Tailoring the magnetic anisotropy of thin films utilizing large persistent stress and pulsed laser irradiation
FacultiesFakultät für Ingenieurwissenschaften und Informatik
LicenseStandard (Fassung vom 01.10.2008)
The magnetic anisotropy plays a major role towards the stability of information stored in the magnetic recording media and the properties of devices using the giant magnetoresistive effect. The objective of this thesis work was to tailor the magnetic anisotropy of thin films and multilayers (MLs) by varying the magnetoelastic and the unidirectional anisotropy energy contributions. The first part of this thesis work addresses the optimization of the perpendicular magnetic anisotropy (PMA) by applying a persistent in-plane biaxial stress. The latter has been applied by a novel method that involves deposition of the functional layers on a Ta substrate, which is subsequently loaded with hydrogen. The method has been successfully demonstrated in Ni and CoFe thin films and Co/Pd MLs. In the case of Co/Pd MLs, which are interesting for perpendicular magnetic recording, an increase of about 100% in the PMA has been observed upon applying a biaxial stress of 2.1 GPa. This shows that the application of the biaxial stress provides an additional degree of freedom to optimize the PMA and therefore the magnetic properties of the Co/Pd MLs. The second part of the thesis addresses the optimization of unidirectional anisotropy associated with the exchange bias in the NiMn/Co system by pulsed laser irradiation. To achieve the antiferromagnetic NiMn phase, annealing at elevated temperatures is required which may cause unwanted interdiffusion between the layers. By applying Nd:YAG Q-switch laser pulses with an optimum fluence, the microstructure of the NiMn layer has been modified without interdiffusion to the Co layer. After subsequent conventional annealing treatment, the laser irradiated samples showed about 100% increase in the exchange bias field compared to that of the non-irradiated samples under identical annealing conditions. This demonstrates that the pulsed laser irradiation provides a novel way to optimize the magnetic properties of NiMn based exchange bias systems.
Subject HeadingsMagnetische Anisotropie [GND]
Nd-YAG lasers [LCSH]
Pulsed laser deposition [LCSH]
X-rays. Diffraction [LCSH]