Colossal Magnetoresistance Manganites Research Articles

Low Temperature Dynamic Polaron Liquid in a Manganite Exhibiting Colossal Magnetoresistance.

Polarons-fermionic charge carriers bearing a strong companion lattice deformation-exhibit a natural tendency for self-localization due to the recursive interaction between electrons and the lattice. While polarons are ubiquitous in insulators, how they evolve in transitions to metallic and superconducting states in quantum materials remains an open question. Here, we use resonant inelastic x-ray scattering to track the electron-lattice coupling in the colossal magneto-resistive bi-layer manganite La_{1.2}Sr_{1.8}Mn_{2}O_{7} across its metal-to-insulator transition. The response in the insulating high-temperature state features harmonic emissions of a dispersionless oxygen phonon at small energy transfer. Upon cooling into the metallic state, we observe a drastic redistribution of spectral weight from the region of these harmonic emissions to a broad high energy continuum. In concert with theoretical calculations, we show that this evolution implies a shift in electron-lattice coupling from static to dynamic lattice distortions that leads to a distinct polaronic ground state in the low temperature metallic phase-a dynamic polaron liquid.

Influence of crystallographic orientation on electronic phase separation in manganite thin films

Thin film epitaxy is a powerful method to control the strain and crystallographic orientation of the thin films using epitaxial relationship with the substrate. For colossal magnetoresistive (CMR) manganites thin films, the strong correlation between spin, charge, orbital and lattice degrees of freedom make their physical properties depend sensitively on the choice of substrate. This is especially true when considering the fact that the physical behaviors of manganites are often governed by electronic phase separation (EPS) phenomena, whose physical origin is strongly tied to lattice strain distribution. While many studies have been conducted on the substrate lattice mismatch induced strain effect, research on the substrate crystallographic orientation effect on EPS has received less attention. In this work, using (La2/3Pr1/3)5/8Ca3/8MnO3 (LPCMO) films grown on SrTiO3 (STO) substrate as a protype system, we show that EPS and its associated physical properties are strongly affected by the substrate crystallographic orientations. Specifically, we observed a clear boost of ferromagnetism in (110)-oriented LPCMO thin films with elongated EPS domains. First principles calculations show that the magnetic phase transitions of LPCMO are dominantly influenced by the spin-lattice coupling.

Energy relaxation in (La0.6Pr0.4)0.7Ca0.3MnO3 films across the metal-insulator transition

The colossal magnetoresistive manganite ${({\mathrm{La}}_{0.6}{\mathrm{Pr}}_{0.4})}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ (LPCMO) undergoes a ferromagnetic (FM) metal to paramagnetic insulator phase transition at around 195 K, which develops via an intermediate polaronic state strongly susceptible to external magnetic fields. Transient reflectivity studies of LPCMO on timescales from sub-picoseconds to nanoseconds reveal that the overall system dynamics are strongly influenced by the phase transition with a sharp and strong decrease in the relaxation time while crossing from the ferromagnetic metallic phase into the paramagnetic insulating phase. We show that the long relaxation times of the reflectivity after nonequilibrium excitation within the FM phase are caused by the slow recovery of the ordered FM state after laser-induced demagnetization. Control of the nonequilibrium dynamics close to the phase transition is demonstrated by applying moderate magnetic fields below 1 T.

Ferroelectricity modulates polaronic coupling at multiferroic interfaces

Physics of the multiferroic interfaces is currently understood mostly within a phenomenological framework based on screening of the polarization field and depolarizing charges. Additional effects still unexplored are the band dependence of the interfacial charge modulation and the associated changes of the electron-phonon interaction, coupling the charge and lattice degrees of freedom. Here, multiferroic heterostructures of the colossal-magnetoresistance manganite La1-xSrxMnO3 buried under ferroelectric BaTiO3 and PbZrxTi1-xO3 are investigated using soft-X-ray angle-resolved photoemission. The experimental band dispersions from the buried La1-xSrxMnO3 identify coexisting two-dimensional hole and three-dimensional electron charge carriers. The ferroelectric polarization modulates their charge density, affecting the coupling of the 2D holes and 3D electrons with the lattice which forms large Fröhlich polarons inherently reducing mobility of the charge carriers. Our k-resolved results on the orbital occupancy, band filling and electron-lattice interaction in multiferroic oxide heterostructures modulated by the ferroelectric polarization disclose most fundamental physics of these systems needed for further progress of beyond-CMOS ferro-functional electronics.

