arXiv subjects

M. Tortarolo

Publications and source records attributed to M. Tortarolo.

4 recordsLinked to original sources

arXiv2024

Spike-timing-dependent-plasticity learning in a planar magnetic domain wall artificial synapsis

Future neuromorphic architectures will require millions of artificial synapses, making understanding the physical mechanisms behind their plasticity functionalities mandatory. In this work, we propose a simplified spin memristor, where the resistance can be controlled by magnetic field pulses, based on a Co/Pt multilayer with perpendicular magnetic anisotropy as a synapsis emulator. We demonstrate plasticity and spike time dependence plasticity (STDP) in this device and explored the underlying magnetic mechanisms using Kerr microscopy imaging and Hall magneto-transport measurements. A well-defined threshold for magnetization reversal and the continuous resistance states associated with the micromagnetic configuration are the basic properties allowing plasticity and STDP learning mechanisms in this device.

physics.app-ph↗

arXiv2024

Evidence for charge mediated coupling in Fe-Ga/PMN-PT composite multiferroic

We present an experimental study of the magnetoelectric coupling (MEC) in the Fe-Ga/PMN-PT thin film multiferroic composite by means of x-ray magnetic circular dichroism (XMCD) and ferromagnetic resonance (FMR). Our measurements show evidence for a charge mediated coupling mechanism, suggested by the asymmetric magnetic remanence (M$_{rem}$) behaviour under opposite electric fields ($\pm$ E) and the asymmetric resonance field (H$_r$) in the FMR measurements. Also, the FMR measurements reveal a perpendicular magnetic anisotropy (PMA), that can be related to an interface charge effect. and it is tunable by E field. Ab initio calculations support the existence of a charge mediated coupling at the Fe-Ga/PMN-PT interface.

cond-mat.mtrl-sci↗

arXiv2021

Influence of the Fermi surface shape on magnetotransport: the MnAs case

We analyze the influence of the Fermi surface (FS) shape on magnetotransport properties, particularly on the Hall effect in the MnAs compound. It has been observed in MnAs films evidence of opposite conduction polarities for different crystal direction (goniopolarity) and a strong dependence of the carrier type with applied magnetic field. In order to understand this behaviour, we developed a model based on the semiclassical equations along with Boltzmann transport theory that takes into account both, the applied magnetic field and the FS shape. The FS of the MnAs compound is obtained by means of density functional theory (DFT), showing a clear dominance of the hyperboloid shape. Our study, corroborate that this specific topology of the FS gives rise to a goniopolar behaviour in the Hall transport. This theoretical results are supported by magnetotransport measurements on MnAs thin layers epitaxially grown on GaAs(001) and GaAs(111), where both configurations allow us to explore the transport characteristics for two different crystal directions of the MnAs.

cond-mat.mtrl-sci↗

arXiv2017

Injection locking at 2f of spin torque oscillators under influence of thermal noise

Experiments, numerical simulations and an analytic model were developed to elucidate the effects of noise in the synchronized state of a tunnel junction based spin torque nano oscillator (STNO). It is demonstrated that in the in plane magnetized structure, while the frequency is locked, much higher reference currents are needed to reduce the noise by phase locking. Our analysis shows that it is possible to control the phase noise by the reference microwave current (IRF) and that it can be further reduced by increasing the bias current (IDC) of the oscillator, keeping the reference current in feasible limits for applications.

physics.app-ph↗