60 research outputs found
Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloy as magnetic electrodes
HRTEM, nano-beam electronic diffraction, energy dispersive X-rays scanning
spectroscopy, Vibrating Sample Magnetometry (VSM) and FerroMagnetic Resonance
(FMR) techniques are used in view of comparing (static and dynamic) magnetic
and structural properties of Co2MnGe (13 nm)/Al2O3 (3 nm)/Co (13 nm) tunnel
magnetic junctions (TMJ), deposited on various single crystalline substrates
(a-plane sapphire, MgO(100) and Si(111)). They allow for providing a
correlation between these magnetic properties and the fine structure
investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and
contains a large concentration of Co atoms, which, however, is significantly
reduced when using a sapphire substrate. The Co layer is polycrystalline and
shows larger grains for films grown on a sapphire substrate. The VSM
investigation reveals in-plane anisotropy only for samples grown on a sapphire
substrate. The FMR spectra of the TMJs are compared to the obtained ones with a
single Co and Co2MnGe films of identical thickness deposited on a sapphire
substrate. As expected, two distinct modes are detected in the TMJs while only
one mode is observed in each single film. For the TMJ grown on a sapphire
substrate the FMR behavior does not significantly differ from the superposition
of the individual spectra of the single films, allowing for concluding that the
exchange coupling between the two magnetic layers is too small to give rise to
observable shifts. For TMJs grown on a Si or on a MgO substrate the resonance
spectra reveal one mode which is nearly identical to the obtained one in the
single Co film, while the other observed resonance shows a considerably smaller
intensity and cannot be described using the magnetic parameters appropriate to
the single Co2MnGe film.Comment: 11 pages, 10 figures, Thin Solid Film
Magnetization dynamics in Co2O3$/Co tunnel junctions grown on different substrates
We study static and dynamic magnetic properties of Co2MnGe (13 nm)/Al2O3 (3
nm)/Co (13 nm) tunnel magnetic junctions (TMJ), deposited on various single
crystalline substrates (a-plane sapphire, MgO(100), Si(111)). The results are
compared to the magnetic properties of Co and of CoMnGe single films
lying on sapphire substrates. X-rays diffraction always shows a (110)
orientation of the CoMnGe films. Structural observations obtained by high
resolution transmission electron microscopy confirmed the high quality of the
TMJ grown on sapphire. Our vibrating sample magnetometry measurements reveal
in-plane anisotropy only in samples grown on a sapphire substrate. Depending on
the substrate, the ferromagnetic resonance spectra of the TMJs, studied by the
microstrip technique, show one or two pseudo-uniform modes. In the case of MgO
and of Si substrates only one mode is observed: it is described by magnetic
parameters (g-factor, effective magnetization, in-plane magnetic anisotropy)
derived in the frame of a simple expression of the magnetic energy density;
these parameters are practically identical to those obtained for the Co single
film. With a sapphire substrate two modes are present: one of them does not
appreciably differ from the observed mode in the Co single film while the other
one is similar to the mode appearing in the CoMnGe single film: their
magnetic parameters can thus be determined independently, using a classical
model for the energy density in the absence of interlayer exchange coupling.Comment: 5 pages, 6 figure
Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study
Microstrip ferromagnetic resonance and Brillouin scattering are used to
provide a comparative determination of the magnetic parameters of thin
permalloy layers interfaced with a non-magnetic (Al2O3) or with an
antiferromagnetic oxide (NiO). It is shown that the perpendicular anisotropy is
monitored by an interfacial surface energy term which is practically
independent of the nature of the interface. In the investigated interval of
thicknesses (5-25 nm) the saturation magnetisation does not significantly
differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy
and exchange-bias anisotropy are also derived from this study of the dynamic
magnetic excitations and compared to our independent evaluations using
conventional magnetometryComment: 7 pages, 6 figures, submited to Journal of Physics: Condensed Matte
Probing the Dzyaloshinskii-Moriya interaction in CoFeB ultrathin films using domain wall creep and Brillouin light spectroscopy
We have characterized the strength of the interfacial Dyzaloshinskii-Moriya
interaction (DMI) in ultrathin perpendicularly magnetized CoFeB/MgO films,
grown on different underlayers of W, TaN, and Hf, using two experimental
methods. First, we determined the effective DMI field from measurements of
field-driven domain wall motion in the creep regime, where applied in-plane
magnetic fields induce an anisotropy in the wall propagation that is correlated
with the DMI strength. Second, Brillouin light spectroscopy was employed to
quantify the frequency non-reciprocity of spin waves in the CoFeB layers, which
yielded an independent measurement of the DMI. By combining these results, we
show that DMI estimates from the different techniques only yield qualitative
agreement, which suggests that open questions remain on the underlying models
used to interpret these results.Comment: 8 page
Anomalous polarization conversion in arrays of ultrathin ferromagnetic nanowires
We study optical properties of arrays of ultrathin nanowires by means of the
Brillouin scattering of light on magnons. We employ the Stokes/anti-Stokes
scattering asymmetry to probe the circular polarization of a local electric
field induced inside nanowires by linearly polarized light waves. We observe
the anomalous polarization conversion of the opposite sign than that in a bulk
medium or thick nanowires with a great enhancement of the degree of circular
polarization attributed to an unconventional refraction in the nanowire medium.Comment: 5 pages, 4 figure
Magnetization pinning in conducting films demonstrated using broadband ferromagnetic resonance
The broadband microstrip ferromagnetic resonance technique has been applied
for detection and characterization of a magnetic inhomogeneity in a film
sample. In the case of a 100nm thick Permalloy film an additional magnetically
depleted top sub-layer, practically unidentifiable by the conventional
ferromagnetic resonance setup, has been detected and characterized. These
results have been confirmed by Brillouin light scattering spectroscopy
revealing the fact that the optical properties of the additional sub-layer do
not differ much from those of the bulk of the film. Subsequent characterization
of a large number of other presumably single-layer films with thicknesses in
the range 30-100nm using the same ferromagnetic resonance technique also
revealed the same effect
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