Single crystal neutron diffraction study of the magnetisation process in Ca3Co2O6

Petrenko, O. A.; Wooldridge, Jenny; Lees, Martin R.; Manuel, Pascal; Hardy, V.

doi:10.1140/epjb/e2005-00308-y

Cited by 46 publications

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“…there exist helical paths [13]. A partial AFM order of chains appears at T C1 =24 K. A weak feature concerned most probably with a transition in a new interchain order was also observed at around T C2 ≈ 12 K. This scenario of magnetic interactions in Ca 3 Co 2 O 6 is consistent with results of x-ray photoemission spectroscopy [14], neutron scattering [15,16], magnetization and specific heat measurements [5,6,7,8,9,17], nuclear magnetic resonance [18], and theoretical calculations of indirect interactions between CoI sites [13].In the previous paper [19] I proposed a model to interpret the step-like magnetization curve of Ca 3 Co 2 O 6 at very low temperatures. It was based on two assumptions.…”

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Magnetic structure and phase diagram in a spin-chain system: Ca ₃ Co ₂ O ₆

Kudasov¹

2007

Europhys. Lett.

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The low-temperature structure of the frustrated spin-chain compound Ca3Co2O6 is determined by the ground state of the 2D Ising model on the triangular lattice. At high-temperatures it transforms to the honeycomb magnetic structure. It is shown that the crossover between the two magnetic structures at 12 K arises from the entropy accumulated in the disordered chains. This interpretation is in an agreement with the experimental data. General rules for for the phase diagram of frustrated Ising chain compounds are formulated.PACS numbers: 75.25.+z, 75.30.Kz, 75.50.Ee A combination of a low dimensionality and frustration in magnetic compounds, which contain weakly bound Ising spin-chains packed into a two-dimensional (2D) frustrated lattice, gives rise to a complex magnetic behavior. Antiferromagnetic (AFM) Ising chains form the triangular lattice in well-known Ising-chain compounds CsCoCl 3 , CsCoBr 3 [1,2,3,4]. In these substances a partial AFM interchain order (honeycomb magnetic structure) appears just below the ordering temperature. While the temperature decreases, two magnetic phase transitions occur to low-temperature ferrimagnetic phases. A theoretical explanation of the magnetic structure of CsCoCl 3 , CsCoBr 3 was proposed by Mekata in the framework of a mean-field theory [1]. To describe the low-temperature phases an interaction between next nearest neighboring chains was included in the model. Recently, Ca 3 Co 2 O 6 has drawn considerable attention to a step-like magnetization curve [5,6,7,8,9]. The number of the steps in the curve depends strongly on a sweep rate of the external magnetic field and temperature [6,7,9]. Two steps become apparent in the temperature range from 12 K to 24 K [9]. The first step takes place at the zero magnetic field. Then the magnetic moment remains constant at about 1/3 of the full magnetization up to the magnetic field of 3.6 T where the second step occurs to the fully magnetized FM state. At least four equidistant steps are clearly visible below 12 K at a very low sweep rate. They are accompanied by a sizeable hysteresis. Similar phenomena were observed in other spin-chain compounds, e.g. Ca 3 CoRhO 6 [10,11].The structure of Ca 3 Co 2 O 6 consists of Co 2 O 6 chains running along the c axis. The Ca ions are situated between them. The chains are made up of alternating, facesharing CoO 6 trigonal prisms and CoO 6 octahedra. The crystalline electric field splits the energy level of Co 3+ions into the high-spin (S = 2) and low-spin (S = 0) states. The Co 3+ ions situated in the trigonal environment (CoI) are in the high-spin state and the octahedral Co sites (CoII) occurs in the low-spin state. In the last case the energy difference between the low-spin and * Electronic address: kudasov@ntc.vniief.ru high-spin states is very small and a tiny fraction of CoII sites is reported to be in the high-spin state. The crystalline electric field leads also to a very strong Ising-like anisotropy at the CoI sites. The chains form triangular lattice in the ab plane that is perpendicula...

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“…The two steps that are observed in the magnetization curve above T C2 [9] together with the neutron scattering data [16] indicate clearly the honeycomb magnetic structure. Using Eq.…”

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Magnetic structure and phase diagram in a spin-chain system: Ca ₃ Co ₂ O ₆

Kudasov¹

2007

Europhys. Lett.

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“…Magnetic reflections appearing below T N =25 K can be indexed by the propagation vector k=(0,0,1) with respect to the hexagonal setting of the rhombohedral space group R3c [23]. The only apparent difference between the data collected at 20 and 2.2 K is an ∼20% drop in the intensity of the magnetic peaks at low T , as previously reported [12,13,14]. All the (hkl) magnetic peaks have even l, which supports the idea that the intrachain ordering is ferromagnetic.…”

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“…There are, however, experimental data which suggest a more complex magnetic structure for Ca 3 Co 2 O 6 . A pronounced drop in the intensity of the magnetic peaks on cooling below 18 K in zero field has been observed in powder [12,13] and single crystal diffraction studies [14]. Recent resonant x-ray scattering (RXS) studies [10] showed a small (∼ 0.01Å −1 ) incommensuration in the magnetic reflections associated with a long-period modulation of the magnetic structure along the c axis.…”

