Colossal Magnetoresistance Research Articles

Аномальное изменение размера спинового полярона в парамагнитной области температур в La-=SUB=-1.2-=/SUB=-Sr-=SUB=-1.8-=/SUB=-Mn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-

In this work, we continued the study of the magnetic and electrical properties of the double perovskite La1.2Sr1.8Mn2O7, which has a colossal magnetoresistance in excess of 1200 near the Curie temperature. It is shown that the colossal magnetoresistance observed in La1.2Sr1.8Mn2O7 is well described on the basis of the “orientational” and “spin-polaron” conduction mechanisms. It was found in the work that in the absence of a magnetic field, the linear size of the spin polaron decreases with increasing temperature in the ferromagnetic region, and upon the transition of manganite to the paramagnetic state, the linear size begins to increase, reaching a maximum at 180 K. At temperatures exceeding 180 K, an anomalous temperature change the size of the spin polaron disappears. In the absence of a magnetic field, the detected peak on the temperature curve of the change in the size of the spin polaron is maximal; with the inclusion of the magnetic field, the peak height decreases. Mechanisms are proposed to explain this anomalous temperature behavior of the spin polaron size.

Colossal magnetoresistance of Nd-doped LaCaMnO3 polycrystalline ceramics

The cation doped polycrystalline compound La0.5Nd0.15Ca0.35MnO3 has been synthesized by a conventional solid state reaction method. The Rietveld analysis of the powder XRD of the composites reveals an orthorhombic structure with Pbnm space group symmetry. The cell parameters are a = 5.4505 ?, b = 5.4457 ? and c = 7.6876?. The AC magnetization studies show a semiconducting paramagnetic to metallic ferromagnetic transition at a temperature below the Curie temperature TC which is found to be 206.3K. It is also observed that metal to semiconductor transition temperature TMS is very close to TC. The sample also possesses high magnetoresistance, which is revealed in MR studies.

Structural and Elastic Behavior of Chromium Doped Pr<sub>0.5</sub>Sr<sub>0.5</sub>MnO<sub>3</sub> System

A series of colossal magneto resistance (CMR) materials with compositional formula Pr0.5Sr0.5Mn1-xCrxO3 (x = 0, 0.1, 0.2, 0.3, 0.4) were prepared by sol-gel technique using pure metal nitrates as the starting materials. These samples were characterized structurally by X-ray diffraction, FTIR and SEM. All the samples exhibit orthorhombic structure without any detectable impurities. The bulk densities for all the compositions were measured from the pellets. The Young’s and Rigidity moduli, Poisson’s ratio and Debye temperature of all the compositions were calculated with the experimentally measured ultrasonic longitudinal and shear velocities at room temperature using pulse transmission technique. As the materials are porous, zero porous elastic moduli have also been calculated using a well-known Hasselmann and Fulrath model. The observed variation of elastic moduli with varying chromium doping concentration has been studied qualitatively.

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.

Magnetic Field Measurements during Magnetic Pulse Welding Using CMR-B-Scalar Sensors.

The possibility of applying CMR-B-scalar sensors made from thin manganite films exhibiting the colossal magnetoresistance effect as a fast-nondestructive method for the evaluation of the quality of the magnetic pulse welding (MPW) process is investigated in this paper. This method based on magnetic field magnitude measurements in the vicinity of the tools and joining parts was tested during the electromagnetic compression and MPW of an aluminum flyer tube with a steel parent. The testing setup used for the investigation allowed the simultaneous measurement of the flyer displacement, its velocity, and the magnitude of the magnetic field close to the flyer. The experimental results and simulations showed that, during the welding of the aluminum tube with the steel parent, the maximum magnetic field in the gap between the field shaper and the flyer is achieved much earlier than the maximum of the current pulse of the coil and that the first half-wave pulse of the magnetic field has two peaks. It was also found that the time instant of the minimum between these peaks depends on the charging energy of the capacitors and is associated with the collision of the flyer with the parent. Together with the first peak maximum and its time-position, this characteristic could be an indication of the welding quality. These results were confirmed by simultaneous measurements of the flyer displacement and velocity, as well as a numerical simulation of the magnetic field dynamics. The relationship between the peculiarities of the magnetic field pulse and the quality of the welding process is discussed. It was demonstrated that the proposed method of magnetic field measurement during magnetic pulse welding in combination with subsequent peel testing could be used as a nondestructive method for the monitoring of the quality of the welding process.

