Thin Film Chromium Oxide Perovskites
Senior Investigator: Riccardo Comin, Assistant Professor, Department of Physics
 

Transition metal oxides (TMOs) have found use in various technologies. There has been mounting interest to harness the spin-charge interplay of TMOs and engineer new data storage devices relying on all-electrical (current or field) writing operations.

The relationship between magnetic order and electronic transport in TM-based compounds suggest that ferromagnets (FM) are typically metals, while antiferromagnets (AFM) are insulators. Compounds as such these are on the verge between different magnetic and electronic ground states, an ideal platform to design materials that are highly tunable by external parameters such as doping or magnetic field. Further, in these materials, the realization of room-temperature metallic conduction with robust AFM order could pave the way to new oxide-based magnetic access memories for fast magnetization switching using spin-transfer torque.

We propose to explore focuses on a family of transition metal oxides with a rich phenomenology: chromium-based oxide perovskites (chromites). We propose to study the combined charge and spin response in Cr-based perovskite thin films in the multidimensional domain spanned by strain, dimensionality (thickness), and doping (chemical substitution or oxygen removal). The novelty of our work lies in the exploration of a relatively new class of materials, and the impact of the proposed work is in the synergistic feedback between synthesis and characterization of the charge and spin response to reveal the driving forces behind the complex phenomenology of chromites.

The IRG is aimed at exploring and exploiting ferroelectric (FE) polarization as a state variable that allows realization of polarization-controlled electronic, transport, and other functional properties of oxide, organic, and hybrid FE-based structures. This involves ferroelectrically induced resistive switching phenomena and the associated memristive behavior, FE modulation of electronic confinement at the hybrid FE/semiconductor and organic interfaces, as well as development of novel functional systems based on newly synthesized organic ferroelectrics where molecular interactions are responsible for macroscopic dipole ordering. These scientifically rich problems comprise the involvement of multiple degrees of freedom, the critical role of interfaces, and the interplay between physical and chemical properties at the nanoscale. They require comprehensive fundamental understanding and hold a lot of promise for technological innovations, including new paradigms for data storage and conceptually novel photovoltaic applications.

Thin Film Chromium Oxide Perovskites

Transition metal oxides (TMOs) have found use in various technologies. There has been mounting interest to harness the spin-charge interplay of TMOs and engineer new data storage devices relying on all-electrical (current or field) writing operations.

The relationship between magnetic order and electronic transport in TM-based compounds suggest that ferromagnets (FM) are typically metals, while antiferromagnets (AFM) are insulators. Compounds as such these are on the verge between different magnetic and electronic ground states, an ideal platform to design materials that are highly tunable by external parameters such as doping or magnetic field. Further, in these materials, the realization of room-temperature metallic conduction with robust AFM order could pave the way to new oxide-based magnetic access memories for fast magnetization switching using spin-transfer torque.

We propose to explore focuses on a family of transition metal oxides with a rich phenomenology: chromium-based oxide perovskites (chromites). We propose to study the combined charge and spin response in Cr-based perovskite thin films in the multidimensional domain spanned by strain, dimensionality (thickness), and doping (chemical substitution or oxygen removal). The novelty of our work lies in the exploration of a relatively new class of materials, and the impact of the proposed work is in the synergistic feedback between synthesis and characterization of the charge and spin response to reveal the driving forces behind the complex phenomenology of chromites.

The grand challenge of this IRG is to understand how to manipulate light on the nanometer length scale and, thereby, implement new amplified sensing and information encoding strategies. Particles and arrays can amplify and confine light through excitation of their localized surface plasmon resonances (LSPRs). The materials of interest include chemically synthesized noble metal nanoparticles, nanofabricated arrays of noble metal nanoparticles and nanoholes, and surface functionalization chemistry for these nanomaterials. It is anticipated that the new materials produced through rational nanoparticle synthesis/fabrication—and in particular through understanding of their growth mechanism(s) and properties—will have a transformative impact on applications such as ultrasensitive chemical and biosensing, nanoscale optical spectroscopy and microscopy, and information processing.

The UMass MRSEC mission 

 Materials research at UMass Amherst has a rich history of fundamental discovery centered in polymers and extending across the landscape of colloidal materials, surface science, and nanoscale structures. NSF support for the UMass MRSEC has been instrumental in landmark findings in polymer crystallization, block copolymer assembly for high density addressable media, ultrathin free-standing nanoscale structures, and state-of-the-art advances in polymer adhesion and self-healing. Our materials research mission merges with vibrant programs designed to educate students towards rewarding careers in science and technology. This is manifest in teaching and mentoring, where UMass Amherst is a national leader in graduate education in polymers and soft materials chemistry, physics, and engineering. Our educational mission extends to all ages and grade levels, thanks to a rich diversity of Center-supported programs designed for undergraduates, teachers, and grade school children alike. Today the UMass MRSEC seeks to define the future of polymer materials science and engineering, with research teams engaged in innovative multidisciplinary projects that push fundamental boundaries and create new technologies. 

