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International audience; The development of rapid, sensitive, portable and inexpensive early diagnostic techniques is a real challenge in the fields of health, defense and in the environment. The current global pandemic has also shown the need for such tests. The World Health Organization has defined ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to end-users) that field diagnostic tests must fulfill, which proves the real need in terms of public health. Giant magnetoresistance (GMR) sensors, which have flourished in a wide variety of spintronic applications (automobile industry, Information Technology, etc.), also have real potential in the field of health, particularly for the development of early diagnostic point-of-care devices. This work presents a new type of innovative biochip, consisting of GMR sensors arranged on both sides of a microfluidic channel which allow on the one hand to count magnetic objects one by one but also to better distinguish false positives (aggregates of beads, etc.) from labelled biological targets of interest by determining their magnetic moment. We present the operating principle of this new tool and its great potential as a versatile diagnostic test.

International audience; In this manuscript we propose a calculation method where the magneto-resistive elements are modelled as fluctuating resistances to correct the output voltage noise of magnetic tunnel junction (MTJ) from standard electronic circuits. This method is validated on single elements, partial and full Wheatstone bridge circuits, giving rise to a correction factor affecting the output voltage noise as well as sensitivity values. Combining the correction factor and a normalization by the number of MTJs pillars and the pillar surface, we show that the performances extracted by this method allow universal comparison between any results from literature.

This paper discloses two high-sensitivity probes for Eddy Current Nondestructive Test (NDT) of buried and surface defects. These probes incorporate eight and 32 magnetoresistive sensors, respectively, which are optimized for high sensitivity and spatial resolution. The signal processing and interfacing are carried out by a full-custom application-specific integrated circuit (ASIC). The ASIC signal chain performs with a thermal input-referred noise of 30 nV/ $\sqrt{\text{Hz}}$ at 1 kHz, with 66 mW of power consumption, in a die with 3.7×3.4 mm $^2$ . NDT results are presented, showing that there is an increase in spatial resolution of surface defects when contrasted to prior art, enabling the probes to resolve defects with diameters of 0.44 mm, pitches of 0.6 mm, and minimum edge distance as low as 0.16 mm. The results also show that the probe for buried defects is a good all-round tool for detection of defects under cladding and multiple-plate flat junctions.

In the above article [1] , unfortunately, errors were present in Table I , for the correction factors of the 1/4 Wheatstone bridge regarding the thermal noise, the shot noise, and the Hooge parameter entry. The errors have no influence on the experimental results, neither on the other table nor on the discussion and conclusions of the article. Table I contained an improper formula for the corrections factor (CF) in the case of the 1/4 Wheatstone bridge configuration (case c).

International audience; Neuronal electrical activity is widely studied in vivo, and the ability to measure its magnetic equivalent to obtain an undisturbed signal with both amplitude and direction information leading to neuronal signal mapping would be a promising tool for neuroscience. To provide such a tool, a probe with spin-electronics-based magnetic sensors with orthogonal axes of sensitivity for two directions of measurement is realized, thanks to a local magnetization re-orientation technique induced by Joule heating. This probe is tested under in vivo measurement conditions in the brain of an anesthetized rat. To be as close as possible to neurons and to create minimal damage during the probe’s insertion, the tip thickness has been drastically decreased using a silicon-on-insulator substrate. Our probes provide the ability to perform in vivo magnetic measurements on two orthogonal axes on a 25 μm thick silicon tip with a sensitivity of 1.7%/mT along one axis and 0.9%/mT along the perpendicular axis in the sensor plane, for a limit of detection at 1 kHz of 1.0 and 1.3 nT, respectively. These probes have been tested through a phantom study and during an in vivo experiment. The robustness and stability over one year are demonstrated.

