Abstract: Entropy-stabilized materials are stabilized by the configurational entropy of the constituents, rather than the enthalpy of formation of the compound. These materials have attracted significant interest due to the apparent deviations from Gibbs phase rule and desirable mechanical properties. Despite the discovery of high entropy crystals nearly 15 years ago, reported investigations outside transition metal alloys have just recently been extended to ionic crystals, particularly oxides, a class of materials which can demonstrate useful and dynamic functional properties such as ferroelectricity, magnetoelectricity, thermoelectricity, and superconductivity. As the magnetic and electronic properties of oxides are strongly correlated to their chemistry and electronic structure, the concept of entropy stabilization could lead to interesting and novel properties. Though known entropy-stabilized oxides contain magnetic constituents, the magnetic properties of the multi-component oxide have yet to be investigated. Here we examine the role of entropy and composition on the exchange coupling and magnetic anisotropy of permalloy/(Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O thin film heterostructures. We observe a strong exchange field and an apparent deviation from the rule of mixtures in the structural and magnetic parameters. This result demonstrates that entropy stabilized oxides can be engineered to show concerted magnetic properties that are dependent on constituent species, yet differ from a simple weighed average of the components and can result in unexpected phenomena.

New Publication!- Meisenheimer, P. B., Kratofil, T. J. & Heron, J. T. Giant Enhancement of Exchange Coupling in Entropy-Stabilized Oxide Heterostructures. Sci. Rep. 7, 13344 (2017).

Abstract: Entropy-stabilized materials are stabilized by the configurational entropy of the constituents, rather than the enthalpy of formation of the compound. A unique benefit to entropy-stabilized materials is the increased solubility of elements, which opens a broad compositional space, with subsequent local chemical and structural disorder resulting from different atomic sizes and preferred coordinations of the constituents. Known entropy-stabilized oxides contain magnetically interesting constituents, however, the magnetic properties of the multi-component oxide have yet to be investigated. Here we examine the role of disorder and composition on the exchange anisotropy of permalloy/(Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O heterostructures. Anisotropic magnetic exchange and the presence of a critical blocking temperature indicates that the magnetic order of the entropy-stabilized oxides considered here is antiferromagnetic. Changing the composition of the oxide tunes the disorder, exchange field and magnetic anisotropy. Here, we exploit this tunability to enhance the strength of the exchange field by a factor of 10x at low temperatures, when compared to a permalloy/CoO heterostructure. Significant deviations from the rule of mixtures are observed in the structural and magnetic parameters, indicating that the crystal is dominated by configurational entropy. Our results reveal that the unique characteristics of entropy-stabilized materials can be utilized and tailored to engineer magnetic functional phenomena in oxide thin films.

Full text available from Nature Scientific Reports.

M-Write aims to transform the teaching and learning across the University of Michigan through increased student engagement and transformative learning. M-Write implements a writing-to-learn pedagogy with the incorporation of an automated peer review process. The writing-to-learn pedagogy is unique in that it seeks to supplement mathematical understanding of core concepts with written expression of understanding. Students are posed with a writing prompt designed to test the understanding of a core class principle and the ability to express it. The peer review process encompasses critique and revision steps which enable students to engage with one another for peer-to-peer learning. The ability to express technical concepts through writing and oral presentations have become critical skills for modern scientists and engineers. M-Write is used in material science and engineering courses in order to build some of these skills.

In the Fall 2017 semester, Peter will work with professor Heron to implement M-Write in the introductory materials science course MATSCIE 220. Throughout the semester, they will become engaged with faculty and students across campus to participate in a semester long seminar that will focus on the development of writing prompts and methodologies for enhanced student involvement.

For further information about M-Write, go to http://lsa.umich.edu/sweetland/m-write.html

This summer Betsy worked at Steelcase in Grand Rapids, Michigan. Her role was cross functional between the Materials Innovation Exploration team and Product Development Engineering to help new product development teams understand the properties and potential applications of new materials. The primary focus was on understanding the technology behind chromic textiles, particularly photochromic, thermochromic, and electrochromic textiles. These textiles have the potential to store information, give user feedback and signal group functions. Additionally, Betsy worked on a project to establish updated sustainability standards for design and engineering in future product development.

For the next month, Peter will be working in the Laboratory for Multifunctional Ferroic Materials with Dr. Morgan Trassin at ETH Zürich to characterize some of our magnetic and magnetoelectric thin films. The group at Zürich is an expert in a number of powerful techniques for exploring magnetic structure, such as Second Harmonic Generation which allows us to look directly at the antiferromagnetic order in crystalline samples. Good luck, and may the data be ever in your favor!

This trip is funded in part by the Weiser Center for Emerging Democracies (WCED) at the University of Michigan International Institute.