Ferroelectronics Lab

Understanding and utilizing non-volatile properties of materials

  • About the Lab
  • People
  • Research
  • Publications
  • Outreach
  • Facilities
  • News

New Publication! Oxides and the high entropy regime: A new mix for engineering physical properties

July 14, 2020 By John Heron

Abstract: Historically, the enthalpy is the criterion for oxide materials discovery and design. In this regime, highly controlled thin film epitaxy can be leveraged to manifest bulk and interfacial phases that are non-existent in bulk equilibrium phase diagrams. With the recent discovery of entropy-stabilized oxides, entropy and disorder engineering has been realized as an orthogonal approach. This has led to the nucleation and rapid growth of research on high-entropy oxides – multicomponent oxides where the configurational entropy is large but its contribution to its stabilization need not be significant or is currently unknown. From current research, it is clear that entropy enhances the chemical solubility of species and can realize new stereochemical configurations which has led to the rapid discovery of new phases and compositions. The research has expanded beyond studies to understand the role of entropy in stabilization and realization of new crystal structures to now include physical properties and the roles of local and global disorder. Here, key observations made regarding the dielectric and magnetic properties are reviewed. These materials have recently been observed to display concerted symmetry breaking, metal-insulator transitions, and magnetism, paving the way for engineering of these and potentially other functional phenomena. Excitingly, the disorder in these oxides allows for new interplay between spin, orbital, charge, and lattice degrees of freedom to design the physical behavior. We also provide a perspective on the state of the field and prospects for entropic oxide materials in applications considering their unique characteristics.

Read the full text open-access in MRS Advances

Filed Under: Publications

New publication! Tunable magnetoelastic anisotropy in epitaxial (111) Tm3Fe5O12 thin films

April 21, 2020 By John Heron

Abstract: Ferrimagnetic insulators with perpendicular magnetic anisotropy are of particular interest for spintronics due to their ability to mitigate current shunting in spin–orbit torque heterostructures and enable low switching energy, high-density storage magnetic devices. Rare earth iron garnet Tm3Fe5O12 (TmIG) is one such material where prior studies have shown that the negative magnetostriction coefficient and isotropic in-plane tensile strain enable the magnetoelastic anisotropy to overcome the demagnetization energy and stabilize perpendicular magnetic anisotropy. However, the investigation of the tunability of the magnetoelastic anisotropy between thin films that possess perpendicular magnetization and quantification of the magnetoelastic constants has not been reported. Here, we quantify the evolution of magnetic anisotropy in (111)-oriented, epitaxial, 17 nm thick thin films of TmIG using a systematic variation of in-plane epitaxial strain (ranging 0.49%–1.83%) imposed by a suite of commercially available garnet substrates. Within the confines of the imposed strain range and deposition condition, the distortion from cubic symmetry is found to be approximately linear within the in-plane strain. The magnetic anisotropy field can be tuned by a factor of 14 in this strain range. The magnetoelastic anisotropy constant, B2, is found to be approximately constant (∼2500 kJ m−3) and more than 2× larger than the reported bulk value (∼1200 kJ m−3) for a cubic distortion between 90.17° and 90.71°. B2 is found to decrease at cubic distortions of 90.74° and larger. Our results highlight strain engineering, and its limitations, for control of perpendicular magnetic anisotropy.

The full text is available as an editor’s choice article from Journal of Applied Physics

Filed Under: Publications

New Publication! Boron arsenide heterostructures: lattice-matched heterointerfaces and strain effects on band alignments and mobility

January 17, 2020 By John Heron

Abstract: BAs is a III–V semiconductor with ultra-high thermal conductivity, but many of its electronic properties are unknown. This work applies predictive atomistic calculations to investigate the properties of BAs heterostructures, such as strain effects on band alignments and carrier mobility, considering BAs as both a thin film and a substrate for lattice-matched materials. The results show that isotropic biaxial in-plane strain decreases the band gap independent of sign or direction. In addition, 1% biaxial tensile strain increases the in-plane electron and hole mobilities at 300 K by >60% compared to the unstrained values due to a reduction of the electron effective mass and of hole interband scattering. Moreover, BAs is shown to be nearly lattice-matched with InGaN and ZnSnN2, two important optoelectronic semiconductors with tunable band gaps by alloying and cation disorder, respectively. The results predict type-II band alignments and determine the absolute band offsets of these two materials with BAs. The combination of the ultra-high thermal conductivity and intrinsic p-type character of BAs, with its high electron and hole mobilities that can be further increased by tensile strain, as well as the lattice-match and the type-II band alignment with intrinsically n-type InGaN and ZnSnN2 demonstrate the potential of BAs heterostructures for electronic and optoelectronic devices.

Full Text available from Nature Computational Materials

Filed Under: Publications

New Article! “Post-silicon computing gets one step closer”

December 10, 2019 By John Heron

The UM College of Engineering newsletter has just published an article on our recent publication, “Magnetic frustration control through tunable stereochemically-driven disorder in entropy-stabilized oxides.”

Read the full article at The Michigan Engineer News Center.

Filed Under: Publications

New Publication! Magnetic frustration control through tunable stereochemically driven disorder in entropy-stabilized oxides

October 28, 2019 By John Heron

Entropy-stabilized oxides possess a large configurational entropy that allows for the unique ability to include typically immiscible concentrations of species in different configurations. Particularly in oxides, where the physical behavior is strongly correlated to stereochemistry and electronic structure, entropic stabilization creates a unique platform to tailor the interplay of extreme structural and chemical disorder to realize unprecedented functionalities. Here, we control stereochemically driven structural disorder in single crystalline, rocksalt, (MgCoNiCuZn)O-type entropy-stabilized oxides through the incorporation of Cu2+ cations. We harness the disorder to tune the degree of glassiness in the antiferromagnetic structure. Structural distortions driven by the Jahn-Teller effect lead to a difference in valence on the Co cation sites, which extends to dilution and disorder of the magnetic lattice. A spin glass model reveals that the fractional spin ordering of the magnetic lattice can be tuned by ∼65%. These findings demonstrate entropy-stabilization as a tool for control of functional phenomena.

Full text available from Physical Review Materials

Filed Under: Publications

  • « Previous Page
  • 1
  • …
  • 3
  • 4
  • 5
  • 6
  • 7
  • Next Page »

News

  • New Publication! “Geometric defects induced by strain relaxation in thin film oxide superlattices.” November 10, 2022
  • New Publication! “Nanophotonic control of thermal emission under extreme temperatures in air” September 29, 2022
  • New Publication! “Germanium dioxide: A new rutile substrate for epitaxial film growth” September 1, 2022

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

About

Our work is multidisciplinary. We employ concepts and tools from the fields of materials science, chemistry, physics and electrical engineering to develop new methods to investigate and engineer … Read More

News

New Publication! “Geometric defects induced by strain relaxation in thin film oxide superlattices.”

November 10, 2022 By Matt Webb

New Publication! “Nanophotonic control of thermal emission under extreme temperatures in air”

September 29, 2022 By Matt Webb

Contact

Ferroelectronics Lab
Address: 2030 H.H. Dow

T: (734) 763-6914
E: jtheron@umich.edu
  • Email

Ferroelectronics Lab · Copyright © 2023 · Website by Super Heron Support

 

Loading Comments...