Studies On TbDyFe Magnetostrictive Film And Its Coupling Effects With Elastic Or Piezoelectric Substrates

Giant magnetostrictive films and magnetoelectric composites have drawn significant interest in recent years due to their multifunctional and potential uses in micro-sensors and micro-actuators. The magnetostriction of TbDyFe film, especially at a low magnetic field, and the coupling effects between the film and elastic or piezoelectric substrates are investigated in this research.TbDyFe films are deposited on Si crystal substrate by magneto sputtering and the effects of technological processes on its magnetostrictive characteristics are studied experimentally. The theoretical analysis reveals that the improvement of magnetization behavior parallel to the film surface, such as the increase of the magnetic susceptibility and saturated magnetization and the decrease of the anisotropic magnetic constant and the saturated magnetic field strength, is benefit to increase the magnetostrictive coefficient X, especially at a low magnetic field. It is found that the film as deposited or vacuum annealed at 450℃ remains amorphous structure and the treatments, such as annealed in vacuum, applied a bias magnetic field parallel to the film surface during sputtering, a smoother substrate or laminated with SmCo can promote the magnetostrictive sensibility of the film. TbDyFe/Fe multi-layer film is superior to the single TbDyFe owing to the coupling effect between TbDyFe and Fe films. The thinner the single layer is, the stronger the coupling effect is. For the TbDyFe/Fe multi-layer film in which the each layer thickness is 5nm, its magnetostrictive coefficient λ can reach to 220 x 10~-6 in as deposited state or 315X10~-6 after 250℃ annealing and the vale of dX/dH is ten times of that of TbDyFe film when the applied magnetic field strength is 50kA/m. The regularity of Fe crystal film decreases with the increase of the annealing temperature.The magnetoelectric (ME) properties of magneto-sputtered TbDyFe/PZT and bonded Ni/PZT laminate composites under a periodical magnetic field are investigated by self-assembled equipment. The results show that a resonance phenomenon appears for magnetostrictive /piezoelectric bimorph cantilever during the test. The ME voltage coefficients at resonance frequency for TbDyFe/PZT and Ni/PZT reach to 14mV/A and 4800mV/A, respectively. The resonance vibration do not taken place for the multilayer in the range of experimental frequency (1-lkHz), but its ME coefficient was high than that of the bimorph at the non resonance frequency. The results of finite element harmonic analysis are coincident with the experimental results.The deformation of magnetostrictive film laminated with an elastic substrate and the magnetic coupling effect of magnetostrictive film laminated with a piezoelectric substrate are studied theoretically based on the elastic theory. The formulae of the deflection of a magnetostrictive/elastic bilayer cantilever and the magnetoelectric voltage coefficients of magnetostrictive/piezoelectric laminate composites with or without the surface restriction are deduced.The deflection of TbDyFe/Si and the ME coefficients of TbDyFe/PZT and Ni/PZT are calculated with a finite element analysis software ANSYS. The research reveals that the deflection of the magnetostrictive/elastic bilayer increases with the increase of the dA/dH and thickness of the magnetostrictive layer. The deflection gets its highest value when the thickness of the magnetostrictive layer is the half of that of the substrate at the condition that the modules of both layers are equal. The stiffer the magnetostrictive layer is and the softer the substrate is, the more sensitive the magnetostrictive/elastic cantilever is. The increase of the magnetostriction and piezoelectricity, the improvement of the interface bonding and the clamping both surfaces along the thickness enhance the ME coupling of the ME laminate composite. The ME voltage also increases with the increase of the volume fraction of magnetostrictive layer. But the maximum ME coefficient per volume of the composite is corresponding to a certain magnetostrictive volume fraction.