Regensburg 2016 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 18: Topical session: Caloric Effects in ferroic materials I - Magnetocalorics

MA 18.4: Vortrag

Dienstag, 8. März 2016, 11:15–11:30, H53

Complex magnetic intermetallics and magnetocaloric effect — •Peter Entel1 — Faculty of Physics and CENIDE, University of Duisburg-Essen, 47048 Duisburg, Germany

We have performed ab initio electronic structure calculations and Monte Carlo simulations of magnetic intermetallics such as Fe-Al, Fe-Rh, Ni-Mn-Ga and Ni-Mn-(In, Sn) alloys. While Fe-Al shows mictomagnetic and metamagnetic features due to disorder and defects, near-stoichiometric Ni-Mn-Ga alloys show magnetic-field induced strain (MFIS), as the external magnetic field can drive the variant boundaries to move so that the magnetic easy axis is aligned parallel to the magnetic field direction. The other unusual type of ferroic shape-memory alloys like Ni-Mn-(In, Sn) (showing large magnetocaloric effects) leads to strongly frustrated magnetic behavior because of competing ferro- and antiferromagnetic interactions, where the parent phase shows considerably larger magnetization than the martensitic phase leading (in difference to Ni-Mn-Ga) to magnetic field-induced transformation (MFIT), namely a metamagnetic phase transition from martensite to austenite with increasing magnetic field. The related magnetostructural transiton leads to the kinetic arrest phenomenon at a critical temperature where the entropy difference between austenitic and martensitic phases and the driving force for further transformation vanish (which, alternatively has been assigned to a Kauzmann point). In addition, we find transitions to supercooled austenite and unfrozen strain glass and to a cluster-spin glass. We argue that this complexity originates from the ferroic frustration and noncollinear magnetism.