Magneto-optical investigations and ion beam-induced modification of materials with high spin polarization
Zusammenfassung der Projektergebnisse
This project addressed the magnetic and magneto-optical properties of Co-based Heusler compounds. In particular we investigated exchange stiffness and magnetic anisotropy using magneto-optical techniques such as Brillouin light scattering (BLS) and the linear and quadratic magneto-optic Kerr effect. Furthermore, we have also investigated the modification of the compounds under He+ and Ga+ ion beam irradiation with the aim of improving and tailoring structural properties. Exchange stiffness was investigated on a variety of Heusler compounds (Co2FeSi, Co2FeAl, Co2MnSi, Co2MnAl, Co2Cr0.6Fe0.4Al, Co2FeAl0.5Si0.5, Co2Mn0.77Ge0.42) using BLS. The samples were provided from members of the Research Unit as well as from other collaborators. A general relation between the value of exchange stiffness, number of valence electrons and crystallographic order was determined. Magnetic anisotropy was investigated using BLS and magneto-optical Kerr effect (MOKE) magnetometry. We have determined the magneto-crystalline anisotropy for various Heusler compounds as a function of the crystallographic order. Both four-fold and two-fold anisotropy contributions were found. Whereas the four-fold anisotropy is related to the cubic symmetry of the crystal, the origin of the occasional appearance of a two-fold anisotropy contribution is open. The investigation of the magneto-optical properties revealed that some of the Heusler compounds (such as Co2FeSi, Co2MnSi, Co2FeAl0.5Si0.5) present a strong quadratic magnetooptical Kerr effect (QMOKE) contribution, suggesting the presence of spin-orbit coupling of higher order. To date, the QMOKE signal we measured for Co2FeSi is the largest ever reported for any thin-film system. For the investigated samples the QMOKE contribution increases with increasing crystallographic L21 order. Investigation of ion irradiation of Heusler compounds was motivated by a possible tailoring of its magnetic and structural properties under light (He+) and heavy (Ga+) ion beam irradiation with the aim of improving and tailoring structural properties. We demonstrate that He+ irradiation can improve crystallographic ordering and the electronic structure of the Co2MnSi compound.
Projektbezogene Publikationen (Auswahl)
-
(2007): Huge quadratic magneto-optical Kerr effect and magnetization reversal in the Co 2 FeSi Heusler compound. In: J. Phys. D: Appl. Phys. 40 (6), S. 1563–1569
Hamrle, J.; Blomeier, S.; Gaier, O.; Hillebrands, B.; Schneider, H.; Jakob, G.; Postava, K. & Felser, C.
-
(2009): Determination of exchange constants of Heusler compounds by Brillouin light scattering spectroscopy: application to Co 2 MnSi. In: J. Phys. D: Appl. Phys. 42 (8), S. 84005
J. Hamrle, O. Gaier, S.-G. Min, B. Hillebrands, Y. Sakuraba, Y. Ando
-
(2009): Improvement of structural, electronic, and magnetic properties of Co2MnSi thin films by He+ irradiation. In: Appl. Phys. Lett. 94 (15), S. 152508
Gaier, O.; Hamrle, J.; Hillebrands, B.; Kallmayer, M.; Pörsch, P.; Schönhense, G.; Elmers, H. J.; Fassbender, J.; Gloskovskii, A.; Jenkins, C. A.; Felser, C.; Ikenaga, E.; Sakuraba, Y.; Tsunegi, S.; Oogane, M. & Ando, Y.
