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The feedback of midlatitude waves onto the Hadley cell in a simple general circulation model
We present self-consistent comparisons of axissymmetric and 3-dimensional simulations of the tropospheric circulation under idealized physical conditions. These reveal a feedback of transient eddies onto the Hadley circulation which, first, strongly depends on equatorial heating and, second, is in case of realistic heating quite different from prescribed eddy forcing. A quantitative estimation for the eddy-induced mixing of vorticity into the poleward flow of the Hadley cell is given. The proposed relation is in accordance with observations. It is derived from the computational result that eddy momentum flux convergence is of the same order as the equatorward flux of relative vorticity generated by the Hadley circulation. Evaluation of the local budgets of sensible heat gives rise to a clear picture of how the poleward heat transports due to Hadley circulation and transient eddies interlock. This mechanism is found to be essential for an interpretation of the eddy feedback
Magneto-optical imaging of voltage-controlled magnetization reorientation
We study the validity and limitations of a macrospin model to describe the
voltage-controlled manipulation of ferromagnetic magnetization in nickel thin
film/piezoelectric actuator hybrid structures. To this end, we correlate
simultaneously measured spatially resolved magneto-optical Kerr effect imaging
and integral magnetotransport measurements at room temperature. Our results
show that a macrospin approach is adequate to model the magnetoresistance as a
function of the voltage applied to the hybrid, except for a narrow region
around the coercive field - where the magnetization reorientation evolves via
domain effects. Thus, on length scales much larger than the typical magnetic
domain size, the voltage control of magnetization is well reproduced by a
simple Stoner-Wohlfarth type macrospin model
Epitaxial growth and magnetic properties of Sr2CrReO6 thin films
The double perovskite Sr2CrReO6 is an interesting material for spintronics,
showing ferrimagnetism up to 635 K with a predicted high spin polarization of
about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition
on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum
crystallographic and magnetic properties were obtained by growing at a
substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films
are c-axis oriented, coherently strained, and show less than 20% anti-site
defects. The magnetization curves reveal high saturation magnetization of 0.8
muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic
anisotropy.Comment: accepted for publicatio
Giant Magnetoelastic Effects in BaTiO3-based Extrinsic Multiferroic Hybrids
Extrinsic multiferroic hybrid structures consisting of ferromagnetic and
ferroelectric layers elastically coupled to each other are promising due to
their robust magnetoelectric effects even at room temperature. For a
quantitative analysis of these magnetoelectric effects, a detailed knowledge of
the piezoelectric and magnetoelastic behavior of both constituents as well as
their mutual elastic coupling is mandatory. We here report on a theoretical and
experimental study of the magnetic behavior of BaTiO3-based extrinsic
multiferroic structures. An excellent agreement between molecular dynamics
simulations and the experiments was found for Fe50Co50/BaTiO3 and Ni/BaTiO3
hybrid structures. This demonstrates that the magnetic behavior of extrinsic
multiferroic hybrid structures can be determined by means of ab-initio
calculations, allowing for the design of novel multiferroic hybrids
Giant magnetic anisotropy changes in Sr2CrReO6 thin films on BaTiO3
The integration of ferromagnetic and ferroelectric materials into hybrid
heterostructures yields multifunctional systems with improved or novel
functionality. We here report on the structural, electronic and magnetic
properties of the ferromagnetic double perovskite Sr2CrReO6, grown as epitaxial
thin film onto ferroelectric BaTiO3. As a function of temperature, the
crystal-structure of BaTiO3 undergoes phase transitions, which induce
qualitative changes in the magnetic anisotropy of the ferromagnet. We observe
abrupt changes in the coercive field of up to 1.2T along with resistance
changes of up to 6.5%. These results are attributed to the high sensitivity of
the double perovskites to mechanical deformation.Comment: 3 figure
Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites
We have investigated the magnetic moment of the W ion in the ferrimagnetic
double perovskites Sr2CrWO6 and Ca2CrWO6 by X-ray magnetic circular dichroism
(XMCD) at the W L(2,3) edges. In both compounds a finite negative spin and
positive orbital magnetic moment was detected. The experimental results are in
good agreement with band-structure calculations for (Sr/Ca)2CrWO6 using the
full-potential linear muffin-tin orbital method. It is remarkable, that the
magnetic ordering temperature, TC, is correlated with the magnetic moment at
the 'non-magnetic' W atom.Comment: accepted for publicatio