Yu. A. Dudin

Bio: Yu. A. Dudin is an academic researcher from N. I. Lobachevsky State University of Nizhny Novgorod. The author has contributed to research in topics: Irradiation & Coercivity. The author has an hindex of 2, co-authored 8 publications receiving 17 citations.

Modification of Magnetic Properties of a CoPt Alloy by Ion Irradiation

Abstract: The effect of ion irradiation on magnetic properties of films of the ferromagnetic CoPt alloy fabricated by electron-beam evaporation has been studied. It is found that the coercive force decreases and the lateral component of the easy-magnetization axis increases as the He+ ion fluence increases from 1 × 1013 to 1 × 1016 cm–2. It is shown by magnetic-force microscopy and the Mandelstam–Brillouin spectroscopy that the formation of isolated circle domains which are magnetic skirmions in the CoPt layer is activated at certain ion-irradiation fluence (3 × 1014 cm–2).

Effect of Ion Irradiation on the Magnetic Properties of CoPt Films

Abstract: The possibility of using implantation of 20-keV He+ ions for modification of the domain structure and magnetic properties of CoPt films (formed by the electron-beam evaporation method) with different cobalt contents (Co0.45Pt0.55 and Co0.35Pt0.65) has been investigated. A decrease in the coercive field (narrowing of the hysteresis loop in the magnetic-field dependences of the Faraday angle and magnetization) with an increase in the He+ ion fluence from 2 × 1014 to 4 × 1014 cm–2 has been found for the irradiated CoPt samples of both compositions. The residual magnetization of the Co0.35Pt0.65 films coincides with the saturation magnetization, and a decrease in the residual magnetization is observed for Co0.45Pt0.55. It is shown by magnetic force microscopy that the largest number of round isolated domains (skyrmions) for the Co0.45Pt0.55 alloy are formed when the ion fluence increases to 3 × 1014 cm–2, while 360-degree domain walls (1D skyrmions) are observed along with round isolated domains for the Co0.35Pt0.65 films irradiated with a He+ fluence of 4 × 1014 cm–2. An analysis of CoPt films by Mandelstam–Brillouin spectroscopy revealed an increase in the shift between the Stokes and anti-Stokes components of the spectrum and a significant enhancement of the Dzyaloshinski–Moriya interaction in the irradiated samples. Model calculations performed using the SRIM program showed that the ion irradiation facilitates asymmetric mixing of Co and Pt atoms in CoPt films, which may underlie the mechanism of the observed effects of ion irradiation on their magnetic properties and domain structure.

Manufacturing of Sputtering Composite Targets Containing Phases of Co 2 FeSi or Co 2 MnSi Heusler Alloy

Abstract: The paper presents a method for manufacturing mechanically strong sputtering composite targets containing the phase of the Co2FeSi or Co2MnSi Heusler alloy of the stoichiometric composition, which can be used for fabrication of spin electronic devices by high-frequency magnetron deposition and pulsed laser deposition of thin films.

Photoluminescence of Si0.9Ge0.1O2 and GeO2 films irradiated with silicon ions

Abstract: We have studied the photoluminescence (PL) of GeO2 and 90 mol % SiO2-10 mol % GeO2 films synthesized by method of RF magnetron sputtering and then irradiated with silicon ions and annealed. The PL of silicon-implanted GeO2 films, related to the presence of Si nanocrystals (nc-Si), was observed for the first time. It is established that the transformation of the defect centers responsible for the PL in the spectral range 350–600 nm, as well as the formation of nc-Si emitting in the region of 700–800 nm, significantly depend on the matrix type. In particular, the PL intensity at 700–800 nm in 90 mol % SiO2-10 mol % GeO2 films is weak. The role of the isovalent substitution of Si and Ge atoms in the transformation of defect centers and the formation of nc-Si is discussed.

High-temperature ferromagnetism in a new n -type Fe-doped ferromagnetic semiconductor (In,Fe)Sb

Abstract: Over the past two decades, intensive studies on various ferromagnetic semiconductor (FMS) materials have failed to realize reliable FMSs that have a high Curie temperature (T C > 300 K), good compatibility with semiconductor electronics, and characteristics superior to those of their nonmagnetic host semiconductors. Here, we demonstrate a new n-type Fe-doped narrow-gap III–V FMS, (In1− x ,Fe x )Sb. Its T C is unexpectedly high, reaching ~335 K at a modest Fe concentration (x) of 16%. The anomalous Hall effect and magnetic circular dichroism (MCD) spectroscopy indicate that the high-temperature ferromagnetism in (In,Fe)Sb thin films is intrinsic and originates from the zinc-blende (In,Fe)Sb alloy semiconductor.

Time-resolved photoluminescence of implanted SiO2:Si+ films

Abstract: In this paper we present results of a low-temperature time-resolved photoluminescence (PL) investigation of thin SiO2 films implanted with silicon ions. In addition to the luminescence of well-known ODCs, some other bands are present in the low-energy region of PL spectra that are attributed to silicon nanoclusters (quantum dots – SiQDs), excitons and hydrogen-related species (HRS). Specific features of SiQD and HRS bands are the nanosecond kinetics and unusual “stepped” PL excitation spectrum in the 3.5–7.5 eV range. The possible origin of discovered phenomena is discussed. The obtained results are interpreted taking into account the interference of exciting radiation and dimensional quantization effects.

Chemical trend in the electronic structure of Fe-doped III–V semiconductors and possible origin of ferromagnetism: A first-principles study

Abstract: The electronic structures of Fe-doped III–V semiconductors were studied by first-principles supercell calculation. It was found that their electronic structures are basically the same as those of Mn-doped ones except that the extra electron of Fe compared to Mn occupies either majority-spin p- d hybridized antibonding states ( t a , ↑) or minority-spin e states ( e ↓), and that the center of gravity of the d partial density of states is higher for Fe than for Mn. The present calculations suggest that ferromagnetism appears when the e ↓ states start to be occupied. The band splitting due to s– d hybridization was found to be significantly smaller than that due to p- d hybridization. This indicates that the s , p- d exchange interaction is not responsible for the high-temperature ferromagnetism of the Fe-doped ferromagnetic semiconductors even in n-type compounds.

Unveiling the effect of annealing on magnetic properties of nanocrystalline Half-metallic Heusler Co2FeSi alloy glass-coated microwires

Abstract: In this article, we present a new Co2FeSi glass-coated microwire obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of a mixture of bcc phase (lattice parameter, a = 5.640 Å, crystalline grain size, Dg = 17.8 nm) in as-prepared sample. The annealing temperature was fixed at 873 K, and the annealing time was 1 and 6 h. The annealing resulted in a significant increase of such nano-grains up to (31.6 nm). Perfect square hysteresis loops have been observed in all annealed samples at a wide temperature range (55–400 K) that are not seen in the as prepared sample. The thermal magnetic behavior for the annealed samples shows dramatic magnetic behavior at low temperature. Large irreversibility magnetic behavior with a blocking temperature (Tb = 150 K) has been observed for annealed sample for 1 h. Critical temperatures of 155 K and 105 K have been detected for annealed samples for 1 h and 6 h, respectively, where the behavior of M−H loops, coercivity and remanence changed. Below the critical point the M−H shows wasp-waisted, multistep magnetic behavior and complex magnetic reversal mechanism is supposed. The anomalous magnetic behavior is due to the coexistence of the ordered and disordered phases induced by annealing conditions below the room temperature. The difference in the magnetization behaviour, remanence, and coercivity values for Co2FeSi glass-coated microwires samples indicates the influence of internal stresses created by the presence of the glass coating. These finding opens the door to design spintronic devices based on the magnetization switching.