arXiv subjects

C. A. Iglesias

Publications and source records attributed to C. A. Iglesias.

5 recordsLinked to original sources

arXiv2022

Fundamental inequalities in the Stoner-Wohlfarth model

We report two fundamental inequalities in the Stoner-Wohlfarth model. Specifically, we investigate the theoretical limit for the initial magnetic susceptibility in a system described by the Stoner-Wohlfarth approach. We also find analytical solutions for the magnetization in the low-field regime and obtain the borderline value for the uniaxial anisotropy constant in such an ideal Stoner-Wohlfarth system. We go beyond and introduce a general mean-field theory for interacting Stoner-Wohlfarth-like systems, thus estimating how the initial magnetic susceptibility is affected by the dipolar and exchange interactions inside the system. By means of a simple insight from a fundamental inequality for the magnetic susceptibility of an ideal Stoner-Wohlfarth system, we show its violation is a signature of the existence of exchange interactions between nanoparticles in an interacting Stoner-Wohlfarth-like system.

cond-mat.soft↗

arXiv2021

Unambiguous signature of exchange interactions between nanoparticles in a collective system

We report a simple, efficient manner to assess magnetic interactions, more specifically the exchange interaction, in systems as blocked magnetic nanoparticles. Specifically, we investigate what is the theoretical limit for the external magnetic susceptibility in a system described by the plain old Stoner-Wohlfarth model. We go beyond and introduce a general mean field theory for interacting systems, thus estimating how the magnetic susceptibility is affected due to the dipolar and exchange interactions inside the system. We disclose a fundamental inequality for the magnetic susceptibility and show its violation is an unambiguous signature of the existence of exchange interactions between nanoparticles in a collective system. To test the robustness of our theoretical achievements, we examine magnetization measurements and Henkel plots for blocked magnetic nanopowders. The agreement between experiment and theory provides evidence to confirm the validity of our findings.

cond-mat.mes-hall↗

arXiv2016

Comment on "Large enhancement in high-energy photoionization of Fe XVII and missing continuum plasma opacity"

Recent R-matrix calculations claim to produce a significant enhancement in the opacity of Fe XVII due to atomic core excitations [S. N. Nahar & A.K. Pradhan, Phys. Rev. Letters 116, 235003 (2016), arXiv:1606.02731] and assert that this enhancement is consistent with recent measurements of higher-than-predicted iron opacities [J. E. Bailey et al., Nature 517, 56 (2015)]. This comment shows that the standard opacity models which have already been directly compared with experimental data produce photon absorption cross-sections for Fe XVII that are effectively equivalent to (and in fact larger than) the new R-matrix opacities. Thus, the new R-matrix results cannot be expected to significantly impact the existing discrepancies between theory and experiment because they produce neither a "large enhancement" nor account for "missing continuum plasma opacity" relative to standard models.

physics.atom-ph↗

arXiv2014

Mechano-sysntesis and structural, magnetic and thermal characterization of $α$-Fe nanoparticles embedded in a Wüstite matrix

Magnetic materials for specific applications require an accurate control and complete comprehension of their magnetic properties. In particular, nanoparticles embedded in a polycrystalline matrix emerge as good candidates for applications due to the possibility of tuning the magnetic properties through interface interaction effects. Here, iron/wüstite composite is prepared using high energy mechanical milling from iron powder and water. The sample is analyzed by X-ray diffraction, dynamic laser light scattering, Mössbauer spectroscopy, field cooling and zero field cooling curves, magnetization curves, and magnetic hyperthermia. Based on the results, we identify that the produced sample is like Fe nanoparticles embedded in a wüstite matrix, with high stability in time, and shows noticeable features such as exchange bias effect at low temperatures and promising temperatures reached in a short time interval when considered magnetic hyperthermia, $\sim 46\,^\circ$C, becoming an interesting candidate for biological applications, such as the one employed for cancer therapy.

cond-mat.mtrl-sci↗

arXiv1995

X-ray spectra from convective photospheres of neutron stars

We present first results of modeling convective photospheres of neutron stars. We show that in photospheres composed of the light elements convection arises only at relatively low effective temperatures (< 3-5*10^4 K), whereas in the case of iron compositon it arises at < 3*10^ K. Convection changes the depth dependence of the photosphere temperature and the shapes of the emergent spectra. Thus, it should be taken into account for the proper interpretation of EUV/soft-X-ray observations of the thermal radiation from neutron stars.

astro-ph↗