It is widely accepted at present that the electronics based information-processing technology has fundamental limitations. A promising alternative to electronic excitations are the spin waves on magnetically ordered systems, which usher a potentially powerful solution towards fabricating devices that transmit and process information (Khitun and Wang 2006). This approach to information-processing technology, known as magnonics, is rapidly growing (Kruglyak and Hicken 2006, Choi et al. 2007), and key magnonic components such as wave guides, emitters, nanojunctions and filters (Khater et al. 2011) are currently explored as basic elements of magnonic circuitry. This paper deals with the theory for ballistic spin wave transport across ultrathin iron-gadolinium nanojunctions, ..-Fe] [Gd]nML [Fe-.. , which are known to present structural interfacial disorder; n is the number of gadolinium monoatomic planes between the iron leads. It is shown that our PFMT-DNCLCPA theory gives a detailed and complete analysis for the properties of the ballistic transmission, and the corresponding reflection and absorption spectra across the structurally disordered nanojunction. We have developed the dynamic non-local coherent phase approximation (DNLCPA), and the phase field matching theory (PFMT) methods (Ghader and Khater 2013), and fully integrate them to study the ballistic spin wave transport across such nanojunctions. The DNCLPA method yields a full description of the dynamics of the spin wave excitations localized on the nanojunction, and their corresponding life-times and local density of states. These are excitations propagating laterally in the nanojunction atomic planes with finite life-times, but their fields are localized along the direction normal to the nanojunction. Moreover, the calculations determine the reflection, transmission, and absorption spectra for the spin waves incident at any arbitrary angle from the iron leads onto the nanojunction. The PFMT-DNCLCPA calculated results vary with nanojunction thickness. In particular, the normal incidence transmission spectra present no absorption effects and resonance assisted maxima are identified, notably at low frequencies at microscopic and submicroscopic wavelengths, which shift to lower frequencies with increasing nanojunction thickness. The results render these systems interesting for potential applications in magnonic circuitry. Fig.1 Calculated DNLCPA-PFMT reflection and transmission spectra for spin waves at normal incidence from the iron leads onto the magnetic ..-Fe] [Gd]3ML [Fe-.. nanojunction, as a function of the spin wave energies in units J(Fe-Fe)S(Fe) of the iron exchange and its spin. Note the transmission assisted maxima. Fig.2 Calculated absorption spectra for obliquely incident spin waves at the nanojunction cited in Fig.1, due to its structural interfacial disorder. Acknowledgements: The authors acknowledge QNRF financial support for the NPRP 4-184-1-035 project. References - S. Choi, K.S. Lee, K.Y. Guslienko, S.K. Kim, Phys. Rev. Lett. 98, 087205 (2007) - D. Ghader and A. Khater, to be published (2013) - A. Khater, B. Bourahla, M. Abou Ghantous, R. Tigrine, R. Chadli, Eur. Phys. J. B: Cond. Matter 82, 53 (2011) - A. Khitun and K. L. Wang, Proceedings of the Third International Conference on Information Technology, New Generations ITNG, 747 (2006) - V.V. Kruglyak and R.J. Hicken, J. Magn. Magn. Mater. 306, 191 (2006)


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