Vertical packaging of multiple giant magnetoresistance (multi-GMR) stacks is a very interesting noise reduction strategy for local magnetic sensor measurements, which has not been reported experimentally so far. Here, we fabricate multi-GMR sensors (up to 12 repetitions) that maintain a good GMR ratio, linearity, and low roughness. From magnetotransport measurements, two different resistance responses are observed with a crossover at around five GMR repetitions: steplike (N 5) and linear (N \ensuremath{\ge} 5) behavior, respectively. With the help of micromagnetic simulations, we analyze, in detail, the two main magnetic mechanisms: the N\'eel coupling distribution induced by the roughness propagation and the additive dipolar coupling between the N free layers. Furthermore, we correlate the dipolar coupling mechanism, which is controlled by the number of GMRs (N) and lateral dimensions (width), to the sensor performance (sensitivity, noise, and detectivity); this is in good agreement with analytical theory. The noise roughly decreases in multi-GMRs as $1/\sqrt{N}$ in both regimes (low-frequency $1/f$ and thermal noise). The sensitivity is even more strongly reduced, scaling as ${N}^{\ensuremath{-}1}$, in the strong dipolar regime (narrow devices), while converging to a constant value in the weak dipolar regime (wide devices). Interestingly, they are more robust against undesirable random telegraphic noise than single GMRs at high voltages, and the linearity can be extended towards a much larger magnetic field range, without dealing with the size and reduction of the GMR ratio. Finally, we identify the optimal conditions for which multi-GMRs exhibit lower magnetic field detectivity than that of single GMRs: wide devices operating in the thermal regime, where much higher voltage can be applied without generating remarkable magnetic noise. These results open the path towards spintronics sensors connected and coupled in three dimensions with reduced noise, compact footprint, and mainly tuned by the dipolar coupling.

The presence of magnetic noise in magnetoresistive-based magnetic sensors degrades their detection limit at low frequencies. In this paper, different ways of stabilizing the magnetic sensing layer to suppress magnetic noise are investigated by applying a pinning field, either by an external field, internally in the stack or by shape anisotropy. We show that these three methods are equivalent, could be combined and that there is a competition between noise suppression and sensitivity reduction, which results in an optimum total pinning field, for which the detection limit of the sensor is improved up to a factor of ten., Comment: 5 pages, 3 figures

International audience; Giant magnetoresistive sensors (GMR) and tunnel magnetoresistive sensors (TMR) can be efficiently used to detect weak magnetic signals corresponding to the field created by the precession of nuclear spins. In this paper, we present two experiments with their advantages and limitations. The first one is Nuclear Magnetic Resonance (NMR) spectroscopy at micron scale using magnetoresistive sensors and the second is very low field Magnetic Resonance Imaging (MRI) using mixed sensors which is a combination of magnetoresistive sensors and superconducting loops.

International audience; This paper reports on the development of spin electronics based probes for 3D magnetic imaging. We have demonstrated the feasibility of using four orientations of magnetoresistive sensors (GMR) for the reconstruction of three dimensional components of magnetic field at the same measurement point. The use of different GMR sensor structures makes it possible to adapt the sensitivity and field range to the signal to detect for a specific application. Their characteristics and field reconstruction steps are also shown. Different examples of magnetic imaging are presented.

The performance of magnetoresistive sensors is today mainly limited by their 1/f low-frequency noise. Here, we study this noise component in vortex-based TMR sensors. We compare the noise level in different magnetization configurations of the device, i.e., vortex state or uniform parallel or antiparallel states. We find that the vortex state is at least an order of magnitude noisier than the uniform states. Nevertheless, by activating the spin-transfer-induced dynamics of the vortex configuration, we observe a reduction of the 1/f noise, close to the values measured in the AP state, as the vortex core has a lower probability of pinning into defect sites. Additionally, by driving the dynamics of the vortex core by a non-resonant rf field or current, we demonstrate that the 1/f noise can be further decreased. The ability to reduce the 1/f low-frequency noise in vortex-based devices by leveraging their spin-transfer dynamics thus enhances their applicability in the magnetic sensors' landscape.

International audience; We have studied the antiferromagnetic coupling at the interface of the La0.7Sr0.3MnO3/SrRuO3 bilayer as function of temperature. We measured the La0.7Sr0.3MnO3 magnetization reversal while the SrRuO3 magnetization is blocked due to a field cooled procedure and because of its high coercive field. Even if in this system, the La0.7Sr0.3MnO3 magnetization cycle may be explained by two exchange couplings which coexist up to 120 K, the exchange bias and the coercive field from 5 K to 300 K have a similar behavior from some ferromagnetic/antiferromagnetic...

