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We consider the nanoscale electronic phase separation in a wide class of different materials, mostly in strongly correlated electron systems. The phase separation turns out to be quite ubiquitous manifesting itself in different situations, where the itineracy of charge carriers competes with their tendency toward localization. The latter is often related to some specific type of magnetic ordering, e.g. antiferromagnetic in manganites and low-spin states in cobaltites. The interplay between the localization-induced lowering of potential energy and metallicity (which provides the gain in the kinetic energy) favors an inhomogeneous ground state such as nanoscale ferromagnetic droplets in an antiferromagnetic insulating background. The present review article deals with the advances in the subject of electronic phase separation and formation of different types of nanoscale ferromagnetic (FM) metallic droplets (FM polarons or ferrons) in antiferromagnetically ordered (AFM), charge-ordered (CO), or orbitally-ordered (OO) insulating matrices, as well as the colossal magnetoresistance (CMR) effect and tunneling electron transport in the nonmetallic phase-separated state of complex magnetic oxides. It also touches upon the compounds with spin-state transitions, inhomogeneous phase-separated state in strongly correlated multiband systems, and electron polaron effect. A special, attention is paid to the systems with the imperfect Fermi surface nesting such as chromium alloys, iron-based pnictides, and AA stacked graphene bilayers., 135 pages, 72 figures, submitted to Physics Reports

La0.7Ca0.3MnO3 has been widely studied as a quintessential example showing colossal magnetoresistance, metal-insulator transition and related temperature coefficient of resistance (TCR). Ag doping was demonstrated as an effective way to enhance the TCR properties of bulk La0.7Ca0.3MnO3. In this article, La0.7Ca0.3MnO3:Ag0.2 thin films were prepared on LaAlO3 (LAO) substrates by pulsed laser deposition with different annealing temperatures. The structure, surface morphology, electrical properties, and magnetic properties of the obtained specimens were investigated. X-ray diffraction results showed that the annealed films exhibited stronger diffraction peaks compared to the unannealed ones, indicating enhanced crystallinity. Resistance-temperature curves revealed metal-insulator transition in thin films annealed at 900–1300 °C. However, the film annealing at 1400 °C exhibited an insulating characteristic due to the evaporation induced non-stoichiometry. A highest TCR of 31.6%·K−1 was achieved in the thin film annealed at 1200 °C. The excellent TCR properties of La0.7Ca0.3MnO3:Ag0.2 films in this study can promote its application in infrared detectors.

A formidable amount of work has been devoted aiming towards the understanding of the structure and properties of colossal magnetoresistance (CMR) manganites. Mixed valent manganites with the general formula R1-xAxMnO3 (R = trivalent rare earth ion and A = divalent ion like Sr+2, Ba+2, Pb+2, Ca+2 etc.) are found to exhibit variety of phenomena such as charge, spin and orbit ordering, electronic, magnetic and structural transitions depending on the type and amount of doping (x). In this paper, doping dependent modifications in the microstructure polycrystalline La0.7Sr0.3Mn1-xTixO3 (LSMTO) (x = 0.03, 0.06 and 0.12) compounds synthesized by hybrid method (sol gel method + solid state reaction method) have been discussed in detail. In the present work, the powder X-ray diffraction patterns reveals that the samples are single phase in nature and the samples show a rhombohedral structure in hexagonal lattice with the space group R 3 - c . The Rietveld refinement was performed using FullProf software for the detailed structural investigation. In this context, the lattice parameters, unit cell volume and χ2 were obtained for LSMTO samples. On the substitution of Mn+4 by Ti+4, the structure does not undergo any phase transformation, but lattice parameters steadily increase as Ti+4 doping concentration increases. It can be related to the larger ionic radius of Ti+4 (rTi+4 = 0.605 A) ion compared to that of Mn+4 (rMn+4 = 0.540 A) ion. FT-IR spectra for LSMTO of different concentration show the four peaks around 400–500 cm−1 (Mn-O-Mn bending mode), 610–670 cm−1 (Mn-O stretching mode), 2330–2400 cm−1 (moisture contain) and 540 cm−1 (Ti-O stretching modes). Weight loss % versus temperature plot (TGA) for the x = 0.06 sample confirms that the precursor shows three step weight loss profiles and does not melt up to the temperature of 1050 °C. A quantitative analysis of the energy dispersive spectroscopy (EDS) data indicates that the observed concentration of elements is very close to the calculated values from its chemical formula. Typical SEM micrographs for all the three samples show that each sample possesses fine and clear grain boundaries (GBs). From the R-T measurements, an increase in resistivity and a decrease in metal to insulator transition temperature (TMI) were observed by increasing doping level of Ti for Mn. All the LSMTO samples show the resistivity suppression under applied magnetic field. The maximum MR % (89%) was observed for x = 0.12 at 5 T compare to other doped samples. This result suggests that the magnetoresistance behavior is improved by addition of Ti at Mn. These results prove that concentration Ti substitution at Mn site enhances the various properties of this manganite system.

La0·7Ca0.3−xSrxMnO3:Ag0.2 (LCSMO:Ag) ceramics with varying strontium (Sr) content (x = 0.0165, 0.03, 0.05, 0.07, and 0.1) were synthesized using a combination of sol–gel and solid-state doping methods and studied as colossal magnetoresistance materials. Significant improvements in the peak temperature coefficient of resistivity (TCR) and resistivity (ρ) were observed across all ceramic samples when the mol% of Sr was adjusted. The low ρ and large TCR values resulted from a combination of two factors. First, the presence of Sr led to the increase in the grain size and decrease in the number of boundaries, which improved the electrical transport and reduced the boundary scattering effects. This resulted in additional improvement in the grain arrangement order. Second, the cell volume (Vcell) and octahedron volume (Voct) both decreased first and then increased. The MnO6 octahedron underwent gradual deformation into a flattened shape, which facilitated carrier migration and increased electrical sensitivity of the material. The ceramic with x = 0.03 maintained high and stable TCR values in different working environments, both without a magnetic field (TCRo, 54.76% K−1) and in the presence of a vertical field (TCR⊥, 33.33% K−1). Furthermore, the material exhibited a low resistivity and a higher insulator–metal transition temperature (Tp). Performance differences among the samples were comprehensively and systematically explained by conducting cross magnetic field tests with field directions parallel and perpendicular to the flat surface of the bulk material, respectively. Overall, the findings of this study indicate that these ceramics act as promising candidates for future applications in information storage devices and magnetic sensors.

