Nanopatterning spin-textures: A route to reconfigurable magnonics

Magnonics is envisioned to enable highly efficient data transport and processing, by exploiting propagating perturbations in the spin-texture of magnetic materials. Despite the demonstrations of a plethora of proof-of-principle devices, the efficient excitation, transport and manipulation of spin-waves at the nanoscale is still an open challenge. Recently, we demonstrated that the spin-wave excitation and propagation can be controlled by nanopatterning reconfigurable spin-textures in a continuous exchange biased ferromagnetic film. Here, we show that by patterning 90° stripe-shaped magnetic domains, we spatially modulate the spin-wave excitation in a continuous film, and that by applying an external magnetic field we can reversibly â\u80\u9cswitch-offâ\u80\u9d the spin-wave excitation. This opens the way to the use of nanopatterned spin-textures, such as domains and domain walls, for exciting and manipulating magnons in reconfigurable nanocircuits

Intraoperative frozen section as a reliable ancillary technique in salivary gland surgery: A cross sectional study

Background. Salivary glands tumours are uncommon, frequently benign lesions, prevalently located in the parotid gland (80%). Surgical decision making is based on the patient's history, examination findings, imaging and fine needle aspiration (FNA). FNA is a pre-operative method with good ability in detecting malignancy. During surgery, therefore, Frozen section (FS) can differentiate benign lesions from malignant tumours, to reduce incorrect treatments, to increase the chances of conservative surgery and to better evaluate surgical margins. The aim of our study is to demonstrate the accuracy of the FS procedure in surgery of the salivary glands and to stress the need for dedicated pathology units specialized in lesions of the oral cavity. Methods. The study included 499 patients who underwent surgery from May 2005 and October 2014. An intra-operative frozen section procedure was done for 288 of them. All frozen sections were compared with the final results. The cases were classified by site, nature of the lesion and histotype, according to the WHO classification. Comparison was made between the intra-operative and the definitive diagnosis. Results. Of the 288 FS procedures, 259 were for neoplastic lesions, 199 of which benign and 60 malignant, and 29 for non-neoplastic lesions. Of the 259 neoplastic FS results, 2 were shown to be false positives and 2 were diagnosed as different malignant types. Of the 29 non-neoplastic FS results, 4 were false negatives. Conclusions. Our results showed that the accuracy of frozen section procedure is 98% for salivary glands tumors. The highest concordance between frozen section and the definitive diagnosis was for inflammatory processes (99%), pleomorphic adenoma (98%), Warthin's tumor (97%) and malignant neoplasms (96%). In conclusion, based on these findings, frozen section of the salivary glands may be proposed as a routine procedure and should be used in decision-making

Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating

Magnon spintronics is a prosperous field that promises beyond-CMOS technology based on elementary excitations of the magnetic order that act as information carriers for future computational architectures. Unidirectional propagation of spin waves is key to the realization of magnonic logic devices. However, previous efforts to enhance the Damon-Eshbach-type nonreciprocity did not realize (let alone control) purely unidirectional propagation. Here we experimentally demonstrate excitations of unidirectional exchange spin waves by a nanoscale magnetic grating consisting of Co nanowires fabricated on an ultrathin yttrium iron garnet film. We explain and model the nearly perfect unidirectional excitation by the chirality of the magneto-dipolar interactions between the Kittel mode of the nanowires and the exchange spin waves of the film. Reversal of the magnetic configurations of film and nanowire array from parallel to antiparallel changes the direction of the excited spin waves. Our results raise the prospect of a chiral magnonic logic without the need for fragile surface states

Control of spin-wave transmission by a programmable domain wall

Active manipulation of spin waves is essential for the development of magnon-based technologies. Here, we demonstrate programmable spin-wave filtering by resetting the spin structure of pinned 90° Néel domain walls in a continuous CoFeB film with abrupt rotations of uniaxial magnetic anisotropy. Using micro-focused Brillouin light scattering and micromagnetic simulations, we show that broad 90° head-to-head or tail-to-tail magnetic domain walls are transparent to spin waves over a broad frequency range. In contrast, magnetic switching to a 90° head-to-tail configuration produces much narrower and strongly reflecting domain walls at the same pinning locations. Based on these results, we propose a magnetic spin-wave valve with two parallel domain walls. Switching the spin-wave valve from an open to a closed state changes the transmission of spin waves from nearly 100 to 0%. Active control over spin-wave transport through programmable domain walls could be utilized in magnonic logic devices or non-volatile memory elements.Peer reviewe

Chapter 8: Magnetic Normal Modes of Nanopatterned Magnets Investigated by Both Wavevector- and Space-Resolved Brillouin Light Scattering Spectroscopy

Results from combined wavevector- and space-resolved Brillouin light scattering (BLS) investigation of the magnetic eigenmodes of nanopatterned magnetic elements and arrays of elements are presented and discussed. Two classes of elements are considered: Elliptical nanorings in the vortex and onion ground states, and uniformly magnetized rectangular elements arranged in close packed arrays in square “artificial spin ice” (ASI) geometries. A careful comparison of the calculated frequency and profiles, as well as of the scattering cross-section, of magnetic modes with the experimental data, allows the identification of the character of the different modes in terms of spatial symmetry and localization. Micromagnetics is used to analyze and identify possible modes that are active in the scattering process. Spatially resolved light scattering is used in the case of elliptical rings to create two-dimensional space-resolved maps of the mode intensity over the ring surface

Waveguides as sources of short-wavelength spin waves for low-energy ICT applications

Spin waves offer intriguing possibilities for transmitting and processing information in future low-power electronics. Most proposed devices, however, require the efficient excitation and detection of spin waves in the sub-micrometer range, that is a rather challenging task. In fact, coplanar and microstrip waveguides have been widely used in the past to excite and detect spin waves with wavelengths of tens of microns in thin films of both metallic ferromagnets and on magnetic insulators, but the scalability of these structures micrometer or sub-micrometer have not been investigated in detail. In this study, we present a combined experimental/computational study of a few possible input structures consisting of either symmetrical or asymmetrical coplanar waveguides on top of CoFe films, with widths going all the way down to 250 nm. The primary goal of this work is to present a case study, aiming to explore the limitations of waveguides in creating short-wavelength spin waves for future nanoelectronic applications. We use micro-focused Brillouin light scattering measurements and micromagnetic simulations to analyze the characteristics of the emitted spin waves, achieving reasonable agreement between experiment and simulations. We find that due to the inherently delocalized field distributions of waveguides, and also to the relatively high resistivity of narrow waveguides, they all show poor efficiency for generating spin waves with wavelength below about 2 μm, corresponding to frequencies above 10 GHz in a moderate external field. This means that the intensity of the generated spin waves for a given input power drops quickly for the frequency/wavelength range which is most relevant for emerging applications. This case study demonstrates many of the inherent inefficiencies and limitations of waveguide-based spin wave generation in this regime. Our work supports the conclusion that one may have to use a different mechanism for spin wave generation, exploiting multiferroic structures, spin-orbit torques or nanopatterned, multi-layered magnetic materials, all being the subject of intense current research