Anomalous phase separation in a correlated electron system: Machine-learning–enabled large-scale kinetic Monte Carlo simulations

SignificancePhase separation is crucial to the functionalities of many correlated electron materials with notable examples including colossal magnetoresistance in manganites and high-Tc superconductivity in cuprates. However, the nonequilibrium phase-separation dynamics in such systems are poorly understood theoretically, partly because the required multiscale modeling is computationally very demanding. With the aid of machine-learning methods, we have achieved large-scale dynamical simulations in a representative correlated electron system. We observe an unusual relaxation process that is beyond the framework of classical phase-ordering theories. We also uncover a correlation-induced freezing behavior, which could be a generic feature of phase separation in correlated electron systems.

Spatially-resolved electronic structure of stripe domains in IrTe2 through electronic structure microscopy

Phase separation in the nanometer- to micrometer-scale is characteristic for correlated materials, for example, high temperature superconductors, colossal magnetoresistance manganites, Mott insulators, etc. Resolving the electronic structure with spatially-resolved information is critical for revealing the fundamental physics of such inhomogeneous systems yet this is challenging experimentally. Here by using nanometer- and micrometer-spot angle-resolved photoemission spectroscopies (NanoARPES and MicroARPES), we reveal the spatially-resolved electronic structure in the stripe phase of IrTe2. Each separated domain shows two-fold symmetric electronic structure with the mirror axis aligned along 3 equivalent directions, and 6 × 1 replicas are clearly identified. Moreover, such electronic structure inhomogeneity disappears across the stripe phase transition, suggesting that electronic phase with broken symmetry induced by the 6 × 1 modulation is directly related to the stripe phase transition of IrTe2. Our work demonstrates the capability of NanoARPES and MicroARPES in elucidating the fundamental physics of phase-separated materials.

Kinetic pathway facilitated by a phase competition to achieve a metastable electronic phase

We show that ground state phase competition significantly decreases the critical cooling rate required for the kinetic avoidance of a first-order phase transition and thus facilitates the creation of metastable electronic states. This principle is revealed for the phase transition between antiferromagnetic charge-orbital-ordered insulating and ferromagnetic metallic states in the so-called colossal magnetoresistive manganite ${\mathrm{Nd}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$. In a phase competition situation, we achieve reversible and nonvolatile control of bulk magnetization by $1{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ and resistivity by $\ensuremath{\sim}1000%$ by applying electric pulses to exploit electric heating and subsequent rapid cooling.

Perovskite Puzzle for Revolutionary Functional Materials.

Widely spread crystal lattices of perovskites represent a natural flexible platform for chemical design of various advanced functional materials with unique features. An interplay between chemical bonding, defects and crystallochemical peculiarities makes the perovskite structure a “LEGO designer” utilizing natural features of chemical elements of the renowned Mendeleev's Periodic Table (PTE) celebrating its 150-year anniversary. In this mini-review, crystal chemistry and bonding features, physical and functional properties, preparation methods and tuning functional properties with periodicity “tools” of the PTE will be exemplified for legendary families of high-temperature superconductive cuprates, colossal magnetoresistive manganites and hybrid lead halides for a new generation of solar cells.

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.

High-Mobility 2D Hole Gas at a SrTiO3 Interface.