We report correlated measurements of magnetothermal and magnetoelectric conductivities in a cobalt-silver mechanical alloy. Their variation with magnetisation indicates that their respective relaxation times have similar origins. At low temperatures the thermal and electric conductivities are similar; however at higher temperatures an increasing phonon contribution reduces the magnetothermal effect.

International audience; Nuclear Magnetic Resonance (NMR) spectroscopy on small volumes, either on microfluidic channelsor in vivo configuration, is a present challenge. We report here a high resolution NMR spectroscopyon micron scale performed with Giant Magnetic Resistance-based sensors placed in a static magnetic$B_0$ field of 0.3 T. The sensing volume of the order of several tens of pL opens the way to highresolution spectroscopy on volumes unreached so far. Published by AIP Publishing.

Since the fundamental discovery of the giant magnetoresistance many spintronic devices have been developed and implemented in our daily life (e.g. information storage and automotive industry). Lately, advances in the sensors technology (higher sensitivity, smaller size) have potentiated other applications, namely in the biological area, leading to the emergence of novel biomedical platforms. In particular the investigation of spintronics and its application to the development of magnetoresistive (MR) biomolecular and biomedical platforms are giving rise to a new class of biomedical diagnostic devices, suitable for bench top bioassays as well as point-of-care and point-of-use devices. Herein, integrated spintronic biochip platforms for diagnostic and cytometric applications, hybrid systems incorporating magnetoresistive sensors applied to neuroelectronic studies and biomedical imaging, namely magneto-encephalography and magneto-cardiography, are reviewed. Also lab-on-a-chip MR-based platforms to perform biological studies at the single molecule level are discussed. Overall the potential and main characteristics of such MR-based biomedical devices, comparing to the existing technologies while giving particular examples of targeted applications, are addressed.

Low-frequency noise has been measured in magnetic tunnel junctions with MgO barriers and magnetoresistance values up to 235%. We present here the noise for different degrees of crystallization and CoFeB/MgO interface quality depending on the annealing temperature. For optimized annealing temperature, an extremely low 1/ f noise, compared to magnetic junctions with Al 2 O 3 barriers, has been observed. The origin of the low-frequency noise can be explained in terms of localized charge traps with the MgO barriers. Results for very thin CoFeB are presented in the second part as a function of temperature. Despite the absence of coercivity at room temperature for thinner free-layer structures, an important increase of H c appears under 180 K. Meanwhile, the random telegraph noise present at room temperature is suppressed due to magnetic domains freezing. These results are discussed in view of various sensors applications of MgO-MTJ, giving advantages and drawbacks in terms of signal-to-noise ratio with respect to the operating temperature.

When coupled to a giant magnetoresistive (GMR) sensor, a superconducting loop containing a constriction can be a very sensitive magnetometer. It has thermal noise levels of few fT/sqrt(Hz), comparable to low-Tc SQUID noise, with a flat frequency response. These mixed sensors are good candidates for detection of weak biomagnetic signals, like a cardiac or neuronal signature. Furthermore, being sensitive to the flux, mixed sensors can be used for nuclear magnetic resonance (NMR) detection and Magnetic Resonance Imaging (MRI) especially at low fields. They are very robust and accept strong RF pulses with a very short recovery time compared to tuned RF coils, which allow measurements of broad signals (short relaxation time or multiple resonances). We will first present the last generation sensors having a noise level of 3 fT/sqrt(Hz) and we will show signals measured at low frequency (magnetocardiography–magnetoencephalography range) and at higher frequency (NMR signals). The use of additional flux transformers for improving the signal-to-noise will be discussed. Finally, we will present perspectives for low-field MRI, which can be combined with neural signal detection (MEG), especially for brain anatomy and temporal response on the same experimental setup.

Les capteurs de champ magnetique ont de nombreuses applications : lecture de disques durs, controle de positionnement dans l’espace, codage de position et d’angle, mesure de courant electrique sans contact, imagerie magnetique, controle non destructif, imagerie medicale… Parmi les differents types de capteurs magnetiques, ceux issus de l’electronique de spin offrent la possibilite d’une grande sensibilite sur une petite echelle spatiale. Utilises systematiquement dans le domaine des tetes de lecture des disques durs (voir l’article de J.P. Nozieres, p. 12), leur production en grande serie pour d’autres applications vient de commencer.

