Colossal Magnetoresistance Phenomenon Research Articles

Magnetic proximity sensor based on colossal magnetoresistance effect

Magnetic proximity sensors are widely used to determine the distance to ferromagnetic or highly conductive materials and to investigate their shape or to detect their motion. In this study, a magnetic proximity sensor incorporating a cylindrical permanent magnet and a scalar magnetic field sensor (measuring the magnitude of the field independently from its orientation) based on the phenomenon of colossal magnetoresistance in manganite films is presented. Two versions of the sensor, one with a solid cylindrical magnet and one with a hollow cylindrical magnet, were constructed and tested. A steel plate and a superconducting YBaCuO disk were used to investigate the static response. The measurements of the dynamic behavior were carried out with rotating steel and duralumin plates. The results of the static experiments and modelling showed that the output response (change of the magnetic field) of the sensor had a hyperbolic relationship with the distance between the sensor and the measured object. This change was positive for solid cylindrical magnet design and negative for hollow cylindrical magnet design when the target was steel. In contrast, the solid magnet-based sensor produced a negative signal for the superconducting material, while the hollow cylindrical magnet sensor showed a positive signal. It was found that the main features of the dynamic response of the proximity sensors can be explained by the magnetization of steel and the induction of eddy currents in duralumin. The present study demonstrates that the proposed magnetic proximity sensor can be successfully used to search for ferromagnetic objects, investigate the properties of superconductors and detect the motion of non-ferromagnetic conductive materials and can have advantages over conventional magnetic proximity sensors.

Dynamics of electronically phase-separated states in the double exchange model

We present extensive large-scale dynamical simulations of phase-separated states in the double exchange model. These inhomogeneous electronic states that play a crucial role in the colossal magnetoresistance phenomenon are composed of ferromagnetic metallic clusters embedded in an antiferromagnetic insulating matrix. We compute the dynamical structure factor of these nanoscale textures using an efficient real-space formulation of coupled spin and electron dynamics. Dynamical signatures of the various underlying magnetic structures are identified. At small hole doping, the structure factor exhibits a dominating signal of magnons from the background N\'eel order and localized modes from magnetic polarons. A low-energy continuum due to large-size ferromagnetic clusters emerges at higher doping levels. Implications for experiments on magnetoresistive manganites are discussed.

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...

Coupling of magnetoresistance switching and glassy magnetic state at the metal–insulator transition in Ruddlesden-Popper manganite Ca4Mn3O10

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 Néel 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.

Pulsed magnetic flux penetration dynamics inside a thin-walled superconducting tube

In this work, we present an investigation of transient magnetic field behavior in thin-walled superconducting tubes. It has been determined that if the thickness of the tube wall is significantly less than Bean’s penetration length, the non-linear magnetic field diffusion equation describing the field propagation process inside the tube can be replaced by a simplified lumped-parameter equation. This makes it possible to quickly calculate the current induced in the tube wall and the magnetic field penetrated in the tube cavity. In order to validate this theory, an experimental study of transient magnetic field penetration into a Pb-doped B-2223 (Bi1.8Pb0.26Sr2Ca2Cu3O10+x) tube was conducted. This was done at the temperature of liquid nitrogen using a search coil (B-dot) and a miniature colossal magnetoresistance (CMR)-B-scalar magnetic field sensor made from manganite films, which exhibit a CMR phenomenon. The experimental results were then compared with the datasheet of the superconducting tube manufacturer and the 2D axisymmetric finite element model. It was demonstrated that combining the measurements of the magnetic field outside and inside the tube with the lumped-parameter description allows one to obtain the following information: the screened and trapped magnetic field, the critical current density vs the magnetic field dependence, and the power law index of the superconducting tube material. This enables the development of a fast, non-destructive method for testing the quality of superconducting tubular current leads.

Unusual electrical behaviour in sol–gel-synthesised PKMO nano-sized manganite

Mixed-valence manganites have gained tremendous attention in the scientific research for its colossal magnetoresistance phenomenon. Nevertheless, the study devoted to praseodymium-based manganites is still limited to date. The present work aims to investigate the grain size effect on sol–gel grown nano-sized Pr0.85K0.15MnO3 (PKMO). The grain size has been modified by heat treatment ranging from 600 °C to 1000 °C. PKMO samples have been studied in detail to elucidate the correlation of spin, charge, orbital and lattice degrees of freedom. The X-ray diffraction analysis revealed that all samples exhibit in single orthorhombic phase with the space group of Pnma (62). The obtained crystallite size and average grain size are in the range of 45–115 nm and 51–210 nm, respectively. The evolution of grains intensively affects the electrical and magneto-transport properties of PKMO. The temperature dependence of the resistivity has been fitted with theoretical expressions in different temperature regimes to investigate their conduction mechanisms. The resistivity exhibits an unusual trend when the grain size increases where a similar pattern also been observed in metal–insulator transition temperature (TMI). This behaviour can be ascribed to the grain size distribution, grain formation and also the occurrence of oxygen vacancies at the grain boundaries. Enhancement of high field magnetoresistance has been discovered below 180 K, whereas low field magnetoresistance is suppressed as the temperature increases and almost vanished at 300 K. The PKMO study demonstrated here is clearly dominated by extrinsic properties (grain evolution) from the evidence of electrical and magneto-transport measurements.