Strontium titanate (SrTiO3 or STO) is important for oxide-based electronics as it serves as a standard substrate for a wide range of high-temperature superconducting cuprates, colossal magnetoresistive manganites, and multiferroics. Moreover, in its heterostructures with different materials, STO exhibits a broad spectrum of important physics such as superconductivity, magnetism, the quantum Hall effect, giant thermoelectric effect, and colossal ionic conductivity, most of which emerge in a two-dimensional (2D) electron gas (2DEG) formed at an STO interface. However, little is known about its counterpart system, a 2D hole gas (2DHG) at the STO interface. Here, a simple way of realizing a 2DHG with an ultrahigh mobility of 24 000 cm2 V-1 s-1 is demonstrated using an interface between STO and a thin amorphous FeOy layer, made by depositing a sub-nanometer-thick Fe layer on an STO substrate at room temperature. This mobility is the highest among those reported for holes in oxides. The carrier type can be switched from p-type (2DHG) to n-type (2DEG) by controlling the Fe thickness. This unprecedented method of forming a 2DHG at an STO interface provides a pathway to unexplored hole-related physics in this system and enables extremely low-cost and high-speed oxide electronics.

High magnetoresistance in La0.5Nd0.15Ca0.25A0.1MnO3 (A = Ca, Li, Na, K) CMR manganites: Correlation between their magnetic and electrical properties

The influence of A-site cation disorder of monovalent alkali ions on structural and magneto-transport properties of colossal magnetoresistive (CMR) materials has been reported. All the compounds crystallize in Pbnm space group with orthorhombic symmetry. At low temperature, the samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition and a semiconductor to metallic one. The variation in both Curie temperature (Tc) and metal-semiconductor transition temperature (TMS) can be explained by the change in Mn4+ content and average A-site cation radius. A decrease in resistivity in the vicinity of TMS has been observed with an increase in the applied magnetic field. The values of Tc are close to TMS, signifying strong correlations between the magnetic and electrical properties. The electrical resistivity data in paramagnetic-semiconducting region (T >TMS) may be described by the adiabatic small polaron hopping (ASPH) model. Maximum magnetoresistance (MR%) has been observed in the vicinity of TMS.

Terahertz Emission Functionality of High‐Temperature Superconductors and Similar Complex Systems

AbstractDuring the past two decades, terahertz (THz) science and technology have rapidly expanded in all fundamental and applied aspects of physical, chemical, and biological sciences. In physical sciences, these developments have been twofolds: i) the use of THz technology in understanding the complexities of materials and ii) the exploration of new THz functionalities of emerging materials for further advancement of THz technology. Here, the THz emission spectroscopy and the ultrafast functionality of three pillars of electronic and magnetic condensed matter systems that emerged in the following order: high‐temperature superconductors, colossal magnetoresistive manganites, and magnetoelectric multiferroics are reviewed. Emission functionality refers to the emitted THz radiation that carries the information of the underlying functional property of the material such that the overall effect evolves as the THz decoding of the information in a noninvasive manner and on an ultrafast timescale.

Titanium effect on the structural, morphological and transport properties of La0.7Sr0.3Mn1-xTixO3 (x = 0.03, 0.06 and 0.12)

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 R3-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 Å) ion compared to that of Mn+4 (rMn+4 = 0.540 Å) 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.

Single-phase multiferroics: new materials, phenomena, and physics.

Multiferroics, where multiple ferroic orders coexist and are intimately coupled, promise novel applications in conceptually new devices on one hand, and on the other hand provide fascinating physics that is distinctly different from the physics of high-TC superconductors and colossal magnetoresistance manganites. In this mini-review, we highlight the recent progress of single-phase multiferroics in the exploration of new materials, efficient roadmaps for functionality enhancement, new phenomena beyond magnetoelectric coupling, and underlying novel physics. In the meantime, a slightly more detailed description is given of several multiferroics with ferrimagnetic orders and double-layered perovskite structure and also of recently emerging 2D multiferroics. Some emergent phenomena such as topological vortex domain structure, non-reciprocal response, and hybrid mechanisms for multiferroicity engineering and magnetoelectric coupling in various types of multiferroics will be briefly reviewed.

