The homogeneous high-entropy wolframite-type solid solution (Mn1/5Co1/5Ni1/5Cu1/5Cd1/5)WO4 was prepared by solid-state reaction at 1000 °C. Elongated “crystals” were grown from the Na2WO4 flux, but ...their strongly broadened powder X-ray diffraction patterns indicated partial dissolution. Nevertheless, successive annealing of the homogeneous solid solution for 3–4 h at 800, 700, and 600 °C did not bring any sign of dissolution. Thus, the material is kinetically stable at low temperatures although thermodynamically unstable. The long-range antiferromagnetic order was established at T N ∼ 24.8 K. Based on magnetization and specific heat measurements, a magnetic phase diagram was built, demonstrating the presence of an additional field-induced phase. In contrast to the parent MnWO4, no dielectric anomaly has been found down to 2 K.
The homogeneous high-entropy wolframite-type solid solution (Mn
Co
Ni
Cu
Cd
)WO
was prepared by solid-state reaction at 1000 °C. Elongated "crystals" were grown from the Na
WO
flux, but their ...strongly broadened powder X-ray diffraction patterns indicated partial dissolution. Nevertheless, successive annealing of the homogeneous solid solution for 3-4 h at 800, 700, and 600 °C did not bring any sign of dissolution. Thus, the material is kinetically stable at low temperatures although thermodynamically unstable. The long-range antiferromagnetic order was established at
∼ 24.8 K. Based on magnetization and specific heat measurements, a magnetic phase diagram was built, demonstrating the presence of an additional field-induced phase. In contrast to the parent MnWO
, no dielectric anomaly has been found down to 2 K.
The concept of high-entropy oxides has triggered extensive research of this novel class of materials because their numerous functional properties are usually not mere linear combinations of those of ...the components. Here, we introduce the new series of compositionally complex honeycomb-layered magnets Na
Li
T
SbO
(T = Cu
Ni
Co
). An unusual feature of the system is its nonmonotonous dependences of the monoclinic lattice parameters
and β on
. Rietveld refinement of the crystal structures of the Na and Li end members reveals apparent Sb-T site inversion in the former and considerable Li-Cu site inversion in the latter. The materials are characterized by measurements of specific heat
, magnetization
, and ac and dc magnetic susceptibility χ. Na
T
SbO
exhibits sharp long-range antiferromagnetic order (
= 10.2 K) preceded by noticeable correlation effects at elevated temperatures. The magnetic phase diagram of Na
T
SbO
is established. Introduction of Li, just at
= 0.8, destroys AFM order, resulting in spin-cluster glass behavior attributed to Li/Cu inversion, with
growing with
to 10.4 K at
= 3.
The concept of high-entropy oxides has triggered extensive research of this novel class of materials because their numerous functional properties are usually not mere linear combinations of those of ...the components. Here, we introduce the new series of compositionally complex honeycomb-layered magnets Na3-xLixT2SbO6 (T = Cu1/3Ni1/3Co1/3). An unusual feature of the system is its nonmonotonous dependences of the monoclinic lattice parameters b and β on x. Rietveld refinement of the crystal structures of the Na and Li end members reveals apparent Sb-T site inversion in the former and considerable Li-Cu site inversion in the latter. The materials are characterized by measurements of specific heat Cp, magnetization M, and ac and dc magnetic susceptibility χ. Na3T2SbO6 exhibits sharp long-range antiferromagnetic order (TN = 10.2 K) preceded by noticeable correlation effects at elevated temperatures. The magnetic phase diagram of Na3T2SbO6 is established. Introduction of Li, just at x = 0.8, destroys AFM order, resulting in spin-cluster glass behavior attributed to Li/Cu inversion, with TG growing with x to 10.4 K at x = 3.
Single-crystals of manganese hydroxide hydrogen vanadate divanadate, Mn
6.75
(OH)
3
H
1.20
(VO
4
)
4-2
z
(V
2
O
7
)
z
(
z
= 0.15), have been synthesized hydrothermally. Its hexagonal crystal ...structure, sp. gr.
P
6
3
mc
, related to mineral ellenbergerite, has been determined by single-crystal X-ray diffraction. It features a three-dimensional framework of vertex- and face-sharing Mn
2+
-centered octahedra with defective Mn
2+
-octahedral chains and disordered V
2
O
7
, HVO
4
and H
2
VO
4
groups located in hexagonal and triangular type channels. The presence of these groups has been confirmed by Fourier transform infrared spectroscopy. According to magnetization and specific heat data, Mn
6.75
(OH)
3
H
1.20
(VO
4
)
4-2
z
(V
2
O
7
)
z
(
z
= 0.15) experiences ordering into a canted antiferromagnetic state at
T
N
= 42.5 K.
We report on the structural features of Mn
6.75
H
1.20
(VO
4
)
4-2z
(V
2
O
7
)
z
(
z
= 0.15), which clarified the mechanism of negative charge compensation of the framework. The compound undergoes phase transition at
T
N
= 42.5 K into canted AF state.
