@article {1846, title = {Inducing skyrmion flop transitions in Co 8 Zn 8 Mn 4 at room temperature}, journal = {Physical Review Materials}, volume = {7}, year = {2023}, month = {04}, doi = {10.1103/PhysRevMaterials.7.044401}, author = {Meynell, Simon and Eggeler, Yolita and Bocarsly, Joshua and Kitchaev, Daniil and Rhodes, Bailey and Pollock, Tresa and Wilson, Stephen and Ven, Anton and Seshadri, Ram and Graef, Marc and Jayich, Ania and Gianola, Daniel} } @article {1661, title = {Influence of plastic deformation on the magnetic properties of Heusler MnAu2Al}, journal = {Phys. Rev. Materials}, volume = {5}, year = {2021}, month = {01/2021}, chapter = {014408}, abstract = {

The Heulser intermetallic\ MnAu2Al\ is shown to undergo a dramatic change in net magnetization in response to plastic deformation. A mechanism is proposed involving antiferromagnetic interactions in the otherwise ferromagnetic compound (when ordered) that arise due to chemical changes at the antiphase boundaries created by the deformation. The coupling between chemical and magnetic order across antiphase boundaries is likely to occur in other ordered magnetic systems and may provide an explanation for otherwise anomalous magnetic behavior across several systems, including other Heusler intermetallics.

}, doi = {https://doi.org/10.1103/PhysRevMaterials.5.014408}, url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.014408}, author = {Levin, Emily E. and Kitchaev, Daniil A. and Eggeler, Yolita M and Mayer, Justin A. and Behera, Piush and Gianola, Daniel S. and Van der Ven, Anton and Pollock, Tresa M. and Seshadri, Ram} } @article {1561, title = {Structural coupling and magnetic tuning in Mn$_{2}$$_{-}$ₓCoₓP magnetocalorics for thermomagnetic power generation}, journal = {APL Materials}, volume = {8}, year = {2020}, pages = {041106}, abstract = {

Promising materials for magnetic refrigeration and thermomagnetic power generation often display strong coupling between magnetism and structure. It has been previously proposed that MnCoP exhibits this strong coupling, contributing to its substantial magnetocaloric effect near TC = 578K. Here, we show from temperature-dependent synchrotron x-ray diffraction that MnCoP displays a discontinuity in the thermal expansion at TC, with spontaneous magnetostriction that is positive in the a direction and negative in the b direction, highlighting the anisotropic nature of the magnetostructural coupling. Varying the Mn:Co ratio of Mn2-xCoxP within the range of 0.6 \≤ x \≤ 1.4 allows the magnetic properties to be tuned. TC decreases as the composition deviates from stoichiometric MnCoP, as does the saturation magnetization. The magnitude of the magnetocaloric effect, |\ΔSM|, decreases as well, due to broadening of the magnetic transition. The large reversible change in magnetization \ΔM accessible over a small temperature range under moderate magnetic fields makes these materials promising for thermomagnetic power generation from waste heat.

}, issn = {2166532X}, doi = {10.1063/1.5142000}, url = {https://doi.org/10.1063/1.5142000}, author = {Levin, Emily E. and Bocarsly, Joshua D. and Grebenkemper, Jason H. and Issa, Ramsey and Wilson, Stephen D. and Pollock, Tresa M. and Seshadri, Ram} } @article {1376, title = {Protocols for High Temperature Assisted-Microwave Preparation of Inorganic Compounds}, journal = {Chemistry of Materials}, volume = {31}, year = {2019}, pages = {7151{\textendash}7159}, abstract = {

Assisted-microwave heating involves the use of a susceptor to initially heat up reactants in a microwave reaction. Once hot, the reactants themselves become directly susceptible to microwave heating and interdiffuse to form products. Assisted-microwave methods are appealing for a wide variety of high temperature solid-state reactions, reaching reaction temperatures of 1500 \°C and more. Among the many advantages are that the direct volumetric heating associated with microwaves allows for rapid reaction times while employing significantly less energy than conventional furnace-based preparation. Shorter reaction times and selective heating permit volatile reactants to be incorporated stoichiometrically in the product. Undesirable reactions with containers or enclosures are also minimized. The morphology of powders obtained through microwave reactions are also more uniform and comprise smaller particles than obtained conventionally. This Methods/Protocols article is presented as a user manual for carrying out assisted-microwave preparation of bulk complex oxides in air or reducing atmospheres and sol-gel based processing of complex oxides, air sensitive intermetallics, and transition metal chalcogenides.

