N. Tiercelin

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.

Thermal effects in magnetoelectric memories with stress-mediated switching

Heterostructures with magneto-electro-elastic coupling (e.g. multiferroics) are of paramount importance for developing new sensors, actuators and memories. With the progressive miniaturization of these systems it is necessary to take into account possible thermal effects, which may influence the normal operating regime. As a paradigmatic example we consider a recently introduced non-volatile memory element composed of a magnetostrictive nanoparticle embedded in a piezoelectric matrix. The distributions of the physical fields in this matrix/inclusion configuration are determined by means of the Eshelby theory, the magnetization dynamics is studied through the Landau?Lifshitz?Gilbert formalism, and the statistical mechanics is introduced with the Langevin and Fokker?Planck methodologies. As result of the combination of such techniques we determine the switching time between the states of the memory, the error probability and the energy dissipation of the writing process. They depend on the ratio kBT/v where T is the absolute temperature and v is the volume of the magnetoelastic particle.

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...

Atomic-scale study of TbCo2.5/Fe multilayers by laser-assisted tomographic atom probe

Sputtered (TbCo2.5 25 nm/Fe 20 nm) multilayers have been analyzed by laser-assisted tomographic atom probe. It allowed us to perform three-dimensional reconstructions of the layers and to determine their composition at the atomic scale. From the concentration profiles inside the multilayer, we show that the diffused interfaces are not symmetric and that a stronger Fe-Co mixing is present at the top of the crystalline iron layers as compared to the top of amorphous TbCo layers.

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.

Frequency agile mechanical antenna for low-cost millimeter-wave applications

This paper presents for the first time a frequency tunable, mechanical patch antenna on PDMS/LCP for low-cost millimeter-wave applications. A pneumatic actuation system controls the height of the antenna, resulting in an analog tuning in frequency. The antenna is fed with a typical microstrip line coupled through a slot aperture patterned in the ground plane at the back side of a liquid crystal polymer substrate where the antenna is bonded to. The proposed antenna has a measured gain of 8 dBi, a 10-dB bandwidth of 4.8 GHz at 61.75 GHz and a tuning frequency range of 450 MHz. The designed antenna can be easily scaled to fit other millimeter-wave frequency applications.