Field-Induced Metal–Insulator Transition in β-EuP3*Supported by the National Natural Science Foundation of China (Grant Nos. U1832214 and 11774007), the National Key R&D Program of China (Grant No. 2018YFA0305601) and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB28000000). The experimental and theoretical work at Princeton University was supported by the Gordon and Betty Moore Foundation

Metal–insulator transition (MIT) is one of the most conspicuous phenomena in correlated electron systems. However such a transition has rarely been induced by an external magnetic field as the field scale is normally too small compared with the charge gap. We present the observation of a magnetic-field-driven MIT in a magnetic semiconductor β-EuP3. Concomitantly, we find a colossal magnetoresistance in an extreme way: the resistance drops billionfold at 2K in a magnetic field less than 3T. We ascribe this striking MIT as a field-driven transition from an antiferromagnetic and paramagnetic insulator to a spin-polarized topological semimetal, in which the spin configuration of Eu2+ cations and spin-orbital coupling play a crucial role. As a phosphorene-bearing compound whose electrical properties can be controlled by the application of field, β-EuP3 may serve as a tantalizing material in the basic research and even future electronics.

Electrostatic-doping-controlled phase separation in electron-doped manganites

The coexistence of distinct insulating and metallic phases within the same manganite sample, i.e., phase separation scenario, provides an excellent platform for tailoring the complex electronic and magnetic properties of strongly correlated materials. Here, based on an electric-double-layer transistor configuration, we demonstrate the dynamic control of two entirely different phases—canted G-type antiferromagnetic metal and C-type antiferromagnetic charge/orbital ordered insulator phase—in electron-doped system Ca1−xCexMnO3 (x = 0.05). The reversible metal-to-insulator transition, enhanced colossal magnetoresistance (∼ 27 000% for Vg = 3.0 V), and giant memory effect have been observed, which can be attributed to an electronic phase separation scenario manipulated by a tiny doping-level-variation of less than 0.02 electrons per formula unit. In addition, the controllable multi-resistance states by the combined application of magnetic and electrostatic fields may serve as an indicator to probe the dynamic multiphase competition of strongly correlated oxides. These results offer crucial information to understand the physical nature of phase separation phenomena in manganite systems.

Enhancement of the Magnetotransport Behavior in a Phase-Separated LaAgCaMnO3 Polycrystalline: Unraveling the Role of a Multi-Double-Exchange Mechanism

Manganese-based perovskite oxides have attracted much attention since the phenomenon of colossal magnetoresistance (CMR) was revived, where the magnetoresistance (MR) can attend higher orders of ma...

Polar Metal Phase Induced by Oxygen Octahedral Network Relaxation in Oxide Thin Films

ABO3 perovskite materials and their derivatives have inherent structural flexibility due to the corner sharing network of the BO6 octahedron, and the large variety of possible structural distortions and strong coupling between lattice and charge/spin degrees of freedom have led to the emergence of intriguing properties, such as high-temperature superconductivity, colossal magnetoresistance, and improper ferroelectricity. Here, an unprecedented polar ferromagnetic metal phase in SrRuO3 (SRO) thin films is presented, arising from the strain-controlled oxygen octahedral rotation (OOR) pattern. For compressively strained SRO films grown on SrTiO3 substrate, oxygen octahedral network relaxation is accompanied by structural phase separation into strained tetragonal and bulk-like orthorhombic phases, and the asymmetric OOR evolution across the phase boundary allows formation of the polar phase, while bulk metallic and ferromagnetic properties are maintained. From the results, it is expected that other oxide perovskite thin films will also yield similar structural environments with variation of OOR patterns, and thereby provide promising opportunities for atomic scale control of material properties through strain engineering.

