341 research outputs found
Analytical modeling of demagnetizing effect in magnetoelectric ferrite/PZT/ferrite trilayers taking into account a mechanical coupling
In this paper, we investigate the demagnetizing effect in ferrite/PZT/ferrite
magnetoelectric (ME) trilayer composites consisting of commercial PZT discs
bonded by epoxy layers to Ni-Co-Zn ferrite discs made by a reactive Spark
Plasma Sintering (SPS) technique. ME voltage coefficients (transversal mode)
were measured on ferrite/PZT/ferrite trilayer ME samples with different
thicknesses or phase volume ratio in order to highlight the influence of the
magnetic field penetration governed by these geometrical parameters.
Experimental ME coefficients and voltages were compared to analytical
calculations using a quasi-static model. Theoretical demagnetizing factors of
two magnetic discs that interact together in parallel magnetic structures were
derived from an analytical calculation based on a superposition method. These
factors were introduced in ME voltage calculations which take account of the
demagnetizing effect. To fit the experimental results, a mechanical coupling
factor was also introduced in the theoretical formula. This reflects the
differential strain that exists in the ferrite and PZT layers due to shear
effects near the edge of the ME samples and within the bonding epoxy layers.
From this study, an optimization in magnitude of the ME voltage is obtained.
Lastly, an analytical calculation of demagnetizing effect was conducted for
layered ME composites containing higher numbers of alternated layers (). The
advantage of such a structure is then discussed
Uniaxial anisotropy and enhanced magnetostriction of CoFeO induced by reaction under uniaxial pressure with SPS
In this study, we have compared magnetic and magnetostrictive properties of
polycrystalline CoFeO pellets, produced by three different methods,
focusing on the use of Spark Plasma Sintering (SPS). This technique allows a
very short heat treatment stage while a uniaxial pressure is applied. SPS was
utilized to sinter cobalt ferrite but also to make the reaction and the
sintering (reactive sintering) of the same ceramic composition. Magnetic and
magnetostrictive measurements show that the reactive sintering with SPS induces
a uniaxial anisotropy, while it is not the case with a simple sintering
process. The induced anisotropy is then expected to be a consequence of the
reaction under uniaxial pressure. This anisotropy enhanced the magnetostrictive
properties of the sample, where a maximum longitudinal magnetostriction of
~ppm is obtained. This process can be a promising alternative to the
magnetic-annealing because of the short processing time required (22 minutes)
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