Strain-mediated Magnetoelectric Coupling Research Articles

Converse magnetoelectric coupling in NiFe/Pb(Mg1/3Nb2/3)O3–PbTiO3 nanocomposite thin films grown on Si substrates

Multiferroic NiFe (∼30 nm)/Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN–PT, ∼220 nm) bilayered thin films were grown on common Pt/Ti/SiO2/Si substrates by a combination of off-axis magnetron sputtering and sol-gel spin-coating technique. By using AC-mode magneto-optical Kerr effect technique, the change in the Kerr signal (magnetization) of the NiFe upon applying a low-frequency AC voltage to the PMN–PT film was in situ acquired at zero magnetic field. The obtained Kerr signal versus voltage loop essentially tracks the electromechanical strain curve of the PMN–PT thin film, clearly demonstrating a strain-mediated converse magnetoelectric coupling, i.e., voltage-modulated magnetization, in the NiFe/PMN–PT nanocomposite thin films.

Evidence for a Thickness-Dependent Crossover from Charge- to Strain-Mediated Magnetoelectric Coupling in La0.7Sr0.3MnO3 / PbZr0.2Ti0.8O3 Thin Film Oxide Heterostructures

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Inverse effect of magnetostriction in magnetoelectric laminates

We introduce the notion of inverse effect of magnetostriction for magnetostrictive-piezoelectric heterostructures and study this effect theoretically and experimentally. It is shown that the inverse effect of magnetostriction may crucially contribute to the mechanism of magnetoelectric coupling. It is shown that the studied effect essentially modifies the saturation magnetostriction of the whole structure as compared to its magnetic phase bulk and also induces an additional magnetic anisotropy. Our consideration provides useful insight into the fundamental issue of strain-mediated magnetoelectric coupling. Understanding this effect may lead to its utilization in original experimental concepts and the improvement of the ME coupling.

A Combined STEM-EELS and Neutron Reflectometry Study of Charge- and Strain-Mediated Magnetoelectric Coupling in LSMO/PZT Heterostructures

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Voltage impulse induced bistable magnetization switching in multiferroic heterostructures

We report on voltage impulse induced reversible bistable magnetization switching in FeGaB/lead zirconate titanate (PZT) multiferroic heterostructures at room temperature. This was realized through strain-mediated magnetoelectric coupling between ferroelectric PZT and ferromagnetic FeGaB layer. Two reversible and stable voltage-impulse induced mechanical strain states were obtained in the PZT by applying an electric field impulse with its amplitude smaller than the electric coercive field, which led to reversible voltage impulse induced bistable magnetization switching. These voltage impulse induced bistable magnetization switching in multiferroic heterostructures provides a promising approach to power efficient bistable magnetization switching that is crucial for information storage.

Thickness-dependent converse magnetoelectric coupling in bi-layered Ni/PZT thin films

The converse magnetoelectric (ME) effect was investigated in bi-layered Ni/Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Si substrates, with different thicknesses of Ni thin layers. By using an AC-mode magneto-optical Kerr effect method, it was revealed that the electric-voltage induced magnetization variation was dependent on the thickness of the Ni thin layer. The results showed that the Ni/PZT bilayered films with thick (about 40 nm) Ni films presented a dominative strain mediated ME coupling, whereas an interface-charge and strain co-mediated ME coupling might coexist in the Ni/PZT bilayered films with decreasing thickness (e.g., about 10 nm) of Ni films.

Switchable voltage control of the magnetic coercive field via magnetoelectric effect

Switchable voltage modulation of the magnetic properties is reported in different multiferroic bilayers with magnetic films grown on pre-poled ferroelectric substrates, based on the magneto-optical Kerr effect observations. The dynamic voltage control of the magnetic coercive field (Hc) is dependent not only on the materials properties of each ferroic layer, but also on the bias voltage history. The Hc versus electric field behaviors essentially track the dependence of the piezostrains of the substrates on the bias voltage. The observations demonstrate that Hc in such multiferroic bilayers can be controlled by voltage via strain-mediated magnetoelectric coupling and that the Hc change is not an artifact due to a heating effect.

