Asynchronous current-induced switching of rare-earth and transition-metal sublattices in ferrimagnetic alloys.

Ferrimagnetic alloys are model systems for understanding the ultrafast magnetization switching in materials with antiferromagnetically coupled sublattices. Here we investigate the dynamics of the rare-earth and transition-metal sublattices in ferrimagnetic GdFeCo and TbCo dots excited by spin-orbit torques with combined temporal, spatial and elemental resolution. We observe distinct switching regimes in which the magnetizations of the two sublattices either remain synchronized throughout the reversal process or switch following different trajectories in time and space. In the latter case, we observe a transient ferromagnetic state that lasts up to 2 ns. The asynchronous switching of the two magnetizations is ascribed to the master-agent dynamics induced by the spin-orbit torques on the transition-metal and rare-earth sublattices and their weak antiferromagnetic coupling, which depends sensitively on the alloy microstructure. Larger antiferromagnetic exchange leads to faster switching and shorter recovery of the magnetization after a current pulse. Our findings provide insight into the dynamics of ferrimagnets and the design of spintronic devices with fast and uniform switching.

Helical surface magnetization in nanowires: the role of chirality.

Nanomagnetism is nowadays expanding into three dimensions, triggered by the discovery of new magnetic phenomena and their potential use in applications. This shift towards 3D structures should be accompanied by strategies and methodologies to map the tridimensional spin textures associated. We present here a combination of dichroic X-ray transmission microscopy at different angles and micromagnetic simulations allowing to determine the magnetic configuration of cylindrical nanowires. We have applied it to permalloy nanowires with equispaced chemical barriers that can act as pinning sites for domain walls. The magnetization at the core is longitudinal and generates at the surface of the wire helical magnetization. Different types of domain walls are found at the pinning sites, which respond differently to applied fields depending on the relative chirality of the adjacent domains.

Novel interpretation of recent experiments on the dynamics of domain walls along ferrimagnetic strips.

Domain wall motion along ferrimagnets is evaluated using micromagnetic simulations and a collective-coordinates model, both considering two sublattices with independent parameters. Analytical expressions are derived for strips on top of either a heavy metal or a substrate with negligible interfacial Dzyaloshinskii-Moriya interaction. The work focuses its findings in this latter case, with a field-driven domain wall motion depicting precessional dynamics which become rigid at the angular momentum compensation temperature, and a current-driven dynamics presenting more complex behavior, depending on the polarization factors for each sublattice. Importantly, our analyses provide also novel interpretation of recent evidence on current-driven domain wall motion, where walls move either along or against the current depending on temperature. Besides, our approach is able to substantiate the large non-adiabatic effective parameters found for these systems.

Controlling All-Optical Helicity-Dependent Switching in Engineered Rare-Earth Free Synthetic Ferrimagnets.

All-optical helicity-dependent switching in ferromagnetic layers has revealed an unprecedented route to manipulate magnetic configurations by circularly polarized femtosecond laser pulses. In this work, rare-earth free synthetic ferrimagnetic heterostructures made from two antiferromagnetically exchange coupled ferromagnetic layers are studied. Experimental results, supported by numerical simulations, show that the designed structures enable all-optical switching which is controlled, not only by light helicity, but also by the relative Curie temperature of each ferromagnetic layer. Indeed, through the antiferromagnetic exchange coupling, the layer with the larger Curie temperature determines the final orientation of the other layer and so the synthetic ferrimagnet. For similar Curie temperatures, helicity-independent back switching is observed and the final magnetic configuration is solely determined by the initial magnetic state. This demonstration of electrically-detected, optical control of engineered rare-earth free heterostructures opens a novel route toward practical opto-spintronics.

Efficient and controlled domain wall nucleation for magnetic shift registers.

Ultrathin ferromagnetic strips with high perpendicular anisotropy have been proposed for the development of memory devices where the information is coded in tiny domains separated by domain walls. The design of practical devices requires creating, manipulating and detecting domain walls in ferromagnetic strips. Recent observations have shown highly efficient current-driven domain wall dynamics in multilayers lacking structural symmetry, where the walls adopt a chiral structure and can be driven at high velocities. However, putting such a device into practice requires the continuous and synchronous injection of domain walls as the first step. Here, we propose and demonstrate an efficient and simple scheme for nucleating domain walls using the symmetry of the spin orbit torques. Trains of short sub-nanosecond current pulses are injected in a double bit line to generate a localized longitudinal Oersted field in the ferromagnetic strip. Simultaneously, other current pulses are injected through the heavy metal under the ferromagnetic strip. Notably, the Slonczewski-like spin orbit torque assisted by the Oersted field allows the controlled injection of a series of domain walls, giving rise to a controlled manner for writing binary information and, consequently, to the design of a simple and efficient domain wall shift register.