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“…In this respect the spin chain system Ca 3 Co 2 O 6 is very interesting because at low temperatures several steps, equally spaced in magnetic field, appear in the magnetization [3,4,5], a behavior reminiscent of quantum tunneling of magnetization in molecular magnets [6]. The origin of this intriguing phenomenon is still an open question [7,8] and the magnetic properties of Ca 3 Co 2 O 6 have been intensely studied in the past decade using many techniques, including x-ray [9,10,11] and neutron [12,13,14] Ca 3 Co 2 O 6 is a rare example of a material where ferromagnetic (FM) 1D Ising spin chains are coupled through a much weaker antiferromagnetic (AF) exchange on a triangular lattice. The spin chains in Ca 3 Co 2 O 6 are made up of alternating face-sharing octahedral (CoI) and trigonal prismatic (CoII) CoO 6 polyhedra, running along the c axis and arranged in a triangular lattice in the ab plane [17].…”

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Nature of the Magnetic Order inCa3Co2O6

et al. 2008

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We present a detailed powder and single crystal neutron diffraction study of the spin chain compound Ca3Co2O6. Below 25 K, the system orders magnetically with a modulated partially disordered antiferromagnetic structure. We give a description of the magnetic interactions in the system which is consistent with this magnetic structure. Our study also reveals that the long-range magnetic order co-exists with a shorter range order with a correlation length scale of ∼ 180Å in the ab plane. Remarkably, on cooling, the volume of material exhibiting short range order increases at the expense of the long-range order.PACS numbers: 75.30. Gw, 75.25.+z, 75.30.Fv, 75.50.Ee The appearance of plateaux in the magnetization curves of low dimensional quantum spin systems (e.g. NH 4 CuCl 3 [1] and SrCu 2 (BO 3 ) 2 [2]) has generated considerable attention from both an experimental and a theoretical point of view. In this respect the spin chain system Ca 3 Co 2 O 6 is very interesting because at low temperatures several steps, equally spaced in magnetic field, appear in the magnetization [3,4,5], a behavior reminiscent of quantum tunneling of magnetization in molecular magnets [6]. The origin of this intriguing phenomenon is still an open question [7,8] and the magnetic properties of Ca 3 Co 2 O 6 have been intensely studied in the past decade using many techniques, including x-ray [9,10,11] and neutron [12,13,14] Ca 3 Co 2 O 6 is a rare example of a material where ferromagnetic (FM) 1D Ising spin chains are coupled through a much weaker antiferromagnetic (AF) exchange on a triangular lattice. The spin chains in Ca 3 Co 2 O 6 are made up of alternating face-sharing octahedral (CoI) and trigonal prismatic (CoII) CoO 6 polyhedra, running along the c axis and arranged in a triangular lattice in the ab plane [17]. The different Co environments leave the Co 3+ ions on the CoI sites in a low-spin (S=0) state, and those on the CoII sites in the high-spin (S=2) state [9,11,15]. Crystalline electric fields also lead to a very strong anisotropy with the moments preferentially aligned along the c axis [3,4]. The zero-field magnetic structure of Ca 3 Co 2 O 6 has yet to be described unambiguously. Most theoretical descriptions of the magnetic structure center around the two stable configurations for 1D Ising chains coupled antiferromagnetically on a 2D triangular lattice, the ferrimagnetic structure (M, M, −M ) and the partially disordered antiferromagnetic (PDA) structure (M, −M, 0) [18] (the labels in parenthesis indicate the relative magnetizations on the triangular lattice). The step-like magnetization has been described using the Ising model on a triangular lattice [7]. There are, however, experimental data which suggest a more complex magnetic structure for Ca 3 Co 2 O 6 . A pronounced drop in the intensity of the magnetic peaks on cooling below 18 K in zero field has been observed in powder [12,13] and single crystal diffraction studies [14]. Recent resonant x-ray scattering (RXS) studies [10] showed a small (∼ 0.01Å −1 ) incommensu...

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Electronic and Magnetic Properties of the “Unidimensional” Cobaltite Ca ₃ Co ₂ o ₆

Raveau

Seikh

2012

Cobalt Oxides

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Single crystal neutron diffraction study of the magnetisation process in Ca3Co2O6

Cited by 46 publications

References 17 publications

Magnetic structure and phase diagram in a spin-chain system: Ca ₃ Co ₂ O ₆

Magnetic structure and phase diagram in a spin-chain system: Ca ₃ Co ₂ O ₆

Nature of the Magnetic Order inCa3Co2O6

Electronic and Magnetic Properties of the “Unidimensional” Cobaltite Ca ₃ Co ₂ o ₆

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Single crystal neutron diffraction study of the magnetisation process in Ca3Co2O6

Cited by 46 publications

References 17 publications

Magnetic structure and phase diagram in a spin-chain system: Ca 3 Co 2 O 6

Magnetic structure and phase diagram in a spin-chain system: Ca 3 Co 2 O 6

Nature of the Magnetic Order inCa3Co2O6

Electronic and Magnetic Properties of the “Unidimensional” Cobaltite Ca 3 Co 2 o 6

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Magnetic structure and phase diagram in a spin-chain system: Ca ₃ Co ₂ O ₆

Magnetic structure and phase diagram in a spin-chain system: Ca ₃ Co ₂ O ₆

Electronic and Magnetic Properties of the “Unidimensional” Cobaltite Ca ₃ Co ₂ o ₆