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### Abstract

Using the effective field theory (EFT) and mean field theory (MFT), we investigate the magnetic properties of the nanojunction system...Co][Co_(1-c)Gd_c]_l ][Co]_l [Co_(1-c)Gd_c ]_l [Co... between Co leads. The amorphous ][Co_(1-c)Gd_c]_l ] composite nanomaterial is modeled as a homogeneous random alloy of concentrations &quot;c&quot; on an hcp crystal lattice, and &quot;l&quot; is the number of its corresponding hcp (0001) atomic planes. In particular, EFT determines the appropriate exchange constants for Co and Gd by computing their single-atom spin correlations and magnetizations, in good agreement with experimental data in the ordered phase. The EFT results for the Co magnetization in the leads serve to seed the MFT calculations for the nanojunction from the interfaces inward. This combined analysis yields the sublattice magnetizations for Co and Gd sites, and compensation effects, on the individual nanojunction atomic planes, as a function of the alloy concentration, temperature and nanojunction thicknesses. We observe that the magnetic variables are different for the first few atomic planes near the nanojunction interfaces, but tend to limiting solutions in the core planes. The EFT and MFT calculated exchange constants and sublattice magnetizations are necessary elements for the computation of the spin dynamics for this nanojunction system, using a quasi-classical treatment over the spin precession amplitudes at temperatures distant from the critical temperatures of $Co_{1-c}Gd_c$ alloy. The full analysis in the virtual crystal approximation (VCA) over the magnetic ground state of the system yields both the spin waves (SWs) localized on the nanojunction, and also the ballistic scattering and transport across the nanojunction for SWs incident from the leads by applying the phase field matching theory (PFMT). The model results demonstrate the possibility of resonance assisted maxima for the SW transmission spectra owing to interactions between the incident SWs and the localized spin resonances on the nanojunction. The spectral transmission results for low frequency spin waves are of specific interest for experimentalist, because these lower frequency SWs correspond to submicroscopic wavelengths which are of present interest in experimental magnonics research and the VCA is increasingly valid as a model approximation for such frequencies. Fig.1: Calculated spin variables sigma_Co and sigma_Gd, in the first layer of [Co_(1-c}Gd_(c)]_2[Co]_2[Co_(1-c}Gd_(c)]_2 layer nanojunction as a function of kT in meV. Fig.2: The total reflection R and transmission T cross sections associated with the scattering at the nanojunction for the cobalt leads SW modes 1, 2, with the selected choices of incident angle (phi_z, phi_y). Acknowledgements: The authors acknowledge QNRF financial support for the NPRP 4-184-1-035 project.

/content/papers/10.5339/qfarf.2013.ICTP-037
2013-11-20
2021-03-06