Investigation of the crystal structure, magnetic and transport properties of both the stoichiometric and anion-deficient Ba 2+ -doped lanthanum cobaltites was performed. Anomalous temperature behavior of the structural parameters as well as the magnetic, electrical and magnetotransport characteristics was found due to concurrence of magnetic interactions. It was shown that the anion deficiency stabilized insulating antiferromagnetism and destroyed conductive ferromagnetism. We argue that the ferromagnetism developed on the basis of Co 3+ /Co 4+ ions with one e g electron (i.e., possessing the intermediate-spin (IS) state), while the presence of two e g electrons (corresponding to the high-spin (HS) state) favored the antiferromagnetic order. The covalent component of the chemical bond stabilized an electronic configuration close to the IS state. The colossal magnetoresistance arose at a concentration or temperature boundary (where ferromagnetic and antiferromagnetic phases or clusters coexist) as a result of the field-induced spin transition from mixed HS/low-spin state (predominantly antiferromagnetic and insulating) to IS (predominantly ferromagnetic and highly conductive) state.

The manganite Nd0.15Ca0.85MnO3 crystallizes in GdFeO3-type, orthorhombic structure (space group Pnma) at 300 K and orders antiferromagnetically at 112 K (TN). Magnetization-field (M-H) isotherms indicate metamagnetic transition at temperatures below TN. However, metamagnetism does not lead to saturation in magnetization. The magnetization value at 2 K in 140 kOe field is only 0.4 μB/f.u. The isothermal magnetic entropy change (ΔSm) has been calculated using the M-H data and inverse magnetocaloric effect is observed around TN and the maximum value of ΔSm is ∼12.2 J kg−1K−1 at 107.5 K for 140 kOe field change. Powder neutron diffraction study in zero applied field reveals monoclinic distortion of Nd0.15Ca0.85MnO3 crystal lattice and antiferromagnetic ordering of Mn sublattice in ac-plane with wave vector K = [1/2, 0, 1/2] at 125 K. From the neutron data, the Mn magnetic moment value at 3 K is found to be 2.54 μB. Electrical resistivity increases tremendously below TN to an insulating state and shows thermal hysteresis near TN in zero field. Large magnetic fields drive insulator to metal-like transition and negative colossal magnetoresistance of about 70% is realized at 50 K in 70 kOe field and that could be due to the field-induced order.

We report on the magnetotransport properties of Cu- and Cr-doped topological insulator Bi 2 Se 3 films grown on silicon (100) substrate by chemical vapor deposition. Upon doping of non-magnetic Cu, Bi 2 Se 3 film's carrier density is reduced and the magnetoresistance changes from a strong positive parabolic magnetoresistance to a linear magnetoresistance. This linear magnetoresistance is similar to the linear magnetoresistance in other gapless topological states of matter and has a strong temperature dependence. In contrast, the magnetoresistance of Cr-doped Bi 2 Se 3 films remains to be parabolic and becomes temperature independent upon increased Cr-doping. These results suggest that the absence of linear magnetoresistance in Cr-doped Bi 2 Se 3 is related to the magnetic dopants that induce time reversal symmetry breaking and surface states gap opening.

Overcoming the unintentional doping of defect-related carriers induced from low oxygen partial pressure is a major challenge to realize multifunctional oxide electronics. In this work, we demonstrate that the two-step deposition in conjunction with layer modulated patterning process can enhance several properties of LaAlO3/SrTiO3 (LAO/STO) heterostructures grown under a low oxygen partial pressure of 5 x 10(-8) Torr. Specifically, our patterned samples exhibit extraordinary electronic properties including positive colossal magnetoresistance of similar to 3500% under 10 T, and enhanced carrier mobility similar to 5000 cm(2)/Vs at 2 K without using buffer layer or using additional elements. These unique phenomena are resulted from inhibition of the multiband conducting behaviour, which likely originates from oxygen vacancy related defects in the STO layers, through the two-step fabrication method. Consequently, by controlling defect behaviour through the two-step deposition jointly with modulated patterning process, several properties for oxide-based electronics can be induced in a single platform even under a low oxygen condition.

Transition metal oxides show remarkably diverse quantum functional properties such as high temperature superconductivity, colossal magnetoresistance, multiferroicity, two-dimensional electron gas, and topological insulators. This diversity manifests as a result of many energy scales of similar magnitude competing rather than any particular one dominating in the system. In this regard, growth of atomically controlled epitaxial thin films and heterostructures would allow to control relevant energy scales by imposing various stimuli, such as reduction of dimensionality, introduction of interfaces, modification of the interfacial octahedral tilts, and symmetry breaking; in turn, modified functional properties or completely new phenomena may emerge in epitaxial thin films and heterostructures. Also of exceeding importance is the fact that atomically controlled epitaxial thin films and heterostructures of the multifunctional oxides offer promising potentials for next generation oxide electronics. In this short review, we collect representative examples of quantum correlated phenomena arising in epitaxial films and heterostructures of transition metal oxides and highlight some of the progresses achieved in thin film research of various functional oxides in the last couple of decades.

Yb14MnSb11 is a member of a remarkable structural family of compounds that are classified according to the concept of Zintl. This structure type, of which the prototype is Ca14AlSb11, provides a flexible framework for tuning structure-property relationships and hence the physical and chemical properties of compounds. Compounds within this family show exceptional high temperature thermoelectric performance at temperatures above 300 K and unique magnetic and transport behavior at temperatures below 300 K. This review provides an overview of the structure variants, the magnetic properties, and the thermoelectric properties. Suggestions for directions of future research are provided.

The effect of yttrium (Y) substitution at La-site on structural, microstructural and electrical transport properties of (La0.7-xYx)Ca0.3MnO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were investigated. Samples were prepared by conventional solid state reaction method and structural properties of the samples were obtained using the Rietveld refinement of X-ray diffraction data. X-ray diffraction patterns show orthorhombic distorted perovskite structures. Resistivity measurement results of the LaYCaMnO3 compounds show that metal–insulator transition temperature, TMI shifts to lower temperature while the resistivity increases by increasing Y3+ substitution. In the metallic region (T TMI), resistivity data were fitted to model of small polaron hopping conduction mechanism and the activation energy, Ea increased as Y substitutions increases. Keywords: Colossal magnetoresistance, Double exchange mechanism, Metal-insulator temperature, Activation energy, Conduction mechanism

Magneto-electric and electronic properties of Nd1-xSrxMnO3-δ (0.3 ≤ x ≤ 0.7) (NSMO) nanoparticles are investigated. NSMO nanoparticles are synthesized by glycine assisted auto combustion method. The structural and morphological properties are probed using X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). NSMO crystallizes in orthorhombic structure and nearly spherical agglomerated morphology is observed. Resistivity of the order of few MOhm-cm is recorded for all the compositions and the transport mechanism is interpreted by using Mott variable range hopping (VRH) model. In absence of magnetic field all samples show insulating nature over the studied temperature region (300- 5 K), while Metal to Insulator transition is observed in the presence of magnetic field (8T). Large Colossal Magnetoresistance (CMR) is noticed below 50 K for NSMO. Observed Curie temperature is in the range of 102–115 K and it is found to be independent of Strontium doping concentration. Bifurcation in FC-ZFC, for all the samples, is at higher temperature than blocking temperature (∼72 K) indicates glassy state. We have calculated thickness of magnetic dead layer by two different ways and it lies between 1.6 and 2.9 nm. Concentration of divalent element and oxygen non-stoichiometry affects the relative fraction of Mn3+/Mn4+ ions. Mn3+/Mn4+ in our samples is determined from areas under the deconvoluted X-Ray Photoelectron Spectra (XPS) of Mn core level. The Mn3+/Mn4+ ratio is higher than the value expected from nominal composition, which indicates oxygen non-stoichiometry. Oxygen non-stoichiometry is also confirmed by chemical titration method.

