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Lattice-mismatch-induced granularity in CoPt-NbN and NbN-CoPt superconductor-ferromagnet heterostructures: Effect of strain
The effect of strain due to lattice mismatch and of ferromagnetic (FM)
exchange field on superconductivity (SC) in NbN-CoPt bilayers is investigated.
Two different bilayer systems with reversed deposition sequence are grown on
MgO (001) single crystals. While robust superconductivity with high critical
temperature (T_c ~ 15.3 K) and narrow transition width DelT_c ~ 0.4 K) is seen
in two types of CoPt-NbN/MgO heterostructures where the magnetic anisotropy of
CoPt is in-plane in one case and out-of-plane in the other, the NbN-CoPt/MgO
system shows markedly suppressed SC response. The reduced SC order parameter of
this system, which manifests itself in Tc, temperature dependence of critical
current density J_c (T), and angular (Phi) variation of flux-flow resistivity
Rho_f is shown to be a signature of the structure of NbN film and not a result
of the exchange field of CoPt. The Rho_f (H,T,Phi) data further suggest that
the domain walls in the CoPt film are of the Neel type and hence do not cause
any flux in the superconducting layer. A small, but distinct increase in the
low-field critical current of the CoPt-NbN couple is seen when the magnetic
layer has perpendicular anisotropy.Comment: 9 figure
Spin dynamics of a one-dimensional spin-1/2 fully anisotropic Ising-like antiferromagnet in a transverse magnetic field
We consider the one-dimensional Ising-like fully anisotropic S=1/2 Heisenberg
antiferromagnetic Hamiltonian and study the dynamics of domain wall excitations
in the presence of transverse magnetic field . We obtain dynamical spin
correlation functions along the magnetic field and
perpendicular to it . It is shown that the line shapes of
and are purely symmetric at the
zone-boundary. It is observed in for that the
spectral weight moves toward low energy side with the increase of . This
model is applicable to study the spin dynamics of CsCoCl in the presence of
weak interchain interactions.Comment: 19 pages, LaTeX, 12 eps figure
Fluid Dynamics
Ripon Professorship Lecture for 1947 delivered at the Indian Association for the
Cultivation of Science, in August-September 195
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