arXiv:1510.02634v1 [cond-mat.mtrl-sci] 9 Oct 2015 Magnetic anisotropy of polycrystalline high-temperature ferromagnetic Mn x Si 1−x ( x ≈ 0.5) alloy films A.B. Drovosekov a,∗ , N.M. Kreines a , A.O. Savitsky a , S.V. Kapelnitsky b,c , V.V. Rylkov b,d , V.V. Tugushev b,e , G.V. Prutskov b , O.A. Novodvorskii f , A.V. Shorokhova f , Y. Wang g , S. Zhou g a P.L.Kapitza Institute for Physical Problems RAS, Kosygina St. 2, 119334 Moscow, Russia b National Research Centre ”Kurchatov Institute”, Kurchatov Sq. 1, 123182 Moscow, Russia c Institute of Physics and Technology RAS, Nakhimovsky av. 36, build 1, 117218 Moscow, Russia d Kotel’nikov Institute of Radio Engineering and Electronics RAS, 141190 Fryazino, Moscow region, Russia e Prokhorov General Physics Institute RAS, Vavilov St. 38, 119991 Moscow, Russia f Institute on Laser and Information Technologies RAS, Svyatoozerskaya St. 1, 140700 Shatura, Moscow region, Russia g Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328 Dresden, Germany Abstract A set of thin film Mn x Si 1−x alloy samples with different manganese concentration x ≈ 0.44 − 0.63 grown by the pulsed laser deposition (PLD) method onto the Al 2 O 3 (0001) substrate was investigated in the temperature range 4 − 300 K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies ( f = 7 − 60 GHz) and magnetic fields (H = 0 − 30 kOe). For samples with x ≈ 0.52 − 0.55, FMR data show clear evidence of ferromagnetism with high Curie temperatures T C ∼ 300 K. These samples demonstrate complex and unusual character of magnetic anisotropy described in the frame of phenomenological model as a combination of the essential second order easy plane anisotropy contribution and the additional forth order uniaxial anisotropy contribution with easy direction normal to the film plane. We explain the obtained results by a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch. The existence of extra strains at the crystallite boundaries leads to an essential inhomogeneous magnetic anisotropy in the film plane. Keywords: magnetic Mn x Si 1−x alloy films, magnetic anisotropy, ferromagnetic resonance PACS: 75.70.-i, 75.30.Gw, 76.50.+g 1. Introduction Development of Si based magnetic semiconductor materials for spintronic applications attracts a lot of attention, since these materials can be easily incorporated into the existing microelec- tronic technology [1]. In particular, Si-Mn alloys demonstrat- ing unusual magnetic and transport properties [2–8] have es- pecial interest to engineer non-conventional integrated-circuit elements. However, there exist significant technological and funda- mental obstacles to adapt Si-Mn based elements to the needs of spintronic. At relatively low Mn content in Mn x Si 1−x al- loys ( x = 0.05 − 0.1), the ferromagnetism (FM) at above room temperature has been revealed. But these alloys turn out to be strongly inhomogeneous materials due to their phase segrega- tion, leading to formation of isolated magnetic MnSi 1.7 precip- itate nanoparticles with the Mn content x ≈ 0.35 in Si matrix [2]. In such alloys, anomalous Hall effect testifying the spin polarization of carriers is absent, that makes impossible to use these materials in spintronic applications. At the same time, the fabrication of well-reproducible homogeneous magnetic alloys with high Mn content x ≈ 0.35 is difficult because of the variety ∗ Corresponding author Email address: drovosekov@kapitza.ras.ru (A.B. Drovosekov) of stable phases of high MnSi y silicides (not less than five) with the close content of components (y = 1.72 − 1.75) [6, 7]. In contrast, nonstoichiometric Mn x Si 1−x alloys with high Mn content ( x ≈ 0.5, i.e. close to stoichiometric MnSi) are not inclined to a phase segregation and formation of isolated mag- netic precipitates, so they seem more promising for spintronic applications than dilute Mn x Si 1−x alloys. Recently we have found that in thin films of such concentrated alloys, the Curie temperature T C increases by more than an order of magnitude as compared with bulk MnSi (T C ≈ 30 K) [6]. Comparative stud- ies of anomalous Hall effect and transverse Kerr effect showed that the ferromagnetic transition in Mn x Si 1−x ( x ≈ 0.52 − 0.55) alloys occurring at T ∼ 300 K, has a global nature and is not as- sociated with the phase segregation [7]. Besides high T C values, the films investigated in [6, 7] show large values of saturation magnetization reaching ≈ 400 emu/cm 3 at low temperatures. The observed magnetization value corresponds to ≈ 1.1 µ B /Mn, that significantly exceeds the value 0.4 µ B /Mn typical for bulk MnSi crystal [9]. High temperature FM in Mn x Si 1−x ( x ≈ 0.5) alloys has been qualitatively interpreted [6, 7] in frame of the early proposed model for dilute Mn x Si 1−x alloys [3], i.e. in terms of com- plex defects with local magnetic moments embedded into the matrix of itinerant FM. However, many details of FM order in Mn x Si 1−x ( x ≈ 0.5) alloys are still not completely clear due to 1