This past week, Steve gave a contributed talk on theoretical calculations of strain dependent spin orbit splitting in PtMn₃ and its effect on intrinsic transport properties.

Abstract: Efficient charge-to-spin current conversion in materials is crucial to the development of spintronic memory or logic devices. A promising and established method of spin current generation is the injection of charge current through a crystal with a strong intrinsic spin Hall conductivity. Recently, a class of antiferromagnets with the composition XMn₃, where X={Pt, Ir, Rh}, have been identified as materials with large intrinsic spin Hall conductivities stemming from their non-trivial spin order. The exact role of antiferromagnetic spin texture on the generated spin current, however, is not fully understood. Temperature-dependent triangular AFM – collinear AFM phase transitions in chemically ordered PtMn₃ can be exploited to probe this directly. Here, we report on the growth and magneto-transport measurement of ordered PtMn3 thin films. Harmonic transport measurement techniques utilizing spin-transfer torques were performed to determine the spin and anomalous Hall conductivities at select temperatures.

Peter gave an invited talk at the recent college of engineering graduate student coffee hour on the novel and distortion dependent magnetic properties of entropy-stabilized oxides. Every two weeks, the graduate student council gives two graduate students the opportunity to give talks at this cross-department meeting.

Peter chaired the ferroelectrics session and gave a contributed talk at the 2018 Conference on Electronic and Advanced Materials this January, in Orlando, FL. His talk was about our recent work on entropy stabilized oxides and disorder dependent effects on magnetic structure. The abstract is provided below, and a big thanks to the American Ceramic Society.

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 entropic stabilization 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. As the magnetic and electronic properties of oxides are strongly correlated to their chemistry and electronic structure, entropy stabilization could lead to interesting and novel properties. Anisotropic magnetic exchange and the presence of a critical blocking temperature indicates that the entropy-stabilized oxides considered here are antiferromagnetic. Changing the composition of the oxide tunes the disorder and exchange bias and 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 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 to engineer magnetic functional phenomena in oxide thin films.

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.

Research Education and Activities for Classroom Teachers is an event where grade school teachers from around Michigan can come and attend workshops to participate in materials science labs that they can then take back to their respective classrooms. Peter helped develop and run the “Introduction to Composite Materials” demo at REACT, where students (teachers) made their own composite concrete mixtures and tested the mechanical properties. The goal of the lab is to get students thinking about how different reinforcement materials can impart different properties into the composites and about how to optimize a material for a given application.