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Static and dynamic X-ray resonant magnetic scattering studies on magnetic
domains
Soriano, J.M.
Publication date
2005
Link to publication
Citation for published version (APA):
Soriano, J. M. (2005). Static and dynamic X-ray resonant magnetic scattering studies on
magnetic domains.
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SUMMARY Y
Thiss thesis provides a broad-scope survey exploring the various possi-bilitiess that soft X-ray resonant magnetic scattering offers for studying out-of-planee magnetic domains found in thin magnetic films.
Thiss technique takes advantage of the strong magneto-optical contrast off the atomic resonances in the soft X-ray range. In the case of the rare-earth elements,, the M^s (3d — 4 / transitions) isotropic, circular and linear dichroic absorptionn spectra are obtained by atomic multiplet calculations. Application off the Kramers-Kronig transforms to these spectra allows us to obtain the com-pletee set of magneto-optical constants: the resonant scattering factors as well ass the specific Faraday and Voigt rotation angles. Precise knowledge of these spectraa is imperative for the planning and the analysis of resonant experiments, whilee at the same time it offers useful insights into the development of novel compactt Cherenkov radiation-based X-ray sources.
AA complete description is presented of the information that can be ex-tractedd from scattering patterns of disordered domains found in amorphous GdFee thin films under quasi-static magnetic fields. The intentionally grown perpendicularr magnetic anisotropy of these systems produces a collection of out-of-planee magnetic domains that are dressed by Bloch walls and closure do-mains.. Magnetic reversal is achieved through nucleation and domain wall mo-tion.. The average domain period, correlation length and reversed domain size weree measured from the remanent state all the way up to magnetic saturation. Inn the case of aligned stripes, the period can be predicted by analytical stripe domainn models, which prove to be non-applicable for the case of disordered domains.. Furthermore, a general relation between the ensemble-averaged out-of-planee magnetization and the total scattered intensity is derived, which is ful-filledd in all the cases studied here.
AA pioneering experiment combining the X-ray resonant scattering tech-niquee and magneto-optical Kerr effect with very strong magnetic pulses al-lowedd us to follow the magnetization and scattering of the same GdFe films
138 8 SUMMARY Y
withh spatial and temporal resolutions of 50 nm and 100 ps respectively. Rather unexpectedly,, for one composition the antiparallel coupling between the two subnetworkss was found to break during and after the magnetic pulse, causing thee Gd out-of-plane magnetization to vanish and relaxation of the system tak-ingg as long as 100 ns. For the other case, the system response followed the pulse temporall evolution, although a decrease in the Gd-subnetwork magnetization wass again seen. This striking novel phenomenon is tentatively explained as the dynamicall analogue of the static magnetically-driven spin-flop transition ob-servedd in other rare-earth/transition-metal alloys. The distinct response of the twoo samples is likely to originate from the different saturation magnetization.
Inn order to control the domain nucleation process, focused-ion-beam ir-radiationn was used to locally modify the magnetic properties of amorphous GdTbFee thin films. These have a high intrinsic perpendicular magnetic anisotro-pyy and display a very uncorrelated domain pattern at remanence. Rather than modifyingg the nucleation field, this process affected the size, position and di-rectionn of the reversed domains upon magnetic saturation to levels depending onn the ion fluence and interdot spacing.
Finally,, we have used X-ray magnetic circular dichroism and resonant magneticc scattering to study the reversal behaviour of two room-temperature perpendicularr exchange-bias [Pt/Co]„ /FeMn multilayer systems. In both cases, uncompensatedd Fe spins at the ferromagnetic/antiferromagnetic interface were foundd and their thickness estimated. However, when the systems exhibited ex-changee bias, a small fraction of these spins was pinned, causing a vertical shift in thee Fe-related absorption hysteresis loop. This constitutes the first experimen-tall proof of this behaviour, previously observed in low-temperature in-plane exchange-biass systems, being reproduced by its perpendicular counterpart.
