Colossal Magnetoresistance Properties Research Articles

Effect of the calcination temperature on temperature coefficient of resistance and magnetoresistance of La0.67Ca0.33MnO3 polycrystalline ceramics

La0.67Ca0.33MnO3 (LCMO) has attracted considerable attention due to its superior colossal magnetoresistance properties, as well as the metal-insulator transition and enhanced temperature coefficient of resistance (TCR) characteristics. Here, the co-precipitation method is utilized in order to prepare the LCMO-based ceramics, whose magnetotransport properties as a function of calcination temperature (Tcal) were thoroughly investigated. The TCR of LCMO exhibits initially an increasing pattern and then decreases by elevating the Tcal, whereas the metal-insulator transition temperature (TMI) is shifted towards a lower temperature value. In addition, the magnetoresistance (MR) was enhanced by enforcing a bigger Tcal and reached the value of 82.4% at Tcal = 800 °C. The underlying mechanism for the manifestation of such improved properties is thoroughly examined by employing electrical measurements in various temperature ranges. An optimal TCR of 32.3%·K−1 in LCMO-based ceramic was attained with Tcal = 500 °C, indicating that the co-precipitation method could be employed in order to facilitate the potential use of LCMO for infrared detecting and magnetoresistive switching applications.

Enhancement of Room-Temperature Low-Field Magnetoresistance in Nanostructured Lanthanum Manganite Films for Magnetic Sensor Applications.

The results of colossal magnetoresistance (CMR) properties of La1-xSrxMnyO3 (LSMO) films grown by the pulsed injection MOCVD technique onto an Al2O3 substrate are presented. The grown films with different Sr (0.05 ≤ x ≤ 0.3) and Mn excess (y > 1) concentrations were nanostructured with vertically aligned column-shaped crystallites spread perpendicular to the film plane. It was found that microstructure, resistivity, and magnetoresistive properties of the films strongly depend on the strontium and manganese concentration. All films (including low Sr content) exhibit a metal–insulator transition typical for manganites at a certain temperature, Tm. The Tm vs. Sr content dependence for films with a constant Mn amount has maxima that shift to lower Sr values with the increase in Mn excess in the films. Moreover, the higher the Mn excess concentration in the films, the higher the Tm value obtained. The highest Tm values (270 K) were observed for nanostructured LSMO films with x = 0.17–0.18 and y = 1.15, while the highest low-field magnetoresistance (0.8% at 50 mT) at room temperature (290 K) was achieved for x = 0.3 and y = 1.15. The obtained low-field MR values were relatively high in comparison to those published in the literature results for lanthanum manganite films prepared without additional insulating oxide phases. It can be caused by high Curie temperature (383 K), high saturation magnetization at room temperature (870 emu/cm3), and relatively thin grain boundaries. The obtained results allow to fabricate CMR sensors for low magnetic field measurement at room temperature.

Impact of NiO nano-particles on colossal magneto-resistance of La0.70Ca0.30MnO3 composite

Mixed-valent perovskite manganite has gained considerable research interest due to the increasing demand for energy storage materials. Herein, we show that colossal magneto-resistance properties of La0.7Ca0.3MnO3 (LCMO) can be changed via nickel oxide (NiO) doping. A two-step conventional solid-state reaction method is used to synthesize LCMO-10% NiO composite. The phase purity, structural, electrical (resistivity), and magneto-transport properties of as-synthesized LCMO-10% NiO composite are detailed. NiO doping shifts metal–insulator transition temperature (TMI) from 263 K to 195 K and increases resistivity. The magneto-resistance (MR) measurements showed 10% NiO doping resulted in a maximum MR of ∼ -70.32% at 200 K (near TMI) and 10 T applied magnetic field. However, -0.0849% MR is seen at 290 K (RT) and 0.3 T. The increased ∼ -63.85% MR is found at 100 K and at 10 T, which is comparatively much higher than the pristine LCMO sample. This is due to the addition of NiO in LCMO that improves physical properties (i.e., grain size).

