G. Jakob

Range and stopping power dependence of heavy ion-induced demagnetizations of ferromagnetic materials

Abstract Heavy ion beams induce by their stopping power severe demagnetizations of ferromagnetic materials of dynamic nature. This perturbation of ferromagnetism causes substantial attenuations of transient magnetic fields on traversing probe ions. A striking stopping power dependence has been found when the probe ions are in the H-like charge state. Due to the uncorrelated behaviour of beam ions and probe ions , moving on different trajectories through the ferromagnetic sample, the demagnetization, initially located at the ionization track of the beam ion, must propagate to the region of the probe ion. The determination of the range of demagnetization from its origin was the subject of the present measurements.

Preparation and analysis of targets with implanted thick Ar layers for in-beam γ-spectroscopy

Abstract Implantation of 80 keV 40 Ar ions into 0.5 mg/cm 2 thick Fe layers, deposited by vacuum evaporation onto a Gd foil, yielded an Ar target of 35(6) μg/cm 2 thickness which is suitable for in-beam γ-spectroscopy. Thin Fe-layer evaporation and implantation were successively applied in several cycles whereby the Ar implantation always occurred into a newly prepared Fe layer. These procedures can principally be extended for obtaining even larger thicknesses. The Ar content of the target and its layer thickness were accurately determined by the Elastic Recoil Detection Analysis technique using a 58 Ni beam.

Transient magnetic fields and electron polarizations of H-like oxygen ions in crystalline iron and amorphous iron-boron compounds

Abstract Transient magnetic fields (TF) have been measured for oxygen ions with the 16 O(3 − ) state as probe traversing thin layers of crystalline Fe and amorphous Fe 80 B 20 compounds. The TF associated with polarized 1s electrons have strengths of B TF (Fe) = 412 (38) T in Fe and B TF (FeB) = 368 (62) T in FeB implying degrees of polarization of p 1s (Fe) = 0.13 (1) and p 1s (FeB) = 0.14 (3), respectively. The strength parameter a = 12.1 (2.3) T deduced for FeB agrees very well with other data rendering it highly suitable for TF measurements.

Large transient magnetic fields of 28Si ions in backscattering through Fe at high velocities

Abstract Transient field (TF) precessions have been measured in Fe for high-velocity 28 Si ions following projectile Coulomb excitation of the first 2 + -state. In contrast to a recent measurement on 24 Mg ions which yielded at comparable velocity with the same geometry for the angular correlation an unexpected small TF, the present observations agree very well with the expectation of large TF: no diminution of the transferred polarization is found.

Evidence for ion beam induced attenuations of the static hyperfine field at recoil implanted 56Fe ions in Fe host

Abstract Measurements of transient (TF) and static (SF) magnetic hyperfine fields at 56 Fe(2 + ) ions, implanted in Fe host after Coulomb excitation using 16 O- and 56 Fe-beams, exhibit attenuations of the SF strength which is shown for the first time to be primarily due to the effect of the ion beam and only secondarily to that of the recoil ion. The beam induced attenuation is of the same nature and magnitude as for TF, which has been determined in former measurements. It must therefore arise from the depolarization of the Fe 3d electrons resulting from the ion stopping. The effect of the recoil implanted ion may be attributed to a thermal spike which seems to be more efficient for heavier probe ions.

Hyperfine interaction studies on swift O-ions emerging with polarized electrons from ferromagnetic layers into vacuum

A precision plunger set-up was used to determine in time-differential measurements of hyperfine interactions the degree of polarization of 1s- and 2s-electrons in H- and Li-like oxygen ions on their emergence from magnetized Ni- and Gd-layers into vacuum. In addition a time-integral measurement with Fe-layers served to obtain the polarization of 2s-electrons only. For all three ferromagnetic materials the degree of polarization of 2s-electrons is found to be twice as large as for 1s-electrons. The data are discussed in the context of transient magnetic fields and their underlying polarization mechanism.