An integrated device including microfluidic channels and incorporated magnetoresistive spin valve sensors has been developed and used to detect single magnetic bead motion at cm/s velocities. The sensitivity of the system is high enough to determine the magnetic orientation, the flowing height and the speed of each particle for velocities between 10-23 mm/s and the counting capability of the device is fully working for this range of velocities and below this limit. Sensor signals (between 3-100 muVp-p) correspond to bead moments at different directions indicating a physical rotation of the beads, and a slow response (seconds) of the bead moment to magnetizing field changes. Subsequent magnetic characterization of the micron-sized beads indicates that they are composed of strongly interacting magnetic nanoparticles.

We have developed a very sensitive field sensor to detect magnetic signals in the femtotesla range. This mixed sensor is based on the association of a superconducting flux-to-field transformer with a magnetoresistive field sensor. The bandwidth of a GMR being wide and only limited in the GHz regime, where the ferromagnetic resonance of the free layer occurs, mixed sensors are good candidates for low field NMR. Advantages of mixed sensors are their robustness and their very fast recovery after the rf pulse (< 1 mus). We have first used these sensors for NQR detection in the MHz range. Here we show results obtained on low field NMR with frequencies up to 210 kHz without pre-polarization, detected with mixed sensors based on high-TC superconductors.

The feasibility to develop mini- and micro-magnetic electro-mechanical systems (MEMS) has been evaluated by prototyping of a single-phase stepper motor. The main targeted application of such device is the watch industry needing micro-motors in huge quantities at low cost. The motor part that required the greatest efforts has been the magnet, which cannot yet be found in film layer. The screen-printing technology has been used for the production of NdFeB-based magnets whose properties have been characterised. The thick film magnets have been integrated in the stepper motor specially designed for this purpose. The whole motor has been characterised and conclusions are drawn on the possibility of producing thick film magnets for magnetic MEMS.

In the last decade, new techniques to increase the data storage density have been one of the major axes of research in magnetism. One direction explored consists of increasing the reading speed of read heads. This implies to understand the behavior of the giant magneto resistive (GMR) effect at high frequency. We offer an original method to isolate the GMR of a spin valve sensor, designed as a yoke shape, by combination of classical ferromagnetic resonance technique and demodulation measurement of the CIP voltage of the sensor. We show that the classical description of the GMR effect, based on a mean field theory, is kept valid in a frequency range from DC to 10 GHz. We also show the direct correlation between the ferromagnetic resonance of the free layer sensor and the GMR amplitude.

Spin-electronics-based magnetic sensors, first developed for magnetic read heads, are now finding their way into many different technological devices from cars to medical systems. They combine very high sensitivity, great robustness, and very small size. Today they are integrated with CMOS electronics into a common process. In this chapter, we give an overview of that technology and describe some example applications, such as speed sensors, current sensors, and biomagnetic signal detection.

8th Spintronics Symposium , AUG 09-13, 2015 , San Diego, CA; International audience; To detect magnetic signals coming from the body, in particular those produced by the electrical activity of the heart or of the brain, the development of ultrasensitive sensors is required. In this regard, magnetoresistive sensors, stemming from spin electronics, are very promising devices. For example, tunnel magnetoresistance (TMR) junctions based on MgO tunnel barrier have a high sensitivity. Nevertheless, TMR also often have high level of noise. Full spin polarized materials like manganite La0.67Sr0.33MnO3 (LSMO) are attractive alternative candidates to develop such sensors because LSMO exhibits a very low 1/f noise when grown on single crystals, and a TMR response has been observed with values up to 2000%. This kind of tunnel junctions, when combined with a high Tc superconductor loop, opens up possibilities to develop full oxide structures working at liquid nitrogen temperature and suitable for medical imaging. In this work, we investigated on LSMO-based tunnel junctions the parameters controlling the overall system performances, including not only the TMR ratio, but also the pinning of the reference layer and the noise floor. We especially focused on studying the effects of the quality of the barrier, the interface and the electrode, by playing with materials and growth conditions

