Margo Staruch

Voltage control of magnetism in FeGaB/PIN-PMN-PT multiferroic heterostructures for high-power and high-temperature applications

We report strong voltage tuning of magnetism in FeGaB deposited on [011]-poled Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ternary single crystals to achieve more than 2 times broader operational range and increased thermal stability as compared to heterostructures based on binary relaxors. Voltage-induced effective ferromagnetic resonance field shift of 180 Oe for electric field from −6.7 kV/cm to 11 kV/cm was observed in FeGaB/PIN-PMN-PT heterostructures. This strong magnetoelectric coupling combined with excellent electric and temperature stability makes FeGaB/PIN-PMN-PT heterostructures potential candidates for high-power tunable radio frequency/microwave magnetic device applications.

Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy.

Multifunctional materials composed of ultrathin magnetic films with perpendicular magnetic anisotropy combined with ferroelectric substrates represent a new approach toward low power, fast, high density spintronics. Here we demonstrate Co/Ni multilayered films with tunable saturation magnetization and perpendicular anisotropy grown directly on ferroelectric PZT [Pb(Zr0.52Ti0.48)O3] substrate plates. Electric fields up to ±2 MV/m expand the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni multilayered film. Modifying the strain with a voltage can reduce the coercive field by over 30%. We also demonstrate that alternating in-plane tensile and compressive strains (less than 0.01%) can be used to propagate magnetic domain walls. This ability to manipulate high anisotropy magnetic thin films could prove useful for lowering the switching energy for magnetic elements in future voltage-controlled spintronic devices.

Frequency reconfigurable phase modulated magnetoelectric sensors using ΔE effect

Magnetoelectric composites have shown promise in low power magnetic field sensing with responsive detection of low frequency fields through the modulation of electromechanical resonance by exploiting a nonlinearity in magnetoelastic properties (ΔE effect). There is also the as-of-yet unrealized potential of tuning this effect to further enhance the shift in resonant frequency of these devices. In the present work, the magnetic field sensitivity was modulated in a bending mode stress reconfigurable sensor through the application of uniaxial tensile stress, reaching up to 8% f0/mT. The minimum magnetic noise floor was determined by detecting the frequency shift using a phase locked loop circuit and was found to directly correspond to the maximum in magnetic field sensitivity that resulted from the ΔE effect.

Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature

The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.

Effects of magnetic field and pressure in magnetoelastic stress reconfigurable thin film resonators

Free-standing CoFe thin-film doubly clamped stress reconfigurable resonators were investigated as a function of magnetic field and pressure. A large uniaxial anisotropy resulting from residual uniaxial tensile stress, as revealed from magnetic hysteresis loops, leads to an easy magnetization axis aligned along the length of the beams. The quality factor of the driven resonator beams under vacuum is increased by 30 times, leading to an enhanced signal-to-noise ratio and a predicted reduction in the intrinsic magnetic noise by a factor of 6, potentially reaching as low as ∼25 pT/√Hz at 1 Torr. Stress reconfigurable sensors operating under vacuum could thus further improve the limit of detection and advance development of magnetic field sensing technology.

Magnetoelectric gradiometer with enhanced vibration rejection efficiency under H-field modulation

A magnetoelectric (ME) gradiometer consisting of two Metglas/Pb(Zr,Ti)O3 fiber-based sensors has been developed. The equivalent magnetic noise of both sensors was first determined to be about 60 pT/√Hz while using an H-field modulation technique. The common mode rejection ratio of a gradiometer based on these two sensors was determined to be 74. The gradiometer response curve was then measured, which provided the dependence of the gradiometer output as a function of the source-gradiometer-normalized distance. Investigations in the presence of vibration noise revealed that a ME gradiometer consisting of two ME magnetometers working under H-field modulation was capable of significant vibration rejection. The results were compared to similar studies of ME gradiometers operated in a passive working mode. Our findings demonstrate that this active gradiometer has a good vibration rejection capability in the presence of both magnetic signals and vibration noise/interferences by using two magnetoelectric sensors ...

Ultra-low-field magneto-elastocaloric cooling in a multiferroic composite device

The advent of caloric materials for magnetocaloric, electrocaloric, and elastocaloric cooling is changing the landscape of solid state cooling technologies with potentials for high-efficiency and environmentally friendly residential and commercial cooling and heat-pumping applications. Given that caloric materials are ferroic materials that undergo first (or second) order phase transitions near room temperature, they open up intriguing possibilities for multiferroic devices with hitherto unexplored functionalities coupling their thermal properties with different fields (magnetic, electric, and stress) through composite configurations. Here we demonstrate a magneto-elastocaloric effect with ultra-low magnetic field (0.16 T) in a compact geometry to generate a cooling temperature change as large as 4 K using a magnetostriction/superelastic alloy composite. Such composite systems can be used to circumvent shortcomings of existing technologies such as the need for high-stress actuation mechanism for elastocaloric materials and the high magnetic field requirement of magnetocaloric materials, while enabling new applications such as compact remote cooling devices.The broad use of elastocaloric materials in cooling applications is hindered by the need to exert large forces onto the material. Compressing a magnetostrictive-elastocaloric composite using a low magnetic field of 0.16 T, temperature changes up to 4 K are achieved without applying external forces.

Large Interfacial Magnetostriction in (Co/Ni)4/Pb(Mg1/3Nb2/3)O3–PbTiO3 Multiferroic Heterostructures

The magnetoelastic behavior of multiferroic heterostructures-coupling of magnetic anisotropy or domain dynamics to structural deformations-has been intensively studied for developing materials for energy-efficient, spin-based applications. Here, we report on a large, interface-dominated magnetostriction in (Co/Ni)4/Pb(Mg1/3Nb2/3)O3-PbTiO3 multiferroic heterostructures. Ferromagnetic resonance spectroscopy under voltage-induced strains enabled estimation of the saturation magnetostriction as a function of Ni thickness. The volume and the interface components to the saturation magnetostriction are (6.6 ± 0.9) × 10-6 and (-2.2 ± 0.2) × 10-14 m, respectively. Similar to perpendicular magnetic anisotropy in Co/Ni, the large, negative magnetostriction originates from the Co/Ni interfaces. This interfacial functionality delivers an effect over 300% larger than the bulk contribution and can enable low-energy, nanoelectronic devices that combine the tunable magnetic and magnetostrictive properties of Co/Ni multilayers with the ferroelectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3.