arXiv subjects

Massimiliano Marangolo

Publications and source records attributed to Massimiliano Marangolo.

10 recordsLinked to original sources

arXiv2026

Micromagnetic Modeling of Surface Acoustic Wave Driven Dynamics: Interplay of Strain, Magnetorotation, and Magnetic Anisotropy

We study the coupling mechanism of surface acoustic waves (SAW) with spin waves (SW) using micromagnetic analysis. The SAW magnetoacoustic excitation field is fully implemented, i.e., all strain and lattice-rotation terms are included. A realistic CoFeB film with a weak in-plane uniaxial anisotropy is considered. We investigate the conditions for efficient SAW--SW coupling, with particular emphasis on the case where the SAW propagates parallel to the external magnetic field, a configuration of special interest for magnonic applications. Remarkably, we find that the anisotropy orientation serves as a knob to tune the parallel resonant interaction. Overall, this work provides a unified and practical picture of SAW--SW coupling in thin magnetized films.

cond-mat.mes-hall↗

arXiv2025

Nonreciprocal Spin-Wave Propagation in Anisotropy-Graded Iron Films Prepared by Nitrogen Implantation

Gradual modification of the magnetic properties in ferromagnetic films has recently been proposed as an effective method to channel and control spin waves for the development of new functionalities in magnonic devices. Here, we investigate graded FeN films prepared by low-dose nitrogen implantation of Fe epitaxial thin films. Combining Brillouin light scattering measurements and a spin-wave theoretical approach, we show that nitrogen implantation induces a graded profile of both the in-plane and the perpendicular anisotropies along the film thickness. This graduation leads to a significant modification of the spin-wave spatial localization and generates a marked frequency asymmetry in the spin-wave dispersion. Moreover, we find that the anisotropy profile, and as a consequence the dispersion relation, can be tuned on changing the implantation dose, opening a way for the potential use of the graded Fe-N films in magnonic applications.

cond-mat.mes-hall↗

arXiv2024

Temperature-invariant heat conductivity from compensating crystalline and glassy transport: from the Steinbach meteorite to furnace bricks

The thermal conductivities of crystals and glasses vary strongly and with opposite trends upon heating, decreasing in crystals and increasing in glasses. Here, we show--both with first-principles predictions based on the Wigner transport equation and with thermoreflectance experiments--that the dominant transport mechanisms of crystals (particle-like propagation) and glasses (wave-like tunnelling) can coexist and compensate in materials with crystalline bond order and nearly glassy bond geometry. We demonstrate that ideal compensation emerges in a sample of silica in the form of tridymite, carved from a meteorite found in Steinbach (Germany) in 1724, and yields a "propagation-tunneling-invariant" (PTI) conductivity that is independent from temperature and intermediate between the opposite trends of $α$-quartz crystal and silica glass. We show how such PTI conductivity occurs in the quantum regime below the Debye temperature, and can largely persist at high temperatures in a geometrically amorphous tridymite phase found in refractory bricks fired for years in furnaces for steel smelting. Last, we discuss implications to heat transfer in solids exposed to extreme temperature variations, ranging from planetary cooling to heating protocols to reduce the carbon footprint of industrial furnaces.

cond-mat.mtrl-sci↗

arXiv2023

Self-biased magnetoelectric Ni/LiNbO3/Ni for body embedded electronic energy harvesters

In this study, we present the fabrication and characterization of Ni/LiNbO3/Ni trilayers using RF sputtering. These trilayers exhibit thick Ni layers (10 microns) and excellent adherence to the substrate, enabling high magnetoelectric coefficients. By engineering the magnetic anisotropy of Nickel through anisotropic thermal residual stress induced during fabrication, and by selecting a carefully chosen cut angle for the LiNbO3 substrate, we achieved a self-biased behavior. We demonstrate that these trilayers can power medical implant devices remotely using a small AC magnetic field excitation, thereby eliminating the need for a DC magnetic field and bulky magnetic field sources. The results highlight the potential of these trilayers for the wireless and non-invasive powering of medical implants. This work contributes to the advancement of magnetoelectric materials and their applications in healthcare technology.

cond-mat.mtrl-sci↗

arXiv2023

Impact of Spin Wave Dispersion on Surface Acoustic Wave Velocity

The dependence of the velocity of surface acoustic wave (SAW) as a function of an external applied magnetic field is investigated in a Fe thin film epitaxially grown on a piezoelectric GaAs substrate. The SAW velocity is observed to strongly depend on both the amplitude and direction of the magnetic field. To interpret the experimental data a phenomenological approach to the relative change in SAW velocity is implemented. We find that the experimental velocity variation can be well reproduced provided that the spin wave dispersion is taken into account. The validity of this phenomenological model is attested by the comparison with a quasi-exact magnetoelastic one.

