Microstrip line ferromagnetic resonance and Brillouin light scattering investigations of magnetic properties ofCo2MnGeHeusler thin films

Abstract

Co 2 MnGe films of different thicknesses ͑34, 55, and 83 nm͒ were grown by rf sputtering at 400°C on single-crystal Al 2 O 3 corundum substrates showing an in-plane c axis. Their dynamic magnetic properties were studied using conventional and microstrip line ͑MS͒ ferromagnetic resonances ͑FMRs͒, as well as Brillouin light scattering ͑BLS͒ techniques. The effective magnetizations and gyromagnetic factors are first deduced from the resonance spectra involving the uniform magnetic mode under in-plane and out-of-plane magnetic applied fields. The angular dependence of the frequency, measured under a weak in-plane magnetic applied field, then allows deriving of the parameters describing the in-plane magnetic anisotropy. In the 34-and 55-nm-thick films, its behavior is described assuming a magnetic energy density showing an orthorhombic symmetry with a twofold axis normal to the film and planar anisotropy axes at Ϯ / 4 of the c axis of the substrate; however, due to the comparative deduced values of the pertinent coefficients, this energy density is predominantly tetragonal. In the thickest film ͑83 nm͒, one of the planar anisotropy axes is parallel to c and approximate tetragonal symmetry is no more observed. Moreover, the orthorhombic symmetry is not completely fulfilled and a small misalignment between the principal directions connected to the uniaxial and the fourfold energy terms appears. Finally, the perpendicular surface standing modes, which are observed in MS-FMR and in BLS spectra, allow evaluation of the exchange stiffness constant. Good agreement between BLS and MS-FMR measurements has been found.

Structural and magnetic properties of Co2MnSi thin films

“…In this latter case the relationship between the magnetic anisotropy and the crystal structure of the film plays an important role. This was pointed out in our previously published work concerning a parent compound, Co 2 MnGe [18,19]. The replacement of Ge by Si, in films intentionally elaborated under identical conditions, is expected to give rise to similar conclusions, as confirmed in the following paper.…”

“…The regions related to the observed maxima correspond to orientation variants which can be grouped into four families. Two of them were observed in a previous study [18,19] concerning thin films of a neighboring Heusler compound, Co 2 MnGe, prepared using an identical protocol: in the first one the threefold ½111 or ½11 1 axis is oriented along the c rhombohedral direction of the sapphire substrate, thus defining two kinds of distinct domains, respectively, characterized by their [001] axis inclined at þ54.58 or at À54.58 with respect to this c orientation. The second family is rotated by 908 from the first one and also contains two variants.…”

“…As in Ref. [18], it is convenient to introduce the effective magnetization 4pM eff ¼ 4pM s À 2K ? /M s , the uniaxial in-plane anisotropy field H u ¼ 2K u /M s and the fourfold in-plane anisotropy field…”

“…[18], we assume a magnetic energy density which, in addition to Zeeman, demagnetizing and exchange terms, is characterized by the following anisotropy contribution:…”

“…The dynamic magnetic properties were scrutinized with the help of a previously described MS-FMR [18,19] setup. The resonance frequencies are obtained from a fit assuming a lorentzian derivative shape of the recorded spectra.…”