Magneto-optical investigations and ion beam-induced modification of materials with high spin polarization
Final Report Abstract
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.
Publications
- (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
J. Hamrle, S. Blomeier, O. Gaier, B. Hillebrands, H. Schneider, G. Jakob, K. Postava, C. Felser
(See online at https://doi.org/10.1088/0022-3727/40/6/S09) - (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
O. Gaier, J. Hamrle, B. Hillebrands, M. Kallmayer, P. Pörsch, G. Schönhense, H. J. Elmers, J. Fassbender, A. Gloskovskii, C. A. Jenkins, C. Felser, E. Ikenaga, Y. Sakuraba, S. Tsunegi, M. Oogane, Y. Ando
(See online at https://doi.org/10.1063/1.3119188)
