V. Preobrazhensky

Room temperature magnetoelectric memory cell using stress-mediated magnetoelastic switching in nanostructured multilayers

We present here the demonstration of magnetoelectric switching of magnetization between two stable positions defined by a combination of anisotropy and magnetic field. A magnetoelastic nanostructured multilayer with the required uni-axial characteristic was deposited onto a commercial piezoelectric actuator. Thanks to the inverse magnetostrictive effect, the effective anisotropy of the magnetic element is controlled by the applied voltage and used to switch magnetization from one state to the other. Both vibrating sample magnetometer and magneto-optical Kerr effect measurements have been performed and demonstrate the magnetoelectric switching.

Magnetoelectric memory using orthogonal magnetization states and magnetoelastic switching

We present here a concept of a memory cell called MELRAM based on a magnetic element with giant magnetostriction, embedded in a piezoelectric matrix. Two equilibrium orientations of magnetization are defined by combining uniaxial anisotropy together with a magnetic polarization in the hard axis direction. Using the piezoelectric matrix, an anisotropic stress is created onto the magnetic element when applying a voltage across electrodes. Thanks to the inverse magnetostrictive effect, the effective anisotropy of the magnetic element is controlled by the applied voltage and used to switch magnetization from one state to the other. Micromagnetic simulations show the effect of applied stress on magnetization and theoretical feasibility of the device. Retrieval of information can be nondestructively made by giant magnetoresistance reading. Details of the principle, simulations, and performance perspectives are discussed.

Sub-harmonic excitation of a planar magneto-mechanical system by means of giant magnetostrictive thin films

Abstract In the present paper, we report the first results concerning the studies on non-linear actuation of cantilevers using giant magneto-strictive thin films in the vicinity of the spin reorientation transition (SRT). Bimorph centimetre beams (24×5xa0mm 2 ) were designed using 160xa0μm thick glass, and 0.4xa0μm thick multilayer TbFe/Fe films deposited via RF sputtering, using several sputtering conditions. Magnetic characteristics of the thin films show the existence of a SRT. Dynamic magneto-elastic excitations were studied experimentally on the few eigen resonance modes of the cantilevers. Sub-harmonic excitation at half or one third of the frequency of an eigen resonance mode has been achieved near the SRT and the efficiency is as good as for eigen frequency excitation. Comparison between theory and experimental results is discussed.

Giant magnetostrictive superlattices: from spin reorientation transition to MEMS. Static and dynamical properties

Abstract The results of development of “giant magnetostrictive” multilayers with spin reorientation transition (SRT) for microactuators are presented. Manifestations of magneto-mechanical instability and nonlinearity near SRT are studied experimentally and simulated numerically. Improvement of magneto-mechanical sensitivity near SRT is demonstrated for various modes of linear and nonlinear actuation of magnetostrictive unimorph. Limitations of sensitivity caused by magnetic field distortions are described by a numerical model, the results are compared with the experimental data.

Low field anisotropic magnetostriction of single domain exchange-coupled (TbFe/Fe) multilayers

Giant magnetostriction (GMS) reported until now in exchange-coupled multilayers (ECML) present quasi-isotropic magnetostrictive behavior. In the present work it is shown the possibility to induce highly anisotropic GMS at low field with the single domain state in (TbFe/Fe)n multilayers when deposited by ion sputtering under a magnetic polarization field Hd. ECML grown under bias field Hd, applied along the large size of rectangular glass substrates present original magnetic and magnetoelastic (ME) properties associated with strong uniaxial behavior. After saturation by an external field H∥ applied parallel to the easy axis induced by Hd, a single domain state is kept by decreasing H∥ down to zero (Mr/Ms=1) which explains why there is no change of the magnetoelastic coefficient bγ,2 by increasing or decreasing H∥. A different behavior arises along the hard magnetization axis with a strong change of bγ,2 by increasing H∥ up to the saturation. ME anisotropy is the origin of high amplitude flexural and torsio...

Non-linear actuation of cantilevers using giant magnetostrictive thin films

In the present paper, we report the first results concerning a centimetre cantilever driven through non-linear effects in thin magnetostrictive films. Bimorph centimetre beams (24 mm x 5 mm) were designed using 160 microns thick glass and 0.4 micron thick multilayer TbFe/Fe films deposited via RF sputtering, using several sputtering conditions. Dynamic magneto-elastic excitations were studied experimentally on the few eigenresonance modes of the cantilevers. Sub-harmonic excitation at half or one-third of the frequency of an eigenresonance mode has been achieved near the spin reorientation transition and the efficiency is as good as for eigenfrequency excitation. Specific magnetic properties of the samples led to a model of the thermodynamic potentials and behaviour of the excited resonator.