We have demonstrated that a very low magnetic field can be detected by a sensor combining a superconducting pick-up loop and a GMR element [1], [2]. In this device, the excitation field applied to the superconductor generates a supercurrent running through the loop. This current is driven through a constriction, where it generates high density magnetic field lines that can be detected by the GMR sensor.We have performed magneto-optical imaging on a YBCO ring with a constriction to estimate the magnetic field—enhancement and the localization of the field lines in this design for applied fields down to 1 μT. The obtained measurements give the vertical component of the local magnetic field. Locally the field lines are enhanced by a factor larger than 200 for fields small enough to induce a current lower than the critical current. A decrease of the gain for higher applied fields is observed, when the critical current is reached.We present also a calculation of the gain, taking into account the precise distribution of current in the rectangular section of the superconductor [3] and the inductance of the loop. These results are in agreement with finite element modeling. The gain for various dimensions and aspect ratio's is given and compared to the experimental results. An optimized design is given for magnetoencephalography applications, in order to replace low-Tc SQUIDs used in the present apparatus. The expected sensitivity of this system is calculated to be in the range of a few fT/Hz.

Low- T c SQUIDs are currently the only devices with a sufficiently low level of noise for magnetic field measurements in the femtotesla range. An alternative to SQUIDs is to combine a superconducting flux-to-field transformer with a high sensitivity magnetoresistive sensor. With a correct design, the excitation field can be sufficiently enhanced to be measured by a magnetoresistance (MR). We have fabricated and tested a micron-sized integrated YBCO-based mixed sensor of small size. It is comprised of a GMR stack separated from a YBCO thin film by an insulating layer. A constriction in the superconducting loop drives the induced current through a small section and therefore creates field lines large enough to be detected by the GMR down to 30 fT/Hz 1/2 , that is in the range of high- T c SQUIDs. The device characteristics at 4.2 and 77 K are shown. Experimental results are compared to the theoretical gain of the structure. Applications of this sensor are for instance in the biomagnetism area, especially for magnetoencephalography, where neural signals emitted by the brain are of the order of few fT/Hz 1/2 . Various other fields are concerned, from earth mapping to fundamental physics (vortex motion, magnetic interactions, etc.).

Parallax error severely limits the use of gas detectors for neutron and X-ray single-crystal diffractometry. This is particularly the case in Neutron Macromolecule Crystallography (NMC), where a large solid angle is needed. High-resolution cylindrical detectors based on Neutron Image Plates provide a large angular coverage but they are gamma sensitive and do not allow time-resolved measurements. We describe the principle of a gas counter, the multi-blade Microstrip Gas Chamber (MSGC), which has the potential to design parallax-free cylindrical detectors. It contains radial MSGC plates, providing a partitioning of the gas volume and a segmentation of the signal readout. The axial coordinate is measured by reading out the charge signal on the anodes and the trans-axial coordinate is deduced from the electron drift distance measured optically using the time difference between the primary and the avalanche light. Expected characteristics are a sub-millimeter position resolution, a sub-microsecond time resolution, and a global counting rate greater than 10 7 s - 1 .

Very low magnetic fields are detected up to now using SQUID-based devices. In the femtotesla range, only low-T/sub c/ SQUIDs have a sufficiently low level of noise to measure extremely low signals, as for instance induced fields of the neural activity of the brain, for magneto-encephalography (MEG). An alternative to SQUIDs is to combine a superconducting flux-to-field transformer with a high-sensitivity giant magnetoresistive sensor (GMR). We have fabricated and performed experiments on such an integrated YBCO-based mixed sensor. It is comprised of a GMR stack separated from a YBCO thin film by an insulating layer. The induced supercurrent in the YBCO is forced through a narrow constriction, thereby creating a local field much larger than the external field. This large local field is detected by the GMR. Effective noise levels are down to 30 fT/sqrtHz, which is in the range of high-Tc Squids. Performance of this device is shown from liquid helium temperature (4.2 K) up to liquid nitrogen temperature (77K). By replacing the GMR by a Tunneling Magneto Resistance (TMR) or a Colossal Magneto Resistance (CMR) sensor, and by adjusting the dimensions to optimize the local enhancement effect, the sensitivity should reach the subfemtotesla range at low frequency. A large number of applications could be investigated by this sensor, especially in the biomagnetism area, as well as in various other fields, from earth mapping to fundamental physics (vortex motion in superconductors, magnetic interactions...).

