Phase Diagrams of Conventional and Inverse Functional Magnetic Heusler Alloys: New Theoretical and Experimental Investigations
In: Disorder and Strain-Induced Complexity in Functional Materials / Kakeshita, Tomoyuki; Fukuda, Takashi; Saxena, Avadh; Planes, Antoni (Hrsg.)
Heidelberg: Springer (2012) (Springer Series in Materials Science ; 148), S. 19-47
Buchaufsatz / Kapitel / Fach: Physik
Fakultät für Physik » Theoretische Physik
First-principles calculations allow to characterize the electronic and magnetic ground-state properties of the full-Heusler alloys of type X2YZ. Functionality of the materials strongly depends on the type of elements and composition. A half-metallic state with 100% spin polarization at the Fermi level, which is an ideal spintronics material for tunneling devices, is, for instance, achieved for (X = Co, Y = Mn, and Z = Ge and Si). Replacing Co by Ni and Ge or Si by Ga yields the prototypical magnetic shape-memory compound Ni2MnGa, which undergoes a (martensitic) tetragonal distortion at ca. 200 K, where the magnetic shape-memory features can be exploited by an external magnetic field and external stress in the martensitic state. Quite another functionality, the conventional or inverse magnetocaloric effect, is observed in the off-stoichiometric samples of (X = Ni, Y = Mn, and Z = Ga, In, Sn, and Sb), where the efficiency of the magnetocaloric effect depends on the size of the isothermal entropy change across the magnetostructural phase transition in an applied magnetic field. Here, we discuss how some of these material properties can be improved in order to obtain room temperature or higher operation temperatures needed for a technological breakthrough.