First-principles investigation of structural modification, fine band gap engineering, and optical response of La1−xBaxGaO3 for optoelectronic applications

Oxide-based perovskites offer intriguing applications in multiple innovative areas due to their structural and physical properties such as photoluminescence, colossal magneto-resistivity, ferroelectricity, superior piezoelectric, optical, and electronic properties. Lanthanum gallate (LaGaO3) is a promising perovskite material for microwave application and as a substrate material for super conductors. Here, we aim to explore the relationship between the structural distortion induced in LaGaO3 octahedra as a function of Barium (Ba) doping concentration (x = 0, 0.03, 0.18, 0.33, 0.37, 0.59, 0.74, 0.96, 1), and its structural, electronic and optical properties. The computed band gap for pure c-LaGaO3 is 2.91 eV, which is in direct in nature, and transforms into direct band gap after Ba doping. In addition, it is observed that the band gap of c-LaGaO3 varies from 2.91 to 2.03 eV, as a function of Ba-doping concentration. The structural properties of c-LaGaO3 are observed to vary significantly w.r.t different Barium concentrations, inserting comprehensive changes in its electronic and optical properties. The static dielectric function $$ \left( {\varepsilon_{1} \left( 0 \right)} \right) $$ , a measure of the polarizability of the material, significantly enhances for Ba-doped system LaGaO3 from 32 to 215.5. Higher static refractive index $$ \left( {n\left( 0 \right)} \right) $$ is also evident after Ba-doping, which explains the increasing transparency as a function of Ba doping. Hence we suggest Ba-doped LaGaO3 as a good material for optoelectronic applications.

Room-Temperature Colossal Magnetoresistance in Terraced Single-Layer Graphene.

Disorder-induced magnetoresistance (MR) effect is quadratic at low perpendicular magnetic fields and linear at high fields. This effect is technologically appealing, especially in 2D materials such as graphene, since it offers potential applications in magnetic sensors with nanoscale spatial resolution. However, it is a great challenge to realize a graphene magnetic sensor based on this effect because of the difficulty in controlling the spatial distribution of disorder and enhancing the MR sensitivity in the single-layer regime. Here, a room-temperature colossal MR of up to 5000% at 9 T is reported in terraced single-layer graphene. By laminating single-layer graphene on a terraced substrate, such as TiO2 -terminated SrTiO3 , a universal one order of magnitude enhancement in the MR compared to conventional single-layer graphene devices is demonstrated. Strikingly, a colossal MR of >1000% is also achieved in the terraced graphene even at a high carrier density of ≈1012 cm-2 . Systematic studies of the MR of single-layer graphene on various oxide- and non-oxide-based terraced surfaces demonstrate that the terraced structure is the dominant factor driving the MR enhancement. The results open a new route for tailoring the physical property of 2D materials by engineering the strain through a terraced substrate.

Effect of annealing temperature on electrical and magnetic properties of La0.7Ca0.3MnO3:Ag0.2 thin films

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.

Structure, charge ordering, and magnetic properties of perovskite Sm0.5Ca0.5MnO3 manganite

Half-doped perovskite Manganese oxide has been widely studied because of its excellent properties such as colossal magnetoresistance (CMR) effect and charge-ordered (CO) phase separation. In this work, four Sm0.5Ca0.5MnO3 samples with different particle sizes are prepared by high-temperature solid-state reaction and ball milling. The crystal structure of the samples is studied by X-ray diffraction (XRD). The Sm0.5Ca0.5MnO3 sample is single phase, which belongs to orthorhombic structure. The surface morphology and particle size of the samples are examined by scanning electron microscope (SEM). The average particle size of the sample without ball milling is about 4 μm. With ball milling time for 12 h, 24 h, and 36 h, the particle size decreases, and finally it reaches hundreds to tens of nanometers. This shows that ball milling is an effective way to control the particle size. The M–T curves and M–H hysteresis loops of the samples are measured by physical properties measurements systems (PPMS). The two M–T curves measured in the warming and cooling processes do not overlap for Sm0.5Ca0.5MnO3 without ball milling, and the phenomenon of thermal hysteresis appears. Meanwhile, the M–T curve has a significant protuberance peak near 270 K. All of these indicate the CO behavior, whereas the particle size of Sm0.5Ca0.5MnO3 decreases with different milling times (12–36 h) and the CO phase is suppressed gradually, which leads to the decrease of CO temperature, magnetization, remanence, and coercivity.

