Магнитные структуры и магнитные фазовые переходы в редкоземельных интерметаллидах RMn-=SUB=-2-=/SUB=-Si-=SUB=-2-=/SUB=- (R=Sm, Tb)

The magnetic structures that form in La_1– x R_ x Mn_2Si_2 ( R = Sm, Tb) layered compounds with various concentrations x have been determined by magnetic neutron diffraction and magnetic measurements, and the magnetic phase diagrams have been built. It is shown that the formation of the magnetic structures is dependent not only on exchange interactions, but also on the type of the magnetic anisotropy of a rare-earth atom. It is found that, in La_1– x Tb_ x Mn_2Si_2 compounds with 0.2 < x < 0.5, the competition of the Tb–Mn and Mn–Mn interlayer exchange interactions and the existence of a strong uniaxial magnetic anisotropy in the Mn and Tb sublattices leads to the frustrated magnetic state and prevents the formation of the long-range magnetic order in the Tb sublattice.

Crystal structures and new perspectives on Y3Au4 and Y14Au51

Y3Au4 (triyttrium tetragold) and Y14Au51 (tetradecayttrium henpentacontagold), two binary representatives of Au-rich rare earth (R) systems crystallize with the space groups R\overline{3} and P6/m, adopting the Pu3Pd4 and Gd14Ag51 structure types, respectively (Pearson symbols hR42 and hP65). A variety of binary R–Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu3Pd4 type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca3Au4, Pr3Au4, Nd3Au4, Gd3Au4, and Th3Au4. Sm6Au7 is suspected to be Sm3Au4 due to identical symmetry and close unit-cell parameters. The Pu3Pd4 structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd14Ag51 type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y3Au4 can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y14Au51, this structure is more complex and is best described in terms of polyhedral `pinwheels' around the tunnel forming polyhedra along the c axis.

The crystal structure of Sm4Ni11In20 and its relation to other indium-rich compounds

Polycrystalline Sm4Ni11In20 was obtained by arc-melting of metal ingots. A subsequent high temperature treatment was used for single crystal growth. The Sm4Ni11In20 crystal structure (U4Ni11Ga20 type; C2/m, a = 22.5457(3) Å, b = 4.34929(5) Å, c = 16.5479(2) Å, β = 124.592(2)°, R1 = 0.0358, wR2 = 0.0934) was determined by single crystal synchrotron radiation X-ray diffraction from 2014 independent reflections with I > 2σ(I). Sm4Ni11In20 extends the R 4Ni11In20 (R = Y, Gd, Tb, Dy, Ho) series of phases. The R 4Ni11In20 and RNi3In6 (LaNi3In6 type; R = La, Ce, Pr, Nd, Eu) series have similar compositions. Their structures share similar fragments; in particular the rare earth atom coordination polyhedra are pentagonal prisms with additional atoms.

PHASE TRANSITION OF PRASEODYMIUM MONO-PNICTIDES UNDER HIGH PRESSURE

The Phase transition and elastic properties of Praseodymium-monopnictides have been investigated under pressure by means of a modified charge-transfer potential model which incorporates the Coulomb screening due to the delocalization of f-electron of rare-earth atom leading to many-body interactions, along with Coulomb interaction, covalency effect and overlap repulsion extended up to second-nearest neighbours. These compunds undergo transition from NaCl structure to high pressure body-centered tetragonal (BCT) structure (distorted CsCl-type P4/mmm). The calculated values of cohesive energy, lattice constant, phase transition pressure, relative volume collapse. Present model explains the Cauchy’s discrepancy correctly.