7 research outputs found
Magnetically frustrated synthetic end member Mn2(PO4)OH in the triplite-triploidite family
The manganese end member of triplite-triploidite series of compounds, Mn2(PO4)OH, is synthesized by a hydrothermal method. Its crystal structure is refined in the space group P21/c with a = 12.411(1) Å, b = 13.323(1) Å, c = 10.014(1) Å, β = 108.16(1), V = 1573.3 Å3, Z = 8, and R = 0.0375. Evidenced in measurements of magnetization M and specific heat Cp, Mn2(PO4)OH reaches a long range antiferromagnetic order at TN = 4.6 K. As opposed to both triplite Mn2(PO4)F and triploidite-type Co2(PO4)F, the title compound is magnetically frustrated being characterized by the ratio of Curie-Weiss temperature Θ to Néel temperature TN of about 20. The large value of frustration strength Θ/TN stems from the twisted saw tooth chain geometry of corner sharing triangles of Mn polyhedra, which may be isolated within tubular fragments of a triploidite crystal structure. © 2017 The Royal Society of Chemistry.We thank E. V. Guseva for the X-ray spectral analysis of the sample and N. V. Zubkova for her help in the X-ray experiment. This work was supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISiS" project K2-2016-066 and by RFBR projects 15-05-06742, 16-02-00021 and 17-02-00211. The work was supported by Act 211 Government of the Russian Federation, contracts 02.A03.21.0004, 02.A03.21.0006 and 02.A03.21.0011
Spin-order-induced multiferroicity in LiCuFe2(VO4)3 and disorder effects in NaCuFe2(VO4)3
Mixed spin chain compounds, ACuFe2(VO4)3 (A= Li,Na), reach magnetically
ordered state at TN ~ 11 K (Li) or ~ 9 K (Na) and experience further
transformation of magnetic order at T* ~ 7 K (Li) or ~ 5 K (Na), evidenced in
magnetic susceptibility chi and specific heat Cp measurements. While no anomaly
has been detected in dielectric property of NaCuFe2(VO4)3, the step-like
feature precedes a sharp peak in permittivity epsilon at TN in LiCuFe2(VO4)3.
These data suggest the spin-order-induced ferroelectricity in Li compound and
no such thing in Na compound. On the contrary, the Moessbauer spectroscopy
study suggests similarly wide distribution of hyperfine field in between T* and
TN for both the compounds. The first principles calculations also provide
similar values for magnetic exchange interaction parameters in both compounds.
These observations lead us to conclude on the crucial role of alkali metals
mobility within the channels of the crystal structure needed to be considered
in explaining the improper multiferroicity in one compound and its absence in
other.Comment: 9 pages, 5 figure
Superconductivity in two-leg spin ladders
The single crystals with two-leg spin-ladder–type structure were
investigated. According to the structural, magnetic, optical
and resistivity data obtained, the studied crystals
were shown, for the first time, to be
high- superconductors (=80 K)
which belong to the class of cuprates with incommensurate-type structure