The interplay between the Kondo effect and the inter-dot magnetic interaction in a coupled-dot system is studied. An exact result for the transport properties at zero temperature is obtained by diagonalizing a cluster, composed by the double-dot and its vicinity, which is connected to leads. It is shown that the system goes continuously from the Kondo regime to an anti-ferromagnetic state as the inter-dot interaction is increased. The conductance, the charge at the dots and the spin-spin correlation are obtained as a function of the gate potential.

Large single-crystals of two polar intermetallic phases, CaMn2Sb2 and SrMn2Sb2, have been grown using In or Sn as metal fluxes and characterized by single-crystal X-ray diffraction. The two compounds are isostructural and crystallize with the CaAl2Si2 structure (space group P3m1, No. 164) with unit cell parameters determined at 120(2) K of a = 4.5204(6) angstroms, c = 7.456(2) angstroms and a = 4.5802(17) angstroms, c = 7.730(5) angstroms for CaMn2Sb2 and SrMn2Sb2, respectively. Temperature- and field-dependent dc- and ac-magnetization measurements suggest complex magnetic ordering of the Mn moments below ca. 250 and 35 K for CaMn2Sb2 and below ca. 265 K for SrMn2Sb2. Resistivity measurements reveal metallic-like temperature dependence with rho(290) = 40 m omega cm for CaMn2Sb2 and rho290 = 100 m omega cm for SrMn2Sb2 with negligible magnetoresistance at 5 K in applied magnetic fields up to 10 kOe. Spin-polarized DFT electronic structure calculations confirm the metallic-like properties and provide further evidence for a magnetic structure where Mn atoms form two magnetic sublattices with ferromagnetic coupling within them and strong antiferromagnetic coupling between them.

A series of new rare-earth indium-germanides RE 2 InGe 2 (RE ) Sm, Gd, Tb, Dy, Ho, Yb) have been prepared from the corresponding elements through high-temperature reactions using an excess of indium as flux. Single-crystal and powder X-ray diffraction studies showed that these ternary phases crystallize in the tetragonal space group P4/mbm, Z ) 2, Pearson's symbol tP10, and represent new members of the Mo 2 FeB 2 family (an ordered ternary variant of the U 3 Si 2 structure type). The temperature dependence of the dc magnetization (5-300 K) indicates that the RE 2 InGe 2 (RE ) Sm-Ho) compounds order magnetically below ca. 60 K, whereas Yb 2 InGe 2 exhibits Pauli-like temperature-independent paramagnetism. Isothermal magnetization, electrical resistivity, and calorimetry measurements are presented as well and confirm the existence of ordered antiferromagnetic states at low temperatures. The structural trends and the evolution of the magnetic properties are also discussed.

We measured the magnetic properties and heat capacity of three DyAl 2 single crystals with the magnetic field oriented along the three principal crystallographic directions: [100], [110], and [111]. The isothermal entropy change versus temperature curves were obtained from heat capacity and magnetization data for these directions. The experimental results were successfully explained by a mean field model that includes spin reorientation, exchange interactions, and crystalline electric field effects. The anomalous magnetocaloric effect along the [111] direction predicted by theory was confirmed experimentally. Keywords Materials Science and Engineering Disciplines Condensed Matter Physics | Metallurgy CommentsThis article is from Physical Review B 72 (2005) We measured the magnetic properties and heat capacity of three DyAl 2 single crystals with the magnetic field oriented along the three principal crystallographic directions: ͓100͔, ͓110͔, and ͓111͔. The isothermal entropy change versus temperature curves were obtained from heat capacity and magnetization data for these directions. The experimental results were successfully explained by a mean field model that includes spin reorientation, exchange interactions, and crystalline electric field effects. The anomalous magnetocaloric effect along the ͓111͔ direction predicted by theory was confirmed experimentally.

Multiple magnetic ordering phenomena, when substituting Dy for Er in (Er 1Ϫx Dy x )Al 2 over a broad range of concentrations 0рxр0.85, observed in low-temperature heat capacity measurements have been explained theoretically. The Hamiltonian that describes the system includes crystalline electric field effects, exchange interaction, and second-order contributions such as quadrupolar and magnetoelastic effects. We show that the discontinuity in the heat capacity, which arises at certain concentrations of the alloying element Dy, is the result of the competition between the magnetoelastic coupling and quadrupolar effects. The existence of the disappearance and reappearance of the magnetic phases in other lanthanide-lanthanide systems is also discussed.

We have explored the influence of sputtering parameters on the structural, mechanical, and electrical properties of nanoscale twinned 330 stainless steel thin films. As the residual stress in the film is changed from tensile to compressive by varying the growth conditions, the nanoscale twinned structure, the average columnar grain size and texture of the film show little or no change. Hardness of the film in compression reaches 7GPa, compared to about 5.5GPa in films with high residual tension, and an order of magnitude higher than that of bulk 330 stainless steel. Molecular dynamics simulations indicate that twin boundaries pose a strong barrier to glide dislocation transmission under applied in-plane biaxial loading, consistent with the GPa level strengths measured in these films. The increase in the room temperature electrical resistivity of these films, compared to bulk 330 stainless steel, is found to be small, indicating that nanoscale twinned structures may provide the best combination of high mechanical strengths and high electrical conductivity.

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Structures and magnetocaloric effects of Gd65− x RE x Fe20Al15 (x=0-20; RE=Tb, Dy, Ho, and Er) ribbons A breakthrough step in the development of magnetic refrigeration would be to find a way to increase the cooling capacity of the magnetic refrigerant material in order to make this technology even more energy efficient. In this paper, we present a theoretical study which shows how to increase the refrigerant capacity using anisotropic materials. We examine some of the well-known Laves phase compounds that can be described by a Hamiltonian which includes second order and spin reorientation effects. Our results indicate that in some cases it is theoretically possible to increase cooling capacity by up to ϳ65%.