New developments in Energy Havesting: US-China collaboration on Magnetocaloric Effect Materials Joseph H. Ross Jr., Texas A&M University Main Campus, DMR Figure 1: The Brayton cycle using the magnetocaloric effect of Heusler-type compounds. Microstructural states are numbered on the entropy vs. temperature diagram. Figure 2: Micrograph of NiMnCoSn optimized ribbon (900C 2hrs + 400C 1hr) (a) and its corresponding MCE response (b). Materials exhibiting the magnetocaloric effect (MCE) have been a focus of great interest due to harmful emissions in traditional vapor compression refrigeration. Effective MCE materials exhibit magnetic transitions coupled to a crystal structure changes. Potentially useful materials have been discovered among rare earth compounds. Unfortunately, such materials are cost prohibitive, relatively brittle, and subject to increasing demand worldwide. On the other hand, off-stoichiometric Heusler alloys can be inexpensive and have recently been demonstrated to yield giant MCE, via reversible first order phase transitions, similar to the highest values previously reported. “Microstructural Design for Enhanced Efficiency in Solid State Energy Conversion”, funded by the NSF Materials World Network program, couples a US team including PI J. Ross and I. Karaman at Texas A&M University with a team from Shanghai Jiao-Tong University (SJTU) led by Jianguo Li, the latter funded by NSF-China. With Ph.D. student Nick Bruno, the US team recently demonstrated that ribbons of NiCoMnSn-based Heusler alloy not only produce a similar MCE compared to the rare earth compunds, but the operating temperature, refrigeration capacity, and efficiency can be optimized by modifying the microstructure and stoichiometry. Fig. 1 shows the Brayton cycle utilizing the MCE response of Heusler-type metamagnetic shape memory alloys. Fig. 2 shows the microstructure of an optimally annealed NiMnCoSn ribbon and its corresponding entropy changes across its operating temperature range. For further work to demonstrate how these materials may be used for applications, the team at SJTU has performed directional solidification of NiMnIn-based compositions which resulted in less brittle samples lending the ability to exhibit simultaneous mechanical stress and magnetic field induced temperature changes, or a multicaloric effect. (a) (b)

The current project includes educational and cultural, as well as research, exchanges between Texas A&M University (TAMU), Shanghai Jiao-tong University (SJTU), and Ningbo Materials Institute (NMI). Currently 3 TAMU Ph.D. students, and 2 SJTU students, are working directly on this project, as part of larger research teams at both institutions. Following an organizational meeting at SJTU in 2012, a research exchange at TAMU in January 2013 allowed SJTU researchers to carry out magneto-thermo- mechanical testing; a further visit in August 2013 allowed N. Bruno to participate in advanced processing at SJTU and NMI. Li (SJTU) and Liu (NMI) will visit TAMU laboratories in November 2013, and additional exchanges will allow TAMU and SJTU students to learn techniques not available in the counterpart laboratories, while also conveying improved cross-cultural and interdisciplinary understanding. Advanced techniques developed through this collaboration will contribute to new science and engineering curricula, including that of the new TAMU Materials Science and Engineering Department established in summer of Karaman (Interim Head of the new Department) is one of the team members developing a Materials Design Studio, to feature advanced techniques such as used here. Presentations at international technical meetings by each Ph.D. student participant allowed results to be communicated to diverse technical audiences, while TAMU’s team organized a symposium on shape memory alloys (SMAs) at the TMS annual meeting which also covered those SMAs that show ferrocaloric effect. They also shared findings at the NSF- International Institute for Multifunctional Materials for Energy Conversion (IIMEC) meeting at TAMU. A TMS congress is actively being organized in the Mediterranean basin on energy and infrastructure materials by Karaman and Ross (TAMU). Further outreach activities encouraged interest in materials and energy among much wider audiences. These included MCE materials demonstrations for thousands of K12 students and families at the physics and engineering festival, an open house of TAMU research facilities for interested staff, faculty, students, and children, and shape-memory related science projects with local minority high school students from Harmony Science Academy, Houston, TX and through the Project Olympiad (I-SWEEEP) program. Broader Impacts of US-China collaboration on Magnetocaloric Effect Materials Joseph H. Ross Jr., Texas A&M University Main Campus, DMR January 2013 at TAMU: Top (left to right) – J. Ross (TAMU PI), J.-H. Chen (TAMU PhD student), I. Karaman (TAMU co-PI), J. Li (SJTU PI), Q. Hu (SJTU Asst. Prof.), Y. Huang (SJTU PhD student); (bottom) N. Bruno (TAMU PhD student). August 2013: Yujin Huang giving demonstration of directional solidification process during stay by Nick Bruno at SJTU.