Nanostructured Manganite Films Grown by Pulsed Injection MOCVD: Tuning Low- and High-Field Magnetoresistive Properties for Sensors Applications.

The results of colossal magnetoresistance (CMR) properties of La0.83Sr0.17Mn1.21O3 (LSMO) films grown by pulsed injection MOCVD technique onto various substrates are presented. The films with thicknesses of 360 nm and 60 nm grown on AT-cut single crystal quartz, polycrystalline Al2O3, and amorphous Si/SiO2 substrates were nanostructured with column-shaped crystallites spread perpendicular to the film plane. It was found that morphology, microstructure, and magnetoresistive properties of the films strongly depend on the substrate used. The low-field MR at low temperatures (25 K) showed twice higher values (−31% at 0.7 T) for LSMO/quartz in comparison to films grown on the other substrates (−15%). This value is high in comparison to results published in literature for manganite films prepared without additional insulating oxides. The high-field MR measured up to 20 T at 80 K was also the highest for LSMO/quartz films (−56%) and demonstrated the highest sensitivity S = 0.28 V/T at B = 0.25 T (voltage supply 2.5 V), which is promising for magnetic sensor applications. It was demonstrated that Mn excess Mn/(La + Sr) = 1.21 increases the metal-insulator transition temperature of the films up to 285 K, allowing the increase in the operation temperature of magnetic sensors up to 363 K. These results allow us to fabricate CMR sensors with predetermined parameters in a wide range of magnetic fields and temperatures.

First principal calculation and Monte Carlo simulations of the Magnetocaloric effect, Electronic and Magnetic properties in perovskite oxide Pr 0.65Sr 0.35MnO 3

We have used the first principal calculation and Monte Carlo simulations (MCS) to investigate the magnetocaloric effect, electronic and magnetic properties of Pr 0.65Sr 0.35MnO 3 (PSMO) perovskite. The exchange-correlation potential was treated with the generalized gradient approximation (GGA) for the electronic and magnetic properties. The ferromagnetic phase of PSMO is half metallic with 100% spin polarization, which is important in the relation to the colossal magnetoresistance properties of this compound. The magnetic moment is obtained. The thermal variation of magnetization of PSMO has been obtained. The temperature dependence of the magnetic entropy change and the adiabatic temperature are obtained by MCS. The Curie temperature of PSMO has been deduced. The field dependence of relative cooling power PSMO has been obtained.

Electronic, Magnetic Properties and Magnetocaloric Effect of La2SrMn2O7 Bilayer Manganite: An Ab Initio calculations and Monte Carlo Study

The structure of La2SrMn2O7 (LSMO) bilayer manganite has been investigated using the Monte Carlo simulations and ab initio calculations based on the full-potential linearized augmented plane-wave method. The ferromagnetic phase of LSMO is half-metallic with 100% spin polarization, which is important in relation to the colossal magnetoresistance properties of this compound. Thermal magnetization of LSMO bilayer manganite is obtained for several external magnetic fields h = 1, 3, 5 and 7 T. We have given the dM/dT as a function of temperatures for several external magnetic fields. The magnetic transition from ferromagnetic to paramagnetic is found. The second-order phase transition is found at the transition temperature. The temperature dependence of the magnetic entropy changes of temperatures of LSMO bilayer manganite for several external magnetic fields h = 1, 3, 5 and 7 T is also found. The field dependence of relative cooling power of LSMO bilayer manganite is given for several temperatures. Finally, the magnetic hysteresis cycle of LSMO bilayer manganite is obtained for several temperatures T = 160, 190, 213 and 220 K. The superparamagnetic behavior has been found around the transition temperature.

Room-temperature large magnetocaloric, electronic and magnetic properties in La0.75Sr0.25MnO3 manganite: Ab initio calculations and Monte Carlo simulations

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.

Electrical conductivity increase by order of magnitude through controlling sintering to tune hierarchical structure of oxide ceramics

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.

