arXiv subjects

Vittorio Basso

Publications and source records attributed to Vittorio Basso.

At least 19 recordsLinked to original sources

arXiv2026

Modeling of a magnetic field sensor based on spin Hall magnetoresistance

Next-generation spintronic sensors aim to overcome the limitations of traditional tunneling-magnetoresistance (TMR) devices, such as complex manufacturing, high $1/f$ noise, and significant offsets. This work presents a comprehensive modeling and experimental validation of a magnetic field sensor based on Spin Hall Magnetoresistance (SMR) in a Wheatstone bridge configuration. Utilizing a multiphysics approach, we simulate the interplay between SMR, Anisotropic Magnetoresistance (AMR), and Spin-Orbit Torque (SOT) using a Stoner-Wohlfarth model complemented by a Fuchs-Sondheimer analysis of current distribution. To account for the presence of magnetic domains, we incorporate a modified Stoner-Wohlfarth framework that considers non-uniform magnetization and domain wall motion through a "truncated astroid" approach, allowing for a statistical distribution of single-domain particles. The model is validated against experimental measurements of Pt/$\text{Fe}_{60}\text{Co}_{20}\text{B}_{20}$ and Ta/$\text{Fe}_{60}\text{Co}_{20}\text{B}_{20}$ bilayers patterned into Hall bars and Wheatstone bridges. The model provides critical design guidelines for optimizing material properties, layer thickness, and device layout to minimize power consumption and maximize sensitivity in SMR-based sensing applications.

cond-mat.mes-hall↗

arXiv2025

Very-low-field MRI scanners: from the ideal to the real permanent magnet array

Very-low-field MRIs are becoming increasingly popular due to their portability and adaptability to different environments. They are being successfully used for various clinical applications, leading to a paradigm shift in the way imaging care is typically performed. The development of low-cost MRI scanner prototypes began a few years ago, with some interesting and promising open-source projects emerging in both hardware and software design. Using permanent magnets (PMs) to generate the static magnetic field B0 can substantially reduce the manufacturing cost while achieving satisfactory homogeneity. This article aims to explore the reasons behind discrepancies between magnet design and prototype performance in terms of magnetic field homogeneity. Understanding the impact of the practical implementation of magnet design could inform the development of more tolerant designs in future, simplifying subsequent B0 shimming procedures or even making them unnecessary. This work also evidences the impact of using different numerical model approximations in the modelling phase, proving how they also impact the quality of the design outcomes.

cs.CE↗

arXiv2025

The spontaneous Nernst coefficient of ferromagnets from the interplay of electron scattering and Berry curvature

We employ the Boltzmann transport approach to derive the spontaneous Nernst coefficient for ferromagnetic metals, explicitly treating the transverse current density due to Berry curvature as a Fermi surface property. We find that the spontaneous Nernst coefficient is proportional to the inverse of the scattering time constant, implying that efficient spontaneous Nernst materials should exhibit relatively strong scattering, a stark contrast to ordinary Nernst materials. Furthermore, we establish a direct connection between the strength and sign of the spontaneous Nernst coefficient and the itinerant contribution to orbital angular momentum density arising from the Bloch bands. Finally we construct a rigid two-bands model to evaluate the thermoelectric coefficients by which we find a good agreement with the signs and orders of magnitude of the experimental coefficients of magnetic 3d transition metal ferromagnets. We finally propose some practical recipes for maximizing the spontaneous Nernst effect through electronic band structure tailoring.

cond-mat.mtrl-sci↗

arXiv2025

Effect of bismuth crystal orientations in Nernst thermomagnetic devices

In this work we report Nernst effect measurements in single crystal bismuth samples, with special emphasis on the characterization of the Nernst coefficient when the magnetic field, heat current and generated voltage are aligned along specific directions relative to the crystal axes. We found significant differences between the different orientations, reflecting the highly anisotropic electronic structure of bismuth and compatible with the Nernst characteristics obtained from polycrystalline samples. These results not only complement the experimental works published in the past but also underline the role of crystalline orientation in the context of transverse thermoelectric effects, towards an efficient design of thermomagnetic devices like the ordinary-Nernst-effect-based energy harvesters.