The missing member of the rosiaite family, CoGeTeO
, was synthesized by mild ion-exchange reactions and characterized by magnetization
and specific heat
measurements. It exhibits a successive short- ...and long-range magnetic ordering at
≈ 45 K and
= 15 K, respectively. Based on these measurements, the magnetic
-
phase diagram was established, showing two antiferromagnetic phases separated by a spin-flop transition. The reason why the pronounced short-range correlation occurs at a temperature nearly three times higher than
was found by evaluating the Co-O⋯O-Co exchange interactions using energy-mapping analysis. Although CoGeTeO
has a layered structure, its magnetic structure consists of three-dimensional antiferromagnetic lattices made up of rhombic boxes of Co
ions. The experimental data obtained at high temperatures agree well with the computational results by treating the Co
ions of CoGeTeO
as
= 3/2 ions, but the heat capacity and magnetization data were obtained at low temperatures by treating the Co
ion as a
= 1/2 ion.
The missing member of the rosiaite family, CoGeTeO6, was synthesized by mild ion-exchange reactions and characterized by magnetization M and specific heat Cp measurements. It exhibits a successive ...short- and long-range magnetic ordering at Tshort-range ≈ 45 K and TN = 15 K, respectively. Based on these measurements, the magnetic H–T phase diagram was established, showing two antiferromagnetic phases separated by a spin-flop transition. The reason why the pronounced short-range correlation occurs at a temperature nearly three times higher than TN was found by evaluating the Co–O⋯O–Co exchange interactions using energy-mapping analysis. Although CoGeTeO6 has a layered structure, its magnetic structure consists of three-dimensional antiferromagnetic lattices made up of rhombic boxes of Co2+ ions. The experimental data obtained at high temperatures agree well with the computational results by treating the Co2+ ions of CoGeTeO6 as S = 3/2 ions, but the heat capacity and magnetization data were obtained at low temperatures by treating the Co2+ ion as a Jeff = 1/2 ion.
Li3Co2SbO6 is prepared by molten salt ion exchange and its structure refined by the Rietveld method confirming the honeycomb-type Co/Sb ordering of its Na precursor. Monoclinic rather than trigonal ...symmetry of Na3Co2SbO6 is directly demonstrated for the first time by peak splitting in the high-resolution synchrotron XRD pattern. The long-range antiferromagnetic order is established at TN ≈ 6.7 K and 9.9 K in Na3Co2SbO6 and Li3Co2SbO6, respectively, confirmed by both the magnetic susceptibility and specific heat. Spin-wave analysis of specific heat data indicates the presence of 3D AFM magnons in Na3Co2SbO6 and 2D AFM magnons in Li3Co2SbO6. The field dependence of the magnetization almost reaches saturation in moderate magnetic fields up to 9 T and demonstrates characteristic features of magnetic field induced spin-reorientation transitions for both A3Co2SbO6 (A = Na, Li). Overall thermodynamic studies show that the magnetic properties of both compounds are very sensitive to an external magnetic field, thus predicting a non-trivial ground state with a rich magnetic phase diagram. The ground state spin configuration of Li3Co2SbO6 has been determined by low-temperature neutron powder diffraction. It represents a ferromagnetic arrangement of moments in the honeycomb layers with antiferromagnetic coupling between adjacent layers.
New nitrosonium manganese(II) nitrate, (NO)Mn
(NO
)
, has been synthesized and structurally characterized. In the temperature range of 45-298 K, the crystal is hexagonal (centrosymmetric sp. gr.
6
/
...). Mn
ions are assembled into tubes along axis
with both NO
filling and coating. The nitrosonium cation is located in the framework cavity and is disordered by a 3-fold axis. At the temperature
= 190 K, a structural phase transition related to the libration of the intertube NO
group and a small variation of Mn polyhedron is observed. Moreover, the anomalies in physical properties of (NO)Mn
(NO
)
allow suggesting that ordering of NO
units occurs at low temperatures. The antiferromagnetic ordering in this compound is preceded by the formation of a short-range correlation regime at about 25 K and takes place in two steps at
= 12.0 K and
= 8.4 K.
New nitrosonium manganese(II) nitrate, (NO)Mn6(NO3)13, has been synthesized and structurally characterized. In the temperature range of 45–298 K, the crystal is hexagonal (centrosymmetric sp. gr. ...P63/m). Mn2+ ions are assembled into tubes along axis c with both NO3 – filling and coating. The nitrosonium cation is located in the framework cavity and is disordered by a 3-fold axis. At the temperature T S1 = 190 K, a structural phase transition related to the libration of the intertube NO3 group and a small variation of Mn polyhedron is observed. Moreover, the anomalies in physical properties of (NO)Mn6(NO3)13 allow suggesting that ordering of NO+ units occurs at low temperatures. The antiferromagnetic ordering in this compound is preceded by the formation of a short-range correlation regime at about 25 K and takes place in two steps at T N1 = 12.0 K and T N2 = 8.4 K.
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