P. Meyer

Irradiation induced effects on magnetic properties of Pt/Co/Pt ultrathin films

Abstract He+ ion irradiation-induced interface mixing modifies the magnetic properties of Pt/Co/Pt sandwiches. A strong decrease in magnetic anisotrophy (hence of the coercivity and Curie temperature) can be controlled without significant changes in sample roughness or optical properties. This opens exciting possibilities to develop a planar technology to pattern the magnetic properties of multilayers by irradiation through a lithographically defined mask.

Modifications of magnetic properties of Pt/Co/Pt thin layers by focused gallium ion beam irradiation

We show how the magnetic properties of the Pt/Co ultrathin film structure can be modified and even controlled under uniform irradiation by Ga+ ions at low fluence in the 20–100 keV range. A systematic magneto-optical study is presented for the Pt/Co(1.4 nm)/Pt(111) ultrathin-film structure. At ion fluences below D=1014 Ga+/cm2, the coercive field is steadily reduced when increasing the fluence. At large fluences, in the range D=(5–10)×1014 Ga+ ions/cm2, the magnetization of the Co layer drops rapidly and the film finally becomes paramagnetic at room temperature for D>2×1015 Ga+ ions/cm2. We demonstrate that these magnetic changes are related to the effect of ion-induced collisional intermixing of the Co/Pt interfaces, leading to the formation of stable Co–Pt alloys with varying composition across the interfaces. A simple model is derived to relate the ion beam-induced mixing to the changes in magnetic properties. The present work allows us to gain a quantitative understanding of previous experiments using...

MAGNETIZATION REVERSAL IN PATTERNED CO(0001) ULTRATHIN FILMS WITH PERPENDICULAR MAGNETIC ANISOTROPY

Using x‐ray lithography we have patterned dot arrays in Au/Co/Au(111) sandwiches based on ultrathin Co layers with perpendicular anisotropy. Large area arrays of dots with diameters of 1 and 2 μm have been obtained, keeping mostly undamaged the ultrathin Co layer. Hysteresis loops of the arrays depend drastically on the dot diameter. Magneto‐optical domain visualization experiments confirm a magnetization reversal mechanism based on a large distribution of nucleation fields in the film, with complete reversal of the magnetization of one dot through the domain wall propagation after a local nucleation process. This could give information on the magnetization reversal processes in Au/Co/Au(111) continuous films.

Magnetooptic depth sensitivity in a simple ultrathin film structure

Abstract Polar magnetooptics (MO) is able to probe the magnetization depth profile in ultrathin magnetic film structures on a nanometer scale. This information can be deduced by modelling the MO effects in the considered layered medium when performing MO experiments with a compensator or changing the wavelength of the incident light beam. Spectroscopic MO measurements are then helpful for analysing this phenomenon in detail. The in-depth selectivity of MO effects for magnetization is demonstrated for a simple ultrathin film structure consisting of two magnetic Co layers with perpendicular anisotropy separated by a non-magnetic Au spacer layer. The individual magnetic contributions of the two Co layers may be observed directly when performing MO Kerr measurements at selected compensator phase shifts or photon energies. The experimental data are interpreted by MO calculations in both cases.

Magneto-optic depth sensitivity to local magnetization in a simple ultrathin film structure

Abstract Starting from experimental results, we show how polar magneto-optics are able to probe the magnetization depth profile at a nanometer scale. This is demonstrated in a simple ultrathin film system built from two magnetic Co layers with perpendicular anisotropy, separated by a non-magnetic Au spacer layer. The individual magnetic contributions of the two ultrathin Co layers may be fully separated when performing Kerr ellipticity measurements at appropriate photon energies. A simple model that takes into account separately the two Co layer contributions to magneto-optical effects is presented. An extension of this treatment to Co/Au multilayers is proposed.

Magnetization reversal in weakly coupled magnetic patterns

Abstract Ion irradiation is an original process to pattern the structural and as a consequence the magnetic properties of ultra-thin films, down to the nanometer scale. Patterns of dots and tracks have been fabricated by focused Ga + ion beam scanned onto a Co layer with perpendicular magnetic anisotropy. Depending on the dose, the magnetic behaviour of the nanometric irradiated lines can be tuned from the ferromagnetic with reduced coercivity to paramagnetic. The larger the fluence, the smaller is the exchange between dots or tracks. These systems enabled investigations of the competition between exchange and dipolar interactions. For arrays designed with high irradiation doses and only coupled by dipolar interactions, the magnetic relaxation proceeds by the magnetization reversal of individual dots and follows a power-law time decay. Monte Carlo simulations reproduce this time dependence.

Kerr study of Pt/Co/Pt(111) sandwiches

We report the magnetic properties of ultrathin cobalt Pt/Co/Pt (111) sandwich films measured by magneto-optical Kerr effect. Magnetic after-effect relaxation curves reveal that the magnetization reversal is dominated either by nucleation processes or by domain wall motion.

Nonlinear magneto‐optical Kerr effect study of quantum‐well states in a Au overlayer on a Co(0001) thin film

We have measured the polar nonlinear magneto‐optical Kerr rotation and the total generated second harmonic intensity from a perpendicularly magnetized Co(0001)/Au(111) thin film (6 ML) versus the thickness of a Au overlayer. For both experiments we find a clear oscillation with a period of about 13.5 ML. This behavior can be interpreted as arising from quantum‐well states (QWSs) in the Au overlayer, though interestingly, the observed period is twice the expected one. Especially for the reflected intensity this oscillation is very pronounced: the intensity changes by a factor of 10 when the Au overlayer thickness changes from 7 to 13 ML. These strong effects make this nonlinear technique very suitable for the study of these QW oscillations.

Random field effects in a disordered metamagnet: magnetic domains and their dynamics

Abstract The low temperature ( H, T ) magnetic phase diagram of the dilute Ising antiferromagnet Fe 0.8 Mg 0.2 Cl 2 has been determined. A strong time-dependent magnetic hysteresis on mixed phase boundaries is evidenced and is analyzed from the magneto-optical imaging of the evolution of the magnetic domain pattern. This behaviour is attributed to random fields creating a metastable mesoscopic multidomain antiferromagnetic state.

Phase diagram and mixed phase dynamics of the dilute Ising antiferromagnet Fex Mg1 − xCl2, 0.7 ≤ x ≤ 1

Abstract Using magneto-optical techniques, i.e. Faraday rotation, imaging and ‘transparent magnetic circular dichroism’, we have investigated the antiferro-paramagnetic mixed phase of Fex Mg1 −x Cl2, 0.7