}, issn = {15205002}, doi = {10.1021/acs.chemmater.9b02594}, author = {Levin, Emily E. and Grebenkemper, Jason H. and Pollock, Tresa M. and Seshadri, Ram} } @article {1421, title = {Enhancing thermoelectric properties through control of Nickel Interstitials and phase separation in Heusler/Half-Heusler TiNi1.1Sn composites}, journal = {Materials}, volume = {11}, year = {2018}, pages = {1{\textendash}12}, abstract = {

Thermoelectric devices, which allow direct conversion of heat into electrical energy, require materials with improved figures of merit (zT) in order to ensure widespread adoption. Several techniques have been proposed to increase the zT of known thermoelectric materials through the reduction of thermal conductivity, including heavy atom substitution, grain size reduction and inclusion of a semicoherent second phase. The goal in these approaches is to reduce thermal conductivity through phonon scattering without modifying the electronic properties. In this work, we demonstrate that Ni interstitials in the half-Heusler thermoelectric TiNiSn can be created and controlled in order to improve physical properties. Ni interstitials in TiNi1.1Sn are not thermodynamically stable and, instead, are kinetically trapped using appropriate heat treatments. The Ni interstitials, which act as point defect phonon scattering centers and modify the electronic states near the Fermi level, result in reduced thermal conductivity and enhance the Seebeck coefficient. The best materials tested here, created from controlled heat treatments of TiNi1.1Sn samples, display zT = 0.26 at 300 K, the largest value reported for compounds in the Ti-Ni-Sn family.