Memory-functionality superconductor/ferromagnet/superconductor junctions based on the high- Tc cuprate superconductors YBa2Cu3O7−x and the colossal magnetoresistive manganite ferromagnets La2/3X1/3MnO3+δ(X=Ca,Sr)

Complex oxides exhibit a variety of unusual physical properties, which can be used for designing novel electronic devices. Here we fabricate and study experimentally nano-scale Superconductor/ Ferromagnet/Superconductor junctions with the high-Tc cuprate superconductor YBa2Cu3O7 and the colossal magnetoresistive (CMR) manganite ferromagnets LaXMnO3 (X: Ca or Sr). We demonstrate that in a broad temperature range the magnetization of a manganite nanoparticle, forming the junction interface, switches abruptly in a mono-domain manner. The CMR phenomenon translates the magnetization loop into a hysteretic magnetoresistance loop. The latter facilitates a memory functionality of such a junction with just a single CMR ferromagnetic layer. The orientation of the magnetization (stored information) can be read out by simply measuring the junction resistance in an applied magnetic field. The CMR facilitates a large read-out signal in a small applied field. We argue that such a simple single layer CMR junction can operate as a memory cell both in the superconducting state at cryogenic temperatures and in the normal state up to room temperature.

Growth and Nanofabrication of All-Perovskite Superconducting/Ferromagnetic/Superconducting Junctions

We fabricate and study experimentally all-perovskite-oxide superconductor/ferromagnetic insulator/superconductor (S/FI/S) tunnel junctions made out of the high-temperature cuprate superconductor YBa2Cu3O7−y (YBCO) and the colossal magnetoresistive manganite LaMnO3 (LMO) in the ferromagnetic insulator state. YBCO/LMO/YBCO heterostructures with different LMO thicknesses (5, 10, and 20 nm) are grown epitaxially via pulsed laser deposition. Nanoscale S/FI/S junctions with sizes down to 300 nm are made by three-dimensional nano-sculpturing with focused ion beam. Junctions with a thick (20 nm) LMO barrier exhibit a large negative magnetoresistance below {T}_{Curie}sim 160 K, typical for colossal magnetoresistive manganites, as well as a kink in the current-voltage characteristics at large bias ( Vsim 1 –2 Volts), attributed to Zener-type tunneling. However, they do not show a measurable Josephson current. On the contrary, junctions with the thinnest 5-nm LMO barrier exhibit a large supercurrent and no signs of magnetism. The latter may indicate the presence of pinholes due to thickness inhomogeneity and/or a sim 2 nm dead magnetic layer at the YBCO / LMO interface caused, e.g., by interdiffusion or strain. The junction with an intermediate 10-nm LMO barrier exhibited a desired S/FI/S junction behavior with significant negative magnetoresistance and signatures of a small Josephson current.

Normal and inverse magnetocaloric effect in colossal magnetoresistive electron-doped manganites R0.15Ca0.85MnO3 (R = Y, Gd and Dy)

Abstract Magnetic, magnetocaloric and electrical transport properties of polycrystalline R0.15Ca0.85MnO3 (R = Y, Gd and Dy) manganites (Orthorhombic, Pnma) have been studied. Magnetization measured in 5 kOe field reveals antiferromagnetic transition at 111 K, 119 K and 112 K (TN) respectively in R0.15Ca0.85MnO3 (R = Y, Gd and Dy). Magnetization in the ordered state undergoes field-induced transition and at 2 K, in 140 kOe field, the magnetic moment values are 1.5 μB/f.u., 2.8 μB/f.u. and 2.7 μB/f.u. respectively for R0.15Ca0.85MnO3 (R = Y, Gd and Dy) samples. While the electrical resistivity above TN shows non-adiabatic, small polaron hopping behavior, the resistivity value increases rapidly below TN. Hysteresis is observed around TN between field cooled cooling (FCC) and field cooled warming (FCW) magnetization data in 100 Oe and also between the cooling and warming data of zero-field electrical resistivity. Electrical resistivity exhibits a metal to insulator-like transition at TN in applied magnetic fields of 50 kOe and above. Colossal, negative magnetoresistance of ∼82%, 85% and 76% is observed at 50 K in 50 kOe field in R0.15Ca0.85MnO3 (R = Y, Gd and Dy) manganites. Magnetocaloric effect (MCE) is estimated in terms of isothermal magnetic entropy change (ΔSm) and inverse MCE (+ΔSm) is observed in the antiferromagnetically ordered state. The ΔSm changes sign for field changes greater than the metamagnetic critical magnetic field (Hc). Sign changing MCE signifies the evolution of underlying mixed magnetic interactions in these systems with variations in magnetic field and temperature.