Investigation of Nano-Sized Al<sub>2</sub>O<sub>3</sub> on Pr-Sr-Mn-O Composites: Structural, Microstructural and Magnetic Properties

Perovskite manganites have always been the research interest attributed to its intriguing colossal magnetoresistive (CMR) properties. Incorporation of an insulating secondary phase into the manganite composites has proven as an effective measure to enhance the low field magnetoresistance (LFMR). This paper reports the structural, microstructural and magnetic properties of (1-x) Pr0.7Sr0.3MnO3 (PSMO): x Al2O3 composites synthesized by the solid-state reaction method. Different compositions of nano-sized Al2O3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were appended into the samples to investigate its effect on the physical properties. X-ray diffraction patterns show all samples exhibit polycrystalline PSMO as the major phase and strong orientation along (121) direction throughout the series. The crystal structural parameter is presented by Rietveld refinement. Nano-sized of Al2O3 has distorted the pure PSMO as changes have been observed in bond length and bond angle observed. Surface roughness and particle size show the increment along with increasing Al2O3 composition from the atomic force microscope (AFM) analysis. All samples possess the narrow hysteresis loop with weak ferromagnetic nature. The PSMO: Al2O3 presented in this study is a promising manganite composite which can be utilized in the magnetic sensor applications.

Control of charge order melting through local memristive migration of oxygen vacancies

The colossal magnetoresistance (CMR) in perovskite manganites and the resistive switching (RS) effect in metal-oxide heterostructures have both attracted intensive attention in the past decades. Up to date, however, there has been surprisingly little effort to study the CMR phenomena by employing a memristive switch or by integrating the CMR and memristive properties in a single RS device. Here, we report a memristive control of the melting of the antiferromagnetic charge ordered (AFM-CO) state in ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3\ensuremath{-}\ensuremath{\delta}}$ epitaxial films. We show that an in situ electrotailoring of the boundary condition, which results in layers of oxygen vacancies at the metal-oxide interface, can not only suppress the critical magnetic field for the AFM-CO state melting in the interfacial memristive domain, but also promote the one in the common pristine domain of the RS device in the high and low resistive states. Our study thereby highlights the pivotal roles of functional oxygen vacancies and their dynamics in strong correlation physics and electronics.

Nanoclusters in magnetoresistance

AbstractElectronic phase separation is one of the most exciting findings during the study of strongly correlated electron systems in past decades. Inhomogeneities at the nanoscale have been proven to not only play a key role in the material properties but also challenge the fundamental concepts of condensed matter physics. In rare earth doped manganites, a nanoscale phase with unique structural modulations has attracted particular attention because of its relationship with the renowned behavior of the material, colossal magnetoresistance (CMR). Direct observations of the nanoscale phases are usually difficult but necessary to unravel the controversies and unveil the underlying physics in this case. In this review paper, recent achievements of direct imaging of the nanoscale phase are shown by using advanced transmission electron microscopic techniques correlated with the material property measurements. Based on those results, the relationship between the nanoscale phase and the CMR effect was established, and unexpected magnetic and physical properties of the nanoscale phase were found. Although the microscopic origin of the nanoscale phase is not fully interpreted yet, the findings here shed light on the pathway to a deeper understanding of the mechanism of CMR and other properties in these materials.

ChemInform Abstract: Colossal Magnetoresistance Manganite Perovskites: Relations Between Crystal Chemistry and Properties

Manganites with the perovskite structure represent a very important family of oxides which are extensively studied for their colossal magnetoresistance (CMR) properties. In the present review we discuss the different factors which govern the magnetic and transport properties of these materials: carrier concentration, average size of the interpolated cation, and mismatch effect on the A-site. Three types of oxides are mainly examined: (i) the hole doped manganites Ln0.7A0.3MnO3 (A = Ca, Sr, Ba), (ii) the “charge ordered” Ln0.5A0.5MnO3 manganites, and (iii) the electron doped manganites Ca1-xLnxMnO3 and Ca1-xThxMnO3. The relationships between structural and magnetic transitions are discussed, and particular attention is paid to charge ordering phenomena. The doping of the Mn sites by various elements (Al, Ga, In, Ti, Sn, Fe, Cr, Co, Ni) is systematically examined. The beneficial effect of “Cr, Co, Ni” elements, which induce CMR properties in these perovskites, is emphasized.

