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The long-lived (176) Lu-(176) Hf and Sm-147-Nd-143 radioisotope systems are commonly used chronometers, but when applied to meteorites, they can reveal disturbances. Specifically, Lu-Hf isochrons commonly yield dates up to similar to 300 Myr older than the solar system and varying initial Hf-176/Hf-177 values. We investigated this problem by attempting to construct mineral and whole rock isochrons for eucrites and angrites. Meteorites from different parent bodies exhibit similar disturbance features suggesting that a common process is responsible. Minerals scatter away from isochron regressions for both meteorite classes, with low-Hf phases such as plagioclase and olivine typically being most displaced above (or left of) reference isochrons. Relatively Hf-rich pyroxene is less disturbed but still to the point of steepening Lu-Hf errorchrons. Using our Lu-Hf and Sm-Nd data, we tested various Hf and Lu redistribution scenarios and found that decoupling of Lu/Hf from Hf-176/Hf-177 must postdate the accumulation of significant radiogenic Hf-176. Therefore early irradiation or diffusion cannot explain the excess Hf-176. Instead, disturbed meteorite isochrons are more likely caused by terrestrial weathering, contamination, or common laboratory procedures. The partial dissolution of phosphate minerals may predominantly remove rare earth elements including Lu, leaving relatively immobile and radiogenic Hf behind. Robust Lu-Hf (and improved Sm-Nd) meteorite geochronology will require the development of chemical or physical methods for removing unsupported radiogenic Hf and silicate-hosted terrestrial contaminants without disturbing parent-daughter ratios. (C) 2017 Elsevier Ltd. All rights reserved.

Ferromagnetic–ferroelectric nanocomposites are of interest for realizing strong strain-mediated coupling between electric and magnetic subsystems due to a high surface area-to-volume ratio. This report is on the synthesis of nickel ferrite (NFO)–barium titanate (BTO) core–shell nanofibers, magnetic field assisted assembly into superstructures, and studies on magneto-electric (ME) interactions. Electrospinning techniques were used to prepare coaxial fibers of 0.5–1.5 micron in diameter. The core–shell structure of annealed fibers was confirmed by electron microscopy and scanning probe microscopy. The fibers were assembled into discs and films in a uniform magnetic field or in a field gradient. Studies on ME coupling in the assembled films and discs were done by magnetic field (H)-induced polarization, magneto–dielectric effects at low frequencies and at 16–24 GHz, and low-frequency ME voltage coefficients (MEVC). We measured ~2–7% change in remnant polarization and in the permittivity for H = 7 kOe, and a MEVC of 0.4 mV/cm Oe at 30 Hz. A model has been developed for low-frequency ME effects in an assembly of fibers and takes into account dipole–dipole interactions between the fibers and fiber discontinuity. Theoretical estimates for the low-frequency MEVC have been compared with the data. These results indicate strong ME coupling in superstructures of the core–shell fibers.

Multiferroic composites with ferromagnetic and ferroelectric phases have been studied in recent years for use as sensors of AC and DC magnetic fields. Their operation is based on magneto-electric (ME) coupling between the electric and magnetic subsystems and is mediated by mechanical strain. Such sensors for AC magnetic fields require a bias magnetic field to achieve pT-sensitivity. Novel magnetic sensors with a permanent magnet proof mass, either on a ferroelectric bimorph or a ferromagnetic-ferroelectric composite, are discussed. In both types, the interaction between the applied AC magnetic field and remnant magnetization of the magnet results in a mechanical strain and a voltage response in the ferroelectric. Our studies have been performed on sensors with a Nd-Fe-B permanent magnet proof mass on (i) a bimorph of oppositely-poled lead zirconate titanate (PZT) platelets and (ii) a layered multiferroic composite of PZT-Metglas-Ni. The sensors have been characterized in terms of sensitivity and equivalent magnetic noise N. Noise N in both type of sensors is on the order of 200 pT/√Hz at 1 Hz, a factor of 10 improvement compared to multiferroic sensors without a proof mass. When the AC magnetic field is applied at the bending resonance for the bimorph, the measured N ≈ 700 pT/√Hz. We discuss models based on magneto-electro-mechanical coupling at low frequency and bending resonance in the sensors and theoretical estimates of ME voltage coefficients are in very good agreement with the data.

