Jacques Miltat | Paris Sud XI University (original) (raw)

Papers by Jacques Miltat

IEEE Transactions on Magnetics, 1991

ABSTRACT The wall state stability of magnetic bubbles in ferrimagnetic as-grown garnet films suit... more ABSTRACT The wall state stability of magnetic bubbles in ferrimagnetic as-grown garnet films suitable for Bloch line memory applications is investigated in order to predict the stability of vertical Bloch line pairs. In the experiment (1, 0) and (0, 2) bubbles are subjected to fast bias pulses (15-ns width) and to an in-plane field. It is found that the winding line pair present in a (0, 2) bubble can be annihilated, resulting in a (1, 0) final state. On the other hand, a (1, 0) bubble can be switched into a (0, 2) bubble with different experimental conditions. These nonconservative switching processes are in most cases irreversible. However, the switching probability never reaches 100%. An interpretation of the annihilation mechanism is given, and the consequences for devices are discussed

Journal of Applied Physics, 1988

ABSTRACT A new technique for observing domain walls and lines in materials with perpendicular ani... more ABSTRACT A new technique for observing domain walls and lines in materials with perpendicular anisotropy is presented. It employs laser light in a laser scan microscope and uses anisotropic diffraction by the wall/line magnetic structure. The contrast obtained can be understood simply and a numerical computation shows good agreement with experimental results. Wall configurations with numerous lines may be obtained when nucleating parallel stripes upon reduction to zero of a saturating in‐plane field.

Spin textures in perfectly ordered antiferromagnetic ultrathin films are evaluated on the basis o... more Spin textures in perfectly ordered antiferromagnetic ultrathin films are evaluated on the basis of atomistic simulations and compared to the results of recent extensions of the (l, m) decomposition model. A comparison between similar textures supported by either a bcc or a fcc lattice shows that the sole inclusion of symmetric Heisenberg exchange interactions suffices to provide, when geometry commands, a natural canting between neighboring s ↑ and s ↓ spins within a texture. Moreover, a pure "at lattice points" dipole model leads to natural symmetries, in clear disagreement with expectations from the (l, m) model. Inversely, properties such as wall mobility under spin-orbit torques depending mostly on wall geometrical characteristics such as chirality and chirality axis orientation prove, as anticipated, primarily lattice immune.

Magnetoresistive Hybrid-Speicherzelle mit: einer ersten Stapelstruktur (9) mit einem magnetischen... more Magnetoresistive Hybrid-Speicherzelle mit: einer ersten Stapelstruktur (9) mit einem magnetischen Tunnelubergang einschlieslich erster und zweiter magnetischer Gebiete (10, 11), die in paralleler, ubereinanderliegender Weise gestapelt und von einer Schicht (12) nichtmagnetischen Materials getrennt sind, wobei das erste magnetische Gebiet (10) einen fixierten ersten magnetischen Momentvektor (17) und das zweite magnetische Gebiet (11) einen freien zweiten magnetischen Momentvektor (18) aufweist, wobei der freie zweite magnetische Momentvektor (18) zwischen einer selben und entgegengesetzten Richtung bezuglich des fixierten ersten magnetischen Momentvektors (17) des ersten magnetischen Gebiets (10) umschaltbar ist; einer zweiten Stapelstruktur (23), die wenigstens teilweise lateral zur ersten Stapelstruktur (9) angeordnet ist und ein drittes magnetisches Gebiet (20) mit einem fixierten dritten magnetischen Momentvektor (21) sowie das zweite magnetische Gebiet (11) aufweist, wobei der ...

Journal of Magnetism and Magnetic Materials, 1993

ABSTRACT Magnetization reversal mechanisms in exchange coupled Permalloy/copper/cobalt systems ha... more ABSTRACT Magnetization reversal mechanisms in exchange coupled Permalloy/copper/cobalt systems have been investigated by Kerr microscopy. In the ferromagnetically (F) coupled layers, a strong wall directional anisotropy and non-reversible wall displacements are observed. In the antiferromagnetic case (AF), experiments indicate that the magnetization reversal partly occurs through the nucleation and propagation of an antiphase boundary. Comparison with a simple hysteresis model provides an estimate of the coupling constant.

The thermal stability of isolated skyrmions is studied in a Co/Pt(111) monolayer, using atomic sc... more The thermal stability of isolated skyrmions is studied in a Co/Pt(111) monolayer, using atomic scale simulations. Langevin dynamics around 80~K is first used to simulate the thermal collapse, with lifetimes of a few tens of nanoseconds under a destabilizing field of 0.25 T. A path method is then employed, to generally and precisely describe the skyrmion collapse. Two mechanisms are found, and discussed in relation with the change of topology between the skyrmion and uniform states. It appears that, for the lowest energy barrier path, skyrmion destabilization occurs much before any topology change, suggesting that topology plays a minor role in the skyrmion stability. On the contrary, an important role appears devoted to the Dzyaloshinskii-Moriya interaction, establishing a route towards improved skyrmion stability.

Journal of Magnetism and Magnetic Materials, 1992

Abstract Micromagnetic simulation of the magnetisation distribution in stripe domains found in co... more Abstract Micromagnetic simulation of the magnetisation distribution in stripe domains found in cobalt foils with an inclined c -axis leads to the conclusion that the walls possess a marked two dimensional nature. Such walls should give rise to strongly asymmetrical profiles when observed experimentally by Lorentz microscopy. Differential phase contrast electron micrographs confirm these findings, although discrepancies in detail still remain.

Journal of Applied Physics, 1997

First, the number of irreducible wall configurations is derived, both for an odd and an even numb... more First, the number of irreducible wall configurations is derived, both for an odd and an even number of magnetic layers. Second, the comparison of simulated wall structures in stacks made of three and four magnetic layers serves as an illustration of the interplay between flux–closure mechanisms and interlayer exchange interactions. Flux closure is shown either to compete or accommodate with ferromagnetic-type interlayer exchange interactions owing to its short- or long-range character. Last, an equivalent single layer behavior is shown to develop with an increasing number of magnetic layers, magnetic layer thickness, and interlayer (ferromagnetic-type) exchange parameter.

Domains were imaged by magnetic force microscopy (MFM) on materials where the domain size exceeds... more Domains were imaged by magnetic force microscopy (MFM) on materials where the domain size exceeds the sample thickness by three orders of magnitude. Selected samples are a magnetooptical medium and ultrathin cobalt films, all with perpendicular magnetization. A strong domain contrast is observed in both cases. This fact is confronted to the usual theory of MFM image formation, in which the stray field from one body (tip or sample) is sensed by the other, without altering of the magnetization distributions. It is shown that the domain contrast in such extreme conditions cannot be explained with that theory. On the contrary, Abraham and McDonald’s model, which considers the response of the sample to the tip field, is quantitatively compared to experiment. It is shown to provide a good qualitative description of the results, but not a quantitative one, because of oversimplification.

Journal of Applied Physics, 1994