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Antonio, D., and H. Pastoriza. "Nonlinear Dynamics of a Micromechanical Torsional Resonator: Analytical Model and Experiments." Journal of Microelectromechanical Systems 18, no. 6 (2009): 1396–1400.
Abstract: Mechanical microoscillators have been valuable tools for magnetic measurements of microscopic samples. This paper presents an analytical model for the dynamics of an electrostatically actuated torsional oscillator and validates it experimentally. While, at low excitations, the system is well described by a damped linear oscillator, at higher oscillation amplitudes, a nonlinear regime is observed. Nonlinearity is originated exclusively by the electrostatic driving and detection and can be tuned by modifying the excitation or detection bias voltages. The parameters of the analytical model are obtained from the device dimensions and material properties. No empirical or fitting parameters are needed except for the quality factor, which is extracted from the linear resonance curve. The proposed model can be a valuable and straightforward tool for the design and analysis of many other similar devices based on electrostatically actuated mechanical resonators.
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Antonio, D., M. I. Dolz, and H. Pastoriza. "Magnetization measurement of single La0.67Ca0.33MnO3 nanotubes in perpendicular magnetic fields using a micromechanical torsional oscillator." Journal of Magnetism and Magnetic Materials 322, no. 5 (2010): 488–493.
Abstract: Using a silicon micromechanical resonator as a sensitive magnetometer, the authors have studied both experimentally and theoretically the magnetic behavior of two isolated ferromagnetic nanotubes of perovskite La0.67Ca0.33MnO3. The article investigates the specific configuration where a magnetic field H is applied perpendicular to the magnetic easy axis of an isolated nanotube characterized by an uniaxial anisotropy constant K. In this situation, the magnetization M reduces the effective elastic constant kM of the resonator. This softening of the mechanical system is opposed to the hardening effect of M observed in a previous work, where H was applied parallel to the easy axis. Moreover, in this magnetic field configuration two distinct magnetization regimes are manifested, depending on the magnitude of H. For H[not double greater-than sign]2K/M the magnetization is almost parallel to the applied magnetic field and for H[double less-than sign]2K/M it is almost parallel to the easy axis of the nanotube. At a certain value of H there is a sharp transition
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Antonio, D., M. I. Dolz, and H. Pastoriza. "Micromechanical magnetometer using an all-silicon nonlinear torsional resonator." Applied Physics Letters 95, no. 13 (2009): 133505–3.
Abstract: In this work, a micromagnetometer employing a nonlinear torsional resonator with a high quality factor Q is presented experimentally. Oscillatory rotation of a conducting plate in the sensed magnetic field H induces eddy currents that dissipate energy. Due to the nonlinear response of the oscillator, the resulting mechanical damping originates frequency shifts in the resonance curve that depend on H. Nonlinearity results from the electrostatic detection, which introduces high order electrical spring constants. The device is fabricated with a standard silicon process and does not incorporate ferromagnetic materials. An analytical nonlinear model that correctly describes the device is also introduced.
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Antonio, D., P. Julian, P. Mandolesi, and H. Pastoriza. "Amplificador de transimpedancia criogénico para detección capacitiva de MEMS." In Actas de la Escuela Argentina de Microelectrónica, Tecnología y Aplicaciones: Trabajos Breves, 49–51. Vol. 1., 2007.
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Dolz, M., D. Antonio, and H. Pastoriza. "Measurement of mesoscopic High-$T_c$ superconductors using Si mechanical micro-oscillators." Physica B 398 (2007): 329–332.
Abstract: In a superconducting mesoscopic sample, with dimensions comparable to the London penetration depth, some properties are qualitatively different to those found in the bulk material. These properties include magnetization, vortex dynamics and ordering of the vortex lattice. In order to detect the small signals produced by this kind of samples, new instruments designed for the microscale are needed. In this work we use micromechanical oscillators to study the magnetic properties of a Bi$2$Sr$2$CaCu$_2$O8 + δ disk with a diameter of $13.5$ microns and a thickness of $2.5$ microns. The discussion of our results is based on the existence and contribution of inter and intra layer currents.
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Dolz, M. I., W. Bast, D. Antonio, H. Pastoriza, R. D. J. Sánchez Curiale, and A. G. Leyva. "Magnetic Behavior of Single La0.67Ca0.33MnO$_3$ Nanotubes: Surface and Shape Effects." J. Appl. Phys. 103 (2008): 083909.
Abstract: We report magnetization experiments in two magnetically isolated ferromagnetic nanotubes of perovskite Lai0.67Ca0.33MnO$_3$. The results show that the magnetic anisotropy is determined by the sample shape, although the coercive field is reduced by incoherent magnetization reversal modes. The temperature dependence of the magnetization reveals that the magnetic behavior is dominated by grain surface properties. These measurements were acquired using a silicon micromechanical oscillator working in its resonant mode. The sensitivity was enough to measure the magnetic properties of these two samples with a mass lower than 14 pg and to obtain for the first time the magnetization loop for one isolated nanotube.
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