insulative phase, causing the increase in resistivity with decreasing temperature. The characteristics of the AFM insulative phase become apparent with increasing film thickness, which leads to a clear AFM transition in the films grown on LAO and a reduction of magnetization and Curie temperature in those on STO. The magnetoresistance effect of the films is also consistent with the above results.

Structural, magnetic and magnetotransport properties of La0.8Sr0.2MnO3/xLaMnO3 composites

Abstract The effect of LMO doping on the structure, magnetic and magnetotransport properties of La 0.8 Sr 0.2 MnO 3 (LSMO)/ x LaMnO 3 (LMO) has been investigated. Two types of LSMO/ x LMO composites, named as SL x (low temperature sintered samples) and SH x (high temperature sintered samples) samples, were prepared by different sintering temperature and solid-state reaction method. The presence of LMO at the grain boundaries increases the disordered states at the surface of the grains and therefore the magnetization and transition temperature decrease by increasing the amount of LMO doping level. Results show that the rate of decreasing of transition temperature is much more for high temperaure sintered samples. Also the resistivity of samples increases by the increase of LMO doping level. Results also show that the LMO doping has an effect on a low field magnetoresistance (LFMR). The value of LFMR increases for low doping level of 0 ≤ x ≤ 15, for SL x samples and 0 ≤ x ≤ 10 for SH x samples. Also LFMR decreases at high doping level. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increase of LFMR at low doping level, while reduction of LFMR at high doping level may result from the grain boundary becoming too thick for electron tunneling.

Electrical resistivity and magnetotransport properties of La0.67Ba0.33MnO3 epitaxial films biaxially compressed by the substrate

The structure, electrical resistivity, and magnetoresistance of La0.67Ba0.33MnO3(20 nm) films grown coherently on an La0.3Sr0.7Al0.65Ta0.35O3(001) substrate with a lattice misfit of about 1% were studied. The rigid connection of the manganite layer with the bulk substrate brought about the unit cell distortion of the substrate (a⊥/a‖ = 1.02) and a decrease in the unit cell volume as compared to that of the corresponding bulk crystals (a‖ and a⊥ are the unit cell parameters measured in the substrate plane and along the surface normal, respectively). The temperature TM ≈ 295 K, at which the electrical resistivity ρ of the (20 nm)La0.67Ba0.33MnO3 films reached a maximum, was 40–45 K lower than that for the corresponding bulk crystals. The negative magnetoresistance (MR ≈ −0.25 for μ0H = 1 T) attained a peak value at TMR ≈ 270 K. The response of ρ to a magnetic field depended substantially on the angle between the current flow in the film and the direction of the magnetic field.