Mixed anion oxides are emerging materials showing a variety of physical and chemical properties. Among them oxynitrides are widely investigated because of notable photocatalytic, dielectric, luminescent and electronic properties. Nitrides show more positive free energies of formation than oxides because of the higher stability of N 2 molecule with respect to O 2 and the unfavourable electron affinity of nitrogen compared to oxygen. However the stability of oxynitrides is higher than for nitrides, and they easily form from oxides in presence of reactive gases as NH 3 . In addition to ammonolysis several synthetic strategies have been developed in the last years leading to the stabilization of relevant materials with a variety of structures. In this review we will discuss recent progress in the synthesis of oxynitrides emphasizing the importance of kinetic factors and the influence of preparative parameters on the structure types and oxidation states of the cations, and the consequences on physical properties.

Bilayer thin film samples consisting of colossal magnetoresistance manganite La0.7Ca0.3MnO3 (LCMO) and superconducting cuprate YBa2Cu3O7−δ (YBCO) were stabilized by means of pulsed laser deposition techniques on single crystal SrTiO3 (001) substrate. The X-ray diffraction measurements confirm the epitaxial relationship of grown bilayer samples. The functional properties of the LCMO/YBCO bilayer were explored through magnetic and electrical transport measurements. The magnetization curve of LCMO/YBCO bilayer sample retains the characteristic ferromagnetic-paramagnetic transition of LCMO and superconducting transition of YBCO. The electrical resistivity was found to show different trend around the superconducting transition depending upon the four probe electrical contacts configuration on bilayer samples and the obtained results lead to direct visualization of proximity effect. A change in sign of magnetoresistance near the superconducting and metal to insulator transition temperature is observed which is attributed to the intrinsic property of YBCO and LCMO layers.

Based on the density functional theory and nonequilibrium Green’s function method, we investigate the electronic structures and thermal spin transport properties of Christmas-tree silicene nanoribbons (CSiNRs). The results show that CSiNRs have ferromagnetic ground state with high Curie temperature far above the room temperature. Obvious spin Seebeck effect with spin-up and spin-down currents flowing in opposite directions by a temperature gradient can be observed in these systems. Furthermore, a thermal colossal magnetoresistance up to 109% can be realized by tuning the external magnetic field. The results show that CSiNRs hold great potential in designing spin caloritronic devices.

The particle size driven modification of the non-Griffiths phase to Griffiths phase in (La0.4Y0.6)0.7Ca0.3MnO3 (LYCMO) compound have been presented here. In the nanocrystal, the decreased lattice distortions together with the quenched disorder arising from the ionic size mismatch of the different A-site ions are the possible reason for the occurrence of Griffiths phase. On the other hand, though in the bulk compound quenched disorder is present but the higher distortions enhance the effective antiferromagnetic superexchange interactions and may be the probable reason for the non-Griffiths phase which is identified by the upturn of the inverse susceptibility versus temperature plot from the Curie-Weiss line. An enhancement of Colossal magnetoresistance (CMR) in the minimal surface disorder nanoparticle ( ∼ 120 nm ) has been observed. The study shows that for LYCMO compound, the enhancement of CMR in 120 nm nanoparticle is due to the conversion from non-Griffiths phase to Griffiths phase.

We report here the interplay of ferromagnetism (FM) and charge density wave (CDW) in manganese oxide systems through the study of tunneling conductance spectra. The model Hamiltonian consists of strong Heisenberg coupling in core t 2 g band electrons within mean-field approximation giving rise to ferromagnetism. Ferromagnetism is induced in the itinerant e g electrons due to Kubo-Ohata type double exchange (DE) interaction among the t 2 g and e g electrons. The charge ordering (CO) present in the e g band giving rise to CDW interaction is considered as the extra-mechanism to explain the colossal magnetoresistance (CMR) property of manganites. The magnetic and CDW order parameters are calculated using Zubarev’s Green’s function technique and solved self-consistently and numerically. The e g electron density of states (DOS) calculated from the imaginary part of the Green’s function explains the experimentally observed tunneling conductance spectra. The DOS graph exhibits a parabolic gap near the Fermi energy as observed in tunneling conductance spectra experiments.

NdxSr1−xMnO3 (0.2 ≤ x ≤ 0.5) systems are widely studied in magnetism, popular for high colossal magnetoresistance and are ferromagnetic oxides with TC ranging from 200 K to 300 K. Recently, many of such compounds are re-visited for exploring the correlation of spin, charge and lattice degrees of freedom. Although, manganite thin films are the ideal candidates for studying the electron-correlation effects, the puzzle of obtaining a high quality epitaxial thin films of NdxSr1−xMnO3 are still unsolved contrary to its sister compound LaxSr1−xMnO3. Hence, in this study, we demonstrate the growth of best quality of Nd0.6Sr0.4MnO3 (NSMO) epitaxial thin films. This is evident from the TC and a sharp insulator-to-metal transition (IMT) coinciding at as high as ∼255 K against the bulk TC (∼270 K). It is the highest reported TC in Nd0.6Sr0.4MnO3 thin films to date. Moreover, as-deposited films with in situ oxygen annealing are not enough to relax the lattice of NSMO films due to the significant Jahn-Teller distortion in the film. With ex situ annealing processes alongside the various deposition and in situ annealing conditions, we have extensively studied the growth of epitaxial NSMO thin films on LaAlO3 (0 0 1) and SrTiO3 (0 0 1) to investigate the evolution of lattice and its one-to-one correspondence with the magnetism and the electrical properties of thin films. Accordingly, the enhanced magnetization, reduced resistivity and the higher TC and IMT of the NSMO films obtained from our extensive growth analysis looks promising for the future applications across the TC and IMT.