Current-Driven Spin Precession in Bulk Nd0.6Sr0.4MnO3

Perovskite manganites are known to exhibit colossal negative magnetoresistance (MR) for direct current. Here, we show that the magnetoresistance of a bulk Nd0.6Sr0.4MnO3 sample carrying radio frequ...

Mechanical Modulation of Colossal Magnetoresistance in Flexible Epitaxial Perovskite Manganite

AbstractHeteroepitaxially flexible oxide systems have been intensely developed and considered as the most promising materials for leading the creation of next‐generation flexible electronic devices. Among them, perovskite manganites have attracted significant attention with their abundant and novel properties such as colossal magnetoresistance (CMR) and metal‐insulator transition. However, the requirement of high quality samples hampers this field, not to mention the advanced nanoengineering. In this study, fluorophlogopite mica (F‐mica) is selected as a flexible substrate to fabricate heteroepitaxial Pr0.5Ca0.5MnO3 (PCMO) with a nanocolumn structure. Through a precise control of thickness, different morphologies are realized to manipulate the magnetotransport properties (reduction of melting field). Moreover, thanks to the excellent flexibility of F‐mica, mechanical modulation of CMR (≈1000%) can be achieved in different flex modes while the magnetic properties remain unaffected. Detailed bending tests are performed to study the behavior of resistive change (≈30%). Through the combination of high flexibility, high quality PCMO, and well‐designed nanocolumn structure, the study exhibits the significant controllability of CMR via mechanical bending, and manifests the potential of such a heteroepitaxially flexible oxide system which can be applied on flexible magnetoresistive devices and sensors.

Giant electron\u2013phonon coupling of the breathing plane oxygen phonons in the dynamic stripe phase of hbox {La}_{1.67}hbox {Sr}_{0.33}hbox {NiO}_4

Doped antiferromagnets host a vast array of physical properties and learning how to control them is one of the biggest challenges of condensed matter physics. hbox {La}_{1.67}hbox {Sr}_{0.33}hbox {NiO}_4 (LSNO) is a classic example of such a material. At low temperatures holes introduced via substitution of La by Sr segregate into lines to form boundaries between magnetically ordered domains in the form of stripes. The stripes become dynamic at high temperatures, but LSNO remains insulating presumably because an interplay between magnetic correlations and electron–phonon coupling localizes charge carriers. Magnetic degrees of freedom have been extensively investigated in this system, but phonons are almost completely unexplored. We searched for electron–phonon anomalies in LSNO by inelastic neutron scattering. Giant renormalization of plane Ni–O bond-stretching modes that modulate the volume around Ni appears on entering the dynamic charge stripe phase. Other phonons are a lot less sensitive to stripe melting. Dramatic overdamping of the breathing modes indicates that dynamic stripe phase may host small polarons. We argue that this feature sets electron–phonon coupling in nickelates apart from that in cuprates where breathing phonons are not overdamped and point out remarkable similarities with the colossal magnetoresistance manganites.

