Modulated magnetic structure in quasi-one-dimensional clinopyroxene NaFeGe2O6

Drokina, T. V.; Petrakovskiı̌, G. A.; Keller, L.; Schefer, J.; Balaev, A. D.; Карташев, А. В.; Иванов, Д. А.

doi:10.1134/s1063776110061093

Cited by 16 publications

(38 citation statements)

References 11 publications

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“…In the paramagnetic phase both compounds possess monoclinic symmetry described by the space group C2/c (C 6 2h ) [52,53]. Upon cooling the compounds show two magnetic phase transitions at T N = 8 K and T c = 6 K for NFSO [51] and T N = 13 K and T c = 11.5 K for NFGO [53] leading to the magnetically ordered phases AF2 and AF1, respectively. Below T N the magnetic structure is found to be incommensurate with k = (0, 0.77, 0) [54] and k = (0.3357, 0, 0.0814) [53] for NFSO and NFGO, respectively.…”

Section: Pyroxenes Nafesi 2 O 6 and Nafege 2 Omentioning

confidence: 99%

Interpretation of magnetoelectric phase states using the praphase concept and exchange symmetry

Ter-Oganessian¹,

Sakhnenko²

2013

J. Phys.: Condens. Matter

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Abstract. The majority of magnetoelectric crystals show complex temperaturemagnetic field or temperature-pressure phase diagrams with alternating antiferromagnetic incommensurate, magnetoelectric, and commensurate phases. Such phase diagrams occur as a result of successive magnetic instabilities with respect to different order parameters, which usually transform according to different irreducible representations (IR) of the space group of the crystal. Therefore, in order to build a phenomenological theory of phase transitions in such magnetoelectrics one has to employ several order parameters and assume the proximity of various instabilities on the thermodynamic path. In this work we analyze the magnetoelectrics MnWO 4 , CuO, NaFeSi 2 O 6 , NaFeGe 2 O 6 , Cu 3 Nb 2 O 8 , α-CaCr 2 O 4 , and FeTe 2 O 5 Br using the praphase concept and the symmetry of the exchange Hamiltonian. We find that in all the considered cases the appearing magnetic structures are described by IR's entering into a single exchange multiplet, whereas in the cases of MnWO 4 and CuO by a single IR of the space group of the praphase structure. Therefore, one can interpret the complex phase diagrams of magnetoelectrics as induced by a single IR either of the praphase or of the symmetry group of the exchange Hamiltonian. Detailed temperature-magnetic field phase diagrams of MnWO 4 and CuO for certain field directions are obtained and the magnetic structures of the field-induced phases are determined.

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Section: Pyroxenes Nafesi 2 O 6 and Nafege 2 Omentioning

confidence: 99%

Interpretation of magnetoelectric phase states using the praphase concept and exchange symmetry

Ter-Oganessian¹,

Sakhnenko²

2013

J. Phys.: Condens. Matter

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“…2; for higher Na contents, the magnetic ordering temperature decreases almost linearly down to 13.2 K in the Na-endmember. The heat capacity measurements clearly give evidence for two peaks in the end-member composition NaFeGe 2 O 6 , the first one at 13.2 K, the second at 11.9 K. The appearance of two peaks in C p of NaFeGe 2 O 6 was first noticed by Drokina et al (2011) and assigned to a change in the macroscopic state of the magnetic subsystem. Similarly, two peaks are also observed for Li 0.1 Na 0.9 FeGe 2 O 6 with maxima at 13.9 and 12.0 K. For the samples with x(Na) = 0.75 and 0.90, the high-temperature peak is well resolved, while the second one is only visible as an illdefined shoulder, for x(Na) = 0.75 two peaks can readily be resolved, while for samples with x(Na) < 0.75 only one peak is found.…”