Neutron reflectometry with spin analysis has allowed us to perform selective hysteresis loops of each magnetic layer in GMR spin valves. The intensities now available on reflectometers and the advances of modelling give the possibility to perform a very precise analysis of the magnetic configuration even in complex systems with five different magnetic layers. Results obtained on GMR spin valves show a rather complex behaviour of the free layer as a function of the magnetic field. The NiFe soft layer exhibits a non-homogeneous rotation which cannot be observed in transport measurements. This non-homogeneous rotation explains the necessity of a rather thick soft layer to avoid 1/f magnetic noise in GMR sensors.

Magnetic dipolar coupling leads to low-energy excitations in magnetic materials named as magnetostatic waves (MSW). The typical energy of these excitations is of the order of a few tens of μeV. We show that working in grazing incidence in a reflectivity geometry makes it possible to study these very low-energy excitations. We present a neutron set-up which allows to study these excitations. The studied samples were permalloy thin films. The MSW were either thermally excited or induced by a microwave (MW) field and the off-specular neutron reflectivity was measured. We have not been able to measure any inelastic scattered signal, even with a large MW excitation (1 W input).

In order to study the in-plane crystallographic structure of magnetic thin films, we have developed a neutron grazing incidence diffraction (GID) set-up that has been mounted on the EROS reflectometer at the LLB. This set-up allows us to observe the diffraction peaks in the plane of epitaxial thin films. As an example, we present polarized GID measurements on an epitaxial ferromagnetic thin film of the perovskite oxide La 0.7 Sr 0.3 MnO 3 (0 0 1) deposited on SrTiO 3 (0 0 1) (of a surface 1 cm 2 ). This is the first report on polarized GID measurements on a very thin magnetic film (20 nm).

SANS offers the possibility to study nanostructures of sizes ranging from 2 to 200 nm. We have explored the possibility of using SANS in a grazing incidence geometry (GISANS) in order to study magnetic nanostructures in thin films (thickness ∼50 nm). Even though the amount of material is tiny in such films (∼50 μg), working in grazing incidence allows to look at the scattered signal from in-plane magnetic nanostructures in the films. We have performed surface diffraction on magnetic nanostructures (∼100 nm in size) on a system consisting of Fe 0.5 Pd 0.5 thin films with a magnetic perpendicular anisotropy. The measurements have been performed in various magnetic field configurations. Magnetic surface diffraction can easily be observed. We present these measurements together with calculations based on a Born approximation. We discuss the information that can be extracted from such polarized neutron measurements.

SUMMARYNeuronal activity generates ionic flows and thereby both magnetic fields and electric potential differences, i.e. voltages. Voltage measurements are widely used, but suffer from isolating and smearing properties of tissue between source and sensor, are blind to ionic flow direction, and reflect the difference between two electrodes, complicating interpretation. Magnetic field measurements could overcome these limitations, but have been essentially limited to magnetoencephalography (MEG), using centimeter-sized, helium-cooled extracranial sensors. Here, we report on in vivo magnetic recordings of neuronal activity from visual cortex of cats with magnetrodes, specially developed needle-shaped probes carrying micron-sized, non-cooled magnetic sensors based on spin electronics. Event-related magnetic fields inside the neuropil were on the order of several nanoteslas, informing MEG source models and efforts for magnetic field measurements through MRI. Though the signal-to-noise ratio is still inferior to electrophysiology, this proof of concept demonstrates the potential to exploit the fundamental advantages of magnetophysiology.HIGHLIGHTSSpin-electronics based probes achieve local magnetic recordings inside the neuropilMagnetic field recordings were performed in vivo, in anesthetized cat visual cortexEvent-related fields (ERFs) to visual stimuli were up to several nanoteslas in sizeERFs could be detected after averaging less than 20 trialsIN BRIEFCaruso et al. report in vivo, intra-cortical recordings of magnetic fields that reflect neuronal activity, using magnetrodes, i.e. micron size magnetic sensors based on spin electronics.

