Trifon Fitchorov

Electrically controlled magnetization switching in a multiferroic heterostructure

A demonstration of magnetization reversal via the application of electric field across a multiferroic heterostructure, consisting of a FeCoV ribbon bonded to a lead magnesium niobate-lead titanate crystal, is presented. The magnetization switching occurs by an abrupt change in magnetization near ferromagnetic coercivity, coinciding with an electrical field-induced magnetic anisotropy field. Experiments reveal a converse magnetoelectric coupling of α=μ0(dM/dE)=1.6×10−7 s m−1 upon magnetization reversal in the strain-mediated heterostructure. The frequency dependence of magnetization switching is presented and explained within the framework of a relaxation model for the multiferroic heterostructure.

Quasi-one-dimensional miniature multiferroic magnetic field sensor with high sensitivity at zero bias field

A miniature, quasi one dimensional, magnetic field sensor based on magnetoelectric coupling is presented. The magnetoelectric sensor makes use of the d31 coupling mode between a piezoelectric lead zirconate titanate tube and FeNi magnetostrictive wire. The sensors demonstrate high sensitivity, high signal-to-noise ratio, and low noise floor at zero DC magnetic bias field and at low frequency resulting in smaller, lower power consumption, and volumetric efficiency. Experiments indicate a zero bias field sensitivity of 16.5 mV/Oe at 100 Hz stemming from a magnetoelectric coefficient of 1.65 V/cm-Oe. The results are quantitatively described by a theoretical model of laminate composites.

Large converse magnetoelectric coupling in FeCoV/lead zinc niobate-lead titanate heterostructure

Multiferroic behavior was directly verified in a laminated ferroelectric-ferromagnetic heterostructure consisting of a FeCoV thick film (70 μm) and lead zinc niobate-lead titanate (PZN-PT) single crystal. This unique heterostructure demonstrates a significant converse magnetoelectric (CME) effect corresponding to a CME coupling constant of 31 Oe/kV cm−1. It derives from the soft magnetic and magnetostrictive properties (λ=60 ppm) of FeCoV alloy and the superior electromechanical properties (d32=−2800 pC/N) of PZN-PT crystal. The electric field controlled magnetic hysteresis is discussed in terms of a stress-induced anisotropy field model. The theoretical calculation is within 7% of the measured induced field of 240 Oe.

Electronic tuning of magnetic permeability in Co2Z hexaferrite toward high frequency electromagnetic device miniaturization

The magnetic and magnetostriction properties of Z-type cobalt-doped barium hexaferrite with perpendicular c-axis crystallographic texture are presented. The hexaferrite was utilized as a component in Co2Z/lead magnesium niobate-lead titanate multiferroic heterostructures whose tunability of permeability with electric field in terms of ferromagnetic resonance shift was supported by experiments and theoretical calculation. A permeability change of 16% was measured by an induced magnetic field of 38 Oe under the application of 6 kV/cm of electric field. These findings lay the foundation for the application of Z-type hexaferrites in tunable rf and microwave devices valued for sending, receiving, and manipulating electromagnetic signals.

Giant enhancement in the magnetostrictive effect of FeGa alloys doped with low levels of terbium

We present the effects of terbium additives upon the microstructure and magnetic properties of Fe83Ga17Tbx alloys (x = 0, 0.2, 0.4, 0.6, and 0.8), prepared by vacuum electric arc-melting and directional solidification techniques. Experiments indicate that small amounts of terbium more than double the saturation magnetostriction of a [110] textured Fe83Ga17 alloy with λ = 72 × 10−6 and lower the magnetostriction saturation field. The pronounced increase in magnetostriction stems from the appearance of [100] texture in polycrystalline alloys. It is verified that [110] and [100] textures are enhanced by the introduction of terbium atoms preferentially residing in a Tb-rich intergranular phase.

Sustained drug release from non-eroding nanoporous templates.

