Spin Glass and ferromagnetism in disordered Kondo lattice

The competition among spin glass (SG), ferromagnetism and Kondo effect has been analysed in a Kondo lattice model where the inter-site coupling $J_{ij}$ between the localized magnetic moments is given by a generalized Mattis model \cite{Mattis} which represents an interpolation between ferromagnetism and a highly disordered spin glass. Functional integral techniques with of Grassmann fields has been used to obtain the partition function. The static approximation and the replica symmetric ansatz has also been used. The solution of the problem is presented as a phase diagram temperature $T$ {\it versus} $J_K$ (the strength of the intra-site interaction). If $J_K$ is small, for decreasing temperature there is a second order transition from a paramagnetic to a spin glass phase For lower temperatures, a first order transition appears where solutions for the spin glass order parameter and the local magnetizations are simultaneously non zero. For very low temperatures, the local magnetizations becomes thermodinamically stables. For high $J_K$, the Kondo state is dominating. These results could be helpful to clarify the experimental situation of $CeNi_{1-x}Cu_{x}$.Comment: 4 pages, 1 figure, accept to be published in Physica

Fermionic Ising glasses with BCS pairing interaction in the presence of a transverse field

In the present work we have analyzed a fermionic infinite-ranged Ising spin glass with a local BCS coupling in the presence of transverse field. This model has been obtained by tracing out the conduction electrons degrees of freedom in a superconducting alloy. The transverse field \Gamma is applied in the resulting effective model. The problem is formulated in the path integral formalism where the spins operators are represented by bilinear combination of Grassmann fields. The problem can be solved by combining previous approaches used to study a fermionic Heisenberg spin glass and a Ising spin glass in a transverse field. The results are show in a phase diagram T/J {\it versus} \Gamma/J (J is the standard deviation of the random coupling J_{ij}) for several values of g (the strength of the pairing interaction). For small g, the line transition T_c(\Gamma) between the normal paramagnetic phase and the spin glass phase decreases when increases \Gamma, until it reaches a quantum critical point. For increasing g, a PAIR phase (where there is formation of local pairs) has been found which disappears when is close to \Gamma_c showing that the transverse field tends to inhibited the PAIR phase.Comment: 2 pages, 2 figures, accepted in Physica C Proceedings M2SRI

A theoretical study of the cluster glass-Kondo-magnetic disordered alloys

The physics of disordered alloys, such as typically the well known case of CeNi1-xCux alloys, showing an interplay among the Kondo effect, the spin glass state and a magnetic order, has been studied firstly within an average description like in the Sherrington-Kirkpatrick model. Recently, a theoretical model (PRB 74, 014427 (2006)) involving a more local description of the intersite interaction has been proposed to describe the phase diagram of CeNi1-xCux. This alloy is an example of the complex interplay between Kondo effect and frustration in which there is in particular the onset of a cluster-glass state. Although the model given in Ref. PRB 74, 014427 (2006) has reproduced the different phases relatively well, it is not able to describe the cluster-glass state. We study here the competition between the Kondo effect and a cluster glass phase within a Kondo Lattice model with an inter-cluster random Gaussian interaction. The inter-cluster term is treated within the cluster mean-field theory for spin glasses, while, inside the cluster, an exact diagonalisation is performed including inter-site ferromagnetic and intra-site Kondo interactions. The cluster glass order parameters and the Kondo correlation function are obtained for different values of the cluster size, the intra-cluster ferromagnetic coupling and the Kondo intra-site coupling. We obtain, for instance, that the increase of the Kondo coupling tends to destroy the cluster glass phase.Comment: 6 pages, 2 figures, Accepted for publication in Physica

Doniach diagram for ordered, disordered and underscreened Kondo lattices

The Doniach's diagram has been originally proposed to describe the competition between the local Kondo effect and the intersite RKKY interactions in cerium compounds. Here we discuss the extension of this diagram to different variations of Kondo lattice model. We consider a) ordered cerium compounds where the competition between magnetic order and Kondo effect plays an important role, as $CeRh_2Si_2$, b) disordered cerium systems with competing spin glass phase, magnetic ordered phases and a Kondo phase, as the heavy fermion cerium alloy $CeCu_xNi_{1-x}$ and, c) uranium compounds where a coexistence between Kondo effect and ferromagnetic order has been observed, as UTe. We show that all these cases can be described by a generalized Doniach phase diagram.Comment: Presented in the Latin American Workshop on Magnetism and Magnetic Materials (LAW3M) Rio de Janeiro, Brazil, August 12-16, 2007. Proceedings to be published in JMM

Stability conditions for fermionic Ising spin-glass models in the presence of a transverse field