}, keywords = {Heusler, Phonon scattering, Point defect, Thermoelectric, TiNi2Sn, TiNiSn}, issn = {19961944}, doi = {10.3390/ma11060903}, author = {Levin, Emily E. and Long, Francesca and Douglas, Jason E. and Buffon, Malinda L.C. and Lamontagne, Leo K. and Pollock, Tresa M. and Seshadri, Ram} } @article {1181, title = {Thermoelectric performance and the role of anti-site disorder in the 24-electron Heusler TiFe2Sn}, journal = {Journal of Physics: Condensed Matter}, volume = {29}, year = {2017}, month = {Apr}, pages = {405702}, doi = {10.1088/1361-648x/aa81e7}, author = {Buffon, Malinda L C and Laurita, Geneva and Lamontagne, Leo and Levin, Emily E and Mooraj, Shahryar and Lloyd, Demetrious L and White, Natalie and Pollock, Tresa M and Seshadri, Ram} } @article {1186, title = {Tuning the magnetocaloric response in half-Heusler/Heusler MnNi1 xSb solid solutions}, journal = {Physical Review Materials}, volume = {1}, year = {2017}, doi = {10.1103/physrevmaterials.1.075003}, author = {Levin, Emily E. and Bocarsly, Joshua D. and Wyckoff, Kira E. and Pollock, Tresa M. and Seshadri, Ram} } @article {buffon2016enhancement, title = {Enhancement of thermoelectric properties in the Nb{\textendash}Co{\textendash}Sn half-Heusler/Heusler system through spontaneous inclusion of a coherent second phase}, journal = {Journal of Applied Physics}, volume = {120}, number = {7}, year = {2016}, pages = {075104}, publisher = {AIP Publishing}, author = {Buffon, Malinda LC and Laurita, Geneva and Verma, Nisha and Lamontagne, Leo and Ghadbeigi, Leila and Lloyd, Demetrious L and Sparks, Taylor D and Pollock, Tresa M and Seshadri, Ram} } @article {douglas2016magnetic, title = {Magnetic hardening and antiferromagnetic/ferromagnetic phase coexistence in Mn 1- x Fe x Ru 2 Sn Heusler solid solutions}, journal = {Physical Review B}, volume = {94}, number = {9}, year = {2016}, pages = {094412}, publisher = {American Physical Society}, author = {Douglas, Jason E and Levin, Emily E and Pollock, Tresa M and Castillo, Juan C and Adler, Peter and Felser, Claudia and Kr{\"a}mer, Stephan and Page, Katharine L and Seshadri, Ram} } @article {verma2016microstructure, title = {Microstructure Evolution of Biphasic TiNi1+ x Sn Thermoelectric Materials}, journal = {Metallurgical and Materials Transactions A}, year = {2016}, pages = {1{\textendash}12}, publisher = {Springer US}, author = {Verma, Nisha and Douglas, Jason E and Kr{\"a}mer, Stephan and Pollock, Tresa M and Seshadri, Ram and Levi, Carlos G} } @article {douglas2015three, title = {Three-dimensional multimodal imaging and analysis of biphasic microstructure in a Ti{\textendash}Ni{\textendash}Sn thermoelectric material}, journal = {APL Materials}, volume = {3}, number = {9}, year = {2015}, pages = {096107}, publisher = {AIP Publishing}, author = {Douglas, Jason E and Echlin, McLean P and Lenthe, William C and Seshadri, Ram and Pollock, Tresa M} } @article {douglas2014nanoscale, title = {Nanoscale structural heterogeneity in Ni-rich half-Heusler TiNiSn}, journal = {Journal of Applied Physics}, volume = {116}, number = {16}, year = {2014}, pages = {163514}, publisher = {AIP Publishing}, author = {Douglas, Jason E and Chater, Philip A and Brown, Craig M and Pollock, Tresa M and Seshadri, Ram} } @article {douglas2014phase, title = {Phase stability and property evolution of biphasic Ti{\textendash}Ni{\textendash}Sn alloys for use in thermoelectric applications}, journal = {Journal of Applied Physics}, volume = {115}, number = {4}, year = {2014}, pages = {043720}, publisher = {AIP Publishing}, author = {Douglas, Jason E and Birkel, Christina S and Verma, Nisha and Miller, Victoria M and Miao, Mao-Sheng and Stucky, Galen D and Pollock, Tresa M and Seshadri, Ram} } @article {birkel2013improving, title = {Improving the thermoelectric properties of half-Heusler TiNiSn through inclusion of a second full-Heusler phase: microwave preparation and spark plasma sintering of TiNi 1+ x Sn}, journal = {Physical Chemistry Chemical Physics}, volume = {15}, number = {18}, year = {2013}, pages = {6990{\textendash}6997}, publisher = {Royal Society of Chemistry}, author = {Birkel, Christina S and Douglas, Jason E and Lettiere, Bethany R and Seward, Gareth and Verma, Nisha and Zhang, Yichi and Pollock, Tresa M and Seshadri, Ram and Stucky, Galen D} } @article {birkel2013influence, title = {Influence of Ni nanoparticle addition and spark plasma sintering on the TiNiSn{\textendash}Ni system: structure, microstructure, and thermoelectric properties}, journal = {Solid State Sciences}, volume = {26}, year = {2013}, pages = {16{\textendash}22}, publisher = {Elsevier Masson}, author = {Birkel, Christina S and Douglas, Jason E and Lettiere, Bethany R and Seward, Gareth and Zhang, Yichi and Pollock, Tresa M and Seshadri, Ram and Stucky, Galen D} } @article {douglas2012enhanced, title = {Enhanced thermoelectric properties of bulk TiNiSn via formation of a TiNi2Sn second phase}, journal = {Applied Physics Letters}, volume = {101}, number = {18}, year = {2012}, pages = {183902}, publisher = {AIP Publishing}, author = {Douglas, Jason E and Birkel, Christina S and Miao, Mao-Sheng and Torbet, Chris J and Stucky, Galen D and Pollock, Tresa M and Seshadri, Ram} }