We report the magnetoresistance studies on Dy 1−x Y x (x ≤ 0.05) alloys across the first order helimagnetic to ferromagnetic phase transition. These alloys exhibit multiple magnetic phases on varying the temperature and magnetic field. The magnetoresistance studies in the hysteresis region shows irreversibility in forward and reverse field cycles. The resistivity values at zero field for these alloys after zero field cooling to the measurement temperatures, are different in both forward and reverse field cycles. The path dependence of magnetoresistance suggests the presence of helimagnetic phase as the supercooled metastable state which transforms to the stable ferromagnetic state on increasing the field. At high magnetic fields negative magnetoresistance following a linear dependence with field is observed which is attributed to the magnon scattering.

We report the magnetic coupling and magneto-transport properties of the epitaxial La0.85Sr0.15MnO3 films, which are fabricated on the (0 0 1)-oriented SrTiO3 substrate by RF magnetron sputtering. The anti-ferromagnetism and metallic state were observed in sequence, and both coexist below a critical temperature of 40 K. Meanwhile, the hysteresis loop exhibits the spin-flop transition. The antiferromagnetic phase originates from the A-type spin structure, in which the antiferromagnetic superexchange interaction between the adjacent MnO2 planes is along the c-axis direction. The metallic behavior stems from the double exchange interaction in the MnO2 plane in-plane. Furthermore, the spin scattering at phase boundaries between the ferromagnetic and antiferromagnetic phases causes a comparatively large magnetoresistance value of about −30% around 100 K. This effect, together with the colossal magnetoresistance, causes the large magnetoresistance values in a wide temperature range. This work helps to understand the magnetic coupling of the antiferromagnetic metallic state and magneto-transport properties in lightly doped manganite films.

Double-perovskite oxides are known to exhibit important electronic, magnetic, and electrochemical properties, including metal-insulator transition, colossal magnetoresistance, and excellent mixed conductivity. Here, single-crystalline PrBaMnFeO5.5+δ thin films were epitaxially grown and sensitively tailored to a tunable ferromagnetic state by post-annealing. The drastically tunable ferromagnetism is attributed to the detailed atomic microstructures, localized oxygen vacancy distribution, and exchange interactions between Mn and Fe ions with different valences. The as-grown PrBaMnFeO5.5+δ epitaxial film exhibits saturation magnetization twice that of undoped PrBaMn2O5.5+δ, probably owing to the synergistic reaction of Mn3+–O–Mn4+ double exchange and Mn3+–O–Fe3+ superexchange interactions. These findings suggest that the PrBaMnFeO5.5+δ double-perovskite film can be an effective ferromagnetic insulator with the strategic magnetic properties of complex manganite oxides tuned by chemical strains.

Double perovskite Sr 2 FeMoO 6 (SFMO) has drawn great attention because of its colossal magnetoresistance at room temperature and promising potential applications in solid oxide fuel cells as an anode material. In this study, the polycrystalline SFMO was prepared by spark plasma sintering (SPS) and its crystal structure, microtopography, magnetic properties, spin-glass phase and anti-site defects were investigated in detail. The effects of the annealing process on the physical properties of the SPS sample were detailedly discussed and studied. The annealing process can effectively suppress the spin-glass phases and impurity phase SrMoO 4 , and simultaneously increase the content of SFMO phases. Besides, the low-temperature magnetic behaviors were confirmed by the field cooling (FC), zero field cooling (ZFC) DC magnetic susceptibility and AC magnetic susceptibility. The TEM results confirm that the annealing process can effectively suppress the impurity phase SrMoO 4 , simultaneously increase the size of the SFMO crystal grains and improve the homogeneity of the crystal grains. This systematic study of double perovskite SFMO will facilitate its potential applications in the field of spin electronics.

The observation of significantly large magnetoresistance at the liquid nitrogen temperature range in the polycrystalline La 0.2 Gd 0.5 Ba 0.3 MnO 3 (LGBMO) compound has been addressed in the present manuscript. The motivation of considering LGBMO sample is the average ‘A’ site ionic radius 〈 r A 〉 and tolerance factor (t), almost same as that of La 0.7 Sr 0.3 MnO 3 (LSMO), which is a well studied colossal magnetoresistive material. Magnetoresistance of the LGBMO compound has been compared with the LSMO as well as parent compound La 0.7 Ba 0.3 MnO 3 (LBMO) to show the enhancement of magnetoresistance in LGBMO compound. This observed nature has been elucidated considering the disorder induced short range magnetic interaction due to the enhance size disorder parameter ( σ 2 ). Our study revels that, size disorder parameter plays the crucial role for enhancing the colossal magnetoresistance.

Functional dependence of magnetoresistance on external magnetic field is of great importance for not only discovering the origin of electrical transport but also tailoring materials for advanced properties in magnetic-field-controlled devices. By utilizing the magnetic domain-rotation model combined with antiphase boundary and charge carrier hopping theories, the formular description of magnetoresistance in magnetite (Fe 3 O 4 ) film has been studied systematically. The calculation shows that the magnetoresistance depends linearly and quadratically on the external magnetic field when the fields are applied parallel and perpendicular to the Fe 3 O 4 film plane, respectively. We give the experimental MR data to verify these theoretical results.

An anomalous Hall constant RH has been observed in various rare earth manganites doped with alkaline earths namely Re1−x Ax MnO3 (where Re = La, Pr, Nd etc., and A = Ca, Sr, Ba etc.) which exhibit colossal magnetoresistance (CMR), metal- insulator transition and many other poorly understood phenomena. We show that this phenomenon of anomalous Hall constant can be understood using two band (l-b) Anderson lattice model Hamiltonian alongwith (l-b) hybridization recently studied by us for manganites in the strong electron-lattice Jahn-Teller (JT) coupling regime an approach similar to the two – fluid models. We use a variational method in this work to study the temperature variation of Hall constant RH (T) in these compounds. We have already used this variational method to study the zero field electrical resistivity ρ (T) and magnetic susceptibility of doped CMR manganites. In the present study, we find that the Hall constant RH (T) reduces with increasing magnetic field parameters h&m and the metal-insulator transition temperature (Tρ) shifts towards higher temperature region. We have also observed the role of the model parameters e.g. local Coulomb repulsion U, Hund’s rule coupling JH between eg spins and t2g spins, ferromagnetic nearest neighbor exchange coupling JF between t2g core spins and hybridization Vk between l-polarons and d-electrons on Hall constant RH (T) of these materials at different magnetic fields. Here we find that RH (T) for a particular value of h and m shows a rapid initial increase, followed by a sharp peak at low temperature say 50 K in our case and a slow decrease at high temperatures, resembling with the key feature of many CMR compounds like La0.8Ba0.2 MnO3.The magnitude of RH (T) reduces and the anomaly (sharp peak) in RH becomes broader and shifts towards higher temperature region on increasing Vk or JH or doping x and even vanishes on further increasing these parameters. Our results of anomalous Hall constant (RH) have same qualitative behavior as the zero-field electrical resistivity. Moreover Hall Constant (RH) shows positive values indicating that the carriers in these manganites are holes.

