We perform a study of domain walls in Co/Irn/Pt(111) (n = 0, . . . , 6) films by a combined approach of first-principles calculations and spin dynamics simulations. We determine the tensorial exchange interactions and the magnetic anisotropies for the Co overlayer in both FCC and HCP geometries, depending on the number of Ir buffer layers. We find strong ferromagnetic nearest-neighbor isotropic exchange interactions between the Co atoms and an out-of-plane magnetic anisotropy for the films in FCC geometry. Our simulations show that the magnetic domain walls are of Néel type, and their rotational sense (chirality) is changed upon the insertion of an Ir buffer layer as compared to the pristine Co/Pt(111) system. Our spin dynamics simulations indicate a twisting of the spins with respect to the planar domain wall profile on the triangular lattice. We discuss this domain wall twisting using symmetry arguments and in terms of an appropriate micromagnetic continuum model considering extra energy terms compared to the available literature.
I. INTRODUCTIONEffective spin models are widely used to investigate the magnetic properties of solids. The breaking of inversion symmetry in noncentrosymmetric crystals, at surfaces or interfaces and the presence of the spin-orbit coupling lead to the appearance of an anisotropic exchange term beyond the isotropic Heisenberg interaction, which is known as the Dzyaloshinskii-Moriya (DM) interaction [1,2]. In collinear ferromagnetic systems, this type of interaction provides domain walls (DWs) with a chiral character [3][4][5][6][7][8], plays a key role in DW dynamics [9][10][11][12], and leads to the stabilization of isolated chiral skyrmions [13][14][15][16]. It may also cause the formation of noncollinear magnetic states [7,17] such as spin spirals [18,19] and condensated skyrmionic phases [16,[20][21][22][23][24]. Furthermore, the DM interaction induces an asymmetry in the spin wave spectrum of thin ferromagnetic films [25,26]. Based on this asymmetry, recently extensive experimental efforts have been directed towards the measurement of the interfacial DM interaction by using inelastic light scattering [27][28][29], highly resolved spinpolarized electron energy loss [30] or propagating spin wave spectroscopy [31].The current-driven motion of domain walls is mainly investigated in ultrathin films and multilayers, paving the way for future applications in spintronic and logic devices [32,33]. In these systems, heavy nonmagnetic elements provide the strong spin-orbit coupling necessary for the appearance of the DM interaction in the adjacent magnetic layers. Using the micromagnetic energy functional determined by Dzyaloshinskii[34], it has been demonstrated [3,35,36] that the DM interaction prefers a cycloidal or Néel-type rotation of spins within a domain wall in the C nv symmetry class to which the majority of these systems belong. The rotational plane of domain walls is determined by the competition between the DM interaction and the magnetostatic dipolar interaction preferring a h...
Carbon diffusion in a SiO 2 /Si system was investigated. The source was provided by chemical vapor deposition of a hydrogenated amorphous carbon layer onto the oxide at low temperature. From layers with low oxygen content, no carbon outdiffusion was detected up to 1190 • C. If the O content was high, the diffusion would start suddenly at 1140 • C, and carbon accumulation would be found on the Si side of the SiO 2 /Si interface in the form of SiC precipitates. These results are interpreted by assuming oxygen-assisted dissociation of carbon atoms from the carbon layer in form of CO molecules, fast CO diffusion through SiO 2 and an exothermic reaction of CO with Si. No carbon segregation was found in SiO 2 . Consequences of carbon island formation during SiC oxidation are pointed out.
The properties of carbon films deposited by high intensity pulsed Nd:Glass laser are reported. Different measurements like TEM, SIMS, EELS, XPS and AFM showed the formation of a high-density amorphous carbon layer with good protection against chemically aggressive alkaline solutions. We demonstrated that instead of excimer lasers, Nd-based solid state lasers can be used successfully for preparation of high quality amorphous carbon films.
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