cond-mat.mtrl-sci↗

arXiv2020

Non-symmetric spin-pumping in a multiferroic heterostructure

We present spin pumping experiments in Co/Pt bilayers grown on Al2O3(0001) and on ferroelectric Y-cut LiNbO3 substrates. Spin pumping is triggered by resonant ferromagnetic resonance induced by surface acoustic waves. We observe that spin pumping efficiency varies when both the magnetization vector and the acoustic wave vector are reversed in Pt/Co/LiNbO3. This phenomenon is not observed in Pt/Co/Al2O3. We propose that the in-plane electric polarization of LiNbO3 is at the origin of the observed phenomenon. These observations open up the perspective of an electric field control of spin pumping efficiency.

cond-mat.mtrl-sci↗

arXiv2020

Thermal conductivity of Bi$_2$Se$_3$ from bulk to thin films: theory and experiment

We calculate the lattice-driven in-plane $(κ_{\parallel})$ and out-of-plane $(κ_{\perp})$ thermal conductivities of Bi$_2$Se$_3$ bulk, and of films of different thicknesses, using the Boltzmann equation with phonon scattering times obtained from anharmonic third order density functional perturbation theory. We compare our results for the lattice component of the thermal conductivity with published data for $κ_{\parallel}$ on bulk samples and with our room-temperature thermoreflectance measurements of $κ_{\perp}$ on films of thickness (L) ranging from 18~nm to 191~nm, where the lattice component has been extracted via the Wiedemann-Franz law. Ab-initio theoretical calculations on bulk samples, including an effective model to account for finite sample thickness and defect scattering, compare favorably both for the bulk case (from literature) and thin films (new measurements). In the low-T limit the theoretical in-plane lattice thermal conductivity of bulk Bi$_2$Se$_3$ agrees with previous measurements by assuming the occurrence of intercalated Bi$_2$ layer defects. The measured thermal conductivity monotonically decreases by reducing $L$, its value is $κ_{\perp}\approx 0.39\pm 0.08$~W/m$\cdot$K for $L=18$ nm and $κ_{\perp}=0.68\pm0.14$~W/m$\cdot$K for $L=191$ nm. We show that the decrease of room-temperature $κ_{\perp}$ in Bi$_2$Se$_3$ thin films as a function of sample thickness can be explained by the incoherent scattering of out-of-plane momentum phonons with the film surface. Our work outlines the crucial role of sample thinning in reducing the out-of-plane thermal conductivity.

cond-mat.mtrl-sci↗

arXiv2017

Straightforward measurement of thermal properties of anisotropic materials: the case of Bi2Se3 single crystal

We show that by a simple two-steps measurement protocol one can extract the thermal properties of anisotropic insulator materials. We focus on Bi2Se3 single crystal, a layered crystal with individual sheets held together by Van der Waals force, presenting strong heat diffusion anisotropy. Since the shape of the sample does not allow experiments in the perpendicular direction the challenge is to measure the in plane and out of plane thermal properties by in plane measurements. The optical properties of Bi2Se3 being known (opaque sample for the pump and probe beams), thermoreflectance microscopy experiments can be done on the bare substrate. In this case, the lateral heat diffusion is governed by the in plane thermal diffusivity. A 100 nm gold layer is then deposited on the sample. In this second experiment it is straightforward to demonstrate that the perpendicular thermal properties of the layer rule the lateral diffusivity. The good agreement of theoretical curves obtained by thermal models with experimental data permit us to evaluate the thermal conductivity coefficients of bulk Bi2Se3.

cond-mat.mtrl-sci↗

arXiv2014

Observation of Distinct Bulk and Surface Chemical Environments in a Topological Insulator under Magnetic doping

The influence of magnetic dopants on the electronic and chemical environments in topological insulators (TIs) is a key factor when considering possible spintronic applications based on topological surface state properties. Here we provide spectroscopic evidence for the presence of distinct chemical and electronic behavior for surface and bulk magnetic doping of Bi2Te3. The inclusion of Mn in the bulk of Bi2Te3 induces a genuine dilute ferromagnetic state, with reduction of the bulk band gap as the Mn content is increased. Deposition of Fe on the Bi2Te3 surface, on the other hand, favors the formation of iron telluride already at coverages as low as 0.07 monolayer, as a consequence of the reactivity of the Te-rich surface. Our results identify the factors that need to be controlled in the realization of magnetic nanosystems and interfaces based on TIs.

cond-mat.mtrl-sci↗

arXiv2014

Suppression of the thermal hysteresis in magnetocaloric MnAs thin film by highly charged ion bombardment

We present the investigation on the modifications of structural and magnetic properties of MnAs thin film epitaxially grown on GaAs induced by slow highly charged ions bombardment under well-controlled conditions. The ion-induced defects facilitate the nucleation of one phase with respect to the other in the first-order magneto-structural MnAs transition with a consequent suppression of thermal hysteresis without any significant perturbation on the other structural and magnetic properties. In particular, the irradiated film keeps the giant magnetocaloric effect at room temperature opening new perspective on magnetic refrigeration technology for everyday use.

cond-mat.mtrl-sci↗