arXiv subjects

L. Saba

Publications and source records attributed to L. Saba.

4 recordsLinked to original sources

arXiv2026

Macroscopic evidence of spatial modulation of conductivity in a microtextured ferromagnetic film

A 75 nm-thick Fe0.5Pt0.5 film is a ferromagnetic metal showing striped magnetic domains in remanence at room temperature. The magnetoresistance is characterized by varying the external temperature and the in-plane magnetic field intensity, thereby affecting its magnetic structure. Qualitatively, the resistivity is well described by using the generalized Ohm's law. High-field magnetotransport properties are successfully explained by considering the competition between the expected metallic behavior and the electron-magnon interaction. In the low-field condition, we size the contribution of the magnetic texture to the macroscopic magnetotransport response by introducing a new quantity. Consistent with the microscopic modulation of the lateral conduction, low-field measurements reveal inhomogeneities attributed to the spatial distribution of ferromagnetic domains and domain walls. By carefully analyzing the macroscopic response near the coercive field, the additional contribution to the resistivity is attributed to the domain walls themselves. In fact, this term could surpass the anisotropic term at low temperatures. In summary, this study demonstrates that spatial magnetic inhomogeneities are not only macroscopically measurable but also comparable in magnitude to other regularly considered terms, mainly at low temperatures.

cond-mat.mes-hall↗

arXiv2025

Van der Waals interaction at short and long distances: a pedagogical path from stationary to time-dependent perturbation theory

The van der Waals interaction between neutral atoms is typically studied using stationary perturbation theory for the short-distance (London) limit, while long-distance (Casimir-Polder) results are usually derived via semiclassical, time-dependent approaches. Here, we demonstrate that reformulating stationary perturbation theory calculations in terms of time-ordered correlation functions significantly simplifies the mathematical treatment. This reformulation is particularly advantageous for higher-order calculations required in the long-distance regime, where retardation effects become important. Our approach provides a unified framework connecting both limiting cases, and is intended as a bridge between advanced quantum mechanics and field-theoretic treatments of dispersion forces, suitable for graduate-level courses or specialized readers.

quant-ph↗

arXiv2025

Temperature and crystallographic orientation dependence of the anisotropic magnetoresistance in epitaxial Fe65Co35 thin films

In this work, we study the anisotropic magnetoresistance (AMR) behavior of [001] epitaxial Fe65Co35 thin films along different crystallographic directions as a function of temperature. The AMR ratio is found to strongly depend on the current orientation relative to the crystal axes, reaching 0.16 % and 0.10 % at room temperature when the current is applied along the magnetic hard and easy axes, respectively. Moreover, the AMR ratio decreases at different rates as the temperature is reduced to 80 K. The longitudinal and transverse magnetoresistance curves were fitted using the Stoner-Wohlfarth formalism to describe the magnetization reversal path and to extract the magnetic anisotropy constants. The fitted cubic and uniaxial anisotropy constants are Kc = -2.36 kJ/m3 and Ku = 2.18 kJ/m3, verifying the change in the cubic anisotropy compared to Fe-richer Fe100-xCox compositions. These results demonstrate that by tailoring the crystalline orientation and temperature dependence of AMR, epitaxial Fe65Co35 thin films can enable the design of magnetic sensors with tunable sensitivity.

cond-mat.mtrl-sci↗

arXiv2025

Magnetization process in epitaxial Fe$_{85}$Co$_{15}$ thin films via anisotropic magnetoresistance

The effects of the crystalline symmetry on the magnetotransport properties in ferromagnetic alloys are being reexamined in recent years particularly due to the role of the anisotropic magnetoresistance on the electrical detection of magnetization dynamics, which is relevant to estimate spin transport parameters such as the spin Hall angle or the damping constant. In this work we investigated the crystalline dependent anisotropic magnetoresistance in epitaxial Fe85Co15 films and discuss the magnetization process through the magnetotransport properties by varying the relative orientations between the electric current, the external magnetic field and the Fe85Co15 crystallographic directions. We have found that the anisotropic magnetoresistance ratio depends on the current direction with respect to the crystal axes of Fe85Co15 and determine a ratio of 0.20 % and 0.17 % when the current is applied along the [110] hard and [100] easy axes, respectively. We fit our experimental data using the Stoner-Wohlfarth model to describe the path followed by the magnetization during the magnetization process and to extract the anisotropy constants. The fitted cubic and uniaxial anisotropy constants are Kc = 21 kJ/m3 and Ku = 11 kJ/m3, which are comparable with reported values from the angular variation of ferromagnetic resonance experiments. Our results contribute to the understanding of the interplay between the crystalline structure and the magnetotransport properties of FeCo alloys.

cond-mat.mtrl-sci↗