Strain-mediated magnetoelectric coupling in magnetostrictive/piezoelectric heterostructures and resulting high-frequency effects

Magnetoelectric coupling terms are derived in piezoelectric/magnetostrictive (multiferroic) thin film heterostructures using Landau-Ginzburg free energy expansions in terms of strain and by considering strain boundary conditions between the two materials. Then, a general effective medium method for solving for the complete electromagnetic susceptibility tensor of such heterostructures is used to calculate the ferromagnetic resonance frequency in a BaTiO$_3$/NiFe$_2$O$_4$ superlattice. This method differs from existing methods for treating magnetoelectric heterostructures since the magnetic and electric dipolar fields are not assumed constant but vary from one film to another. The ferromagnetic resonance frequency shift is calculated as a function of applied electric field and is compared to some experimental results.

Tunable magnetoresistance devices based on multiferroic heterostructures

Surface-effect induced strong magnetoelectric (ME) coupling was investigated in ultrathin Ni80Fe20/PZN-PT (lead zinc niobate-lead titanate) multiferroic heterostructures. Giant electric field (E-field) tuning of the magnetic anisotropy, ferromagnetic resonance field, coercive field and anisotropic magnetoresistance were demonstrated through strain mediated ME coupling in 10 nm thick Ni80Fe20/PZN-PT multiferroic heterostructures. E-field dynamic modulation of magnetoresistance was also displayed. These provide great opportunities for electrostatic tunable MR devices.

Voltage control of the magnetic coercive field: Multiferroic coupling or artifact?

The ability to dynamically tune the coercive field of magnetic thin films is a powerful tool for applications, including in magnetic recording disk technologies. Recently, a number of papers have reported the electrical voltage control of the coercive field of various magnetic thin films in multiferroic composites. Theoretically, this is possible in magneto-electric (ME) multiferroics due to the piezoferroelectric component that can be electrically activated to dynamically modify the properties of the magnetic component of the composite via a direct or strain mediated ME coupling. In this paper we fabricated and examined such structures and we determined that the magnetic coercive field reduction is most likely due to a heating effect. We concluded that this effect is probably an artifact that cannot be attributed to a multiferroic coupling.

Local probing of magnetoelectric coupling in multiferroic composites of BaFe12O19–BaTiO3

The BaFe12O19–BaTiO3 composite ferroelectric/ferromagnetic ceramics were prepared by conventional solid-state sintering technique. The magnetic properties are consistent with the ratio of the magnetic phase present but ferroelectric properties are degraded due to a sufficiently high degree of conductivity in the ceramics. Magnetoelectric coupling was observed at a local level by means of the scanning probe microscopy (SPM). Piezoresponse and magnetic force modes of SPM were both utilized to assess strain-mediated magnetoelectric coupling between neighboring grains. The observed variation in the magnetic signal after the electrical poling with SPM was attested to the changes in the magnetic interactions and magnetic anisotropy leading to broadening of the magnetic domain wall.

Eliminating the Temperature Dependence of the Response of Magnetoelectric Magnetic-Field Sensors

Magnetic fields may be electrically detected by exploiting strain-mediated magnetoelectric coupling between a ferromagnet showing magnetostriction and a ferroelectric showing piezoelectricity. We argue that by electrically and thermally connecting two appropriately oriented anisotropic magnetoelectric elements that are identical, it is possible to cancel the strong unwanted pyroelectric response of the ferroelectric without cancelling the magnetoelectric response of interest. This result may be achieved using magnetoelectric elements that are merely similar, by measuring sensor voltage using an instrument with sufficiently low internal resistance. Using this strategy, we eliminate the influence of slow thermal fluctuations on the output of a sensor comprising two cheap magnetoelectric multilayer capacitors. This sensor can easily detect ~200 mT, suggesting the possibility of low-tech applications, e.g., detecting fields from cheap permanent magnets.

Investigation of true remnant polarization response in heterostructured artificial biferroics

Abstract Epitaxial bilayered thin films composed of ferromagnetic La 0.6 Sr 0.4 MnO 3 and ferroelectric 0.7Pb (Mg 1/3 Nb 2/3 )O3–0.3(PbTiO 3 ) were fabricated on LaAlO 3 (100) substrates by pulsed laser ablation. Ferroelectric, ferromagnetic and magneto–dielectric characterizations performed earlier indicated the possible existence of strain-mediated magneto–electric coupling in these biferroic heterostructures. In order to investigate their true remnant polarization characteristics, usable in devices, room-temperature polarization versus electric field, positive-up negative-down (PUND) pulse polarization studies and remnant hysteresis measurements were carried out. The PUND and remnant hysteresis measurements revealed the significant contribution of the non-remnant component in the observed polarization hysteresis response of these heterostructures.