cond-mat.mtrl-sci↗

arXiv2024

Disentangling electric field effect on spin waves in ferromagnetic insulators

In this paper we extend the micromagnetic theory of magnetostatic surface waves in insulating ferromagnetic thin films to include the applied electric field effects. We start by identifying the two main effects on the dispersion relation: the first one is of relativistic nature and emerges as a consequence of the Ahronov-Casher effect, while the second one is a consequence of the electric field induced symmetry breaking operating at the level of magnetic exchange interactions. We support our theory by comparing its predictions with experimental data on ittrium iron garnet thin films taken from the literature. The main result is to evidence the limitations of using the same value of the applied electric field to address both effects and to emphasize that crystal symmetry breaking due to the applied electric field brings about the contributions of the crystal field and determines different amplitudes for the two effects.

cond-mat.mes-hall↗

arXiv2023

Hard Ferromagnets as a New Perspective on Materials for Thermomagnetic Power Generation Cycles

We consider the ways in which magnetically hard materials can be used as the working materials in thermomagnetic power generation (TMG) cycles in order to expand the area in the magnetisation vs. applied field ($M-H$) plane available for energy conversion. There are 3 parts to this Perspective. First, experiments on commercially available hard ferrites reveal that, while these materials are not yet good TMG candidates, hard ferromagnets with higher thermal conductivity and a greater change of magnetization with temperature could outperform existing TMG materials. Second, computational results indicate that biasing a soft magnet with a hard ferromagnet is essentially equivalent to shifting the $M-H$ loop by an amount proportional to the field of the biasing magnet. Work outputs under biased conditions show a substantial improvement over unbiased cycles, but experimental verification is needed. Third, we discuss the rationale for exploring artificial spin reorientation materials as novel TMG working materials.

cond-mat.mtrl-sci↗

arXiv2022

Magnetocaloric effect at the reorientation of the magnetization in ferromagnetic multilayers with perpendicular anisotropy

We investigate the magnetocaloric effect obtained by the rotation of a magnetic field applied to an exchange-coupled multilayer system composed of two different ferromagnetic (FM) materials. We specifically consider a system in which the two FMs have perpendicular uniaxial anisotropy axes and utilise conditions which yield a reorientation of the total magnetization when compensation between the anisotropies of the two layers occurs. We calculate the consequent entropy change associated with the "artificial" reorientation. By using known parameters from MnBi and Co we predict an entropy change of $\Delta s = 0.34$ Jkg$^{-1}$K$^{-1}$ for perfect coupling. Lastly, we study the behavior of the multilayer under a rotating magnetic field via a micromagnetic model. When the layer thicknesses are of the order of the local domain wall width, the magnetic field-induced entropy change can be obtained with magnetic fields one order of magnitude lower than in the uncoupled case.

cond-mat.mtrl-sci↗

arXiv2022

Polycrystalline MnBi as a transverse thermoelectric material

To assess the potential of polycrystalline MnBi as a transverse thermoelectric material, we have experimentally investigated its anomalous Nernst effect (ANE) by means of the heat flux method. We prepared MnBi samples by powder metallurgy; this technique allows the preparation of samples in arbitrary shapes with the possibility to tailor their magnetic properties. In the material exhibiting the highest remanent magnetization, we found a value of the ANE thermopower of -1.1 $μ$V/K at 1 T, after the compensation of the ordinary Nernst effect from pure bismuth present inside the polycrystalline sample. This value is comparable with those reported in the literature for single crystals.

cond-mat.mtrl-sci↗

arXiv2021

Temperature dependence of the mean magnon collision time in a spin Seebeck device

Based on the relaxation time approximation, the mean collision time for magnon scattering $τ_c(T)$ is computed from the experimental spin Seebeck coefficient of a bulk YIG / Pt bilayer. The scattering results to be composed by two processes: the low temperature one, with a $T^{-1/2}$ dependence, is attributed to the scattering by defects and provides a mean free path around 10 $μ$m; the high temperature one, depending on $T^{-4}$, is associated to the scattering by other magnons. The results are employed to predict the thickness dependence of the spin Seebeck coefficient for thin films.

