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MM: Fachverband Metall- und Materialphysik

MM 72: Magnetic Shape Memory Alloys (joint with MA)

MM 72.2: Talk

Friday, March 16, 2018, 09:45–10:00, TC 010

Ab initio design strategies for NiMn-based magnetocaloric materials: The effect of Co and Fe — •Biswanath Dutta, Fritz Körmann, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, 40237 Düsseldorf, Germany

In the quest to improve magnetocaloric properties of NiMn-based Heusler alloys, doping with ferromagnetic elements is found to be a promising strategy. Recent experiments show a large magnetization drop also known as metamagnetic transition and a giant inverse magnetocaloric effect (MCE) upon martensitic transformation in Co and Fe substituted NiMn-based Heusler alloys. In spite of this huge potential, a complete understanding of the role of different substitutional elements in these materials is still missing. Using ab initio calculations, we study the impact of Co and Fe on the martensitic transformation and the magnetic properties in Mn-excess Ni-Mn-Al alloy (B. Dutta et al., Phys. Status Solidi B 1700455 (2017)). Our calculations reveal an antiferromagnetic to ferromagnetic transition above a critical amount of Co or Fe doping in the austenite phase. The martensite phase, however, remains antiferromagnetic, which explains the experimentally observed metamagnetic transition in these alloys. The obtained magnetic properties are explained on the basis of magnetic exchange interactions. We also find that both Co and Fe substitution reduces the martensitic transformation temperature with the effect being larger in the case of the Fe containing alloy. Based on the achieved results on saturation magnetization and transformation temperature, Co containing alloys are found to be more promising for future MCE applications.