Based on the structural and magnetoresistive properties of Gd1−xCaxMnO3 (GCMO) ( 0 ≤ x ≤ 1 ) polycrystalline manganites, the magnetic phase diagram of GCMO is deduced. The results show that all of the compounds are ferrimagnetic in the ground state due to polarization of the large magnetic moments of Gd in the opposite direction of Mn ions. However, even disregarding the ordering of the Gd spins in the applied magnetic field direction, the series exhibit complicated magnetic behavior below magnetic ordering temperature ( T C or T N ). In the hole doped region x ≤ 0.5 , Mn ions order ferromagnetically. In the middle doping region ( 0.5 ≤ x ≤ 0.7 ), charge ordering can be observed above T N and, below T N , Mn ions are in antiferromagnetic state which is more obvious in the case with x = 0.8 . In the electron doped region 0.8 ≤ x ≤ 0.9 , Mn ions reveal magnetic cluster glass properties. Except for x = 0.9 , which exhibits degenerate semiconductive behavior, the temperature dependence of resistance shows insulating behavior for all other GCMO concentrations. This can be associated with the small average ionic radius of rare earth cations and colossal magnetoresistance (CMR) is observed for GCMO with x = 0.8 and x = 0.9 when the applied magnetic field exceeds 9 T.

In this paper, BiFeO 3 /La 0.7 Sr 0.3 MnO 3 heterostructure is fabricated on the SrTiO (100) substrate using the pulsed laser deposition method (PLD). Magnetization hystersis loops of the BiFeO 3 /La 0.7 Sr 0.3 MnO 3 heterostructure are obtained at 300 K and 80 K. The heterostructure exhibits evident ferromagnetic characteristic at both room temperature and 80 K. At 80 K, magnetization of the heterostructure is stronger than room temperature magnetic measure. The temperature dependence of resistance of the heterostructure with different currents is also studied. With different currents, there appears to be a peak resistance about 180 K. When I is 50 uA, Δ R is 68.4%. And when I is 100 uA, Δ R is 79.3%. The BiFeO3/La0.7Sr0.3MnO3 heterostructure exhibits a positive colossal magnetoresistance (MR) effect over a temperature range of 80–300 K. In our heterostructure, maximum magnetic resistance appears in 210 K, and MR = 44.34%. Mechanism analysis of the leakage current at room temperature shows that the leakage current is the interface-limited Schottky emission, but not dominated by the Poole-Frenkel emission or SCLC.

Double perovskite oxides have gained in importance and exhibit negative magnetoresistance, which is known as colossal magnetoresistance (CMR) effect. Using a La2CoMnO6 (LCM) thin film layer, we proved that the physical consequences of the CMR effect do also influence the electron energy loss spectrometry (EELS) signal. We observed a change of the band gap at low energy losses and were able to study the magnetisation with chemical sensitivity by employing energy loss magnetic chiral dichroism (EMCD) below the Curie temperature TC, where the CMR effect becomes significant.

Double perovskite La 2 Co 1−x Fe x MnO 6 (x = 0.1, 0.2, 0.5, 1.0) ceramic samples were synthesized by the standard solid-state reaction method. The powder x-ray diffraction (Cu- Kα ) results confirm that this type of compounds has orthorhombic perovskite structure with space group of Pbnm at room temperature. The exchange bias can be observed in all samples. The random distribution of the Fe 3+ ions increases the disorder in La 2 Co 1−x Fe x MnO 6 system, which leads the decreasing of Curie temperature, coercive field, saturation magnetization and remanent magnetization. Griffiths phase may exist below certain temperature in La 2 Co 1−x Fe x MnO 6 samples. The electrical resistivity of La 2 Co 1−x Fe x MnO 6 exhibits obvious semiconducting-like behavior, while the conduction model gradually changed from 3-dimensional variable range hopping model to thermal activation model with the increasing of Fe 3+ -substitution. The negative magnetoresistance effects observed in all samples may be suppressed by Fe 3+ -substitution.

We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La$_{1-x}$Ca$_{x}$MnO$_{3}$ in the overdoped region of the phase diagram for $x > 0.5$, where a charge--ordered (CO) and an antiferromagnetic (AF) phase are present. Resistivity, magnetoresistance and angular dependence of magnetoresistance were measured in the temperature interval $4.2 ~\mathrm{K} < T < 300 ~\mathrm{K}$, for three concentrations $x = 0.52, 0.58$ and $0.75$ and in magnetic fields up to 5 T. The semiconductor/insulator--like behavior in zero field was observed in the entire temperature range for all three concentrations \textit{x} and the electric conduction, at lower temperatures, in the CO state obeys 3D Mott's variable--range hopping model. A huge negative magnetoresistance for $x = 0.52$ and $x = 0.58$, a metal--insulator transition for $B > 3 ~\mathrm{T}$ for $x = 0.52$ and the presence of anisotropy in magnetoresistance for $x = 0.52$ and $x = 0.58$ show the fingerprints of colossal magnetoresistance (CMR) behavior implying the existence of ferromagnetic (FM) clusters. The declining influence of the FM clusters in the CO/AF part of the phase diagram with increasing $x$ contributes to a possible explanation that a phase coexistence is the origin of the CMR phenomenon., 33 pages, 7 figures, 1 table, accepted in Thin Solid Films

The nonequilibrium processes of “self-heating” arising during the flow of electric current are studied for ferromagnetic semiconductors with colossal magnetoresistance near the Curie temperature. These processes lead to the emergence of “hot” paramagnons and the destruction of ferromagnetic order. The solution to the heat balance equation takes into account the temperature dependence of the electrical conductivity caused by Anderson localization of electrons due to their scattering on magnetic inhomogeneities. Description of delocalized electrons subsystem takes into account the spin-flip processes leading to the double exchange. At that, the value of the Anderson percolation threshold and the double exchange depends on the amplitude of spin fluctuations. It was found that N-shaped current-voltage characteristics and hysteresis dependencies of magnetization on the voltage arise in a steady state due to the emergence of “hot” (by internal sample temperature) semiconductor paramagnetic phase. It is shown that the occurrence of self-oscillations of current and magnetization there may be.

