arXiv subjects

Mauro Giovannini

Publications and source records attributed to Mauro Giovannini.

6 recordsLinked to original sources

arXiv2026

II. Exploring the role of the Crystal Electric Field in the vicinity of a Quantum Critical Point

Very low temperature thermodynamic properties of the Yb$M_{5-x}X_x$ (with $M$= Ni, Cu, and $X$= Cd, Mg, Au, Zn, Ag) cubic compounds are analyzed covering a broad range of behavior between magnetic and Fermi-liquid ground states GS using the {\it chemical doping}: $ζ$ as control parameter. This allows to gain insight into the evolution of the GS behavior including a quantum critical point QCP. Doniach-Lavagna phase diagram limitations are improved by taking into account crystal electric field CEF splittings. Three regions are recognized as a function of $ζ$: i) a magnetic one with long range magnetic order and $T_{ord}\propto T_N \approx 1$\,K, that weakens the interactions between $0.8\,K \geq T_m\geq 0.4$\,K, exhibiting very low Kondo temperature $T_K^{GS}$ in respective doublets GS. Then, for $T_Q\leq 0.4$\,K, quantum fluctuations start to dominate the scenario with the specific heat $C_{4f}/T(T\geq T_Q)$ showing $T$ power law dependencies, and a very heavy-fermion {\it plateau} below $T_Q$. ii) beyond the QCP the typical Non-Fermi-Liquid logarithmic $T$ dependence: $C_{4f}/T \propto \ln(T/T_0)$, with traces of magnetic order. At the non-magnetic limit: iii) the alloys behave as valence-fluctuation systems with growing $T_K$ that overcomes the CEF splitting. With this experimental information, a realistic phase diagram can be drawn around the QCP where the scenario is dominated by low lying quantum fluctuations, without $C_{4f}/T|_{Lim T\to 0}$ divergences but a clear drop entering into the non-magnetic phase.

cond-mat.str-el↗

arXiv2026

Resilience of the physicochemical properties of graphene-based materials for applications in harsh radiation environments

The development of radiation-tolerant materials capable of maintaining structural, electrical, and thermal stability in extreme, radiation-rich environments remains a critical challenge in materials science. In this work, the effects of 60 MeV 35Cl ion irradiation on highly oriented pyrolytic graphite (HOPG) and multilayer reduced graphene oxide (ML-rGO) were investigated. The samples were exposed to fluences of 5.11 x 10^9 and 1.3 x 10^10 ions/cm^2 and characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrical transport measurements. The results show that the irradiation response is strongly influenced by the initial structural organization of the material. In HOPG, ion exposure leads to a progressive loss of crystalline order, evidenced by XRD peak broadening and an increase in the Raman ID/IG ratio, accompanied by a reduction in electrical transport performance. In contrast, ML-rGO exhibits distinct behavior at higher fluences, suggesting partial structural reorganization. The appearance of more defined graphitic features in XRD and Raman analyses, along with changes in surface morphology and electrical response, suggests the formation of more ordered sp2 domains. These findings indicate that irradiation effects vary with the initial degree of order, providing useful insights for selecting carbon-based materials for devices operating under severe radiation conditions.

cond-mat.mtrl-sci↗

arXiv2025

Measurement of photo- and radio-luminescence of thin ThF4 films

We conducted measurements on the photo- and radio-luminescence of thin ThF$_4$ films in both the UV and visible ranges. In the UV range, we found that both luminescences are at a similar level as the internal dark counting noise of the photo-multiplier-tube (PMT). Our results suggest that thin ThF$_4$ crystals could be used as a target for the search for $^{229m}$Th and as a medium for the future nuclear clock. The measurements indicate that using a small and thin ThF$_4$ film can reduce background noise while maintaining the signal at the same level, achieved by increasing the $^{229}$Th enrichment. Our developed apparatus is now ready for direct measurements of $^{229m}$Th excitation and decay in ThF$_4$.

physics.ins-det↗

arXiv2024

Magnetic phase diagram of EuPdSn_2

A magnetic phase diagram for EuPdSn_2 is constructed based on magnetization, DC-susceptibility and specific heat as a function of applied field, and neutron diffraction results at zero field. The contribution of the ferromagnetic FM and antiferromagnetic AFM components to the measured magnetic susceptibility can be separated and weighted as a function of the applied field B by taking the temperature dependence of the neutron counts from the FM phase at B=0 as a reference. In the magnetically ordered phase, the temperature dependence of the specific heat does not follow the mean-field prediction for the Eu^{2+} J=7/2 quantum number rather that for J=5/2. This deviation and the consequent discrepancy for the entropy is discussed in the context of a non-Zeeman distribution of the eight fold ground state. Comparing the respective variations of magnetization M(T,B) and entropy S(T,B), the thermodynamic relationship dM/dT=dS/dB=0 is observed for the ranges: 0<T<10K and 0<B<0.4T.

cond-mat.str-el↗

arXiv2021

Deep insights into the local structure of amorphous Ta2O5 thin films by X-ray pair distribution function analysis

Amorphous films of tantalum oxide (Ta2O5) are widely applied to build highly reflective mirrors used in interferometric gravitational wave detectors, such as the Laser Interferometer Gravitational Wave Observatory (LIGO). Despite a large number of studies, the structural properties of amorphous Ta2O5 at the local scale still deserve several further investigations. Such information is essential to any attempt to understand the properties of this important material and no property modelling efforts can be expected to yield reliable information until the local structure in the amorphous phase is better understood. In this paper we report the results obtained by analysing the synchrotron X-ray pair distribution functions of pure and Ti-doped amorphous Ta2O5 film, deposited by ion beam sputtering, as prepared and after a thermal treatment. As a result, it is found that 1) the arrangement of Ta atoms in amorphous Ta2O5 strongly resembles that characterizing the high-pressure Z-Ta2O5 polymorph, whereas the topological properties of O atoms resembles that observed in delta-Ta2O5; 2) structural correlations in amorphous Ta2O5 start to vanish above ~ 5 Angstrom and are completely suppressed for r > 10 Angstrom on account of disorder; 3) Ti substitution retains the short-range topological ordering characterizing the as prepared Ta2O5 amorphous film even after thermal treatment; conversely, pure Ta2O5 films undergoes a significant rearrangement of the local structure after thermal treatment.

cond-mat.mtrl-sci↗

arXiv2021

The magnetic field induced ferromagnetism in EuPd$_2$Sn$_4$ novel compound

We report on crystal structure, magnetic and thermal physical properties of EuPd$_2$Sn$_4$ stannide. From the magnetic susceptibility measurements a divalent state of Eu rare earth element was determined together with an antiferromagnetic (AFM) order at 11 K. By applying magnetic field, the magnetic behavior variation reveals a complex magnetic structure. Above a critical field Bc a ferromagnetic (FM)-like character starts to prevail. AFM and FM regimes are separated by a metamagnetic region. Heat capacity measurements confirm this behavior.

cond-mat.str-el↗