The stability of spin-glass (SG) phase is analyzed in detail for a fermionic Ising SG (FISG) model in the presence of a magnetic transverse field $\Gamma$. The fermionic path integral formalism, replica method and static approach have been used to obtain the thermodynamic potential within one step replica symmetry breaking ansatz. The replica symmetry (RS) results show that the SG phase is always unstable against the replicon. Moreover, the two other eigenvalues $\lambda_{\pm}$ of the Hessian matrix (related to the diagonal elements of the replica matrix) can indicate an additional instability to the SG phase, which enhances when $\Gamma$ is increased. Therefore, this result suggests that the study of the replicon can not be enough to guarantee the RS stability in the present quantum FISG model, especially near the quantum critical point. In particular, the FISG model allows changing the occupation number of sites, so one can get a first order transition when the chemical potential exceeds a certain value. In this region, the replicon and the $\lambda_{\pm}$ indicate instability problems for the SG solution close to all range of first order boundary.Comment: 15 pages, 4 figures, accepted in Physica

Study of the requirements of an autonomous system for surface water quality monitoring

In recent years, there has been increasing awareness of the preservation, protection and sustainable use of natural resources. Water resources, being one of the most important natural resources, face major threats due to contamination by pollutants of various types and origins. Maintaining the quality of water resources requires more robust, reliable and more frequent monitoring than traditional techniques of data collection based on sporadic, discontinuous and manual processes. The management of large geographical areas, the insufficient spatiotemporal discretization of the values of samples collected by traditional processes and the unpredictability of natural phenomena, require a new approach to data collection procedures. This article, which is the result of ongoing research, defines the technical requirements and technologies used in a continuous and regular monitoring of surface water quality in freshwater systems, whose data acquisition system helps to identify the sources of pollution and the contaminants flow along the waterways. The design of a versatile real-time water quality monitoring system, which, due to its environmental constraints should be based on renewable energies and wireless transfer of energy, will contribute to improve the management and effective protection of water resources.This work was supported by Centro2020, Portugal 2020 and European Union (EU) under the grants, CENTRO-01-0145-FEDER-024052E – Libélula: Mobile robotic surface water quality monitoring system.info:eu-repo/semantics/publishedVersio

TOPOGRAFIA DO CONE MEDULAR EM UM GATO MOURISCO, Herpailurus yagouaroundi (Severtzow, 1858)(FELIDAE)

A anestesia caudal foi proposta pela primeira vez em 1926 e diversas técnicas foram desenvolvidas para anestesiar os nervos espinhais lombares e sacrais. Os métodos para anestesia epidural exigem conhecimento da anatomia da região envolvida. O objetivo deste estudo foi determinar a topografia do cone medular do gato mourisco, tornando possível a realização desta técnica anestésica em um felino silvestre de nossa fauna. Uma gata mourisca, adulta, proveniente do Zoológico Parque do Sabiá, Uberlândia-MG, foi encaminhado ao Laboratório de Pesquisa em Animais Silvestres (LAPAS), com o objetivo de determinar a topografia do cone medular para tornar possível a realização desta técnica anestésica em um felino silvestre de nossa fauna. Este animal foi fixado em solução de formol a 10%. Feita incisão de pele, os músculos da coluna vertebral foram retirados, os arcos vertebrais foram seccionados para visualização da medula espinhal e seus envoltórios. O cone medular neste animal iniciou-se na sexta vértebra lombar (L6) e terminou na segunda vértebra sacral (S2), com comprimento total de 50mm. O comprimento corporal deste felino foi de 473mm. Conclui-se que o melhor local para a anestesia epidural do membro pélvico no gato mourisco está entre as vértebras L6 e S2. Topographycal study on the medullar cone in jaguarundi, Herpailurus yagouaroundi (Severtzow,1858)(FELIDAE Abstract Since the caudal anesthesia was first proposed in 1926 many techniques were developed to anesthethize the lumbar and sacral nerves. Such methods for epidural anesthesia require knowledge of the relative anatomical regions. The objetive of the present study was to determine the topographic anatomy of the jaguarundi medullar cone as a morphological basis for application of anesthesis techniques. One adult female jaguarondi that perished by natural death has been obtained form the Sabiá Zoo Park, Uberlândia, MG, Brazil and conducted to tha Wild Animals Laboratory. The animal was fixes in 10% formalin solution. Following skin incision, muscles of the vertebral column were removed and the vertebral arcs sectioned for the visualization of hte spinal cord and its wrappers. Epidural anesthesic drug in the medullar cone. The medullar cone in this jaguarundi startet in the sixth lumbar vertebra (L6) and ended in the second sacral vertebra (S2); the spinal cord length was 50mm. The corporal length of this feline measured 473mm. The best region to perform the pelvic anesthesia in a jaguarundi is between the vertebra L6 and S2

Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms

We present the design, implementation and characterization of a dual-species magneto-optical trap (MOT) for fermionic 6Li and 40K atoms with large atom numbers. The MOT simultaneously contains 5.2x10^9 6Li-atoms and 8.0x10^9 40K-atoms, which are continuously loaded by a Zeeman slower for 6Li and a 2D-MOT for 40K. The atom sources induce capture rates of 1.2x10^9 6Li-atoms/s and 1.4x10^9 40K-atoms/s. Trap losses due to light-induced interspecies collisions of ~65% were observed and could be minimized to ~10% by using low magnetic field gradients and low light powers in the repumping light of both atomic species. The described system represents the starting point for the production of a large-atom number quantum degenerate Fermi-Fermi mixture