The influence of magnetic field on the crystal structure of colossal magnetoresistance (CMR) material La0.5Sr0.5MnO3+delta has been investigated. Low temperature high-magnetic field powder X-ray diffraction (XRD) measurements were carried out on La0.5Sr0.5MnO3+delta in temperature range from 4.2 to 300 K and magnetic field range from 0 to 8 T. A first order structural phase transition from tetragonal I4/mcm to orthorhombic Fmmm phase, coupled with reported electronic and magnetic phase transition from ferromagnetic metal to antiferromagnetic insulator state has been started at similar to 200 K and completed at similar to 100 K. On the application of 8 T magnetic field this magneto-structural phase transition shifted to lower temperature (similar to 162 K) with phase coexistence regime down to 4.2 K. Isothermal X-ray diffraction measurements at 150 K infer the evidence of magnetic field driven first order structural phase transition from Fmmm to I4/mcm. These results consistent with the resistivity and magnetoresistance results; present the microscopic evidence of strong spin-lattice coupling and reveal the magnetic field driven structural phase transition as the origin of observed colossal magnetoresistance in this material. (C) 2016 Published by Elsevier B.V.

The structural, electrical, and magnetic properties of La0.67Sr0.33Mn1−xCrxO3 (0 ≤ x ≤ 0.10) manganites have been studied by substitution of antiferromagnetic trivalent Cr ion at Mn-site. Systematic efforts have been carried out to understand the electrical resistivity behavior in the ferromagnetic metallic and paramagnetic semi-conducting phases of Cr substituted La0.67Sr0.33Mn1−xCrxO3 manganites. Polycrystalline samples show a resistivity minimum at a temperature (Tmin) of

Process of magnetization and magnetoresistance have been studied in nanoisland bilayer systems of FeNi-Co. Hysteresis loops show characteristic features (steps) most clearly observed in certain orientations of the sample in a magnetic field. To explain these features the concept of flat magnetic exchange spring has been introduced for nanoisland bilayers. It has been proposed that additional magnetoresistance can be the result of spin-dependent scattering of electrons in the area of flat magnetic exchange spring. Magnetoresistance studies of bilayer systems has shown that additional magnetoresistance occurs at the same magnetic fields as steps on hysteresis loops.

By using the Ab initio and Monte Carlo calculations, we have studied the magnetism of the crystalline La0.75Sr0.25MnO3 perovskite. The ferromagnetic phase of La0.75Sr0.25MnO3 is half-metallic, which is important in the relation to the colossal magnetoresistance properties of this compound. The total magnetic moment and the exchange couplings deduced from ab initio calculations lead, by using Monte Carlo simulations, to a quantitative agreement with the experimental transition temperatures. The maximum magnetic entropy change and the specific heat are found to be 9.23 J K−1 kg −1 and 191 J mol − 1 K−1, respectively for H = 6 T. Our results suggest that this material a promising candidate for magnetic refrigeration application near to room temperature at moderate fields.

ABO3-type perovskites LaMnO3 is a colossal magnetoresistance material that undergoes an orthorhombic-rhombohedral phase transition as the temperature increases. Phase transition determines its structural properties and thermal conductivity that are important in industrial application. Structural transition is reflected mainly in Mn-O bond lengths and Mn-O-Mn angles between MnO6 octahedrons for Jahn-Teller effect during this progress and traditional born–mayer (BM) model has difficulty in description of structural distortion and thermal properties. In this paper, a new classic interatomic potential model for LaMnO3 was developed within the framework of bond valence (BV) theory. First-principles and intelligent optimization algorithm were used to fit the parameters, enabling the study of temperature-dependent structures by accurate large-scale molecular dynamics (MD) simulations. Calculated structural distortions by our model and thermal properties calculated with equilibrium molecular dynamics (EMD) method accorded with the experimental values within a reasonable error, and had higher accuracy than traditional born-mayer model. These results provided further insight about temperature-depended phase transition and further performance mining of LaMnO3. Most importantly, our potential model showed better accuracy than traditional potential model and is applicable for all crystal materials with perovskite structures.

Structural, magnetic and magneto-transport properties of polycrystalline Pr0.5Ca0.5Mn0.9V0.1O3 have been studied. The incorporation of vanadium attributes to enhancement in the Mn3+/Mn4+ ratio as well as density of conducting eg carriers, which affects the magnetic and electrical behavior of the system. On cooling, a multi-phase separated “paramagnetic (PM) – charge-ordered antiferromagnetic (COAFM) – ferromagnetic (FM) – reentrant spin glass (RSG)” phases are observed with the characteristic charge ordering temperature TCO = 233 K and Neel temperature TN = 143 K. Field-induced first-order magnetic phase transition from a charge-ordered antiferromagnetic state to a ferromagnetic cluster glass state takes place at TC = 44 K. A 7 T magnetic field induces metal–insulator transition at TMI = 163 K. At low temperatures, strong memory-effect and colossal magnetoresistance (CMR) ~ 99.99% are observed in resistivity data. The sample shows a high field coefficient of resistance (FCR) value of about 855% in the low-temperature regime.

Perovskite calcium manganate CaMnO3-δ is representative of an essential group of semiconductors with unique physical phenomena including colossal magnetoresistance and thermoelectric properties. For the large-scale applications that require the utilization of oxide ceramics, the polycrystalline materials’ physical properties such as conductivity can be controlled and ultimately optimized through tuning the ceramics sintering conditions. In the present study, the impact of the sintering temperature on the structure and thermoelectric performance of CaMnO3-δ is systematically studied. For the ceramics pellets made of precursors powders synthesized using the chemical sol-gel reaction, the increase in the sintering temperature dramatically increases the electrical conductivity by order of magnitude and simultaneously increases the Seebeck coefficient. Meanwhile, the thermal conductivity increases with the rise of the sintering temperature. Among the samples sintered at different temperatures, the peaking thermoelectric Figure of Merit ZT of pristine CaMnO3-δ reached 0.28, which is a factor of 2.5 higher than the highest reported ZT for pristine CaMnO3-δ and approached that of the doped single-phase CaMnO3-δ. The electrical and thermal properties changes were interpreted based on the oxide ceramics hierarchical structure evolutions, from unit cell level to micron scales, induced by changes of sintering temperatures.

We present a report of the interfacial reaction between ferromagnetic (FM) Pr 0.7 Sr 0.3 MnO 3 (PSMO-3) in proximity to charge ordered (CO) La 0.5 Ca 0.5 MnO 3 (LCMO-5) in a bilayer structure. PSMO-3/LCMO-5 bilayer film with high crystalline quality was epitaxially grown on SrTiO 3 (001) substrate by pulsed laser deposition. The bilayer loses 20% of its resistance for only 0.5 T, and loses 50% of its resistance for 2 T. This large low-field magnetoresistance (LFMR) is comparable to some FM/CO multilayers and other mixed compounds including strongly competing phases. LFMR of ∼−73% has been achieved at H = 1 T and T = 185 K. The maximum MR reaches a value of ∼−641% at H = 9 T and T = 205 K and the corresponding MR at room temperature is ∼−30%. The formation of CO anti-ferromagnetic state in LCMO-5 and its collapse (melting) under the applied magnetic field may be responsible for the enhanced MR mentioned above. In other words, the enhancement of MR can be explained by a FM phase percolation. Moreover, exchange bias (EB) cannot be observed in the bilayer at low temperature of 3 K, further confirming the occurrence of FM phase percolation at the PSMO-3/LCMO-5 interface. The disappearance of EB can be explained by a combination of the preferable distribution of FM clusters and FM clusters percolation at the PSMO-3/LCMO-5 interface. Large MR can be realized by using a CO material as a sublayer, which can provide potential application in the used devices.