Results of our ONR supported activities on miniature, rapid-response, frequency agile multiferroic RF components are discussed here. Ferrite-ferroelectric bilayers were synthesized by techniques including electrophoretic deposition, eutectic bonding and MOCVD and were characterized in terms of strain mediated magneto-electric coupling by ferromagnetic resonance. Devices studied include 1-3GHz ferrite-ferroelectric band-pass filter, 18-36 GHz magneto-dielectric band-pass filter, 12-24 GHz hexaferrite-ferroelectric phase shifter and beam-forming antennas.

A method is presented for increasing the operating frequency of symmetric and asymmetric magnetoelectric (ME) sensors so that the operating frequency can be equal to the mechanical resonance frequency of the sensor. This increase improves the signal to noise ratio of a symmetric sensor by at least two orders of magnitude because it mitigates the effect of 1/f noise and the sensor has an increased response at its resonant frequency. The method is based on the strong, nonlinear magnetic field dependence of the magnetostriction. Our method has lowered the detection limit to 4 pT/root Hz at 1 Hz in a magnetically unshielded environment. (C) 2012 American Institute of Physics. [doi:10.1063/1.3677840]

The sensitivity of magnetoelectric (ME) sensors is more than an order of magnitude higher at their mechanical resonant frequency fr. By applying a restoring torque to an asymmetric ME sensor, we have increased its effective stiffness and, thus, fr by 20% while maintaining the enhanced sensitivity at resonance. The torque was dependent on both the tensile force from a suspended weight and the length of the wire attaching it. This provides two alternative routes for tuning fr to optimize performance. We have detected fields below 10 pT at both the shifted and unshifted fr of 132.2 Hz., The original document contains color images. Published in Applied Physics Letters, v99 p043504-1/043504-3, 2011.

We present a field modulation technique that increases the operating frequency of magnetoelectric ( ME) sensors so that it can match the mechanical resonance frequency of the sensor. This not only improves the sensitivity but also reduces the effect of 1/f noise that is inherent at low frequencies. The technique, which is shown to apply to both symmetric and asymmetric ME sensors, relies on the strong, nonlinear magnetic field dependence of the magnetostriction. The combination of a lower 1/f noise and enhanced response at resonance has increased the signal to noise ratio of a symmetric sensor by two orders of magnitude. The detection limit of this sensor was lowered from 90 to 7 pT/root Hz at 1Hz in a magnetically unshielded environment. (C) 2011 American Institute of Physics. [doi:10.1063/1.3668752]

This project was on dual electric and magnetic field tunable miniature, rapid-response, frequency agile resonators, filters, phase shifters, and delay lines for use in communication devices and the next generation of phased array radars for Naval systems over the frequency range 1-67 GHz. The efforts involved layered ferrite-ferroelectric composites. Anticipated impacts of this research are new technologies for reception and processing of EM signals and a path toward dominance of the EM spectrum.

Layered magnetostrictive-ferroelectric structures are multifunctional due to their response to mechanical and electromagnetic forces. Investigations on microwave magneto-electric (ME)interactions were performed on ferrite-ferroelectrics layered structures. Systems studied include yttrium iron garnet (YIG)-lead zirconate titanate (PZT) or YIG-barium strontium titanate (BST). Our efforts have resulted in the following breakthroughs in experimental and theoretical understanding: (i) The observation of strong microwave ME interactions in YIG-PZT; (ii) Theory and experiments on the creation and propagation characteristics of hybrid spin-electromagnetic waves in YIG-BST; and (iii) Fabrication of electric field tunable YIG-PZT and YIG-BST resonators and phase shifters operating at 3-12 GHz. These results have been published in 35 journal articles., The original document contains color images.

A model is provided for the image formation by a three-dimensional lens with negative index of refraction (n) and compared with results for an array of split-ring resonators (SRRs) and wires. For n=-1, a linear decrease in image distance r is expected with increasing object distance l. A nonlinear r vs l is anticipated for other n values. A lens of an array of SRRs and wires was made and characterized over 1-18 GHz and n=-1, and a gain of similar to 8 dB at 11.25 GHz was achieved. Results on r vs l are in excellent agreement with the model. (C) 2007 American Institute of Physics.