Structural, Magnetic and Magnetotransport Properties of Sol-Gel Synthesized La<sub>0.67</sub>Ca<sub>0.33</sub>MnO<sub>3</sub>:TiO<sub>2</sub> Nanocomposite

Colossal magnetoresistive (CMR) materials have been widely studied because of their huge potential in spintronic technology. An introduction of secondary phase to the manganite matrix is able to improve the low field magnetoresistance (LFMR). This method is favoured by recent research works as it requires a lower magnetic field compared to intrinsic magnetoresistance. Structural, magnetic properties and magnetotransport properties of polycrystalline (1-x) La0.67Ca0.33MnO3 (LCMO): x TiO2 composites where x = 0.00, 0.05, 0.10, 0.15 and 0.20 were investigated in this work. Polycrystalline La0.67Ca0.33MnO3 (LCMO) was synthesized via sol-gel method and pre-sintered at 800 °C before appending with nano-sized TiO2. All samples are in LCMO phase having an orthorhombic structure with space group Pnma. The crystal structural parameter is studied by using Rietveld refinement. As TiO2 content increases, the magnetization is getting higher as observed via vibrating sample magnetometer (VSM) analysis at room temperature. Magnetotransport properties of the pure LCMO sample have been studied from 80 – 220 K. The LFMR is enhanced as the temperature drops. The results have shown LCMO: TiO2 manganite composite is an excellent candidate for future magnetic sensors and memory devices.

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.

Colossal Negative Magnetoresistance Effect in a La1.37Sr1.63Mn2O7 Single Crystal Grown by Laser-Diode-Heated Floating-Zone Technique

We have grown La 1.37 Sr 1.63 Mn 2 O 7 single crystals with a laser-diode-heated floating-zone furnace and studied the crystallinity, structure, and magnetoresistance (MR) effect by in-house X-ray Laue diffraction, X-ray powder diffraction, and resistance measurements. The La 1.37 Sr 1.63 Mn 2 O 7 single crystal crystallizes into a tetragonal structure with space group I4/mmm at room temperature. At 0 T, the maximum resistance centers around ∼166.9 K. Below ∼35.8 K, it displays an insulating character with an increase in resistance upon cooling. An applied magnetic field of B = 7 T strongly suppresses the resistance indicative of a negative MR effect. The minimum MR value equals −91.23% at 7 T and 128.7 K. The magnetic-field-dependent resistance shows distinct features at 1.67, 140, and 322 K, from which we calculated the corresponding MR values. At 14 T and 140 K, the colossal negative MR value is down to −94.04(5)%. We schematically fit the MR values with different models for an ideal describing of the interesting features of the MR value versus B curves.

Antiferromagnetic fluctuations and charge carrier localization in ferromagnetic bilayer manganites: electrical resistivity scales exponentially with short-range order controlled by temperature and magnetic field

The compound La2−2xSr1+2xMn2O7, x = 0.30–0.40, consists of bilayers of ferromagnetic metallic MnO2 sheets that are separated by insulating layers. The materials show colossal magnetoresistance—a reduction in resistivity of up to two orders of magnitude in a field of 7 T—at their three-dimensional ordering temperatures, TC = 90–126 K, and are the layered analogues of the widely studied pseudo-cubic perovskite manganites, R1−xAxMnO3 (R = rare earth, A = Ca, Sr, Ba, Pb). Two distinct short-range orderings—antiferromagnetic fluctuations and correlated polarons, which are related to the magnetic and the lattice degrees of freedom respectively—have previously been discovered in La2−2xSr1+2xMn2O7, x = 0.40, and have each been qualitatively connected to the resistivity. Here, in a comprehensive study as a function of both temperature and magnetic field for the different hole-concentrations per Mn site of x = 0.30 and 0.35, we show that antiferromagnetic fluctuations also appear at temperatures just above TC, and that the intensities of both the antiferromagnetic fluctuations and polaron correlations closely track the resistivity. In particular, for x = 0.35 we show that there is a simple scaling relation between the intensities of the antiferromagnetic fluctuations and the in-plane resistivity that applies for the temperatures and magnetic fields used in the experiments. The results show that antiferromagnetic fluctuations are a common feature ofLa2−2xSr1+2xMn2O7 with ferromagnetic bilayers, and that there is a close connection between the antiferromagnetic fluctuations and polarons in these materials.