cond-mat.mes-hall↗

arXiv2020

Local spin Seebeck imaging with scanning thermal probe

In this work we present the results of an experiment to locally resolve the spin Seebeck effect in a high-quality Pt/YIG sample. We achieve this by employing a locally heated scanning thermal probe to generate a highly local non-equilibrium spin current. To support our experimental results, we also present a model based on the non-equilibrium thermodynamic approach which is in a good agreement with experimental findings. To further corroborate our results, we index the locally resolved spin Seebeck effect with that of the local magnetisation texture by MFM and correlate corresponding regions. We hypothesise that this technique allows imaging of magnetisation textures within the magnon diffusion length and hence characterisation of spin caloritronic materials at the nanoscale.

cond-mat.mes-hall↗

arXiv2019

Electric field effect on spin waves and magnetization dynamics: role of magnetic moment current

We show that a static electric field $E_x$ gives rise to a shift of the spin wave dispersion relation $ω(q_y-q_E)$ in the direction of the wavenumber $q_y$ of the quantity $q_E=-γ_LE_x/c^2$. This effect is caused by the magnetic moment current carried by the spin wave itself that generates an additional phase proportional to the electric field, as in the Aharonov-Casher effect. This effect is independent from the possibly present magneto-electric effects of insulating ferromagnets and superimposes to them. By extending this picture to arbitrary magnetization dynamics, we find that the electric field gives rise to a dynamic interaction term which has the same chiral from of the Dzyaloshinskii-Moriya interaction but is fully tunable with the applied electric field.

cond-mat.mes-hall↗

arXiv2018

Experimental proof of the reciprocal relation between spin Peltier and spin Seebeck effects in a bulk YIG/Pt bilayer

We verify for the first time the reciprocal relation between the spin Peltier and spin Seebeck effects in a bulk YIG/Pt bilayer. Both experiments are performed on the same YIG/Pt device by a setup able to accurately determine heat currents and to separate the spin Peltier heat from the Joule heat background. The sample-specific value for the characteristics of both effects measured on the present YIG/Pt bilayer is $(6.2 \pm 0.4)\times 10^{-3} \,\, \mbox{KA$^{-1}$}$. In the paper we also discuss the relation of both effects with the intrinsic and extrinsic parameters of YIG and Pt and we envisage possible strategies to optimize spin Peltier refrigeration.

cond-mat.mes-hall↗

arXiv2017

Kinetics of heat flux avalanches at the first order transition in La(Fe-Mn-Si)$_{13}$-H$_{1.65}$ compounds

We study heat flux avalanches occurring at the first order transition in La(Fe-Mn-Si)$_{13}$-H$_{1.65}$ magnetocaloric material. As the transition is associated to the phase boundaries motion that gives rise to the latent heat, we develop a non equilibrium thermodynamic model. By comparing the model with experimental calorimetry data available for Mn=0.18, we find the values of the intrinsic kinetic parameter $R_L$, expressing the damping for the moving boundary interface, at different magnetic fields. We conclude that by increasing field, thus approaching the critical point, the avalanches increase in number and their kinetics is slowed down.

cond-mat.mtrl-sci↗

arXiv2017

Basics of the magnetocaloric effect

This chapter reviews the basic physics and thermodynamics that govern magnetocaloric materials. The thermodynamics of magnetic materials is discussed by introducing relevant free energy terms together with their microscopic origin leading to a discussion of the sources of entropy that can change in an applied magnetic field. Such entropies account for measurable magnetocaloric effects, especially in the vicinity of magnetic phase transitions. Particular attention is devoted to first order magnetic transitions that involve the coupling of spin, lattice, electronic and anisotropic magneto-crystalline degrees of freedom. The problem of irreversibility and hysteresis, present in magnetocaloric materials with first order phase transitions is discussed in the context of out-of-equilibrium thermodynamics and hysteresis modeling.

