126 research outputs found
Controlled enhancement or suppression of exchange biasing using impurity -layers
The effects of inserting impurity -layers of various elements into a
Co/IrMn exchange biased bilayer, at both the interface, and at given points
within the IrMn layer a distance from the interface, has been investigated.
Depending on the chemical species of dopant, and its position, we found that
the exchange biasing can be either strongly enhanced or suppressed. We show
that biasing is enhanced with a dusting of certain magnetic impurities, present
at either at the interface or sufficiently far away from the Co/IrMn interface.
This illustrates that the final spin structure at the Co/IrMn interface is not
only governed by interface structure/roughness but is also mediated by local
exchange or anisotropy variations within the bulk of the IrMn
Reply on the comment on the paper "Superconducting transition in Nb nanowires fabricated using focused ion beam"
In this communication we present our response to the recent comment of A.
Engel regarding our paper on FIB- fabricated Nb nanowires (see Vol. 20 (2009)
Pag. 465302). After further analysis and additional experimental evidence, we
conclude that our interpretation of the experimental results in light of QPS
theory is still valid when compared with the alternative proximity-based model
as proposed by A. Engel.Comment: 3 pages, 1 figure, accepted by Nanotechnolog
Growth and Characterization of -Mn Structured CoZn Thin Films
Thin films of polycrystalline -Mn structure CoZn have been grown on
thermally oxidized Si substrates by co-sputtering from elemental targets
followed by annealing. A range of films grown with variable Co deposition power
and fixed Zn deposition power were produced, so as to vary the proportions of
the two elements reaching the substrate, which were annealed post-growth.
Whilst all films exhibited a (211) -Mn structure CoZn texture in X-ray
diffraction, transmission electron microscopy showed that the composition with
the highest integrated intensity for that Bragg peak contained large vacancies
and was covered by a thick ZnO cap owing to being Co-deficient overall. CoZn
films deposited at ratios tuned to give the optimal volume fraction of
-Mn were continuous, with crystallites up to 200~nm in size, with a much
thinner ZnO cap layer. Magnetic measurements show that such optimal CoZn films
have a Curie temperature ~K and saturation magnetization
of 120~emu/cm, properties close to those reported for bulk crystals. The
-Mn structure is chiral (P432/P432 space group) and is known
to give rise to a Dzyaloshinkii-Moriya interaction (DMI) that stabilizes
room-temperature skyrmions in the bulk. Our thin films are thus a potential
materials platform, compatible with planar processing technology, for magnetic
skyrmions arising from a bulk DMI.Comment: v2 corrects minor typographical error
Angular dependence of domain wall resistivity in artificial magnetic domain structures
We exploit the ability to precisely control the magnetic domain structure of
perpendicularly magnetized Pt/Co/Pt trilayers to fabricate artificial domain
wall arrays and study their transport properties. The scaling behaviour of this
model system confirms the intrinsic domain wall origin of the
magnetoresistance, and systematic studies using domains patterned at various
angles to the current flow are excellently described by an angular-dependent
resistivity tensor containing perpendicular and parallel domain wall
resistivities. We find that the latter are fully consistent with Levy-Zhang
theory, which allows us to estimate the ratio of minority to majority spin
carrier resistivities, rho-down/rho-up~5.5, in good agreement with thin film
band structure calculations.Comment: 14 pages, 3 figure
Exchange anisotropy pinning of a standing spin wave mode
Standing spin waves in a thin film are used as sensitive probes of interface
pinning induced by an antiferromagnet through exchange anisotropy. Using
coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin
wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was
studied for a range of IrMn thicknesses. We show that pinning of the standing
mode can be used to amplify, relative to the fundamental resonance, frequency
shifts associated with exchange bias. The shifts provide a unique `fingerprint'
of the exchange bias and can be interpreted in terms of an effective
ferromagnetic film thickness and ferromagnet/antiferromagnet interface
anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic
Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in
the pinning fields. The pinning strength magnitude is found to grow with
cooling of the sample, while the effective ferromagnetic film thickness
simultaneously decreases. These results suggest that exchange bias involves
some deformation of magnetic order in the interface region.Comment: 7 pages, 7 figure
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