Hand-Held Magnetic Field Meter Based on Colossal Magnetoresistance-B-Scalar Sensor

This paper describes a newly developed hand-held magnetic field meter, which enables the measurement of the magnitude of pulsed, alternating, or permanent magnetic flux density in a range from 0.06 up to 10 T. The device measures the magnitude of magnetic flux density independent of the field direction (B-scalar) and its measurement frequency ranges from dc to 100 kHz. This magnetometer consists of a hand-held magnetic field measurement meter and a pluggable probe whose main element is a spintronic sensor based on the colossal magnetoresistance (CMR) phenomenon. The new design of a probe containing a temperature sensor and a CMR-B-scalar sensor made from two manganite films with different resistivity versus temperature dependences ensures a reduced response signal dependence on temperature and thus increased the accuracy of the measurements. The hand-held meter has a graphical color touch screen for the display of the waveforms and provides measurements without the use of external oscilloscopes or other analog graphing devices. This magnetometer can be used for various industrial and scientific applications such as for the investigation of high-power electrical motors, fast high electrical current transients appearing in cases of the commutation of pulsed power circuits, for the measurement of pulsed magnetic fields in magnetic coils, or for measuring the dynamics of magnetic fields during electromagnetic metal forming and welding.

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.

Magnetotransport properties of La1−xCaxMnO3 (0.52 ≤ x ≤ 0.75): Signature of phase coexistence

We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La1−xCaxMnO3 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 4.2K <T < 300K, for three concentrations x=0.52,0.58 and 0.75 and in magnetic fields up to 5T. The semiconductor/insulator–like behavior in zero field was observed in the entire temperature range for all three concentrations 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 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.

The possibility of colossal magnetoresistance in heterostructures based on epitaxial graphene

The magnetoresistance of a heterostructure comprising parallel-connected epitaxial graphene on a metal substrate and graphene on a dielectric substrate has been studied in the framework of the Drude theory. The phenomenon of colossal magnetoresistance in this system is predicted on the basis of previous results for the conductivity of epitaxial graphene.

Spin Glasses in Cu0.5Fe0.5Cr2S4-based solid solutions

The discovery of the phenomenon of colossal magnetoresistance in spinel Cu0.5Fe0.5Cr2S4 as one of the effects contributing to the progress in magnetoelectronics stimulated the appearance of a cycle of works on studying physical properties of this and affine materials. This survey generalizes our investigations on synthesizing and studying magnetic and crystallochemical parameters of solid solutions based on this spinel in the context of searching for novel promising magnetic semiconductor phases.

Investigation of orbital disorder in Ca-doped LaMNO3

Studies of materials that exhibit colossal magnetoresistance (CMR) have been well documented over the past decade [1]. La1-xCaxMnO3 is one such CMR material that has attracted significant attention as it is relatively cheap and straightforward to synthesize. CMR materials have potential use among the next generation of magnetic memory devices, magnetic-field sensors, and transitors. For that to be possible a clear understanding has to be determined for the origin of the CMR phenomenon. Recent studies of CMR manganites have shown that a `polaron glass' phase precedes CMR behaviour at high temperatures (figure 1) [2]. This glasslike state sits midway between the high-temperature polaron liquid and the fully orbital-ordered solid with polarons. The polarons are localized charge density fluctuations associated with lattice deformation which gives rise to static, short-range correlations. At low temperature these polaron correlations are thought to evolve into the nanoscale polarons responsible for CMR itself. This poster describes our reasoning for the anticipated connection between the orbital disorder and CMR in La1-xCaxMnO3 revealed via reverse Monte Carlo modelling of X-ray and neutron total scattering data.

The Phenomenon of Colossal Magnetoresistance and Some Experimental Results

The Phenomenon of Colossal Magnetoresistance and Some Experimental Results

The phenomenon of Colossal Magnetoresistance and some experimental results

The phenomenon of Colossal Magnetoresistance and some experimental results

Hole-Induced Magnetic Solitons and Colossal Magnetoresistance Phenomena in Doped Manganites

We have introduced the hole-induced magnetic soliton by using the gauge-invariant Lagrangian density and the path-integral method. The percolation-like dynamics of hole-induced magnetic solitons and the colossal magnetoresistance mechanism in doped manganites have been proposed from the standpoint of the random resistor network and percolation-scaling method. The long-relaxation behaviour of the spin has been discussed by using the effective Hamiltonian and the frustration-limited domain model.

