Solid state phase equilibria in the Gd–Si–B system at 1270K

Engineering of a Layered Ferromagnet via Graphitization: An Overlooked Polymorph of GdAlSi

Layered magnets are stand-out materials because of their range of functional properties that can be controlled by external stimuli. Regretfully, the class of such compounds is rather narrow, prompting the search for new members. Graphitization─stabilization of layered graphitic structures in the 2D limit─is being discussed for cubic materials. We suggest the phenomenon to extend beyond cubic structures; it can be employed as a viable route to a variety of layered materials. Here, the idea of graphitization is put into practice to produce a new layered magnet, GdAlSi. The honeycomb material, based on graphene-like layers AlSi, is studied both experimentally and theoretically. Epitaxial films of GdAlSi are synthesized on silicon; the critical thickness for the stability of the layered polymorph is around 20 monolayers. Notably, the layered polymorph of GdAlSi demonstrates ferromagnetism, in contrast to the nonlayered, tetragonal polymorph. The ferromagnetism is further supported by electron transport measurements revealing negative magnetoresistance and the anomalous Hall effect. The results show that graphitization can be a powerful tool in the design of functional layered materials.

Flux synthesis, crystal structure and electronic properties of the layered rare earth metal boride silicide Er3Si5–x B. An example of a boron/silicon-ordered structure derived from the AlB2 structure type

The ternary rare earth metal boride silicide Er3Si5–x B (x = 1.17) was synthesized from the elements using the tin flux method. It crystallizes in a new structure type in the space group R32 (a = 6.5568(1) Å, c = 24.5541(1) Å, Z = 6). The structural arrangement can be derived from the AlB2 structure type with boron/silicon ordering in the layered metalloid substructure made of [Si5B] hexagons. The presence or absence of the boron atoms involved in this ordered structure is discussed on the basis of difference Fourier syntheses and structural analysis, in relation with the binary parent structures AlB2 and Yb3Si5 (Th3Pd5 type). The electronic and bonding properties of Er3Si5–x B were analyzed and discussed via density functional theory (DFT) calculations and a crystal orbital Hamiltonian population (COHP) bonding analysis.

Tin flux synthesis of rare-earth metal silicide compounds RESi1.7(RE = Dy, Ho): a novel ordered structure derived from the AlB2type

The binary rare-earth metal silicides RESi1.7(RE = Dy, Ho) were prepared by tin flux synthesis between 800–1000 °C. Single crystals were obtained after electrochemical dissolving of molten ingots. Their crystal structures were determined from single-crystal X-ray data: orthorhombic symmetry, space groupImm2; unit cell parametersa= 19.144(1),b= 8.2562(3),c= 6.6571(3) Å anda= 19.063(1),b= 8.2120(2),c= 6.6313(2) Å for DySi1.7and HoSi1.7, respectively. They represent a new ordered structure type, which is a derivative of the defect AlB2type. The main structural feature is the occurrence of a vacancy ordering in the two-dimensional planar network of silicon atoms, leading to rows of edge-shared twelve-membered rings separated by distorted hexagonal rings. Structural comparison with the parent hexagonal silicide Yb3Si5(Th3Pd5type), the structure of which has been re-determined on single crystal, is also given.