Ultra-low temperature sensors provide unprecedented performances in X-ray and far infrared astronomy by taking advantage of physical properties of matter close to absolute zero. CESAR is an FP7 funded project started in December 2010, that gathers six European laboratories around the development of high performances cryogenic electronics. The goal of the project is to provide far-IR, X-ray and magnetic sensors with signal-processing capabilities at the heart of the detectors. We present the major steps that constitute the CESAR work, and the main results achieved so far.

The propagating spin wave spectroscopy (PSWS) technique is applied for the first time to metallic thin film patterns, allowing to measure their magnetostatic wave modes. Using micrometer scale local excitation and detection, we show that magnetostatic surface waves propagate on a distance as long as 40 μm in a continuous permalloy film. In micrometer wide permalloy stripes, we observe both quantized spin wave modes and quasi-saturation modes, well explained by existing models. In addition, low-frequency additional modes were observed which, we suggest, are generated in the magnetically inhomogeneous edge regions.

An overview of the current status of the study of spin wave excitations in arrays of magnetic dots and wires is given. We describe both the status of theory and recent inelastic light scattering experiments addressing the most important issues; the quantization of localized spin waves due to the in-plane confinement of spin waves in elements, dipolar coupling between the quantized modes, and the localization of the modes within rectangular elements due to an inhomogeneous demagnetizing field.

Standard polarised neutron reflectometry allows one to determine magnetic in-depth profiles in multilayer magnetic thin films. We are trying to develop methods to also obtain magnetic information in the plane of the layers by using off-specular diffraction in a reflectivity geometry, which allows to probe length scales ranging from 1 to 50 μm . We present a fully dynamical treatment of the scattering of a neutron beam on a grating at grazing incidence. We have studied several model systems consisting of magnetic gratings in the micron scale range to compare calculated and measured results.

The resistive effect of domain walls in FePd films with perpendicular anisotropy was studied experimentally as a function of field and temperature. The films were grown directly on MgO substrates, which induces an unusual virgin magnetic configuration composed of 60 nm wide parallel stripe domains. This allowed us to carry out the first measurements of the anisotropy of domain wall resistivity in the two configurations of current perpendicular and parallel to the walls. At 18 K, we find $8.2%$ and $1.3%$ for the domain wall magnetoresistance normalized to the wall width (8 nm) in these two respective configurations. These values are consistent with the predictions of Levy and Zhang.

We present results of neutron diffraction on periodic gratings. The periodicities of the gratings range from 2 to 10 μm. These experiments have been performed on the time-of-flight spectrometer EROS at the Laboratoire Leon Brillouin. We show that dynamical calculations (based on a matrix formalism) can quantitatively account for the results. Experiments have been performed on several systems (with various periodicities, materials and structures) to study the diffraction efficiency effects. We show that optimised gratings can exhibit diffraction efficiencies as high as 30% over a scattering wave-vector range 0

We present the new polarised neutron reflectometer for the investigation of surface magnetism (PRISM), which has been built at the Laboratoire Leon Brillouin. This polarised neutron reflectometer with polarisation analysis has been optimised for the study of small magnetic samples (1 cm2 range).

We have studied the interface magnetism of La 0.7 Sr 0.3 MnO 3 epitaxial thin films deposited on MgO and SrTiO 3 single crystal substrates by polarised neutron reflectometry. Magnetisation measurements show that the magnetisation never reaches the full value of 3.7 μ B /atom expected for the 0.7/0.3 stoichiometry. Although the coercivity of the films is rather low (H c < 10 mT), the magnetic saturation value is reached only for fields larger than 200 mT. By polarised neutron reflectometry we have observed that the magnetisation is clearly inhomogeneous through the thickness of the films and decreases markedly when approaching the bottom and top interfaces of the film. A study of the magnetisation profile variation as a function of temperature shows that a thin top layer of 3-5 nm is greatly perturbed. The magnetisation is also reduced on a rather large depth into the core of the film where a depression of 15-20% from the substrate to the top interface can be observed.