H. Bernas

Chemical order induced by ion irradiation in FePt (001) films

We demonstrate that the long-range order parameter S of sputtered FePt (001) films may be improved by using postgrowth He ion irradiation. This was demonstrated both on disordered (S∼0) and partially ordered (S∼0.4) films in which S was increased up to 0.3 and 0.6, respectively. X-ray diffraction analysis showed that these changes are due to irradiation-induced chemical ordering. The changes in the magnetic hysteresis loops correlate with the expected perpendicular magnetic anisotropy increase. This method may find applications in ultrahigh-density magnetic recording.

Sub-50 nm planar magnetic nanostructures fabricated by ion irradiation

He+ ion irradiation of Co–Pt multilayers through a silica mask obtained by a combination of high resolution lithography and reactive ion etching can produce an optical contrast-free, entirely planar, sub-50 nm magnetically patterned array. Furthermore, the specificity of magnetization reversal in such arrays leads to a weak dispersion of coercive forces. The technique holds promise for both present hard disk technology and future near field magneto-optical recording.

Ordering intermetallic alloys by ion irradiation: a new way to tailor magnetic media

In this paper, we describe ordering mechanism under irradiation by combining experiments and Kinetic Lattice Monte Carlo (KLMC) simulations on the FePt and FePd equiatomic systems. Both experiments and simulations confirm that our irradiation conditions (small energy transfer, low collision cross section, irradiation temperature under 550K) specifically affect DSRO.

Irradiation-induced Ag nanocluster nucleation in silicate glasses: Analogy with photography

The synthesis of Ag nanoclusters in soda lime silicate glasses and silica was studied by optical absorption and electron spin resonance experiments under both low (gamma ray) and high (MeV ion) deposited energy density irradiation conditions. Both types of irradiation create electrons and holes whose density and thermal evolution---notably via their interaction with defects---are shown to determine the clustering and growth rates of Ag nanocrystals. We thus establish the influence of redox interactions of defects and silver (poly)ions. The mechanisms are similar to the latent image formation in photography: Irradiation-induced photoelectrons are trapped within the glass matrix, notably on dissolved noble metal ions and defects, which are thus neutralized (reverse oxidation reactions are also shown to exist). Annealing promotes metal atom diffusion, which, in turn, leads to cluster nuclei formation. The cluster density depends not only on the irradiation fluence but also---and primarily---on the density of deposited energy and the redox properties of the glass. Ion irradiation (i.e., large deposited energy density) is far more effective in cluster formation, despite its lower neutralization efficiency (from

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

{mathrm{Ag}}^{+}

Chemical order induced by He+ ion irradiation in FePt (001) films

to

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

{mathrm{Ag}}^{0}

Metal Nanoclusters for Optical Properties

) as compared to gamma photon irradiation.

Magnetization reversal in irradiation-fabricated nanostructures

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.

Chemical ordering at low temperatures in FePd films

We show that partial chemical ordering can be obtained at moderate processing temperatures by using postgrowth ion bombardment. This was demonstrated both on disordered (S∼0) and partially ordered (S∼0.4) sputtered FePt(001) films in which the order parameter S was increased up to 0.3 and 0.6, respectively. X-ray diffraction measurements indicate that the high crystalline quality of the films is not modified as irradiation proceeds. The changes on the magnetic hysteresis loops are compatible with the expected perpendicular magnetic anisotropy increase. This novel method could have a great impact on the current race toward high anisotropy materials to increase magnetic recording density.