cond-mat.mtrl-sci↗

arXiv2016

Thermodynamics of the heat currents in the longitudinal spin Seebeck and spin Peltier effects

We employ the non-equilibrium thermodynamics of currents and forces to describe the heat transport caused by a spin current in a Pt/YIG bilayer. By starting from the constitutive equations of the magnetization currents in both Pt and YIG, we derive the magnetization potentials and currents. We apply the theory to the spin Peltier experiments in which a spin current, generated by the spin Hall effect in Pt, is injected into YIG. We find that efficient injection is obtained when: i) the thickness of each layer is larger than its diffusion length: $t_{Pt} > l_{Pt}$ and $t_{YIG} > l_{YIG}$ and ii) the ratio $(l_{Pt}/τ_{Pt})/(l_{YIG}/τ_{YIG})$ is small, where $τ_i$ is the time constant of the intrinsic damping ($i=Pt, YIG$). We finally derive the temperature profile in adiabatic conditions. The scale of the effect is given by the parameter $ΔT_{SH}$ which is proportional to the electric current in Pt. Using known parameters for Pt and YIG we estimate $ΔT_{SH}/j_e = 4 \cdot 10^{-13}$ K A$^{-1}$m$^2$. This value is of the same order of magnitude of the spin Peltier experiments.

cond-mat.mtrl-sci↗

arXiv2016

Thermodynamic transport theory of spin waves in ferromagnetic insulators

We use the Boltzmann transport theory in the relaxation time approximation to describe the thermal transport of spin waves in a ferromagnet. By treating spin waves as magnon excitations we are able to compute analytically and numerically the coefficients of the constitutive thermo-magnetic transport equations. As a main result, we find that the absolute thermo-magnetic power coefficient $ε_M$, relating the gradient of the potential of the magnetization current and the gradient of the temperature, in the limit of low temperature and low field, is a constant $ε_M = -0.6419 \, k_B/μ_B$. The theory correctly describes the low-temperature and magnetic-field dependencies of spin Seebeck experiments. Furthermore, the theory predicts that in the limit of very low temperatures the spin Peltier coefficient $Π_M$, relating the heat and the magnetization currents, tends to a finite value which depends on the amplitude of the magnetic field. This indicates the possibility to exploit the spin Peltier effect as an efficient cooling mechanism in cryogenics.

cond-mat.mtrl-sci↗

arXiv2016

Determining the First Order Character of La(Fe,Mn,Si)13

Definitive determination of first order character of the magnetocaloric magnetic transition remains elusive. Here we use a microcalorimetry technique in two modes of operation to determine the contributions to entropy change from latent heat and heat capacity separately in an engineered set of La(Fe, Mn, Si)13 samples. We compare the properties extracted by this method with those determined using magnetometry and propose a model independent parameter that would allow the degree of first order character to be defined across different families of materials. The microcalorimetry method is sufficiently sensitive to allow observation of an additional peak feature in the low field heat capacity associated with the presence of Mn in these samples. The feature is of magnetic origin but is insensitive to magnetic field, explicable in terms of inhomogeneous occupancy of Mn within the lattice resulting in antiferromagnetic ordered Mn clusters.

cond-mat.mtrl-sci↗

arXiv2016

Non-equilibrium thermodynamics of the spin Seebeck and spin Peltier effects

We study the problem of magnetization and heat currents and their associated thermodynamic forces in a magnetic system by focusing on the magnetization transport in ferromagnetic insulators like YIG. The resulting theory is applied to the longitudinal spin Seebeck and the spin Peltier effects. By focusing on the specific geometry with one YIG layer and one Pt layer, we obtain the optimal conditions for generating large magnetization currents into Pt or large temperature effects in YIG. The theoretical predictions are compared with experiments from the literature permitting to derive the values of the thermomagnetic coefficients of YIG: the magnetization diffusion length $l_M \sim 0.4 \, μ$m and the absolute thermomagnetic power coefficient $ε_M \sim 10^{-2}$ TK$^{-1}$.

cond-mat.mtrl-sci↗