High-energy ion beam irradiation of Co/NiFe/Co/Cu multilayers: Effects on the structural, transport and magnetic properties

Abstract

The aim of this work is to investigate the effects of 593 MeV Au irradiation using two different projectile charges, namely Au 30+ and Au 46.3+ on the structural, transport and magnetization properties of Co/NiFe/Co/Cu multilayers. X-Ray diffraction and extended x-ray absorption fine structures measurements show no significant structural change for as deposited and irradiated multilayers. On the other hand, the magnetoresistance amplitude decreases with the ion fluence but it is insensitive to the projectile charge state.The correlation between changes in the magnetoresistance and remanent magnetization suggests that the main effect responsible for the decrease of the magnetoresistance is the creation of ferromagnetic pinholes. These results are discussed on basis of the electronic thermal spike model and nuclear cascades theory and show similarities to the effects observed at low-energy ion-beam irradiation.61.80.Jh, 75.70.Pa 1 I -IntroductionFast heavy ions may lead to permanent material changes in a small cylinder along the nearly straight ion path, giving rise to the so-called ion tracks. Different explanations for the basic mechanisms for the track production have been proposed [1][2][3][4][5][6][7][8][9], but all of them depend on the electronic ionization along the ion path and thus on the projectile charge. All these mechanisms may finally yield an unordered atomic motion and if a critical local lattice temperature is exceeded, permanent atomic rearrangement may result. The influence of the nuclear tracks has been widely studied in polymers, semiconductors and metallic glasses [10][11], but in much less extension for magnetic materials.Multilayer (ML) magnetic systems have been widely investigated since the discovery of the phenomenon of giant magnetoresistance (GMR) [12], because of their great potential for applications in magnetic recording technology [13]. In particular studies using low energy ions, where nuclear stopping power predominates, show that the ion bombardment can promote local atomic diffusion and modification of the magnetic properties of the target. For instance changes in the coercivity , uniaxial magnetic texture, interface mixing and phase transformation have been reported for Fe/Co systems [14][15][16][17]. Furthermore the suppression of exchange bias [18] and modification of the perpendicular interface anisotropy [19] have been observed by keV He ions irradiation.Also these low energy ions may be used to control of interlayer exchange coupling [20] and to induce chemical order in intermetallic alloys [21]. Swift ion irradiations with 350MeV Au ions also lead to changes in magnetism and microstructure as recently observed in Fe/Si systems [22,23]. 2The ion irradiation at low energies may increase the GMR in few cases (depending on the ion fluence) but mostly it leads to a degradation of the GMR [24][25][26][27].The observed reduction of the GMR and the partial loss of antiferromagnetic coupling were interpreted in terms of the creation of ferromagnetic pinholes. We have stu...

Impact Features Induced by Single Fast Ions of Different Charge-State on Muscovite Mica

“…Electronic stopping power for 593 MeV Au beams of different charge states q in mica as calculated by the code CasP6.0. These Au charge states are obtained from 593 MeV Au 30+ ions exiting amorphous carbon foils of different thicknesses (see inset with data from Grande et al [50]). Well-defined initial charge states reach the targets, as the beam passes through a series of magnetic analysers in the way to the irradiation chamber.…”