Magnetization Study of the Heavy-Fermion System Yb(Rh1-xCox)2Si2 and of the Quantum Magnet NiCl2-4SC(NH2)2

This thesis presents a comprehensive study of the magnetic properties and of quantum phase transitions (QPTs) of two different systems which have been investigated by means of low-temperature magnetization measurements. The systems are the heavy-fermion Yb(Rh1-xCox)2Si2 (metallic) and the quantum magnet NiCl2-4SC(NH2)2 (insulator). Although they are very different materials, they share two common properties: magnetism and QPTs. Magnetism originates in Yb(Rh1-xCox)2Si2 from the trivalent state of the Yb3+ ions with effective spin S = 1=2. In NiCl2-4SC(NH2)2, the magnetic Ni2+ ions have spin S = 1. These magnetic ions are located on a body-centered tetragonal lattice in both systems and, in this study, the QPTs are induced by an external magnetic field. In Yb(Rh1-xCox)2Si2 the evolution of magnetism from itinerant in slightly Co-doped YbRh2Si2 to local in YbCo2Si2 is examined analyzing the magnetic moment versus chemical pressure x phase diagram in high-quality single crystals, which indicates a continuous change of dominating energy scale from the Kondo to the RKKY one. The physics of the antiferromagnet YbCo2Si2 can be completely understood. On the other hand, the physics of pure and slightly Co-containing YbRh2Si2 is much more complex, due to the itinerant character of magnetism and the vicinity of the system to an unconventional quantum critical point (QCP). The field-induced AFM QCP in Yb(Rh0.93Co0.07)2Si2 and in pure YbRh2Si2 under a pressure of 1.5GPa is characterized by means of the magnetic Grüneisen ratio. The final part of this thesis describes quantum criticality near the field-induced QCP in NiCl2-4SC(NH2)2 . These results will be compared to the theory of QPTs in Ising and XY antiferromagnets. Since the XY -AFM ordering can be described as BEC of magnons by mapping the spin-1 system into a gas of hardcore bosons, the temperature dependence of the magnetization for a BEC is analytically derived and compared to the results just below the critical field. The remarkable agreement between the BEC theory and experiments in this quantum magnet is one of the most prominent examples of the concept of universality.:1 Introduction 1 2 Theoretical concepts 5 2.1 Ce- and Yb-based 4f-electron systems . . . . . . . . . . . . . . . . 5 2.1.1 Crystalline electric field . . . . . . . . . . . . . . . . . . . . 6 2.2 Heavy-fermion systems . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.1 Fermi liquid theory . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.2 Kondo eff ect . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.3 RKKY interaction . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.4 Doniach phase diagram . . . . . . . . . . . . . . . . . . . . . 12 2.3 Quantum phase transitions . . . . . . . . . . . . . . . . . . . . . . . 14 2.3.1 Spin density wave scenario . . . . . . . . . . . . . . . . . . . 16 2.3.2 Local quantum critical point scenario . . . . . . . . . . . . . 17 2.3.3 Global phase diagram . . . . . . . . . . . . . . . . . . . . . 18 2.3.4 The Grüneisen ratio . . . . . . . . . . . . . . . . . . . . . . 21 2.4 Spins are almost bosons . . . . . . . . . . . . . . . . . . . . . . . . 22 3 Experimental methods 31 3.1 Magnetization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.1.1 Magnetization measurements . . . . . . . . . . . . . . . . . 32 3.2 Experimental techniques . . . . . . . . . . . . . . . . . . . . . . . . 34 3.2.1 Faraday magnetometer . . . . . . . . . . . . . . . . . . . . . 35 3.2.1.1 Measurement of the force . . . . . . . . . . . . . . 35 3.2.1.2 Capacitive cell . . . . . . . . . . . . . . . . . . . . 35 3.2.1.3 Design and performance of the cell . . . . . . . . . 37 3.2.1.4 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . 42 3.2.1.5 Background contributions . . . . . . . . . . . . . . 42 3.2.1.6 Calibration . . . . . . . . . . . . . . . . . . . . . . 42 3.2.1.7 Magnets characteristics . . . . . . . . . . . . . . . 44 3.2.1.8 Installation in a dilution refrigerator . . . . . . . . 45 3.2.2 SQUID magnetometer . . . . . . . . . . . . . . . . . . . . . 47 3.3 Magnetization measurements at high pressure . . . . . . . . . . . . 48 3.3.1 Experimental setup for M(H - T) under pressure . . . . . . . 50 4 Yb(Rh1-xCox)2Si2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51 4.1 Introduction and motivation . . . . . . . . . . . . . . . . . . . . . . 51 4.1.1 The heavy-fermion compound YbRh2Si2 . . . . . . . . . . . 53 4.1.2 The antiferromagnet YbCo2Si2 . . . . . . . . . . . . . . . . 58 4.1.3 Isoelectronic substitution of Co for Rh: Yb(Rh1-xCox)2Si2 . . . .62 4.2 Itinerant vs. local magnetism in Yb(Rh1-xCox)2Si2 . . . . . . . . . 67 4.2.1 Magnetization of Yb(Rh1-xCox)2Si2 with 0 x 0.27 . . . 67 4.2.1.1 YbRh2Si2 and Yb(Rh0.93Co0.07)2Si2 . . . . . . . . . 67 4.2.1.2 Yb(Rh0.88Co0.12)2Si2 . . . . . . . . . . . . . . . . . 71 4.2.1.3 Yb(Rh0.82Co0.18)2Si2 . . . . . . . . . . . . . . . . . 73 4.2.1.4 Yb(Rh0.73Co0.27)2Si2 . . . . . . . . . . . . . . . . . 74 4.2.1.5 Summary . . . . . . . . . . . . . . . . . . . . . . . 78 4.2.2 Magnetization of Yb(Rh1-xCox)2Si2 with x = 0.58 and x = 1 . . . . . 79 4.2.3 Evolution from itinerant to local magnetism . . . . . . . . . 83 4.3 Field-induced QCP in Yb(Rh0.93Co0.07)2Si2 . . . . . . . . . . . . . . 88 4.4 YbRh2Si2 under hydrostatic pressure . . . . . . . . . . . . . . . . . 96 4.4.1 Magnetization vs. field . . . . . . . . . . . . . . . . . . . . . 97 4.4.2 Comparison with 1.28 GPa . . . . . . . . . . . . . . . . . . . 99 4.4.3 Magnetization vs. temperature . . . . . . . . . . . . . . . . 101 4.4.4 Field-induced QCP at 1.5 GPa . . . . . . . . . . . . . . . . 103 4.4.5 The magnetic Grüneisen ratio . . . . . . . . . . . . . . . . . 105 4.5 The magnetic phase diagrams of YbCo2Si2 . . . . . . . . . . . . . . 107 4.5.1 Magnetization vs. temperature . . . . . . . . . . . . . . . . 107 4.5.2 Magnetization vs. fi eld . . . . . . . . . . . . . . . . . . . . . 109 4.5.3 H - T phase diagrams . . . . . . . . . . . . . . . . . . . . 114 4.5.4 Ac-susceptibility . . . . . . . . . . . . . . . . . . . . . . . . 117 4.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5 NiCl2-4SC(NH2)2 . . . . . . . . . . . . . . . . . . . . . . . .121 5.1 Introduction and motivation . . . . . . . . . . . . . . . . . . . . . . 121 5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.2.1 Magnetization . . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.2.2 Comparison between theory and experiment . . . . . . . . . 126 5.2.3 Magnetic phase diagram . . . . . . . . . . . . . . . . . . . . 129 5.2.4 Speci c heat . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 5.2.5 The magnetic Grüneisen ratio . . . . . . . . . . . . . . . . . 131 5.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 6 General conclusions . . . . . . . . . . . . . . . . . . . . . . . .135 Appendix 1 . . . . . . . . . . . . . . . . . . . . . . . .13