Statics and dynamics in giant magnetostrictive Tb/sub x/Fe/sub 1-x/-Fe/sub 0.6/Co/sub 0.4/ multilayers for MEMS

In the present paper, giant magnetostrictive (GMS) thin films have been investigated for future microelectromechanical systems (MEMS) purposes. To this end, flexural and torsional motions have been studied in low-field anisotropic GMS single-domain state (SDS) exchange-coupled TbFe-FeCo multilayers (ECML). The magnetoelastic (ME) coefficient b/sup /spl gamma/,2/ depends strongly on the ECML structures, compositions, and sputtering deposition parameters. GMS multilayers with a high b/sup /spl gamma/,2/ (18 MPa for TbFe/sub 2//Fe/sub 0.6/Co/sub 0.4/ compared to 11 MPa for TbFe/sub 2//Fe) were obtained with or without an in-plane easy axis with a controlled direction, and without any annealing postprocess. Dynamical excitations of the actuators have been investigated under various conditions. An enhancement up to a factor 5 of the oscillations compared to the TbFe-Fe multilayers is observed with the possibility to tune the flexural/torsional dynamical behavior of these cantilevers. The corresponding very large dynamical ME susceptibility of these improved uniaxial ECML gives the possibility to control GMS MEMS with further reduction of the excitation field down to a few oersteds.

Synthetic jets based on micro magneto mechanical systems for aerodynamic flow control

A magneto-mechanical micro-actuator providing an axisymmetric synthetic microjet for active flow control was designed, fabricated and characterized. The micro-actuator consists of an enclosed cavity with a small orifice in one face and a high flexible elastomeric (PDMS) membrane in the opposite one. The membrane vibration is achieved using a magnetic actuation chosen for its capacity for providing large out of plane displacements and forces necessary for the performances aimed for. The paper presents first numerical simulations of the flow performed during the design process in order to identify a general jet formation criterion and optimize the devices performances. The fabrication process of this micro-magneto-mechanical system (MMMS) is then briefly described. The full size of the device, including packaging and actuation, does not exceed 1 cm3. The evaluation of the performances of the synthetic jet with 600 µm orifice was performed. The results show that the optimum working point is in the frequency range 400–700 Hz which is in accordance with the frequency response of the magnet-membrane mechanical resonator. In this frequency range, the microjet reaches maximum speeds ranging from 25 m s−1 to 55 m s−1 for an electromagnetic power consumption of 500 mW. Finally the axial velocity transient and stream-wise behaviours in the near and far fields are reported and discussed.

Finite element analysis and experimental study of surface acoustic wave propagation through two-dimensional pillar-based surface phononic crystal

We study both theoretically and experimentally the interaction of surface elastic waves with 2D surface phononic crystal (PnC) on a piezoelectric substrate. A rigorous analysis based on 3D finite element method is conducted to calculate the band structure of the PnC and to analyze the transmission spectrum (module and phase). Interdigital transducers (IDTs) are considered for electrical excitation and detection, and absorbing boundary conditions are used to suppress waves reflection from the edges. The PnCs are composed of an array of 20 Nickel cylindrical pillars arranged in a square lattice symmetry, and deposited on a LiNbO3 substrate (128°Y cut-X propagating) between two dispersive IDTs. We investigate by means of band diagrams and transmission spectrum the opening band-gaps originating from pillars resonant modes and from Bragg band-gap. The physical parameters that influence and determine their appearance are also discussed. Experimental validation is achieved through electrical measurement of the transmission characteristics, including amplitude and phase.

Patterned L10-FePt for polarization of magnetic films

In various micro and nanosystems applications comprising magnetic films, the polarizing field still needs to be integrated. We hereby present a solution for the self biasing of magnetic films using micropatterned permanent magnets. Micromagnetic simulations were used as a designing and optimization tool to create a biasing structure. The samples were fabricated with varying geometric parameters using classical silicon microfabrication techniques. Nanostructured TbCo/FeCo magnetostrictive thin films were sputtered over coercive FePt filled trenches etched in silicon. Magnetic and magneto-elastic characterizations confirmed the numerical simulations. In particular, nonlinear actuation of a self-biased magnetostrictive cantilever has been obtained at a zero external polarizing field.