Magnetic interactions in martensitic Ni-Mn-based Heusler systems [Elektronische Ressource] / Seda Aksoy

Magnetic interactions in martensiticNi-Mn based Heusler systemsFakult˜at fur˜ Physikder Universit˜at Duisburg-Essen(Campus Duisburg)zur Erlangung des akademischen Grades einesDoktors der Naturwissenschaften (Dr. rer. nat.)genehmigte Dissertation vonSeda Aksoy, M. Sc.aus AnkaraReferent: Dr. Mehmet AcetKorreferent: Prof. Dr. Ing. Eckhard QuandtTag der mundlic˜ hen Prufung:˜ 22 April 2010iAbstractIn this work, magnetic, magnetocaloric and structural properties are investigated in Ni-Mn-based martensitic Heusler alloys with the aim to tailor these properties as well asto understand in detail the magnetic interactions in the various crystallographic statesof these alloys. We choose Ni Mn In as a prototype which undergoes a marten-50 34 16sitic transformation and exhibits fleld-induced strain and the inverse magnetocaloricefiect. Using the structural phase diagram of martensitic Ni-Mn-based Heusler alloys,we substitute gallium and tin for indium to carry these efiects systematically closer toroom temperature by shifting the martensitic transformation. A magneto-calorimeteris designed and built to measure adiabatically the magnetocaloric efiect in these alloys.The temperature dependence of strain under an external magnetic fleld is studiedin Ni Mn Z (Z: Ga, Sn, In and Sb) and Ni Mn In Z (Z: Ga and Sn).