La estatua que cruzó la calle. Similitudes y diferencias entre dos novelas de D. Pío Baroja Nessi

El presente trabajo de fin de grado es un estudio que pretende analizar las similitudes y las diferencias entre dos novelas de Pío Baroja Nessi. Estas dos novelas, según su fecha de publicación, son La Busca, obra que inaugura la trilogía de La lucha por la vida, que incluye además Mala Hierba y Aurora Roja y que fueron publicadas en Madrid, en 1904. La edición empleada para este trabajo es la del año 1973, publicada por la editorial Caro Raggio, edición ilustrada conmemorativa del centenario del nacimiento de Pío Baroja.Grado en Español: Lengua y Literatur

Strong pinning of vortices by antiferromagnetic domain boundaries in CeCo(In1−x_{1-x}Cdx_x)5_5

We have studied the isothermal magnetization $M(H)$ of CeCo(In$_{1-x}$Cd$_x$)$_5$ with $x$ = 0.0075 and 0.01 down to 50 mK. Pronounced field-history dependent phenomena occur in the coexistence regime of the superconducting and antiferromagnetic phases. At low-fields, a phenomenological model of magnetic-flux entry well explains $M(H)$ implying the dominance of bulk pinning effect. However, unless crystallographic quenched disorder is hysteretic, the asymmetric peak effect (ASPE) which appears at higher fields cannot be explained by the pinning of vortices due to material defects. Also the temperature dependence of the ASPE deviates from the conventional scenario for the peak effect. Comparison of our thermodynamic phase diagrams with those from previous neutron scattering and magnetoresistance experiments indicates that the pinning of vortices takes place at the field-history dependent antiferromagnetic domain boundaries.Comment: 13 pages,4 figures, to be published in New Journal of Physic

