The compound NaFeGe
2
O
6
was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature ...evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe
2
O
6
is isotypic to the clinopyroxene-type compound aegirine and adopts the typical H
T
-
C
2/
c
clinopyroxene structure down to 2.5 K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5 K and room temperature, while the GeO
4
tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33 K, which marks the onset of low-dimensional magnetic ordering. Below 12 K NaFeGe
2
O
6
transforms to an incommensurately modulated magnetic spin state, with
k
= 0.323, 1.0, 0.080 and a helical order of spins within the M1-chains of FeO
6
octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe
2
O
6
with NaFeSi
2
O
6
is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with
C
2′/
c
′ symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.
The clinopyroxene-type compound ... was synthesized using ceramic sintering techniques at 1273 K in evacuated silica tubes and investigated by powder neutron diffraction between 4 and 300 K, X-ray ...diffraction, SQUID magnetometry, and ... Mossbauer spectroscopy. The title compound shows space group C2/c symmetry (high pressure, HP-topology) between 4 and 900 K. No structural phase transition is present within this temperature interval, whereas lattice parameters show discontinuities around 50 and 15 K, which are due to magnetic phase transitions and the associated magneto-elastic coupling of the lattice. The magnetic susceptibility data show two maxima in their temperature dependence, one at ~47 K, the second around 12 K (depending on the external field), indicative of two magnetic transitions in the title compound. Neutron data shows that for T < 45 K, ... orders magnetically, having a simple collinear structure, with space group C2/c, and with the spins aligned parallel to the crystallographic b-axis, both on M1 and M2. The coupling within the M1/M2 band is ferromagnetic, whereas between them it is antiferromagnetic. As the bulk magnetic measurements in the paramagnetic state revealed a dominating ferromagnetic coupling, the intra-chain interactions dominate the inter-chain interaction. At 12 K, additional magnetic reflections appear, revealing a second magnetic phase transition. Spins are rotated away from the b-axis toward the a-c plane. The coupling within the M1 chain is still ferromagnetic and antiferromagnetic between the M1 chains. However, spins on M1 and M2, are no longer collinear. The moment on the M2 site is rotated further away from the b-axis than on M1. (ProQuest: ... denotes formulae/symbols omitted.)
The clinopyroxene-type compound FeGeO3 was synthesized using ceramic sintering techniques at 1273 K in evacuated silica tubes and investigated by powder neutron diffraction between 4 and 300 K, X-ray ...diffraction, SQUID magnetometry, and 57Fe Mossbauer spectroscopy. The title compound shows space group C2/c symmetry (high pressure, HP-topology) between 4 and 900 K. No structural phase transition is present within this temperature interval, whereas lattice parameters show discontinuities around 50 and 15 K, which are due to magnetic phase transitions and the associated magneto-elastic coupling of the lattice. The magnetic susceptibility data show two maxima in their temperature dependence, one at approximately 47 K, the second around 12 K (depending on the external field), indicative of two magnetic transitions in the title compound. Neutron data shows that for T<45 K, FeGeO3 orders magnetically, having a simple collinear structure, with space group C2/c, and with the spins aligned parallel to the crystallographic b-axis, both on M1 and M2. The coupling within the M1/M2 band is ferromagnetic, whereas between them it is antiferromagnetic. As the bulk magnetic measurements in the paramagnetic state revealed a dominating ferromagnetic coupling, the intra-chain interactions dominate the inter-chain interaction. At 12 K, additional magnetic reflections appear, revealing a second magnetic phase transition. Spins are rotated away from the b-axis toward the a-c plane. The coupling within the M1 chain is still ferromagnetic and antiferromagnetic between the M1 chains. However, spins on M1 and M2, are no longer collinear. The moment on the M2 site is rotated further away from the b-axis than on M1.