The complex interplay between order parameters of different nature that dominates the physics of co- lossal magnetoresistance manganites is analysed from a symmetry based perspective.Phenomenological energies are given for the different competing phases.It is shown that the general trends observed in different systems,such as the mutual exclusion of orbital order and A-AFM order and the related sta- bilization of theCE-AFM order,stem to large extend from the symmetry of the parameters involved.The possible stabilization of complex phases where charge and orbital order coexist with magnetic and ferroelectric states is also anticipated., This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the frame work of the Strategic Projects of CFUM [PEst-C/FIS/UI0607/2013 (F-COMP-01-0124-FEDER022711)].

The electrical and magnetoresistance behavior of L a 0.8 N a 0.2 − x □ x M n O 3 (0.00≤ x ≤0.15) polycrystalline sample was investigated. Resistivity measurements versus temperature under different magnetic fields were performed to investigate the electronic transport and magnetoresistance properties. The abnormal transport properties were induced by the sodium deficiency content, characterized by the double metal–insulator transitions ( T P 1 and T P 2 ). The present results have been discussed and possible explanations given based on the related theory and previous reported results. The conduction mechanism was explained by the adiabatic small polaron hopping (ASPH) in the insulating region and by the competition between the small-polaron and spin-wave scattering in the metallic region. Moreover, a resistivity minimum has been observed for all samples in the temperature range from 2 to 70 K, which is strongly influenced by an applied magnetic field explained by a Kondo-like scattering mechanism. Therefore, the percolation theory is introduced to understand the transport mechanism in the whole temperature range. Hence, the estimated values of the resistivity was found to be in good agreement with the experimental data. Magnetoresistance measurements show high values reaching 60% for x =0.15 sample.

We have synthesized the single phase polycrystalline sample of silver doped disordered Sm0.55Sr0.45−xAgxMnO3 using the conventional solid state method. They have been investigated by X-ray diffraction for phase evolution and their Rietveld refined X-ray diffraction pattern indicates an increase in lattice parameters and unit cell volume with Ag doping. The magnetization analysis shows the presence of a first order paramagnetic to ferromagnetic transition; the transition temperature and amount of thermal hysteresis decreases on Ag doping. The transport, magneto-transport results indicates decrease in metal to insulator transition, drastic increase in resistance and temperature coefficient of resistance (TCR %) with nearly unaffected colossal magnetoresistance effect which indicates that at least a part of silver is incorporated in the lattice. Scanning electron micrographs indicate that silver has also increased the grain growth sharpness and thus decrease the effect of grain boundary scattering. The significant value of TCR of ∼43% of our samples indicates their applied nature for bolometric application.

The samples of La0.6Dy0.1Sr0.3MnO3/x(CuO)(x = 0.00, 0.08, 0.12, 0.16, 0.20) were prepared by the solid-state reaction method. Electric transport property and temperature stability of magnetoresistance of the samples were studied through X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) photograph, resistivity–temperature (ρ–T) curves in zero field and in applied magnetic field, and magnetoresistance–temperature (MR–T) curves. With the increase of CuO content, resistivity increases, and ρ–T curves exhibit a peak near 320 K, which is induced by double exchange. In the meantime, ρ–T curves exhibit a “shoulder peak” in the temperature range of 250–220 K, which is induced by boundary effect. MR–T curves exhibit a sharp peak at high temperature, MR increases continuously with temperature decreasing in low temperature range, and MR exhibits a platform in the intermediate temperature range, then the temperature stability of magnetoresistance appears. For the sample with x = 0.16, magnetoresistance keeps at 9.0 ± 0.2% without change in the temperature range of 222–272 K in the magnetic field of 0.8 T. The intrinsic magnetoresistance and extrinsic magnetoresistance of samples have been discussed, and the mechanism of temperature stability of magnetoresistance is provided.

Composites of (1 − x)La0.7Ca0.3MnO3/xLa0.7Sr0.2Ca0.1MnO3 were prepared via the sol–gel method combined with the energy milling method. The electrical transport and low-field magnetoresistance properties of the composites were systematically studied. As the La0.7Sr0.2Ca0.1MnO3 level increased, the metal-insulator transition temperature of the composites shifted to a higher temperature. The transport mechanisms in the insulating region of the composites were comprehensively analyzed via small polaron hopping (SPH) and variable range hopping (VRH) models. The combination of electron–electron interaction and spin wave scattering was considered to estimate the conduction mechanism in the metallic region of the composites. Both intrinsic magnetoresistance and extrinsic low-field magnetoresistance were enhanced from 30 K to the Curie temperature for the system. The results were explained on the basis of the competition between spin-dependent scattering and spin-polarized tunneling at La0.7Ca0.3MnO3 grain boundaries induced by interactions between La0.7Ca0.3MnO3 and La0.7Sr0.2Ca0.1MnO3 manganites.

Electronic phase separation is a frequent ingredient of the physics of manganites for which the colossal magnetoresistance (CMR) phenomenon is at debate. We investigate the switchable magnetoresistance (MR) effect of the Ruddelsden-Popper (RP) oxide Ca4Mn3O10 (CMO), which shows a metal-to-insulator transition (MIT) at 70 K (TMIT). The static (DC) and dynamic (AC) magnetic susceptibilities of CMO indicate an unusual magnetic phase coexistence below the Neel temperature (TN) i.e., at TMIT, which we describe as a glassy magnetic behavior. Furthermore, by means of synchrotron X-ray diffraction, we observed a structural anomaly directly associated with the MIT. Hence, the onset of glassiness correlates with a slight structural distortion. Interestingly, CMO displays a large positive magneto-resistance (PMR) effect (up to 550% at 4 K) in the metallic state below TMIT, while a small negative magneto-resistance (NMR) effect (-3.5% at 112 K) in the insulating region above TMIT. At TMIT, the PMR switches to NMR behavior. PMR is probably induced via enhancing the exchange interaction by localization of itinerant moment resulting in formation of magnetic polarons, whereas NMR is possibly due to reduced electron-spin scattering. This appears to be a special type of magnetoresistance, different from regular observations, and may open a new avenue in searching for exotic phenomena in manganese-based CMR materials.

