Abstract
10 nm and 50 nm thick Co 2 FeAl (CFA) thin films have been deposited on thermally oxidized Si(001) substrates by magnetron sputtering using a Tantalum cap layer and were then ex-situ annealed at 415°C, 515°C and 615°C during 15 minutes in vacuum. X-rays diffraction indicates that films CFA are polycrystalline and exhibit an in-plane isotropy growth. Ferromagnetic resonance measurements, using a microstrip line (MS-FMR), reveal a huge interfacial perpendicular magnetic anisotropy and small in-plane uniaxial anisotropy both annealing temperature-dependent. The MS-FMR data also allow concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with annealing temperature. Finally, the FMR linewidth decreases with increasing annealing temperature due to the enhancement of the chemical order, and allow deriving a very low intrinsic damping parameter (1.3×10 −3 at 615°C).
Highlights
Spintronics, which is an emerging technology, where electron spin is used as an information vector, is facing three big challenges
The critical current density for the current-induced magnetization switching [1], which is proportional to Gilbert damping constant α and to the inverse of the spin polarization, should be reduced to low values for realizing the high density magnetic random access memory
It is of great interest to investigate the annealing temperature (Ta) effects on the structural and magnetic properties of CFA thin films
Summary
Spintronics, which is an emerging technology, where electron spin is used as an information vector, is facing three big challenges. Co2FeAl (CFA) is one of the Co-based Heusler alloys having a very high Curie temperature (1000 K) and is theoretically predicted to have a half-metallic character of their spin-split band structure It can provide giant tunnelling magnetoresistance (360% at room temperature) [4] when used as an electrode in magnetic tunnel junctions, which makes CFA promising for practical applications. The purpose of this paper is to use ferromagnetic resonance in microstrip line (MS-FMR) under an in-plane and out of plane applied magnetic field combined to vibrating sample magnetometer (VSM) to investigate the correlation between structural and magnetic properties of CFA thin films grown on Si substrate and annealed at different temperatures. In spite of the relative low diffracted signal, the XRD pattern clearly shows peaks corresponding to the Ta (110) and CFA (220), (400) and (422) reflections, respectively This indicates that the CFA film has a polycrystalline structure. All the measurements presented here have been made at room temperature and analysed using the model presented in [5]
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