Magnetothermopower and giant magnetoresistance in the spin-glass CuCrTiS4 thiospinel

The transport properties of the thiospinel CuCrTiS4 have been investigated in detail, focusing on the possible interplay between charges and spins, and its consequence on transport, and more specifically on the thermoelectric properties. The chemical homogeneity of a CuCrTiS4 polycrystalline sample synthesized by a direct reaction of the constitutive elements has been carefully probed by X-ray diffraction and transmission electron microscopy techniques. This thiospinel exhibits below 75 K, in its paramagnetic regime, a variable range hopping (VRH) conduction, associated with a giant magnetoresistance (MR), which persists below the spin-glass transition temperature at 8 K, reaching -95% in 9 T at 5 K. All the MR data can be rescaled as a function of H/T and described using a Brillouin function with S = 3/2. This demonstrates that the paramagnetic fluctuations strongly impact the transport properties, and this is confirmed by the Seebeck coefficient which depends on the magnetic field at low temperature, with a large negative magnetothermopower (MTEP) effect of -26% at 20 K, i.e., the thermopower is reduced as the spin alignment reduces the spin entropy. This first report of MTEP in CuCrTiS4 shows that this thiospinel behaves rather similarly to strongly correlated oxides, with MR and MTEP enhanced in the case of VRH transport with paramagnetic spins, such as in cobalt misfits or colossal MR manganites.

Electronic phase separation and magnetic-field-induced phenomena in molecular multiferroic (ND4)2FeCl5·D2O

Electronic phase separation has been increasingly recognized as an important phenomenon in understanding many of the intriguing properties displayed in transition metal oxides. It is believed to produce fascinating functional properties in otherwise chemically homogenous electronic systems, e.g., colossal magnetoresistance manganites and high-${T}_{\mathrm{c}}$ cuprates. While many well-known electronically phase-separated systems are oxides, it has been argued that the same phenomenon should occur in other electronic systems with strong competing interactions. Here we report the observation of electronic phase separation in molecular $({\mathrm{ND}}_{4}{)}_{2}{\mathrm{FeCl}}_{5}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{D}}_{2}\mathrm{O}$, a type-II multiferroic. We show that two magnetic phases, one of which is commensurate and the other of which is incommensurate, coexist in this material. Their evolution under applied magnetic field produces emergent properties. In particular, our measurements reveal a field-induced exotic state linked to a direct transition from a paraelectric/paramagnetic phase to a ferroelectric/antiferromagnetic phase, a collective phenomenon that hasn't been seen in other magnetic multiferroics.

Role of external and internal perturbations on ferromagnetic phase transitions in manganites: existence of tricritical points

A phenomenological mean-field theory is presented to describe the role of external magnetic field, pressure and chemical substitution on the nature of ferromagnetic (FM) to paramagnetic (PM) phase transition in manganites. The application of external field (or pressure) shifts the transition, leading to a field (or pressure) dependent phase boundary along which a tricritical point is shown to exist where a first-order FM-PM transition becomes second-order. We show that the effect of chemical substitution on the FM transition is analogous to that of external perturbations (magnetic field and pressure); this includes the existence of a tricritical point at which the order of transition changes. Our theoretical predictions satisfactorily explain the nature of FM-PM transition, observed in several systems. The modeling hypothesis has been critically verified from our experimental data from a wide range of colossal magnetoresistive manganite single crystals like Sm0.52Sr0.48MnO3. The theoretical model prediction of a tricritical point has been validated in this experiment which provides a major ramification of the strength of the model proposed.