Defect-induced high-temperature ferromagnetism in Si _1-x Mn _x (x ≈ 0.52−0.55) alloys

Abstract

We present a comparative study of the anomalous Hall effect (AHE) and of the transverse Kerr effect (TKE) in the nonstoichiometric alloys. The data on AHE and TKE are consistent with each other and clearly indicate the intrinsic above room-temperature ferromagnetic order in the studied samples. We argue that this order is not produced by the phase segregation effects, but rather has a global character, while even a small level of the nonstoichiometry in alloys drastically changes their magnetic, electrical, optical and magneto-optical properties as compared to those of the stoichiometric manganese monosilicide MnSi. We propose a qualitative explanation of the obtained experimental results in the frame of the model of defect-induced ferromagnetic order using the first-principles calculations of the electronic and magnetic structure of the system.

Ferromagnetism of MnxSi1-x(x ∼ 0.5) films grown in the shadow geometry by pulsed laser deposition method

“…1 Recently we reported the HT FM appearance with T C ≈ 330 K in 70 nm thick Mn x Si 1-x (x ≈ 0.52-0.55) films grown on the Al 2 O 3 (0001) substrates by pulsed laser deposition (PLD) technique. 3,4 We argued that the observed HT FM has a defect-induced nature: it is due to formation of local magnetic moments on the Si vacancies inside the MnSi matrix and the strong exchange coupling between these moments mediated by spin fluctuations of itinerant carriers. 12 The Mn x Si 1-x films in 3,4 were deposited at a relatively slow deposition rate (∼2 nm/min) using PLD method in a conventional "direct" geometry (DG) when the surface of Al 2 O 3 (0001) substrate is exposed to the Mn-Si laser plume.…”

“…3,4 We argued that the observed HT FM has a defect-induced nature: it is due to formation of local magnetic moments on the Si vacancies inside the MnSi matrix and the strong exchange coupling between these moments mediated by spin fluctuations of itinerant carriers. 12 The Mn x Si 1-x films in 3,4 were deposited at a relatively slow deposition rate (∼2 nm/min) using PLD method in a conventional "direct" geometry (DG) when the surface of Al 2 O 3 (0001) substrate is exposed to the Mn-Si laser plume. Accordingly to atomic-force microscopy (AFM) measurements, the structure of thus grown films is mosaic, with the crystallite size ∼0.5-1 µm.…”

“…[1][2][3][4][5][6][7] The perfect single crystal ε-MnSi with B20-type of structure possesses at low temperatures (≤ 30 K) intriguing magnetic and transport phenomena caused by formation of new magnetic quasiparticles -skyrmions (see Ref. 6 and references therein).…”

“…On the other hand, the Mn x Si 1-x (x≈0.5) thin layers grown on Si(001) or Al 2 O 3 (0001) substrates demonstrate the high-temperature (HT) ferromagnetism (FM) with the Curie temperature T c of the order of room temperature. [2][3][4] This fact is in contrast to the case of bulk ε-MnSi single crystal, where only the low-temperature (LT) FM was reported with T C ≈ 30 K. 8,9 The HT FM order at x 0.506 (that just corresponds to the single crystal ε-MnSi belonging to berthollides 9,10 ) was observed in the Mn x Si 1-x /Si(001) structures but at enough small Mn x Si 1-x film thickness less than one ε-MnSi monolayer. 2,11 This order is explained by the formation of c-MnSi phase with B2-like (CsCl) crystal structure stabilized with tetragonal distortion due to favorable lattice mismatch between the film and substrate.…”

Magnetic anisotropy of polycrystalline high-temperature ferromagnetic Mn x Si 1-x (x≈0.5) alloy films

“…In particular, Si-Mn alloys demonstrating unusual magnetic and transport properties [2][3][4][5][6][7][8] have especial interest to engineer non-conventional integrated-circuit elements.…”