Sensing fT magnetic fields by magnetoelectric metglas / bidomain y+140°-cut lithium niobate compositeTuesday (18.06.2019) 16:15 - 16:30
Bidomain lithium niobate crystals are a promising material for precise actuators and magnetic sensors based on composite multiferroic structures. Previously it was shown that a magnetoelectric (ME) coefficient of at least 578 V/(cm·Oe) can be obtained under resonance conditions in a laminate composite “bidomain crystal – metglas”.
In this study we investigated ME properties of a composite based on Y+140°-cut lithium niobate plates with an antiparallel polarized “head-to-head” domain structure; metglas was used as a magnetostrictive layer. Samples with a length of 20 mm and a width of 5 mm were studied. The thicknesses of the piezoelectric and magnetostrictive layers were 410 μm and 29 μm, respectively.
A series of bidomain samples was prepared by annealing upon out-diffusion of Li2O from LiNbO3 with a resultant growth of an inversion domain. The best sample for further studies was selected by testing the crystals as cantilevered piezoelectric actuators and measuring the deflection at the voltage of ±500 V. The movement amplitude of the free end of the chosen specimen was only 13% smaller than the theoretically predicted value for an ideal bimorph. This confirmed a high quality of the domain structure.
Measurements of the direct ME effect were carried out at room temperature and at a frequency of 110 Hz in the quasistatic regime with an applied modulation magnetic field δH = 0.1 Oe. The maximum measured quasistatic ME coefficient was as large as |αE31| = 1.9 V/(cm·Oe).
The dynamic ME coefficient was measured as a function of the modulation frequency with an applied optimum bias field of 5 Oe corresponding to the maximum ME effect as measured in the quasistatic regime. We found giant bending resonant ME coefficients of up to 1704 V/(cm·Oe) at a resonance frequency of 6862 Hz. The ME composite exhibits a giant conversion value of 69.9 V/Oe, and in this case the measured magnetic noise density is only 92 fT/Hz1/2, which is quite respectable for this resonance frequency. We observed a good correspondence between the experimental results and the ones calculated in the framework of the unidimensional model.