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The magnetic and superconducting properties of the end point compounds AT2As2 (A = Ca,
Sr, Ba and T = Cu, Co, Pd) of the family of the iron arsenide superconductors A(Fe1−xTx)2As2 will
be presented. The iron arsenides represent a new class of high-Tc superconductor that share a
common generic phase diagram of the emergence of superconductivity with the high-Tc cuprates;
superconductivity is observed upon suppression of antiferromagnetic/spin density wave transition.
The complete substitution of Fe by Pd leads to superconductivity in (Ca,Sr)Pd2As2 and substitution
of Fe by Co leads to an A-type antiferromagnetic ordering in CaCo2As2 at TN = 52 K whereas
BaCo2As2 remains paramagnetic down to 0.45 K. The K-substitution in BaCo2As2 leads to weak
ferromagnetism in Ba1-xKxCo2As2.
CeRuSn3 is a Kondo lattice heavy fermion system exhibiting the peculiar Kondo-clusterglass
state below 0.6 K. Glassy spin-dynamics in this compound is inferred from the μSR study
which also shows the time-field scaling at 0.75 K. The power law behaviors of the magnetic
susceptibility, magnetization and specific heat reveal quantum Griffiths phase in this compound. A
brief discussion of ferromagnetic cluster spin-glass behavior in crystallographically well-ordered
stoichiometric Pr-compound PrRhSn3 will follow. A novel mechanism due to the dynamic
fluctuations of the crystal field levels is believed to be the origin of the cluster-glass behaviour in
PrRhSn3. |