Current-Induced Generation and Synchronous Motion of Highly Packed Coupled Chiral Domain Walls.

Chiral domain walls of Neel type emerge in heterostructures that include heavy metal (HM) and ferromagnetic metal (FM) layers owing to the Dzyaloshinskii-Moriya (DM) interaction at the HM/FM interface. In developing storage class memories based on the current induced motion of chiral domain walls, it remains to be seen how dense such domain walls can be packed together. Here we show that a universal short-range repulsion that scales with the strength of the DM interaction exists among chiral domain walls. The distance between the two walls can be reduced with the application of the out-of-plane field, allowing the formation of coupled domain walls. Surprisingly, the current driven velocity of such coupled walls is independent of the out-of-plane field, enabling manipulation of significantly compressed coupled domain walls using current pulses. Moreover, we find that a single current pulse with optimum amplitude can create a large number of closely spaced domain walls. These features allow current induced generation and synchronous motion of highly packed chiral domain walls, a key feature essential for developing domain wall based storage devices.

Universal chiral-triggered magnetization switching in confined nanodots.

Spin orbit interactions are rapidly emerging as the key for enabling efficient current-controlled spintronic devices. Much work has focused on the role of spin-orbit coupling at heavy metal/ferromagnet interfaces in generating current-induced spin-orbit torques. However, the strong influence of the spin-orbit-derived Dzyaloshinskii-Moriya interaction (DMI) on spin textures in these materials is now becoming apparent. Recent reports suggest DMI-stabilized homochiral domain walls (DWs) can be driven with high efficiency by spin torque from the spin Hall effect. However, the influence of the DMI on the current-induced magnetization switching has not been explored nor is yet well-understood, due in part to the difficulty of disentangling spin torques and spin textures in nano-sized confined samples. Here we study the magnetization reversal of perpendicular magnetized ultrathin dots, and show that the switching mechanism is strongly influenced by the DMI, which promotes a universal chiral non-uniform reversal, even for small samples at the nanoscale. We show that ultrafast current-induced and field-induced magnetization switching consists on local magnetization reversal with domain wall nucleation followed by its propagation along the sample. These findings, not seen in conventional materials, provide essential insights for understanding and exploiting chiral magnetism for emerging spintronics applications.

Older people's preferences for involvement in their own care: a qualitative study in primary health care in 11 European countries.

OBJECTIVE: The aim of the study was to explore the views of people aged over 70 years on involvement in their primary health care in 11 different European countries. METHODS: Older patients were asked about their views on patient involvement in a face-to-face interview. All interviews were audio-recorded, transcribed and analysed in accordance with the principles of 'qualitative content analysis'. An international code list was used. RESULTS: Four hundred and six primary care patients aged between 70 and 96 years were interviewed. Their views could be categorized into four major groups: doctor-patient interaction, GP related topics, patient related issues and contextual factors. CONCLUSION: People over 70 do want to be involved in their care but their definition of involvement is more focussed on the 'caring relationship', 'person-centred approach' and 'receiving information' than on 'active participation in decision making'. PRACTICE IMPLICATIONS: The desire for involvement in decision making is highly heterogeneous so an individual approach for each patient in the ageing population is needed. Future research and medical education should focus on methods and training to elicit older patients' preferences. The similar views in 11 countries suggest that methods for enhancing patient involvement in older people could be internationally developed and exchanged.

Elderly patients' and GPs' views on different methods for patient involvement: an international qualitative interview study.

BACKGROUND: Elderly patients' interaction with the GP may be improved through patient involvement techniques, and there is a variety of such techniques which improve patients' involvement in their own care, although little is known about their acceptability. OBJECTIVES: The aim of this study was to identify barriers and facilitators for using patient information leaflets and patient satisfaction questionnaires as methods for increasing elderly patients' involvement in general practice care by comparing their views with the GPs' views on these two types of methods. METHODS: In seven countries (Austria, Denmark, Germany, The Netherlands, Portugal, Slovenia and Switzerland) 146 GPs and 284 patients aged 70 and over were interviewed about the use and the acceptability of these two methods. Interviewers followed a semi-structured interview guide, and all interviews were tape-recorded and transcribed verbatim. RESULTS: The arguments for using patient satisfaction questionnaires were that they would provide the GP with more information, function as a basis for change, increase patients' self-confidence and make them more conscious of what to expect. Barriers for their use were cognitive impairment among patients, fear that they would not answer honestly and opposition to written material. The arguments for patient information leaflets were that they could support patients' memories, educate patients and promote their self-responsibility. The barriers were cognitive impairment among patients and fear that they would give them false impressions of what to expect. CONCLUSION: Both instruments were generally well accepted by both GPs and patients. Their use seemed to be dependent upon the individual GP's attitude and the patients' cognitive capacities.