Sudesh K. Dhar

CeMnNi4: A soft ferromagnet with a high degree of transport spin polarization

In this letter we introduce a soft ferromagnetic compound, i.e., CeMnNi4, which exhibits a large moment (∼4.95μB∕Mn) and high degree of spin polarization. The system has a ferromagnetic transition temperature of 140K. Isothermal magnetization measurements at 5K reveal that the material is a soft ferromagnet with a magnetization saturating at about 1500Oe and a coercive field of <5Oe. We determine the transport spin polarization of this material from point contact Andreev reflection measurements to be 66% thereby making this material potentially important for spintronic applications.

Gold-rich R3Au7Sn3: Establishing the interdependence between electronic features and physical properties

Two new polar intermetallic compounds Y3Au7Sn3 (I) and Gd3Au7Sn3 (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P63/m; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu10Sn3 type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au6 antiprisms connected through R3 (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au6 prisms forming Au@Au6 clusters with Au–Au distances of 2.906–2.960 A, while the R–R contacts in the R3 groups are considerably larger than the sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd3Au7Sn3 shows an antiferromagnetic ordering at 13 K, while Y3Au7Sn3 is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R3Au7Sn3 (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. Chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au–Gd and Au–Sn interactions, while homoatomic Au–Au bonding is evident within the Au@Au6 clusters.

Kondo Lattice and Antiferromagnetic Behavior in Quaternary CeTAl4Si2 (T = Rh, Ir) Single Crystals

We have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materials as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two co...

Synthesis, Crystal and Electronic Structure of the Quaternary Magnetic EuTAl4Si2 (T = Rh and Ir) Compounds

Single crystals of the quaternary europium compounds EuRhAl4Si2 and EuIrAl4Si2 were synthesized by using the Al-Si binary eutectic as a flux. The structure of the two quaternary compounds has been refined by single crystal X-ray diffraction. Both compounds are stoichiometric and adopt an ordered derivative of the ternary KCu4S3 structure type (tetragonal tP8, P4/mmm). The two compounds reported here represent the first example of a quaternary and truly stoichiometric 1:1:4:2 phase crystallizing with this structure type. In light of our present results, the structure of the BaMg4Si3 compound given in literature as representing a new prototype is actually isotypic with the KCu4S3 structure. Local spin density approximation including the Hubbard U parameter (LSDA + U) calculations show that Eu ions are in the divalent state, with a significant hybridization between the Eu 5d, Rh (Ir) 4d (5d), Si 3p and Al 3p states. Magnetic susceptibility measured along the [001] direction confirms the divalent nature of the Eu ions in EuRhAl4Si2 and EuIrAl4Si2, which order magnetically near ∼11 and ∼15 K, respectively.

R2Sn3 (R = La - Nd, Sm): A family of intermetallic compounds with their own triclinic structure

A new family of intermetallic compounds with stoichiometry R2Sn3 has been identified in the R-Sn system for R = La, Ce, Pr, Nd and Sm. All compounds have a new triclinic crystal structure: P1̄, a = 6.378(1), b = 8.422(1), c = 11.098(1) Å , α = 107.37(1)◦, β = 96.78(1)◦, γ = 100.03(1)◦ for Nd2Sn3. As a characteristic motif, the structure contains infinite chains of neodymium trigonal prisms centred by tin and sharing alternately a lateral face and an edge of a triangular face. Heat capacity measurements reveal that the compounds with R = Ce, Pr, Nd and Sm order magnetically and undergo multiple magnetic transitions; from entropy considerations it appears that the four symmetry in-equivalent Ce atoms in Ce2Sn3 and the Sm atoms in Sm2Sn3 are all in the trivalent state. The highest transition temperature of nearly 24 K is observed for Sm2Sn3. The magnetisation and heat capacity data of La2Sn3 indicate a superconducting transition with a Tc of about 2.5 K.

Study of spin fluctuations in Ni3±xAl1∓x using point contact Andreev reflection spectroscopy

We report point contact Andreev reflection (PCAR) spectroscopy studies on Ni3Al with composition range (24, 26 and 27 at. % of Al in the solid solution) spanning the ferromagnetic to paramagnetic phase boundary. PCAR studies performed using Nb tip as counter electrode reveal that the superconducting quasiparticle lifetime (\tao) and superconducting energy gap (\delta) decreases with increasing spin fluctuation in the normal metal electrode. Our study reveals that PCAR could be a useful probe to study spin fluctuations in systems which are on the verge of a magnetic instability.

The R10Pd21 compounds (R = Y, Pr, Nd, Sm, Gd–Lu). Crystal structure and magnetism of the ‘RPd2’ phases

We have investigated the formation and stability of the binary rare-earth phases, previously reported in the literature as “RPd2”. Although these phases apparently showed a simple stoichiometry, their structure was not that of a Laves phase. After more than half of a century their crystal structure and true stoichiometry have been finally established. The exact stoichiometry of the “RPd2” phases is R10Pd21. The formation of the R10Pd21 compounds has been ascertained for R = Y, Pr, Nd, Sm, Gd to Lu, including Yb; Sc does not form the 10 : 21 phase. Pr10Pd21 forms only as a high temperature phase. These compounds crystallize in the monoclinic Sm10Pd21-type (mS124-C2/m, No. 12, Z = 4); the lattice parameters and unit cell volume decrease linearly on going from Pr to Lu in agreement with the lanthanide contraction. The crystal structure has been determined by X-ray powder diffraction and refined by Rietveld method for the Y, Nd, Tb and Lu compounds. These phases form by a peritectic reaction; the formation temperature, Tf, of some of them has also been measured and compared with the values reported for the “RPd2” phases for which the literature data are available. The increase of both the volume contraction and Tf on going from Pr10Pd21 to Lu10Pd21 suggests an increase of the thermodynamic stability along the series from the lighter to the heavier R. Physical properties (heat capacity, magnetic susceptibility and magnetization, electrical resistivity and magnetoresistance) have been measured for some members of the series (Nd10Pd21, Gd10Pd21, Tb10Pd21, Dy10Pd21, Ho10Pd21, Lu10Pd21 and Y10Pd21). Antiferromagnetic ordering is found for compounds with magnetic R ions at low temperature; the highest Neel temperature, TN, is 10 K for Tb10Pd21. The present experimental work represents a valuable contribution towards a more complete knowledge of the R–Pd systems. In the light of these results, all the binary R–Pd phase diagrams have to be reinvestigated (mainly those based on data assessed by the CALPHAD technique, using optimized thermodynamic parameters) and updated to furnish the material scientists consistent information to challenge the study of more complex systems.

Crystallographic & Electrical Properties of Pr Substituted Gd-123 Nanometre Sized High Temperature Superconductors

The samples of Gd1-xPrxBa2Cu3O7-δ with compositions x = 0.0, 0.1 & 0.3 were prepared by ceramic route. The XRD study of all samples is carried out. The XRD studies of the samples prepared by ceramic route show GdPr-123 system have an orthorhombic pervoskite structure. The lattice parameters, oxygen content, volume of unit cell, orthorhombic distortion, hole concentration in CuO2 plane and charge on Cu-O plane were evaluated using XRD data. It is found that the lattice parameters, volume of unit cell increase while oxygen content orthorhombic distortion, hole concentration (Psh) and average charge (p) decrease as doping percentage of Pr increases. The resistivity measurement shows the transition temperature decreases while transition width increases with increasing Pr concentration. The suppression of superconductivity may be due to reduction in hole concentration or magnetic pair breaking. We report such qualitative results of Pr substituted Gd-123 in this paper quantitatively.