Influence of loudspeaker directivity on the measurement uncertainty

One of the most significant aspects of a building’s acoustic behavior is the airborne sound insulation of the room façades, since this determines the protection of its inhabitants against environmental noise. For this reason, authorities in most countries have established in their acoustic regulations for buildings the minimum value of sound insulation that must be respected for façades. In order to verify compliance with legal requirements it is usual to perform acoustic measurements in the finished buildings and then compare the measurement results with the established limits. Since there is always a certain measurement uncertainty, this uncertainty must be calculated and taken into account in order to ensure compliance with specifications. The most commonly used method for measuring sound insulation on façades is the so-called Global Loudspeaker Method, specified in ISO 140-5:1998. This method uses a loudspeaker placed outside the building as a sound source. The loudspeaker directivity has a significant influence on the measurement results, and these results may change noticeably by choosing different loudspeakers, even though they all fulfill the directivity requirements of ISO 140-5. This work analyzes the influence of the loudspeaker directivity on the results of façade sound insulation measurement, and determines its contribution to measurement uncertainty. The theoretical analysis is experimentally validated by means of an intermediate precision test according to ISO 5725-3:1994, which compares the values of sound insulation obtained for a façade using various loudspeakers with different directivitie

Magnetization study of the energy scales in YbRh2_{2}Si2_{2} under chemical pressure

We present a systematic study of the magnetization in YbRh$_{2}$Si$_{2}$ under slightly negative (6?% Ir substitution) and positive (7% Co substitution) chemical pressure. We show how the critical field $H_{0}$, associated with the high-field Lifshitz transitions, is shifted to lower (higher) values with Co (Ir) substitution. The critical field $H_{\mathrm{N}}$, which identifies the boundary line of the antiferromagnetic (AFM) phase $T_{\mathrm{N}}(H)$ increases with positive pressure and it approaches zero with 6% Ir substitution. On the other side, the crossover field $H^{*}$, associated with the energy scale $T^{*}(H)$ where a reconstruction of the Fermi surface has been observed, is not much influenced by the chemical substitution.}{Following the analysis proposed in Refs.\,\cite{Paschen2004,Gegenwart2007,Friedemann2009,Tokiwa2009a} we have fitted the quantity $\tilde{M}(H)=M+(dM/dH)H$ with a crossover function to indentify $H^{*}$. The $T^{*}(H)$ line follows an almost linear $H$-dependence at sufficiently high fields outside the AFM phase, but it deviates from linearity at $T \le T_{\mathrm{N}}(0)$ and in Yb(Rh$_{0.93}$Co$_{0.07}$)$_{2}$Si$_{2}$ it changes slope clearly inside the AFM phase. Moreover, the FWHM of the fit function depends linearly on temperature outside the phase, but remains constant inside, suggesting either that such an analysis is valid only for $T \ge T_{\mathrm{N}}(0)$ or that the Fermi surface changes continuously at $T = 0$ inside the AFM phase.}}Comment: 6 pages, 4 figure

Audio communication in the face of the renaissance of digital audio

In recent years, digital audio has undergone an explosion. The transformation of radio and its expansion to new channels and consumer devices, added to the rise of podcasts and streaming music platforms, have led to the transformation of the audio ecosystem. This transition from the audio medium to audio media has involved an integral change in content, as well as in its production and reception processes. In this regard, the aim of this paper is to approach the present digital audio scene from the standpoint of its content, formats, and broadcasting models as well as of the new professional profiles, business models, and consumer–relationship practices, providing a snapshot that is completed with a prospective reflection on the challenges facing radio in this new ecosystem

