Spin Freezing in the Spin Liquid Compound FeAl2O4

Spin freezing in the $A$-site spinel FeAl$_2$O$_4$ which is a spin liquid candidate is studied using remnant magnetization and nonlinear magnetic susceptibility and isofield cooling and heating protocols. The remnant magnetization behavior of FeAl$_2$O$_4$ differs significantly from that of a canonical spin glass which is also supported by analysis of the nonlinear magnetic susceptibility term $\chi_3 (T)$. Through the power-law analysis of $\chi_3 (T)$, a spin-freezing temperature, $T_g$ = 11.4$\pm$0.9~K and critical exponent, $\gamma$ = 1.48$\pm$0.59 are obtained. Cole-Cole analysis of magnetic susceptibility shows the presence of broad spin relaxation times in FeAl$_2$O$_4$, however, the irreversible dc susceptibility plot discourages an interpretation based on conventional spin glass features. The magnetization measured using the cooling-and-heating-in-unequal-fields protocol brings more insight to the magnetic nature of this frustrated magnet and reveals unconventional glassy behaviour. Combining our results, we arrive at the conclusion that the present sample of FeAl$_2$O$_4$ consists of a majority spin liquid phase with "glassy" regions embedded.Comment: 5 pages, 6 figs, 2-column, Accepted to Phys. Rev.

DIE BEHOEFTES VAN ADOLESSENTE EN RIGLYNE VIR 'N MIV-/VIGS-HULPVERLENINGSPROGRAM TER VOORBEREIDING OP OUERS SE AFSTERWE

Research was undertaken to determine the needs of adolescents and their experience of the death of their parents due to AIDS. AIDS is a still growing pandemic that is eliminatingthousands of lives in South Africa, whilst influencing the lives of relatives in a dramatic manner. Adolescents, in this particular unique stage of life, suffer most from the consequences of this disease. It is of special significance to adolescents when one or both of their parents die due lo AIDS-related causes. Adolescents have unique physical and emo1ional needs and when a parent or parents die, a vacuum is created in the fulfillment of their needs. In this study, some guidelines for an intervention programme, for adolescents who lost a parent or both parents due to AIDS, are suggested in order to empower adolescents to cope with the situation and to deal with the losses that they have to deal wilh. Community-based care and /he buddy system are but two current social work programmes that can partly be incorporated into this specific programme

Double-phase transition and giant positive magnetoresistance in the quasi-skutterudite Gd3_3Ir4_4Sn13_{13}

The magnetic, thermodynamic and electrical/thermal transport properties of the caged-structure quasi-skutterudite Gd$_3$Ir$_4$Sn$_{13}$ are re-investigated. The magnetization $M(T)$, specific heat $C_p(T)$ and the resistivity $\rho(T)$ reveal a double-phase transition -- at $T_{N1}\sim$ 10~K and at $T_{N2}\sim$ 8.8~K -- which was not observed in the previous report on this compound. The antiferromagnetic transition is also visible in the thermal transport data, thereby suggesting a close connection between the electronic and lattice degrees of freedom in this Sn-based quasi-skutterudite. The temperature dependence of $\rho(T)$ is analyzed in terms of a power-law for resistivity pertinent to Fermi liquid picture. Giant, positive magnetoresistance (MR) $\approx$ 80$\%$ is observed in Gd$_3$Ir$_4$Sn$_{13}$ at 2~K with the application of 9~T. The giant MR and the double magnetic transition can be attributed to the quasi-cages and layered antiferromagnetic structure of Gd$_3$Ir$_4$Sn$_{13}$ vulnerable to structural distortions and/or dipolar or spin-reorientation effects. The giant value of MR observed in this class of 3:4:13 type alloys, especially in a Gd-compound, is the highlight of this work.Comment: 20 pages single column, 7 figures, 1 table; Accepted to J. Appl. Phys., 201