Substitutional disorder and charge localization in manganites

In the manganites RE1 − xAExMnO3 (RE and AE being rare-earth and alkaline-earth elements, respectively) the random distribution ofRE3 + andAE2 + induces random, but correlated, shifts of site energies of charge carriers in the Mn sites. Weconsider a realistic model of this diagonal disorder, in addition to the double-exchangehopping disorder, and investigate the metal–insulator transition as a function oftemperature, across the paramagnetic–ferromagnetic line, and as a function of doping x. Contrary to previous results, we find that values of parameters, estimated fromthe electronic structure of the manganites, are not incompatible with thepossibility of a disorder-induced metal to insulator transition accompanyingthe ferromagnetic to paramagnetic transition at intermediate doping (x ∼ 0.2–0.4). These findings indicate clearly that substitutional disorder has to be considered as animportant effect when addressing the colossal magnetoresistance properties of manganites.

Spin waves and metallic state of magnetoresistive manganites

La1−x(B = Sr,Ca,Ba)xMnO3 manganites are known to undergo upon doping a transition from an insulating ferromagnetic state to a puzzling metallic ferromagnetic phase showing colossal magnetoresistance properties. Revisiting spin wave measurements in this metallic phase, we observe strong similarities with the insulating x ~ 1/8 regime, suggesting that the same physics of small ferromagnetic domains is at play [1, 2]. We argue that all the anomalies in this metallic state could be explained in this inhomogeneous picture, in continuity with the x ~ 1/8 range.

Colossal magnetoresistance properties of Nd-doped Bi0.5Sr0.5MnO3

We have studied structure, transport, and magnetic properties of NdxBi0.5−xSr0.5MnO3 (NBSMO) (x=0.2 and 0.4) through x-ray diffraction, magnetoresistance, and magnetization measurements. The Rietveld analysis of the x-ray diffraction data shows that the NBSMO crystallizes in an orthorhombic perovskite structure with Pbnm space group for x=0.2 and Imma space group for x=0.4. The lattice variations indicate that the highly polarizable 6s2 lone pair of Bi ion is screened and the structural changes occur in accordance with change in the average radius of A-site cations. Magnetotransport studies reveal that both samples are variable range hopping semiconductors and the hopping depends on the orientation of localized spin moment of the electrons. Magnetic studies confirm that substituting Bi with Nd collapses the charge ordered antiferromagnetic (AFM) state of Bi0.5Sr0.5MnO3 to ferromagnetic state, with TC’s∼276 and ∼278K, for x=0.2 and 0.4, respectively. The observed enhancement in colossal magnetoresistance effect in NBSMO compared to Bi0.5Sr0.5MnO3 is attributed to the presence of competing ferromagnetic and charge ordered AFM state.

The Nanoscale Phase Separation in Hole-Doped Manganites

A macroscopic phase separation, in which ferromagnetic clusters are observed in an insulating matrix, is sometimes observed, and believed to be essential to the colossal magnetoresistive (CMR) properties of manganese oxides. The application of a magnetic field may indeed trigger large magnetoresistance effects due to the percolation between clusters allowing the movement of the charge carriers. However, this macroscopic phase separation is mainly related to extrinsic defects or impurities, which hinder the long-ranged charge–orbital order of the system. We show in the present article that rather than the macroscopic phase separation, an homogeneous short-ranged charge–orbital order accompanied by a spin glass state occurs, as an intrinsic result of the uniformity of the random potential perturbation induced by the solid solution of the cations on the A -sites of the structure of these materials. Hence the phase separation does occur, but in a more subtle and interesting nanoscopic form, here referred as “homogeneous”. Remarkably, this “nanoscale phase separation” alone is able to bring forth the colossal magnetoresistance in the perovskite manganites, and is potentially relevant to a wide variety of other magnetic and/or electrical properties of manganites, as well as many other transition metal oxides, in bulk or thin film form as we exemplify throughout the article.

