Novel Intermetallic Compound UFe₅Si₃:  A New Room-Temperature Magnet with an Original Atomic Arrangement

Abstract

The new compound UFe5Si3 was prepared by rapid solidification of the melt using a splat cooling technique, followed by annealing at 1173 K for 10 days. Its crystal structure was determined ab initio from powder X-ray diffraction data. It crystallizes in the tetragonal space group P4/mmm, with lattice parameters at room temperature of a = 3.9298(3) Å and c = 7.7133(6) Å. The structure of UFe5Si3, which is new among intermetallic compounds, can be viewed as built up from an infinite three-dimensional framework of Fe and Si atoms defining along the a direction, tunnels of hexagonal sections, where the U atoms lie. Alternating and direct current magnetic measurements reveal that UFe5Si3 behaves as a hard ferromagnet with a Curie temperature of about 310 K. Measurements on magnetically oriented powder suggest that UFe5Si3 has a uniaxial anisotropy with c as the easy axis. The electrical resistivity decreases monotonously with decreasing temperature suggesting no other magnetic transition below 300 K. In line with this metallic behavior the thermal variation of the thermoelectric power remains of the order of several μV/K. A maximum around 60 K with a value of 12 μV/K can be ascribed to Kondo interactions and/or crystalline electrical field effects.

Phase relations and stabilities at 900°C in the U–Fe–Si ternary system

“…The structure of UFe 5 Si 3 can be viewed as built up from an infinite three-dimensional framework of Fe and Si atoms, which defines tunnels with hexagonal section where the U atoms reside. No evidence for any deviation from stoichiometry could be detected from microprobe analyses and X-ray powder experiments [7]. U 6 Fe 16 Si 7 crystallizes in the cubic Mg 6 Cu 16 Si 7 -type with lattice parameter refined from powder data, a ¼ 11.7217(5) Å , which compares well with the value obtained from single crystal refinement [8].…”

“…The temperature dependences of the electrical resistivity and thermopower of U 3 Fe 2 Si 7 , U 2 FeSi 3 , U 1.2 Fe 4 Si 9.7 , U 2 Fe 3 Si 5 and UFe 2 Si 2 ternary phases have been recently presented [6]. The novel intermediate phases UFe 5 Si 3 [7] and U 6 Fe 16 Si 7 [8] have been structurally characterized, and their magnetic and transport properties measured. As a final step on the crystal-chemistry investigation of the intermediate phases of the UeFeeSi ternary system, we present here the assessment in an extended concentration range of the isothermal section of this phase diagram at 900 C as well as information about the phase formation.…”

Complex Intermetallic Compounds: CaNi5Ge3, Ca15Ni68Ge37, and Ca7Ni49Ge22 – Three Multifaceted Ni‐Ge Framework Structures Combining the Structural Motifs of Ni3Ge and CaNi2Ge2

“…A very similar structure has been observed recently for UFe 5 Si 3 . [33] The symmetry and the atom arrangement are close to CaNi 5 Ge 3 , however, due to a weak distortion in CaNi 5 Ge 3 , the unit cell is doubled along the a and b axes. As the structure of UFe 5 Si 3 was determined by means of ab initio Rietveld refinement from powder X-ray diffraction data, the possibility that both compounds crystallize in the same "distorted" structure type cannot be ruled out.…”

Crystal structure and electronic properties of the new compounds, U6Fe16Si7 and its interstitial carbide U6Fe16Si7C

“…Beside UFe 10 Si 2 [5], U 2 Fe 17Àx Si x (3.3oxo4.5) [6] and UFe 5 Si 3 [7] which order ferromagnetically at high temperature, but with low values of the magnetic moments on iron atoms, U 1.2 Fe 4 Si 9.7 [8] is the only compound showing Curie-Weiss behavior. Its effective magnetic moment of 2.4 m B /U is significantly reduced from the free ion values of 3.62 and 3.58 m B /U for U 3+ and U 4+ , respectively, and also suggests that the local magnetic moment carried by the Fe atoms is negligible.…”

“…All [9], UFeSi [10], U 2 Fe 3 Si [11], U 3 Fe 2 Si 7 [12], U 2 Fe 3 Si 5 [13] and UFe 2 Si 2 [14] exhibit magnetic behaviors that are governed by itinerant electrons. To probe the influence of the U concentration on the magnetic moment carried by iron atoms, a detailed investigation of the Fe-rich corner of the U-Fe-Si ternary phase diagram, as well as the measurement of the electronic properties of the intermediate phases have been undertaken [7,15]. During this experimental work, the new compound U 6 Fe 16 Si 7 has been found.…”