Social work in South Africa: context, concepts and some critical reflections

South Africa adopted a social development approach towards social welfare after the first democratic elections of the country in 1994. On a continuum of social service delivery, the primary target group is the poorest of the poor and the most vulnerable people. It appears however after two decades of democracy, that social development, as intended in government policies, differs drastically from practice realities. However, strengths imbedded in the social work profession throughout the history of South Africa are shielding social workers from despair and disillusionment that may erode their pride and professionalism.Sudáfrica adoptó un enfoque de desarrollo social orientado hacia el bienestar social después de las primeras elecciones democráticas que hubo en el país en 1994. Una asistencia continua de servicios sociales se destina al grupo más pobre entre los indigentes y las personas más vulnerables. Después de dos décadas de democracia, se tiene la impresión que el desarrollo social así como lo consideran las políticas de gobierno no corresponde con las prácticas en la realidad. Sin embargo, los puntos fuertes de la profesión en el ámbito del trabajo social a través de la historia de Sudáfrica, protegen a los trabajadores sociales de la desesperación y la desilusión que afectan su orgullo y profesionalidad.Il Sudafrica ha adottato un approccio allo sviluppo nelle proprie politi-che sociali dopo le prime elezioni democratiche del 1994. Nell'ambito dell'erogazione dei servizi sociali, il principale gruppo dei destinatari è rappresentato dai più poveri tra la popolazione indigente e vulnerabile. Dopo due decenni di democrazia appare chiaro che lo sviluppo sociale, come inteso nelle politiche del governo, sia drasticamente diverso dalla realtà. Tuttavia, i punti di forza sviluppati dal servizio sociale profes-sionale nel corso della storia del Sudafrica stanno proteggendo gli assi-stenti sociali dallo sconforto e dalla disillusione che potrebbero erodere il loro orgoglio e la loro professionalità

Crystal field states of Kondo lattice heavy fermions CeRuSn3 and CeRhSn3

Inelastic neutron scattering experiments have been carried out to determine the crystal field states of the Kondo lattice heavy fermions CeRuSn3 and CeRhSn3. Both the compounds crystallize in LaRuSn3-type cubic structure (space group Pm-3n) in which the Ce atoms occupy two distinct crystallographic sites with cubic (m-3) and tetragonal (-4m.2) point symmetries. The INS data of CeRuSn3 reveal the presence of a broad excitation centered around 6-8 meV which is accounted by a model based on crystal electric field (CEF) excitations. On the other hand, the INS data of isostructural CeRhSn3 reveal three CEF excitations around 7.0, 12.2 and 37.2 meV. The neutron intensity sum rule indicates that the Ce ions at both cubic and tetragonal Ce sites are in Ce3+ state in both CeRuSn3 and CeRhSn3. The CEF level schemes for both the compounds are deduced. We estimate the Kondo temperature T_K = 3.1(2) K for CeRuSn3 from neutron quasielastic linewidth in excellent agreement with that determined from the scaling of magnetoresistance which gives T_K = 3.2(1) K. For CeRhSn3 the neutron quasielastic linewidth gives T_K = 4.6 K. For both CeRuSn3 and CeRhSn3, the ground state of Ce3+ turns out to be a quartet for the cubic site and a doublet for the tetragonal site.Comment: 12 pages, 13 figures, 2 tables, to appear in Phys. Rev.

Contiguous 3d and 4f magnetism: towards strongly correlated 3d electrons in YbFe2Al10

We present magnetization, specific heat, and 27Al NMR investigations on YbFe2Al10 over a wide range in temperature and magnetic field. The magnetic susceptibility at low temperatures is strongly enhanced at weak magnetic fields, accompanied by a ln(T0/T) divergence of the low-T specific heat coefficient in zero field, which indicates a ground state of correlated electrons. From our hard X-ray photo emission spectroscopy (HAXPES) study, the Yb valence at 50 K is evaluated to be 2.38. The system displays valence fluctuating behavior in the low to intermediate temperature range, whereas above 400 K, Yb3+ carries a full and stable moment, and Fe carries a moment of about 3.1 mB. The enhanced value of the Sommerfeld Wilson ratio and the dynamic scaling of spin-lattice relaxation rate divided by T [27(1/T1T)] with static susceptibility suggests admixed ferromagnetic correlations. 27(1/T1T) simultaneously tracks the valence fluctuations from the 4f -Yb ions in the high temperature range and field dependent antiferromagnetic correlations among partially Kondo screened Fe 3d moments at low temperature, the latter evolve out of an Yb 4f admixed conduction band.Comment: To appear in Phys. Rev. Let