Deviations from bulk behavior in TbFe(Co) thin films: Interfaces contribution in the biased composition

Abstract

Ferrimagnetic TbFe or TbFeCo amorphous alloy thin films have been grown by coevaporation in ultrahigh vacuum. They exhibit an out-of-plane magnetic anisotropy up to their Curie temperature with a nucleation and propagation reversal mechanism suitable for current induced domain wall motion. Rutherford backscattering experiments confirmed a fine control of the Tb depth-integrated composition within the evaporation process. However, a large set of experimental techniques were used to evidence an interface related contribution in such thin films as compared to much thicker samples. In particular, scanning transmission electron microscopy experiments evidence a depth dependent composition and perturbed top and bottom interfaces with preferential oxidation and diffusion of terbium. Despite that, amorphous and homogeneous alloy film remains in a bulklike part. The composition of that bulklike part of the magnetic layer, labeled as effective composition, is biased when compared with the depth-integrated composition. The magnetic properties of the film are mostly dictated by this effective composition, which we show changes with different top and bottom interfaces.

Measurement of the tilt of a moving domain wall shows precession-free dynamics in compensated ferrimagnets

“…Due to the migration of Gd during patterning 12 the M S values have changed. By measuring the T MC pre-and post-patterning, we corrected this M S temperature shift of − 31 K. A relatively low and temperature-dependent magnetisation has been measured as expected 12 . The magnetic compensation temperature where the net magnetisation vanishes is clearly visible.…”

“…In the RETM ferrimagnetic case, the DW velocity can still be described with the same model 32 . Since the spin current interacts mainly with the TM sub-lattice ( 12 and references therein), φ in Eq. ( 1 ) corresponds to the DW angle of the TM sub-lattice (see Fig.…”

“…Indeed, they have two antiferromagnetically-coupled sublattices, corresponding roughly to the RE and TM moments, and their spin transport is carried mainly by the TM sub-lattice 11 . Furthermore, RETM thin films can exhibit perpendicular magnetic anisotropy, are conductors, and present large spin transport polarization and spin torques, even when integrated in complex stacks 12 . Additionally, their magnetic properties can be controlled by changing either their composition or temperature, as described by the mean-field theory 11 .…”

“…(b) Measured net magnetisation M S (squares) of the virgin film and coercivity H C (dots) of the patterned track versus temperature T . The M S points were shifted by − 31 K to account for migration of Gd during patterning 12 . The continuous line is the result of the mean-field model (see suppl.).…”

Strong current actions on ferrimagnetic domain walls in the creep regime

“…The studied film is 7 nm of the amorphous alloy Tb 21 Fe 79 with 5 nm Al cover with perpendicular magnetic anisotropy deposited by co-evaporation on a Si/SiO x (500 nm) substrate in ultrahigh vacuum. Details of growth and basic properties of the stacks are published elsewhere [20]. The film was characterized by using the magneto-optic Kerr effect (MOKE) and the anomalous Hall effect (AHE) resistivity measurements which are mainly proportional to spin polarization of electrons at the Fermi level (equivalent to P) [8,10].…”