42 research outputs found
Indirect localization of a magnetic domain wall mediated by quasi walls
International audienceThe manipulation of magnetic domain walls in thin films and nanostructures opens new opportunities for fundamental and applied research. But controlling reliably the position of a moving domain wall still remains challenging. So far, most of the studies aimed at understanding the physics of pinning and depinning processes in the magnetic layer in which the wall moves (active layer). In these studies, the role of other magnetic layers in the stack has been often ignored. Here, we report an indirect localization process of 180° domain walls that occurs in magnetic tunnel junctions, commonly used in spintronics. Combining Scanning Transmission X-Ray Microscopy and micromagnetic simulations, magnetic configurations in both layers are resolved. When nucleating a 180° domain wall in the active layer, a quasi wall is created in the reference layer, atop the wall. The wall and its quasi wall must then be moved or positioned together, as a unique object. As a mutual effect, a localized change of the magnetic properties in the reference layer induces a localized quasi wall in the active layer. The two types of quasi walls are shown to be responsible for an indirect localization process of the 180° domain wall in the active layer
Domain-wall motion induced by spin transfer torque delivered by helicity-dependent femtosecond laser
In magnetic wires with perpendicular anisotropy, moving domain with only
current or only circularly polarized light requires a high power. Here, we
propose to reduce it by using both short current pulses and femtosecond laser
pulses simultaneously. The wires were made out of perpendicularly magnetized
film of Pt/Co/Ni/Co/Pt. The displacement of the domain wall is found to be
dependent on the laser helicity. Based on a quantitative analysis of the
current-induced domain wall motion, the spin orbit torque contribution can be
neglected when compared to the spin transfer torque contribution. The effective
field of the spin transfer torque is extracted from the pulsed field domain
wall measurements. Finally, our result can be described using the
Fatuzzo-Labrune model and considering the effective field due to the polarized
laser beam, the effective field due to spin transfer torque, and the Gaussian
temperature distribution of the laser spot.Comment: 14 pages, 4 figure
Fragmentation of magnetism in artificial kagome dipolar spin ice
Geometrical frustration in magnetic materials often gives rise to exotic,
low-temperature states of matter, like the ones observed in spin ices. Here we
report the imaging of the magnetic states of a thermally-active artificial
magnetic ice that reveal the fingerprints of a spin fragmentation process. This
fragmentation corresponds to a splitting of the magnetic degree of freedom into
two channels and is evidenced in both real and reciprocal space. Furthermore,
the internal organization of both channels is interpreted within the framework
of a hybrid spin-charge model that directly emerges from the parent spin model
of the kagome dipolar spin ice. Our experimental and theoretical results
provide insights into the physics of frustrated magnets and deepen our
understanding of emergent fields through the use of tailor-made magnetism.Comment: 9 pages, 5 figures. Published version available on the Nat. Comm. web
site:
http://www.nature.com/ncomms/2016/160513/ncomms11446/full/ncomms11446.htm
Tunable stochasticity in an artificial spin network
Metamaterials present the possibility of artificially generating advanced
functionalities through engineering of their internal structure. Artificial
spin networks, in which a large number of nanoscale magnetic elements are
coupled together, are promising metamaterial candidates that enable the control
of collective magnetic behavior through tuning of the local interaction between
elements. In this work, the motion of magnetic domain-walls in an artificial
spin network leads to a tunable stochastic response of the metamaterial, which
can be tailored through an external magnetic field and local lattice
modifications. This type of tunable stochastic network produces a controllable
random response exploiting intrinsic stochasticity within magnetic domain-wall
motion at the nanoscale. An iconic demonstration used to illustrate the control
of randomness is the Galton board. In this system, multiple balls fall into an
array of pegs to generate a bell-shaped curve that can be modified via the
array spacing or the tilt of the board. A nanoscale recreation of this
experiment using an artificial spin network is employed to demonstrate tunable
stochasticity. This type of tunable stochastic network opens new paths towards
post-Von Neumann computing architectures such as Bayesian sensing or random
neural networks, in which stochasticity is harnessed to efficiently perform
complex computational tasks.Comment: 24 pages, 10 figure
Intrinsic versus shape anisotropy in micro-structured magnetostrictive thin films for magnetic surface acoustic wave sensors
International audienceThis work aims at studying the interaction between surface acoustic waves (SAW) and micro-structured magnetostrictive layers under a magnetic field with a perspective to develop magnetic field sensors. The impact of the competition between the strong intrinsic magnetic anisotropy of the magnetic material and the shape anisotropy of the interdigitated transducer (IDT) fingers introduced by the micro-structuration is investigated. Therefore, the macroscopic and microscopic magnetic properties of the IDT and their influence on the magneto-acoustic response are studied. A SAW resonator with the IDTs made of the magnetostrictive thin film was elaborated and the magnetic surface acoustic wave (MSAW) response under a magnetic field was performed and discussed. Depending on the energy balance, the anisotropy gets modified and a correlation with the MSAW sensitivity to an externally applied magnetic field is made
Size distribution of magnetic charge domains in thermally activated but out-of-equilibrium artificial spin ice
International audienceA crystal of emerging magnetic charges is expected in the phase diagram of the dipolar kagome spin ice. An observation of charge crystallites in thermally demagnetized artificial spin ice arrays has been recently reported by S. Zhang and coworkers and explained through the thermodynamics of the system as it approaches a charge-ordered state. Following a similar approach, we have generated a partial order of magnetic charges in an artificial kagome spin ice lattice made out of ferrimagnetic material having a Curie temperature of 475 K. A statistical study of the size of the charge domains reveals an unconventional sawtooth distribution. This distribution is in disagreement with the predictions of the thermodynamic model and is shown to be a signature of the kinetic process governing the remagnetization
Single shot time-resolved magnetic x-ray absorption at a Free Electron Laser
Ultrafast dynamics are generally investigated using stroboscopic pump-probe
measurements, which characterize the sample properties for a single, specific
time delay. These measurements are then repeated for a series of discrete time
delays to reconstruct the overall time trace of the process. As a consequence,
this approach is limited to the investigation of fully reversible phenomena. We
recently introduced an off-axis zone plate based X-ray streaking technique,
which overcomes this limitation by sampling the relaxation dynamics with a
single femtosecond X-ray pulse streaked over a picosecond long time window. In
this article we show that the X-ray absorption cross section can be employed as
the contrast mechanism in this novel technique. We show that changes of the
absorption cross section on the percent level can be resolved with this method.
To this end we measure the ultrafast magnetization dynamics in CoDy alloy
films. Investigating different chemical compositions and infrared pump
fluences, we demonstrate the routine applicability of this technique. Probing
in transmission the average magnetization dynamics of the entire film, our
experimental findings indicate that the demagnetization time is independent of
the specific infrared laser pump fluence. These results pave the way for the
investigation of irreversible phenomena in a wide variety of scientific areas.Comment: 9 pages, 5 figure
Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe's terrestrial ecosystems : a review
Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.Peer reviewe