Podcast as a transmedia sound extension of audio-visual fiction

La ductilidad del podcast, un formato que favorece la autonomía y el control del oyente en el acceso al contenido y la intimidad y personalización en su escucha, permite expandir el alcance de la ficción audiovisual a través de relatos transmedia que amplían las posibilidades de conexión del usuario con sus historias, entornos y personajes. Esta investigación analiza los quince podcasts producidos en España durante el periodo 2015-2021 como extensiones de series estrenadas en cadenas de televisión en abierto (La1, Telecinco y Antena 3), canales de pago (FOX) y plataformas de video bajo demanda (Movistar+, HBO Max y Amazon Prime Video). El estudio confirma que todos ellos dan continuidad al universo narrativo original mediante una amplia variedad de géneros sonoros –audioficciones, entrevistas, tertulias, reportajes y documentales– y aportaciones argumentales exclusivas, distintivas y valiosas. Al mismo tiempo, se constata que, en algunos casos, las estrategias de distribución no están bien definidas ni aprovechan todas las plataformas y dispositivos de acceso al contenido. En todo caso, se evidencia el gran potencial del audio digital como un recurso creativo, eficiente y económicamente asequible tanto a nivel artístico como comercial. Con él se favorece la generación del engagement y se promueve una cultura de participación e interacción entre los fans que se convierte en una efectiva réplica a la creciente fragmentación de las audiencias en el contemporáneo ecosistema digital.The flexibility of the podcast, a format which favors the listener autonomy and control in the access to the content and the intimacy and personalization in the listening, allows us to expand the reach of audiovisual fiction through transmedia stories that expand the possibilities of the user’s connection with their stories, backgrounds, and characters. This paper analyses the fifteen podcasts produced in Spain during the period 2015-2021 as extensions of series launched on broadcast television channels (La1, Telecinco and Antena 3), pay channels (FOX) and video-on-demand platforms (Movistar+, HBO Max and Amazon Prime Video). The analysis confirms that all of them give continuity to the original narrative universe through a wide variety of sound genres –audio-fictions, interviews, talk shows, reports, and documentaries– and exclusive, distinctive, and valuable story contributions. At the same time, it is notable that, in some cases, distribution strategies are not well defined and do not take advantage of all platforms and devices for accessing content. In any case, the great potential of digital audio as a creative, efficient, and economically accessible resource, both artistically and commercially, is evident. It favors the generation of engagement and promotes a culture of participation and interaction among fans that becomes an effective response to the growing fragmentation of audiences in the contemporary digital ecosystem

Teenagers, smartphones and digital audio consumption in the age of Spotify

The consolidation of smartphones as dominant devices for access to digital information and entertainment has redefined the processes of production and commercialization of cultural communication industries. The nature of these screens, which prioritize the visual content over the sound, decisively influences distribution strategies in the audio market: radio operators, streaming music platforms and podcast creators need to adapt their value chains to the habits derived from this mediation, especially in the younger audience. This research identifies the practices of mobile use as an audio receiver among adolescents in Colombia, Spain and Mexico –the most representative countries of Spanish-speaking digital sound consumption– based on a descriptive study on a thousand subjects from 13 to 19 years of age. The results confirm the overwhelming dominance in this music menu in the face of low penetration of radio and podcast word content. The selection is based on personal criteria, with little margin for the prescription of family or friends. There is evidence of the roots of individual listening, linked to the brand and the visibility of audio providers, who are obliged to develop diffusion logics based not only on thematic or genre preferences, but also on the user experience

Predict the effects of dolutegravir (DTG) plus lamivudine (3TC) on immunological responses in people living with HIV (PLWHIV)

Producción CientíficaBackground: Immune recovery in people living with HIV (PLWHIV) is a residual aspect of antiretroviral treatment (ART) in most patients, but in a non-negligible proportion of them, the CD4+ lymphocytes count, or CD4/CD8 ratio remains suboptimal. Methods: We performed a model of the immune response after 24 weeks of switching to a 2DR with DTG plus 3TC in a retrospective multicenter cohort of undetectable and experienced patients using significant predictor variables associated with the parameters or situations defined as success and failure. Clinical variables studied were CD4+ and CD8+ lymphocyte count, percentage of CD4, and CD4/CD8 ratio. These parameters were assessed at baseline and 24 weeks after the switch. Based on the evolution of each variable, four categories of immune response and four categories of non-immune response were defined. Immune response was defined as CD4+ count > 500 cells/mm3, %CD4 > 30%, CD8+ count 500 cells/mm3 (p = 0.054); CD4 > 30% (p = 0.054, p = 0.084); CD8 < 1000 cells/mm3 (p = 0.018), and CD4/CD8 ≥ 0.9 (p = 0.013, p = 0.09) are detected as stimulating or conducive to DTG plus 3TC treatment success. Conclusion: These models represent a proof of concept that could become a valuable tool for clinicians to predict the effects of DTG plus 3TC on immunological responses prior to the switch in undetectable pre-treated PLWHIV with immune dysfunction. The main predictors for immunological failure were late HIV diagnosis, stage of AIDS, and current age over 50 years. In contrast, starting with a normalized immune status was detected as stimulating or conducive to DTG plus 3TC treatment success