Origin of the perpendicular anisotropy in FePt alloys

NADIA ÁLVAREZ; JAVIER GÓMEZ; ALEJANDRO BUTERA

Buenos Aires

Conferencia; X Latin American Workshop on Magnetism, Magnetic Materials and Their Applications, Buenos Aires, April 8-12, 2013; 2013

FePt intermetallic alloys have been thoroughly studied in the past years, mainly because of possibleapplications in the field of magnetic recording. This interest arises from the presence of a very large coercitivity and anisotropy in the ordered crystalline phase.However, lms deposited by sputtering techniques at room temperature tend to grow in an FCC crystalline structure with the atoms randomly distributed and with soft magnetic properties. Although the coercive field and the magnetocrystalline anisotropy are not as high as in the ordered phase, this system presents a magnetic behavior with many unusual properties from the fundamental point of view.It has been reported that as-made FePt thin films presents a component of the anisotropy perpendicular to the plane of the film that can give a particular kind of magnetic structure called "stripe-domains". This conguration presents a small out-of-plane component of the magnetization which periodically changes from the "up" to the "down" direction inducing the formationof a stripe structure. The origin of the out of plane anisotropy is due to the combined effects ofmagnetocrystalline anisotropy and magnetoelastic energy.The aim of this work has been to separate these two contributions to the perpendicular anisotropy for a better understanding of the process that originates the stripes. To do so, we have fabricated a series of six samples in which we gradually varied the Ar pressure in the sputtering chamber from 3 to 13 mTorr. The increment of the Ar pressure results in the relaxation of the residual stress of the films but preserves the [111] crystalline texture. We could see, with the aim of an AFM-MFM microscope, the transition from a striped pattern to in plane magnetic domains for a pressureof 11 mTorr. We also correlate these images with in plane and out-of-plane magnetic measurements with a VSM and ferromagnetic resonance spectra.