Transport properties of microstructured ultrathin films of La0.67Ca0.33MnO3 on SrTiO3

The authors have investigated the electrical transport properties of 8nm thick La0.67Ca0.33MnO3 (LCMO) films, sputter deposited on SrTiO3 (STO), and etched into 5μm wide bridges by Ar-ion etching. The authors find that even slight overetching of the film leads to conductance of the STO substrate, and asymmetric and nonlinear current-voltage (I-V) characteristics. However, a brief oxygen plasma etch allows full recovery of the insulating character of the substrate. The I-V characteristics of the bridges are then fully linear over a large range of current densities. The authors find colossal magnetoresistance properties typical for strained LCMO on STO but no signature of nonlinear effects (the so-called electroresistance) connected to electronic inhomogeneites. In the metallic state below 150K, the highest current densities lead to heating effects and nonlinear I-V characteristics.

Magnetic order and electrical conductivity scaling of the spinel oxideMn0.5Ru0.5Co2O4

We report the magnetic order and electrical (ac and dc) conductivity of bulk ${\mathrm{Mn}}_{0.5}{\mathrm{Ru}}_{0.5}{\mathrm{Co}}_{2}{\mathrm{O}}_{4}$ spinel oxide. The system is a ferrimagnet, which undergoes from ferrimagnetic to paramagnetic state above the Curie temperature $({T}_{C})\ensuremath{\sim}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Low field $(\ensuremath{\leqslant}100\phantom{\rule{0.3em}{0ex}}\mathrm{Oe})$ measurement shows a peak at ${T}_{p}\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in zero field cooled (ZFC) magnetization, whereas field cooled magnetization continuously increases down to $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. As long as the applied magnetic field is not large enough in comparison with the coercive field, a sharp decrease in ZFC magnetization is always observed below ${T}_{p}$. The peak temperature at ${T}_{p}\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is shifted to lower temperatures by applying sufficiently large magnetic field. ac susceptibility (${\ensuremath{\chi}}^{\ensuremath{'}}$ and ${\ensuremath{\chi}}^{\ensuremath{''}}$) also shows a sharp peak at $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which is independent of frequencies $(0.5\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}--1\phantom{\rule{0.3em}{0ex}}\mathrm{kHz})$ of ac magnetic field (amplitude $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$). These observations, including other measurements, suggest strong pinning effects in domain wall dynamics. We have noted that electrical behavior of the system is significantly affected by the magnetic ordering of the spins. Our results have shown the contribution of short range interactions above ${T}_{C}$ to the formation of small polarons. The system shows colossal magnetoresistance properties with a semiconductor to metallic transition below $80\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. A simple scaling law is used as a tool for the identification of short range magnetic interactions that may be difficult to determine using conventional magnetization experiments.

High-pressure / High-temperature Synthesis of Transition Metal Oxide Perovskites

Perovskite and related Ruddlesden-Popper type transition metal oxides synthesised at high pressures and temperatures during the last decade are reviewed. More than 60 such new materials have been reported since 1995. Important developments have included perovskites with complex cation orderings on A and B sites, multiferroic bismuth-based perovskites, and new manganites showing colossal magnetoresistance (CMR) and charge ordering properties.

Elastic properties ofGd5Si2Ge2studied with an ultrasonic pulse-echo technique

We present the results of a study of the elastic properties of ${\mathrm{Gd}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$, an alloy with giant magnetocaloric, magnetostrictive, and colossal magnetoresistive properties. Sound wave velocities measured in a number of different geometries allowed us to determine the whole elastic tensor for the monoclinic phase of this material. The anisotropy of the crystal is explored using the polar plots of the variations in the main crystallographic planes of the sound speed, the Young's modulus, the shear modulus, and the linear compressibility. The effect of hydrostatic pressure on the ${\mathrm{Gd}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$ properties is clarified. The acoustical axes are determined. The bulk modulus is estimated as $68.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$; the Debye temperature is $250\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.