The Materials Research Science and Engineering Center (MRSEC) at the University of Houston supports research on the synthesis and characterization of oxide materials that have technologically important applications in ionic devices in one interdisciplinary research group. The devices include membrane and electrocatalytic reactors, solid oxide fuel cells, and chemical sensors. The devices promise major advances in industrial chemical processes by improving product selectivity, process efficiency and environmental compatibility. Special emphasis is on complex oxides that are active catalysts for hydrocarbon oxidation and oxygen reduction and have the high ionic conductivity and electronic conductivity required for ionic devices. The MRSEC supports the development, operation and maintenance of shared experimental facilities for materials research. It provides seed funding for exploratory research, fosters research participation by undergraduates and pre-college students, and is developing strong industrial relationships. The Center currently supports 11 senior investigators, 3 postdoctoral research associates, 10 graduate students, and 6 undergraduates. The MRSEC is directed by Professor Paul C.W. Chu. %%% Changing needs in transportation fuels, increasing availability of natural gas, and the emphasis on energy efficient, environmentally benign processes are driving new demands for advanced catalytic and ceramic materials. These trends suggest new opportunities for improved catalytic and separation processes that apply novel oxide materials in new energy production approaches. The Materials Research Science and Engineering Center (MRSEC) at the University of Houston supports research on the synthesis and characterization of oxide materials that have technologically important applications. The MRSEC supports the development, operation and maintenance of shared experimental facilities for materials research. It provides seed funding for explora tory research, fosters research participation by undergraduates and pre-college students, and is developing strong industrial relationships. The Center currently supports 11 senior investigators, 3 postdoctoral research associates, 10 graduate students, and 6 undergraduates. The MRSEC is directed by Professor Paul C.W. Chu.

The Center on Polymer Interfaces and Macromolecular Assemblies (CPIMA) is an NSF sponsored partnership among Stanford University, IBM Almaden Research Center, the University of California Davis and the University of California Berkeley. CPIMA is dedicated to fundamental research on interfaces found in systems containing polymers and low molecular weight amphiphiles.

Joe Checkelsky, Assistant Professor, Department of Physics

A relatively unexplored parameter in topological insulators is electronic correlation. Motivated by the metal-insulator transition observed in the pyrochlore iridates R₂Ir₂O₇ (R is a rare earth) it has been suggested that a combination of weak to moderate correlation effects and large spin-orbit interaction may exist that could give rise to new topologically non-trivial electronic states. In particular, it is expected that this compound’s principle bulk excitations may be described by a 3-dimensional analog of graphene known as a Weyl semimetal with helical excitations in all 3 dimensions with a several exotic and potentially useful properties. Despite these sharp theoretical predictions, the experimental situation is unsettled owing largely to the difficulty in producing single crystal specimens.  While optical furnace techniques used for other pyrochlores have thus far proven unsuccessful in producing single crystals, we propose to extend a flux technique reported for R=Eu and Pr across this series to develop high quality single crystals and perform incisive studies of the magnetic transition and transport properties of the electronic ground state.  If successful, this study would open the door for other optical and scattering experiments as well as extensions to Os oxides and spinel candidate compounds.

Research Summary: Recent studies on magneto-transport properties of topological insulators

(TIs) have attracted great attention due to the rich spin-orbit physics and promising applications

in spintronic devices. Particularly, the strongly spin-momentum coupled electronic states have

been extensively pursued to realize efficient spin-orbit torque (SOT) switching (Figure 1(a)).

However, so far current-induced magnetic switching with TIs has only been observed at

cryogenic temperatures. The goal of this seed project is to understand whether the topologically

protected electronic states in TIs could benefit spintronic applications at room temperature.

In this seed project, full SOT switching has been demonstrated in a TI/ferromagnet

heterostructure with perpendicular magnetic anisotropy (PMA) at room temperature (Figure

1(b)) [1]. Ferrimagnetic cobalt-terbium (CoTb) alloy with bulk PMA was used to overcome the

effects of the interfacial lattice mismatch, permitting direct growth on the classical TI material

Bi2Se3. The low switching current density (~ 3 × 106 A/cm2) provides definitive proof of the high

SOT efficiency from the TI. The SOT efficiency was measured by the current-induced shift of

the Hall resistance-versus-magnetic field hysteresis loops (Figure 1(c)), which is consistent with

the model of the current-induced Néel-type domain wall motion. Accordingly, the effective spin

Hall angle of the TI was determined to be several times larger than in commonly used heavy

metals (Figure 1(c)). Moreover, power consumption for switching a ferromagnetic layer with

either a TI or a heavy metal was calculated, indicating that magnetization switching with TIs

presents much higher energy efficiency than with conventional heavy metals. These results

demonstrate the robustness of TIs as an SOT switching material and provide an avenue

towards applicable TI-based spintronic devices.

Rearrangements & Softness in Disordered Solids aims to develop fundamental understanding of the organization and proliferation of localized particle-scale rearrangements in disordered solids deformed just beyond the onset of yield, and thereby  identify strategies for controlling nonlinear mechanical response and enhancing toughness. The materials studied by the team span a wide range of length scales from amorphous carbon and atomic/molecular glasses, to nanoparticles and colloids, to macroscopic bubbles and grains. When pushed beyond yield, some materials crack or shatter due to rearrangements that collect along planes, whereas others flow smoothly because  rearrangement events remain separated. New theoretical concepts, some based on machine learning, will be developed to understand this dramatic difference, and these theories will be tested by atomistic simulations and experiments on systems for which it is possible to measure microstructure versus time during a large imposed deformation. Ultimately, these factors will be optimized to widen the window between yield and failure and hence to improve toughness.