Section: Calorimetric Datamentioning

confidence: 81%

“…Most of the "magnetic pyroxenes" order in a rather simple way below T ~40 K, from fully ferromagnetic to fully antiferromagnetic within and between the M1 chains (Cheng et al 2013;Janson et al 2014;Nenert et al 2009bNenert et al , 2010bRedhammer et al 2008Redhammer et al , 2009Redhammer et al , 2010bRedhammer et al , 2011bRedhammer et al , 2012Redhammer et al , 2013Redhammer et al , 2015. Only a few compounds are reported exhibiting a complex cycloidal magnetic ordering, among them NaFeGe 2 O 6 and NaFeSi 2 O 6 (Drokina et al 2011;Redhammer et al 2011a). These two compounds feature a dielectric polarization and were proven to be multi-ferroic materials (Jodlauk et al 2007;Kim et al 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Very recently Drokina et al (2015) found a magnetic structure for the intermediate compound Li 0.5 Na 0.5 FeGe 2 O 6 with P2 1 /c symmetry at low temperature and found a very similar magnetic structure to the one of the LiFeGe 2 O 6 endmember. In contrast NaFeGe 2 O 6 shows complex magnetic ordering with a cycloidal incommensurate ordering of spins within the M1-chains and k = (0.323 1.0 0.080) (Drokina et al 2011;Redhammer et al 2011a). For NaFeGe 2 O 6 , Kim et al (2012) concluded from ferroelectric measurements that the compound orders magnetically in a two-steps process.…”

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confidence: 97%

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A neutron diffraction study of crystal and low-temperature magnetic structures within the (Na,Li)FeGe2O6 pyroxene-type solid solution series

et al. 2017

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an antiferromagnetic (AFM) coupling within the Fe 3+ O 6 octahedra zig-zag chains and an alternating AFM and ferromagnetic (FM) interaction between the chains, depending on the nature of the tetrahedral GeO 4 chains. The magnetic structure can be described in magnetic space group P a 2 1 /c. Close to the structural phase transition for sample with x(Na) = 0.75, magnetic ordering is observed below 15 K; however, it becomes incommensurately modulated with k = (0.344, 0, 0.063). At 4 K, the magnetic spin structure best can be described by a cycloidal arrangement within the M1 chains, the spins are within the a-c plane. Around 12 K the cycloidal structure transforms to a spin density wave (SDW) structure. For the C2/c structures, a coexistence of a simple collinear and an incommensurately modulated structure is observed down to lowest temperatures. For 0.78 ≤ x(Na) ≤ 0.82, a collinear magnetic structure with k = (0 1 0), space group P C 2 1 /c and an AFM spin structure within the M1 chains and an FM one between the spins is dominating, while the incommensurately modulated structure becomes dominating the collinear one in the samples with x(Na) = 0.88. Here the magnetic propagation vector is k = (0.28, 1, 0.07) and the spin structure corresponds again to a cycloidal structure within the M1 chains. As for the other samples, a transition from the cycloidal to a SDW structure is observed. Based on the neutron diffraction data, the appearance of two peaks in the heat capacity of Na-rich samples can now be interpreted as a transition from a cycloidal magnetic structure to a spin density wave structure of the magnetically ordered phase for the Na-rich part of the solid solution series.Keywords Clinopyroxenes · LiFeGe 2 O 6 · NaFeGe 2 O 6 · Neutron diffraction · Magnetic ordering · Cycloidal incommensurate structure · Spin density wave Abstract Solid solution compounds along the Li 1-x Na x FeGe 2 O 6 clinopyroxene series have been prepared by solid state ceramic sintering and investigated by bulk magnetic and calorimetric methods; the Na-rich samples with x(Na) > 0.7 were also investigated by lowtemperature neutron diffraction experiments in a temperature range of 4-20 K. For samples with x(Na) > 0.76 the crystal structure adopts the C2/c symmetry at all measuring temperatures, while the samples display P2 1 /c symmetry for smaller Na contents. Magnetic ordering is observed for all samples below 20 K with a slight decrease of T N with increasing Na content. The magnetic spin structures change distinctly as a function of chemical composition: up to x(Na) = 0.72 the magnetic structure can be described by a commensurate arrangement of magnetic spins with propagation vector k = (½, 0 0), Electronic supplementary material The online version of this article

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“…The magnetic structure of LiFeGe 2 O 6 pyroxene is described to have an antiferromagnetic arrangement of spins within and between the octahedral B chains ( T N = 20.5 K) [2]. NaFeGe 2 O 6 characterized by Néel temperature T N = 13 K, below T = 11.5 K the incommensurate magnetic structure with a helical spin modulation is realized [6,12].…”

Section: Introductionmentioning

confidence: 99%