Study of doping effect, phase separation and heterojunction in CMR manganites

Mixed-valence manganites have attracted considerable research focus in recent years not only because of the potential application of colossal magnetoresistance (CMR) in magnetic devices, but also because of many intriguing physical properties observed in these materials. Doping elements at A-site can alter the filling of 3d Mn band and the tolerance factor. Therefore the hole- and electron-doped CMR manganites exhibit a rich phase diagram. In addition, more theoretical and experimental results suggest that phase separation is a critical factor for the understanding of CMR phenomena. Recently, there is an increasing interest in the fabrication and investigation on manganite-based heterojunction, which demonstrated excellent rectifying property, large MR, and photovoltaic effect.

Long-range transfer of electron–phonon coupling in oxide superlattices

The electron-phonon interaction is of central importance for the electrical and thermal properties of solids, and its influence on superconductivity, colossal magnetoresistance and other many-body phenomena in correlated-electron materials is the subject of intense research at present. However, the non-local nature of the interactions between valence electrons and lattice ions, often compounded by a plethora of vibrational modes, presents formidable challenges for attempts to experimentally control and theoretically describe the physical properties of complex materials. Here we report a Raman scattering study of the lattice dynamics in superlattices of the high-temperature superconductor YBa(2)Cu(3)O(7) (YBCO) and the colossal-magnetoresistance compound La(2/3)Ca(1/3)MnO(3) that suggests a new approach to this problem. We find that a rotational mode of the MnO(6) octahedra in La(2/3)Ca(1/3)MnO(3) experiences pronounced superconductivity-induced line-shape anomalies, which scale linearly with the thickness of the YBCO layers over a remarkably long range of several tens of nanometres. The transfer of the electron-phonon coupling between superlattice layers can be understood as a consequence of long-range Coulomb forces in conjunction with an orbital reconstruction at the interface. The superlattice geometry thus provides new opportunities for controlled modification of the electron-phonon interaction in complex materials.

Role of structurally and magnetically modified nanoclusters in colossal magnetoresistance

It is generally accepted that electronic and magnetic phase separation is the origin of many of exotic properties of strongly correlated electron materials, such as colossal magnetoresistance (CMR), an unusually large variation in the electrical resistivity under applied magnetic field. In the simplest picture, the two competing phases are those associated with the material state on either side of the phase transition. Those phases would be paramagnetic insulator and ferromagnetic metal for the CMR effect in doped manganites. It has been speculated that a critical component of the CMR phenomenon is nanoclusters with quite different properties than either of the terminal phases during the transition. However, the role of these nanoclusters in the CMR effect remains elusive because the physical properties of the nanoclusters are hard to measure when embedded in bulk materials. Here we show the unexpected behavior of the nanoclusters in the CMR compound La(1-x)Ca(x)MnO(3) (0.4 ≤ x < 0.5) by directly correlating transmission electron microscopy observations with bulk measurements. The structurally modified nanoclusters at the CMR temperature were found to be ferromagnetic and exhibit much higher electrical conductivity than previously proposed. Only at temperatures much below the CMR transition, the nanoclusters are antiferromagnetic and insulating. These findings substantially alter the current understanding of these nanoclusters on the material's functionality and would shed light on the microscopic study on the competing spin-lattice-charge orders in strongly correlated systems.

Anderson Localization Triggered by Spin Disorder—With an Application to Eu x Ca1−x B6

The phenomenon of Anderson localization is studied for a class of one-particle Schr\"odinger operators with random Zeeman interactions. These operators arise as follows: Static spins are placed randomly on the sites of a simple cubic lattice according to a site percolation process with density x and coupled to one another ferromagnetically. Scattering of an electron in a conduction band at these spins is described by a random Zeeman interaction term that originates from indirect exchange. It is shown rigorously that, for positive values of x below the percolation threshold, the spectrum of the one-electron Schr\"odinger operator near the band edges is dense pure-point, and the corresponding eigenfunctions are exponentially localized. Localization near the band edges persists in a weak external magnetic field, H, but disappears gradually, as H is increased. Our results lead us to predict the phenomenon of colossal (negative) magnetoresistance and the existence of a Mott transition, as H and/or x are increased. Our analysis is motivated directly by experimental results concerning the magnetic alloy Eu_x Ca_1-x B_6.

First Order Colossal Magnetoresistance Transitions in the Two-Orbital Model for Manganites

Large-scale Monte Carlo simulation results for the two-orbital model for manganites, including Jahn-Teller lattice distortions, are presented here. At hole density x=1/4 and in the vicinity of the region of competition between the ferromagnetic metallic and spin-charge-orbital ordered insulating phases, the colossal magnetoresistance (CMR) phenomenon is observed with a magnetoresistance ratio ∼10,000%. Our main result is that this CMR transition is found to be of first order in some portions of the phase diagram, in agreement with early results from neutron scattering, specific heat, and magnetization, thus solving a notorious discrepancy between experiments and previous theoretical studies. The first order characteristics of the transition survive, and are actually enhanced, when weak quenched disorder is introduced.