Jiefang Li

Dramatically enhanced polarization in (001), (101), and (111) BiFeO3 thin films due to epitiaxial-induced transitions

Dramatically enhanced polarization has been found for (001), (101), and (111) films, relative to that of BiFeO3 crystals. The easy axis of spontaneous polarization lies close to (111), for the various oriented films. BiFeO3 films grown on (111) have a rhombohedral structure, identical to that of single crystals; whereas films grown on (101) or (001) are monoclinically distorted from the rhombohedral structure, due to the epitaxial constraint.

Near-ideal magnetoelectricity in high-permeability magnetostrictive/piezofiber laminates with a (2-1) connectivity

Theoretically, the two-phase laminated configurations should have even much higher magnetoelectric (ME) effects—however, prior experimental studies have failed to find such an enhancement. Here, the authors report the unleashing of the potential of the (2-1) connectivity configuration: a piezofiber (one-dimension connectivity) layer laminated between two high-permeability magnetostrictive FeBSiC alloy ones (two-dimension connectivity) has near-ideal ME coupling. Very high ME effects of up to 22V∕cmOe (4×10−7s∕m) at 1Hz—an order of magnitude higher than the giant ones—have been found.

Destruction of spin cycloid in (111)c-oriented BiFeO3 thin films by epitiaxial constraint: Enhanced polarization and release of latent magnetization

In BiFeO3 films, it has been found that epitaxial constraint results in the destruction of a space modulated spin structure. For (111)c films, relative to corresponding bulk crystals, it is shown (i) that the induced magnetization is enhanced at low applied fields; (ii) that the polarization is dramatically enhanced; whereas, (iii) the lattice structure for (111)c films and crystals is nearly identical. Our results evidence that eptiaxial constraint induces a transition between cycloidal and homogeneous antiferromagnetic spin states, releasing a latent antiferromagnetic component locked within the cycloid.

Enhanced magnetoelectric effects in laminate composites of Terfenol-D/Pb(Zr,Ti)O3 under resonant drive

We have found that laminate composites consisting of longitudinally magnetized magnetostrictive Terfenol-D and longitudinally poled piezoelectric Pb(Zr,Ti)O3 layers have dramatically enhanced magnetoelectric effects when driven near resonance. The maximum induced magnetoelectric voltage at resonance was ∼10 Vp/Oe, which is ∼102 times higher than previous reports at subresonant frequencies.

Detection of pico-Tesla magnetic fields using magneto-electric sensors at room temperature

The measurement of low-frequency (10−2–103Hz) minute magnetic field variations (10−12Tesla) at room temperature in a passive mode of operation would be critically enabling for deployable neurological signal interfacing and magnetic anomaly detection applications. However, there is presently no magnetic field sensor capable of meeting all of these requirements. Here, we present new bimorph and push-pull magneto-electric laminate composites, which incorporate a charge compensation mechanism (or bridge) that dramatically enhances noise rejection, enabling achievement of such requirements.

Ultrahigh magnetic field sensitivity in laminates of TERFENOL-D and Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals

It has been found that laminate composites of longitudinally magnetized magnetostrictive TERFENOL-D and a transversely poled piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 crystal have extremely high magnetic field sensitivity. At room temperature, an output voltage with an exceptionally good linear response to an ac magnetic field Hac was found over the range of 10−11

Longitudinal and transverse magnetoelectric voltage coefficients of magnetostrictive/ piezoelectric laminate composite: experiments

This paper presents a novel, long-type of magnetostrictive and piezoelectric laminate composite design in which the layers are, respectively, magnetized/poled along their length axes, and a theory for modeling its behavior. Using piezoelectric and magnetostrictive constitutive equations, and an equation of motion, a magneto-elasto-electric bieffect equivalent circuit is developed. The circuit is used to predict the longitudinal and transverse magnetoelectric (ME) voltage coefficients of our Terfenol-D/Pb(Zr/sub 1-x/Ti/sub x/)O/sub 3/ laminate design. It is found that the longitudinal ME voltage coefficient is significantly higher (/spl sim/5x) than the transverse one, and that our new laminate design has significantly higher ME voltage coefficients under small applied direct current (DC) magnetic bias fields than designs reported previously by other groups. Experimental values were found to be coincidental with predicted ones.Magnetostrictive Terfenol-D (Tb/sub x/Dy/sub 1-x/Fe/sub 2/) and piezoelectric (Pb(Zr/sub 1-x/Ti/sub x/)O/sub 3/) magnetoelectric (ME) laminate composites have been investigated experimentally for various modes of operation: longitudinal magnetized/longitudinal polarized (L-L mode), transverse magnetized/longitudinal polarized (T-L mode), and transverse magnetized/transverse polarized (T-T mode) ME modes. We report their experimentally determined performance characteristics based on our previously developed equivalent circuits for these various modes. Predicted and experimental results are in agreement that the L-L mode laminates have enhanced ME effects, and that, under low or zero magnetic bias, the L-L mode ME voltage coefficients are up to a factor of 5-20/spl times/ higher than those of the T-L mode or T-T mode laminates. The maximum ME voltage coefficient of the L-L mode laminates is over 86 mV/Oe under a bias of 500 Oe.

An Extremely Low Equivalent Magnetic Noise Magnetoelectric Sensor

As a result of the coupling between their dual order parameters, multiferroic materials exhibit unusual physical properties and, in turn, promise new device applications. [ 1 , 2 ] Of particular interest is the existence of a cross-coupling between the magnetic and electric orders, termed the magnetoelectric (ME) effect. [ 3–5 ] Because no single-phase material has been put forward demonstrating a practical capacity for such coupling at room temperature, [ 8 ] many of the most promising applications offered by the ME effect, including magnetic fi eld sensors and electric write-magnetic read memory devices, have not been forthcoming. [ 6 , 7 ] Furthermore, the exploitation of high magnetic fi eld sensitivity in two-phase ferromagnetic/ferroelectric composites requires development and identifi cation of end users. [ 7 ]

Giant magnetoelectric effect in Metglas/polyvinylidene-fluoride laminates

Here, the authors report thin (<100μm) and flexible magnetoelectric (ME) composites consisting of Metglas (high-μ magnetostriction) and polyvinylidene-fluoride (piezopolymer) layers laminated together. Both unimorph and three-layer configurations have been studied. The authors find that these ME laminates (i) require dc magnetic biases as low as 8Oe to (ii) induce giant ME voltage coefficients of 7.2V∕cmOe at low frequencies, and up to 310V∕cmOe under resonant drive.

Push-pull mode magnetostrictive/piezoelectric laminate composite with an enhanced magnetoelectric voltage coefficient

A magnetoelectric (ME) laminate composite consisting of a symmetric longitudinally poled piezoelectric Pb(Mg1∕3Nb2∕3)O3–PbTiO3 crystal and two longitudinally magnetized magnetostrictive Tb1−xDyxFe2 layers has been developed that has a notably superior ME voltage coefficient, relative to previous laminate configurations. The symmetric nature of the longitudinally poled piezoelectric layer allows for operation in a push-pull mode that optimizes elastic coupling between layers. Our small laminate has a giant ME voltage coefficient of ∼1.6V∕Oe at low frequencies, a significant enhancement of this coefficient to ∼20V∕Oe under resonance drive, and an exceptional low-level magnetic field sensitivity of ∼10−12T at f=f0.