arXiv subjects

Julio Larrea Jiménez

Publications and source records attributed to Julio Larrea Jiménez.

4 recordsLinked to original sources

arXiv2025

Two lock-in amplifiers based $3ω$ technique: a practical guide for thermal conductivity experiments in bulk samples

The accurate determination of thermal conductivity $κ(T)$ in bulk materials at room temperature and above is crucial for evaluating their compatibility for specific applications. The 3$ω$ technique is an established methodology for studying the thermal conductivity of thin films, becoming particularly suitable in the case of bulk specimens for $T\gtrsim$300K, where standard stationary techniques require significant corrections for radiative losses. Although this method has been employed in several works, it remains not widely adopted because its implementation demands considerable sophistication, including experiment design, thin film deposition techniques, and choices of the geometry of the current/heat transducer, electronics, and analytical treatment of the signals. Based on a critical review of the technique's key technical aspects, this work provides practical support for a rapid and user-friendly implementation, from the design phase through to execution and analysis. We release a Python-based graphical user interface that supports a quantitative estimation of the investigated temperature profiles based on the geometrical parameters (width/length) of the deposited transducer (heater/thermometer metal line) before an experiment, guaranteeing an optimal design of the experimental conditions for each given material under scrutiny.

cond-mat.mtrl-sci↗

arXiv2022

Magnetic, electronic, and structural investigation of the strongly correlated Y$_{1-x}$Sm$_x$Co$_5$ system

SmCo$_5$ and YCo$_5$ are isostructural compounds both showing large magnetocrystalline anisotropy, where the former originates mainly from the crystal-electric field and magnetic interactions. We investigate the contribution of both interactions by partially substituting Y by Sm in as-cast polycrystalline Y$_{1-x}$Sm$_{x}$Co$_5$ (with $x$=0, 0.1, 0.2, 0.3, and 0.4) and measuring their structural, magnetic, and electrical properties through X-ray diffraction, magnetization, and electrical transport measurements. Our results suggest an interplay between microstructure strain in as-cast samples and the electronic and magnetic interactions.

cond-mat.str-el↗

arXiv2021

Thermal diffusivity and its lower bound in orthorhombic SnSe

The orthorhombic monochalcogenide SnSe has attracted much attention in recent years as a promising high-temperature thermoelectric material. We present a study of its thermal conductivity and specific heat of SnSe between 2~K and 300~K and quantify its anisotropic thermal diffusivity, $D$. For both crystallographic orientations, thermal diffusivity remains above the recently identified Planckian limit ($D > v_s^2 τ_P$, where $v_s$ is the sound velocity and $τ_P= \hbar/k_BT$) and its anisotropy in $D$ is set by the anisotropy of $v_s$. Comparison with cubic members of the IV-VI family leads to a consistent picture, where the diffusivity in all members of the family is set by the product of v$_s$, $τ_P$ and the 'melting' velocity derived from the melting temperature.

cond-mat.mtrl-sci↗

arXiv2018

Thermal transport and phonon hydrodynamics in strontium titanate

We present a study of thermal conductivity, $κ$, in undoped and doped strontium titanate in a wide temperature range (2-400 K) and detecting different regimes of heat flow. In undoped SrTiO$_{3}$, $κ$ evolves faster than cubic with temperature below its peak and in a narrow temperature window. Such a behavior, previously observed in a handful of solids, has been attributed to a Poiseuille flow of phonons, expected to arise when momentum-conserving scattering events outweigh momentum-degrading ones. The effect disappears in presence of dopants. In SrTi$_{1-x}$Nb$_{x}$O$_{3}$, a significant reduction in lattice thermal conductivity starts below the temperature at which the average interdopant distance and the thermal wavelength of acoustic phonons become comparable. In the high-temperature regime, thermal diffusivity becomes proportional to the inverse of temperature, with a prefactor set by sound velocity and Planckian time ($τ_{p}=\frac{\hbar}{k_{B}T}$).

cond-mat.mtrl-sci↗