The compounds CaFeSi{sub 2}O{sub 6} (hedenbergite), CaNiGe{sub 2}O{sub 6}, CaCoGe{sub 2}O{sub 6} and CaMnGe{sub 2}O{sub 6} have been synthesized by hydrothermal or ceramic sintering techniques and ...were subsequently characterized by SQUID magnetometry and powder neutron diffraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z=4 at all temperatures investigated. Below 35 K hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite M1 chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a-c plane and form an angle of 43 deg. with the crystallographic a-axis. Magnetic ordering in CaFeSi{sub 2}O{sub 6} causes significant discontinuities in lattice parameters, Fe-O bond lengths and interatomic Fe-Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutron diffraction data. CaCoGe{sub 2}O{sub 6} and CaNiGe{sub 2}O{sub 6} show magnetic ordering below 18 K, the spin structures are similar to the one in hedenbergite with an FM coupling within and an AFM coupling of spins between the M1 chains. The moments lie within the a-c plane. The paramagnetic Curie temperature, however, decreases from CaFeSi{sub 2}O{sub 6} (+40.2 K) to CaCoGe{sub 2}O{sub 6} (+20.1 K) and CaNiGe{sub 2}O{sub 6} (-13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the M1 chains. CaMnGe{sub 2}O{sub 6} finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a-c plane. - Graphical abstract: The magnetic properties and magnetic spins structures of 4 members of the clinopyroxenes are determined from susceptibility measurements and neutron diffraction. The magnetic ordering is accompanied by distinct alterations in structural parameters such as unit cell dimensions and interatomic distances.
The clinopyroxene compounds LiFeSi{sub 2}O{sub 6} and LiFeGe{sub 2}O{sub 6} have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. ...Both compounds are monoclinic, space group P2{sub 1}/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi{sub 2}O{sub 6} shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P2{sub 1}/c' and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe{sub 2}O{sub 6} is different to the silicate: the space group is P2{sub 1}{sup '}/c and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron. - Graphical abstract: Section of the nuclear and magnetic structure of the synthetic clinopyroxene-type compound LiFeGe{sub 2}O{sub 6} displaying the antiferromagnetic coupling of spins within the chains of Fe{sup 3+}O{sub 6} octahedra and the antiferromagnetic (via GeB sites) and ferromagnetic (via GeA sites) coupling between these chains.
The clinopyroxene compounds LiFeSi
2O
6 and LiFeGe
2O
6 have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are ...monoclinic, space group
P2
1/
c and do not exhibit a change in nuclear symmetry down to 1.4 and 5
K respective. However, they transform to a magnetically ordered state below 20
K. LiFeSi
2O
6 shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is
P2
1/
c′ and the structure is described by a ferromagnetic coupling of spins within the infinite
M1 chains of edge-sharing octahedra, while the coupling between these
M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe
2O
6 is different to the silicate: the space group is
P
2
1
′
/
c
and the magnetic unit cell doubled along the
a-direction. Within the
M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the Ge
B tetrahedron and ferromagnetic when it goes via the Ge
A tetrahedron.
Section of the nuclear and magnetic structure of the synthetic clinopyroxene-type compound LiFeGe
2O
6 displaying the antiferromagnetic coupling of spins within the chains of Fe
3+O
6 octahedra and the antiferromagnetic (via Ge
B sites) and ferromagnetic (via Ge
A sites) coupling between these chains.
The compounds CaFeSi
2O
6 (hedenbergite), CaNiGe
2O
6, CaCoGe
2O
6 and CaMnGe
2O
6 have been synthesized by hydrothermal or ceramic sintering techniques and were subsequently characterized by SQUID ...magnetometry and powder neutron diffraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group
C2/
c,
Z=4 at all temperatures investigated. Below 35
K hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite
M1 chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the
a–
c plane and form an angle of 43° with the crystallographic
a-axis. Magnetic ordering in CaFeSi
2O
6 causes significant discontinuities in lattice parameters, Fe–O bond lengths and interatomic Fe–Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutron diffraction data. CaCoGe
2O
6 and CaNiGe
2O
6 show magnetic ordering below 18
K, the spin structures are similar to the one in hedenbergite with an FM coupling within and an AFM coupling of spins between the
M1 chains. The moments lie within the
a–
c plane. The paramagnetic Curie temperature, however, decreases from CaFeSi
2O
6 (+40.2
K) to CaCoGe
2O
6 (+20.1
K) and CaNiGe
2O
6 (−13.4
K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the
M1 chains. CaMnGe
2O
6 finally shows an AFM ordering below 11
K. Here the magnetic moments are mainly oriented along the
a-axis with a small tilt out from the
a–
c plane.
The magnetic properties and magnetic spins structures of 4 members of the clinopyroxenes are determined from susceptibility measurements and neutron diffraction. The magnetic ordering is accompanied by distinct alterations in structural parameters such as unit cell dimensions and interatomic distances.