Interfacial strain-mediated magnetoelectric coupling as reflected in extended X-ray absorption spectra of CoFe 2O 4-dispersed Pb(Zr,Ti)O 3 matrix composites

An atomic-scale picture of the strain-mediated magnetoelectric (ME) coupling is delineated by carefully examining the effect of an applied electric field on the extended X-ray absorption fine structure (EXAFS) spectra of a CoFe 2O 4-dispersed Pb(Zr,Ti)O 3 matrix (CFO–PZT) composite. These studies demonstrated a tensile-compressive strain relation between the PZT matrix and the dispersed CFO phase, thereby providing an X-ray spectroscopic evidence of the interfacial strain-mediated ME coupling. Both the dielectric anomaly observed at ∼480 °C and the decrease in the remanent magnetization under an applied electric field support the strain-mediated ME coupling in the CFO–PZT composite.

Strain-mediated magnetoelectric coupling in BaTiO3-Co nanocomposite thin films

The authors present a metal-ceramic type composite film in which Co particles with the mean size of 70nm are uniformly dispersed in an insulating ferroelectric BaTiO3 (BTO) matrix. Transmission electron microscopy images revealed that the Co particle was tightly surrounded with the BTO matrix in atomic scales. The magnetostrictive strain-induced change in the relative dielectric permittivity was demonstrated by observing pronounced magnetodielectric effects under a static bias magnetic field. The present BTO-Co composite thin film also exhibited large dynamic magnetoelectric responses (160–170mV∕cmOe at 50kHz) at room temperature by virtue of a tight bonding between the two constituting piezoelectric and magnetostrictive phases.

Phase field approach for strain-induced magnetoelectric effect in multiferroic composites

The strain-mediated magnetoelectric coupling in piezoelectric-piezomagnetic composites with arbitrary spatial arrangement of particles of constituent phases is investigated. The free energy of such a composite is formulated as a functional of a phase field that is a shape function describing a spatial distribution of the phases. The free energy is obtained by a minimizing of the extended Landau free energy complemented by the electrostatic and strain-induced interactions caused by piezoelectric and piezomagnetic strains. The magnetoelectric coupling tensor derived from this functional also depends on a composite microstructure. A minimization of this functional with respect to configurational variables gives the optimal composite architecture. It is shown that a platelike configuration of constituent phases provides the largest strength of magnetoelectric coupling. The phase field computer modeling confirms this conclusion.

Nd-Fe-B MELT - SPUN POWDER QUALITY ESTIMATION BASED ON STONER - WOHLFARTH MODEL

The microstructure, crystallographic structure and magnetic properties of ferroelectric-ferromagnetic PZT/CoCr heterostructures have been investigated by using XRD, SEM and VSM.~Upon applying an electric field, the in-plane magnetization of the heterostructures decreases at various bias magnetic fields. The change in magnetization and the magnetization reversed voltage were obtained. The results demonstrate that the change in magnetic anisotropy can be controlled by electric field via strain-mediated magnetoelectric coupling.

Dynamic strain in magnetic films on piezoelectric crystals

Reversible biaxial strain has been induced in ferromagnetic films of several lanthanum manganites which have been epitaxially grown on the (0 0 1) face of high-strain piezoelectric crystals of Pb(Mg 1/3Nb 2/3) 0.72Ti 0.28O 3 (PMN-PT). The strain-induced changes of the Curie temperature and the remanent magnetization have been observed. PMN-PT(0 0 1) crystals used as substrates are characterized with respect to their lattice parameters, domain-related surface topology and electric relaxation behavior. A sample consisting of a magnetic film on a piezo-crystal forms a simple and well-defined model system for strain-mediated magnetoelectric coupling.

Comment on "Epitaxial BiFeO 3 Multiferroic Thin Film Heterostructures"

Wang et al recently reported multiferroic behavior, with ferromagnetic and ferroelectric polarizations that are both large at room temperature, in thin strained films of BiFeO3 (BFO). Although at room temperature, bulk BFO is ferroelectric and anti-ferromagnetic , Wang et al. reported that a 70-nm film shows both an enhanced ferroelectric polarization (90 μC cm–2) and a substantial magnetization (1 μB/Fe). This remains the only report of a robust room-temperature multiferroic and suggests the potential for novel devices that exploit the anticipated strain-mediated magnetoelectric coupling between the two ordered ground states. In this Comment, we argue that epitaxial strain does not enhance the magnetization and polarization in BiFeO3