Inthosesituationsitisnecessarytohaveareservoirthatdoesnotdegradeorerode.Non-eroding nanoporousoxide coatingsofferanattractivealternativeplatformsincetheyarenonerodibleandtheir nanofeatures allow control of the elution profile.Herein, we present the results for the release of a modeldrug,doxorubicin(Dox),fromdifferentnon-erodingnanopor-ous coatings. Detailed studies of drug release from theseplatforms in the form of anodic aluminum oxide (AAO) andanodictitaniumoxide(ATO)werecarriedout.Therearemanyapproaches to sputter metals, such as titanium and aluminum,on different materials and to anodize them afterwards,

Time domain analyses of the converse magnetoelectric effect in a multiferroic metallic glass-relaxor ferroelectric heterostructure

The dynamic time domain response of the converse magnetoelectric effect in a multiferroic Metglas®/Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) heterostructure, under the application of a square waveform electric field excitation of 8 kV/cm at a frequency of 0.4 Hz, is reported. The relaxation behavior followed a stretched power-law function allowing the calculation of an intrinsic time constant. Aging behavior of magnetoelectric coupling was observed after polarization switching of 1000 cycles. These phenomena are predominantly attributed to the temporal response of polarization within the PMN-PT crystal. Results elucidate the dynamic properties of relaxor-based multiferroic heterostructures and importantly define operational constraints for low frequency device operation.

Tunable fringe magnetic fields induced by converse magnetoelectric coupling in a FeGa/PMN-PT multiferroic heterostructure

The fringe magnetic field, induced by magnetoelectric coupling in a bilayer Fe-Ga/Pb(Mg1/3Nb2/3)O3_PbTiO3 (PMN-PT) multifunctional composite, was investigated. The induced external field is characterized as having a butterfly hysteresis loop when tuned by an applied electric field. A tuning coefficient of the electrically induced fringe magnetic field is derived from the piezoelectric and magnetostrictive properties of the composite. A measured maximum tuning coefficient, 4.5 Oe/(kV cm−1), is found to agree well with theoretical prediction. This work establishes a foundation in the design of transducers based on the magnetoelectric effect.The fringe magnetic field, induced by magnetoelectric coupling in a bilayer Fe-Ga/Pb(Mg1/3Nb2/3)O3_PbTiO3 (PMN-PT) multifunctional composite, was investigated. The induced external field is characterized as having a butterfly hysteresis loop when tuned by an applied electric field. A tuning coefficient of the electrically induced fringe magnetic field is derived from the piezoelectric and magnetostrictive properties of the composite. A measured maximum tuning coefficient, 4.5 Oe/(kV cm−1), is found to agree well with theoretical prediction. This work establishes a foundation in the design of transducers based on the magnetoelectric effect.

Topochemical growth of textured polycrystalline barium hexaferrite from oriented antiferromagnetic α-FeOOH nanorods

Nanorods of goethite, i.e. alpha-FeOOH, were mixed with BaCO3, dispersed in a polymer solution, and oriented under a 90 kOe magnetic field during polymerization. The orientation arose principally from the interaction of the magnetic field with the anisotropic antiferromagnetism of the goethite particles. The oriented antiferromagnetic particles act as seeds for the topochemical growth of BaFe12O19 ferrite grains along the [0001] direction. The degree of grain orientation was determined using magnetic measurements and orientation distribution functions and pole figures determined by electron backscatter diffraction analysis.

Electric field controlled magnetic hysteresis loops in a Metglas?/PMN?PT heterostructure

An electric field tunable magnetic hysteresis loop was studied in a multiferroic heterostructure consisting of a 25??m thick Metglas? ribbon affixed to a lead magnesium niobate?lead titanate (PMN?PT) crystal. This multiferroic heterostructure exhibits a considerably strong converse magnetoelectric effect, CME = ?80%, where CME = [M(E) ? M(0)]/M(0), and a converse magnetoelectric coupling constant, A = 23?Oe?cm?kV?1, in the vicinity of the saturation electric polarization. This work systematically demonstrates the tunability of magnetic parameters including magnetization, coercivity, remanence and squareness, under the application of an electric field of 0?8?kV?cm?1. Additionally, the physical mechanism of the CME is discussed. These results provide useful resources for the design of a new generation of electrically controlled devices.