Electrical-transport and magneto-transport in bulk nanocrystalline (BNC) La 1 - x Ca x MnO 3 + δ (x = 1/8 with either δ = 0.00 or δ = 0.06, x = 3/8 with δ = 0.00) (LCMO) manganite system have been studied treating the bulk crystalline (BC) counterparts as the reference systems. Irrespective of the value of δ in under hole-doped (x = 1/8) LCMO, the metal-insulator (M-I) transition (not observed in the BC counterpart) appears at a temperature T MI ≪ T C , where T C is the temperature at which the ferromagnetic (FM)–paramagnetic (PM) second-order phase transition occurs. Oxygen off-stoichiometry makes the M-I transition more pronounced and reduces the overall magnitude of resistivity. Reducing the average crystallite size d below 150 nm, lowers both T MI and T C in the BNC samples with x = 1/8 and δ = 0.00 or 0.06 but decreases T MI while increasing T C in the optimally hole-doped x = 3/8 LCMO. The single-orbital double-exchange model, which predicts the coincidence, or otherwise, of the M-I and FM-PM transitions with some success in the BC LCMO, fails to correctly describe the above-mentioned results in BNC LCMO. The resistivity minima at low temperatures ( T min ), completely absent in BC, occur in BNC LCMO, regardless of the value of x , δ , d and the strength of the magnetic field (H). The mechanism for resistivity, ρ (T), changes from the adiabatic small polaron nearest-neighbor hopping (for x = 3/8) or from the Shklovskii-Efros variable range hopping, SE-VRH, (for x = 1/8), prevalent in BC, to the Mott-VRH in the PM insulating state in the BNC counterparts when d falls below 150 nm. At T T min , the contributions due to the Mott-VRH (present only in the samples with x = 1/8 and δ = 0.00 or δ = 0.06) and the enhanced electron-electron Coulomb interaction (in all the BNC LCMO samples) are responsible for the negative temperature coefficient of resistivity (TCR). By contrast, the coherent electron-magnon scattering accounts for the positive TCR observed at T > T min . H suppresses the mean hopping energy difference between the hopping sites but increases the electron localization length. The field-induced enhancement in the localization length far outweighs the field-induced drop in the mean hopping energy difference to produce an increase in the mean hopping distance with H.

Classical magnetoresistance generally follows the quadratic dependence of the magnetic field at lower field and finally saturates when field is larger. Here, we report the large positive non-saturating linear magnetoresistance in topological crystalline insulator, Pb0.6Sn0.4Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. Magnetoresistance value as high as ∼200% was achieved at 3 K at magnetic field of 9 T. Linear magnetoresistance observed in Pb0.6Sn0.4Te is mainly governed by the spatial fluctuation carrier mobility due to distortions in the current paths in inhomogeneous conductor.

The magnetotransport properties like electrical resistivity and Thermoelectric power of rare earth manganites doped with alkaline earths namely Re 1− x A x MnO 3 (where Re=La, Pr, Nd etc., and A=Ca, Sr, Ba etc.) which exhibit colossal magnetoresistance (CMR), metal–insulator transition and many other poorly understood phenomena, have been studied in this work by means of a Variational method. We have used two band (l-b) model for manganites in the strong electron–lattice Jahn–Teller (JT) coupling regime, an approach similar to the two-fluid models along with (l-b) hybridization. We have already used this Variational method to study the zero field electrical resistivity ρ ( T ) of doped CMR manganites. In the present study we find that the resistivity decreases with increasing magnetic field and the metal–insulator transition temperature ( T ρ ) shifts towards higher temperature region. This may happen because of the delocalized charge carriers, induced by applied magnetic field, decreasing the resistivity which in turn leads to the local ordering of the electron spins. Due to this ordering, the ferromagnetic metallic state might have suppressed the paramagnetic insulating regime resulting in the observed increase in T ρ under applied magnetic field. We have also shown the temperature dependent magneto-resistance (MR) ratio at different magnetic fields. We obtained large MR value at low temperatures. An interesting feature of the Magnetic field dependent thermoelectric power Q ( T ) is that it rises gradually with decreasing temperatures and a broad peak appears at low temperatures and as the temperature is lowered further, the value of Q ( T ) drops sharply (i.e. Q →0 as T →0 ), which is suggested to originate from the weak carrier localization effect. In the external magnetic field, the phonon-drag effect is expected to become weaker so that value of Q ( T ) reduces.

Magnetic properties of Mn-site doped La 0.7 Ca 0.3 Mn 0.94 TM 0.06 O 3+ Δ (TM=Cu, Zn) were experimentally and theoretically studied. The low-temperature magnetization and magnetic phase transition temperature T C of the samples combining with simulations of 2D doped Ising model suggest that Cu 2+ ions have an antiferromagnetic interaction with their nearest neighboring Mn ions. Interestingly, an anomalous magnetic behavior, a “step-like” magnetic phase transition, is observed. The existence and magnitude of this step vary with different doping ions and oxygen ratio, which is experimentally suggested to be relevant to the interaction between magnetic ions and oxygen content. A superposition between two independent magnetic systems with different values of an exchange integral J well explains the anomalous magnetic phase transition, which suggests that this step-like behavior results from extrinsic inhomogeneity and negligible coupling between grains in polycrystalline.

The Metropolis algorithm and the classical Heisenberg approximation were implemented by the Monte Carlo method to design a computational approach to the magnetization and resistivity of La2/3Ca1/3MnO3, which depends on the Mn ion vacancies as the external magnetic field increases. This compound is ferromagnetic, and it exhibits the colossal magnetoresistance (CMR) effect. The monolayer was built with L×L×d dimensions, and it had L=30 umc (units of magnetic cells) for its dimension in the x–y plane and was d=12 umc in thickness. The Hamiltonian that was used contains interactions between first neighbors, the magnetocrystalline anisotropy effect and the external applied magnetic field response. The system that was considered contains mixed-valence bonds: Mn3+eg’–O–Mn3+eg, Mn3+eg–O–Mn4+d3 and Mn3+eg’–O–Mn4+d3. The vacancies were placed randomly in the sample, replacing any type of Mn ion. The main result shows that without vacancies, the transitions TC (Curie temperature) and TMI (metal–insulator temperature) are similar, whereas with the increase in the vacancy percentage, TMI presented lower values than TC. This situation is caused by the competition between the external magnetic field, the vacancy percentage and the magnetocrystalline anisotropy, which favors the magnetoresistive effect at temperatures below TMI. Resistivity loops were also observed, which shows a direct correlation with the hysteresis loops of magnetization at temperatures below TC.