Metamagnetism of NaNiO2

Borgers, P.F.; Enz, U.

doi:10.1016/0038-1098(66)90001-9

Cited by 53 publications

(32 citation statements)

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“…In NaNiO 2 a ferro-distortive orbital order (a collective JahnTeller distortion) is observed below 480 K [4] and a long range antiferromagnetic order appears below 20 K [5]. This magnetic order was first described as an A type antiferromagnet with ferromagnetic planes coupled antiferromagnetically [5] [6]. The magnetic superlattice has indeed been observed recently in neutron diffraction measurements [7].…”

Section: Introductionmentioning

confidence: 71%

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Spin excitations in the antiferromagnetNaNiO2

et al. 2007

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In NaNiO2 , Ni 3+ ions form a quasi two dimensional triangular lattice of S = 1/2 spins. The magnetic order observed below 20K has been described as an A type antiferromagnet with ferromagnetic layers weakly coupled antiferromagnetically. We studied the magnetic excitations with the electron spin resonance for frequencies 1-20 cm −1 , in magnetic fields up to 14 T. The bulk of the results are interpreted in terms of a phenomenological model involving bi-axial anisotropy for the spins: a strong easy-plane term, and a weaker anisotropy within the plane. The direction of the easy plane is constrained by the collective Jahn-Teller distortion occurring in this material at 480 K.

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Section: Introductionmentioning

confidence: 71%

“…The main branch (M) is a broad signal, with frequency approximately proportional to the field, signifi- cantly above the g = 2 line. Mode (A) and (B) are related to the spin-flop transition observed at 1.8 T in the magnetization curve [6]. Mode (A) has been discussed previously [5] in terms of an easy axis antiferromagnet model [5].…”

Section: Resultsmentioning

confidence: 99%

Spin excitations in the antiferromagnetNaNiO2

et al. 2007

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“…NaNiO 2 is a Mott insulator with a gap of 0.24eV. 9) This compound shows a first-order structural transition accompanied by cooperative Jahn-Teller distortions at 480K 8,10) and a second-order magnetic transition at 20K. [10][11][12] At the lowest temperature(T ), the system exhibits orbital-ferro and A-type antiferro-spin order (antiferromagnetic stacking of spin-ferro ordered layers).…”

Section: +mentioning

confidence: 99%

“…9) This compound shows a first-order structural transition accompanied by cooperative Jahn-Teller distortions at 480K 8,10) and a second-order magnetic transition at 20K. [10][11][12] At the lowest temperature(T ), the system exhibits orbital-ferro and A-type antiferro-spin order (antiferromagnetic stacking of spin-ferro ordered layers). 11,13) LiNiO 2 is also a Mott insulator with a gap of 0.2eV, 14) however, it shows no clear phase transition down to 1.4K in contrast to NaNiO 2 .…”

Section: +mentioning

confidence: 99%

Mean-Field Study of Charge, Spin, and Orbital Orderings in Triangular-Lattice CompoundsANiO₂(A= Na, Li, Ag)

2011

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We present our theoretical results on the ground states in layered triangular-lattice compounds ANiO2 (A=Na, Li, Ag). To describe the interplay between charge, spin, orbital, and lattice degrees of freedom in these materials, we study a doubly-degenerate Hubbard model with electron-phonon couplings by the Hartree-Fock approximation combined with the adiabatic approximation. In a weakly-correlated region, we find a metallic state accompanied by √ 3 × √ 3 charge ordering. On the other hand, we obtain an insulating phase with spin-ferro and orbital-ferro ordering in a wide range from intermediate to strong correlation. These phases share many characteristics with the low-temperature states of AgNiO2 and NaNiO2, respectively. The charge-ordered metallic phase is stabilized by a compromise between Coulomb repulsions and effective attractive interactions originating from the breathing-type electronphonon coupling as well as the Hund's-rule coupling. The spin-orbital-ordered insulating phase is stabilized by the cooperative effect of electron correlations and the Jahn-Teller coupling, while the Hund'-rule coupling also plays a role in the competition with other orbital-ordered phases. The results suggest a unified way of understanding a variety of low-temperature phases in ANiO2. We also discuss a keen competition among different spin-orbital-ordered phases in relation to a puzzling behavior observed in LiNiO2.

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“…Especially intriguing is the absence of any kind of long range magnetic or orbital order [2,3] at low temperature even in the purest samples synthesized up to now. That is especially remarkable since the isostructural compound NaNiO 2 shows orbital order and a collective Jahn-Teller transition at T o = 480 K from the trigonal high-temperature phase to the monoclinic low-temperature one, followed by an antiferromagnetic (AFM) order of ferromagnetic (FM) planes at the Néel temperature of T N = 20 K [4,5]. To explain the strange behavior of LiNiO 2 the proposal of an orbital liquid was pursued in terms of the SU(4) model [6,7,8].…”

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Orbital and spin exchange in LiNiO ₂

Daré¹,

Hayn²,

Richard³

2003

Europhys. Lett.

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We study the planar spin exchange couplings in LiNiO2 using a perturbative approach. We show that the inclusion of the trigonal crystal field splitting at the Oxygen sites leads to the appearance of antiferromagnetic exchange integrals in deviation from the Goodenough-Kanamori-Anderson rules for this 90 degree bond. That gives a microscopic foundation for the recently observed coexistence of ferromagnetic and antiferromagnetic couplings in the orbitally-frustrated state of LiNiO2 (F. Reynaud et al, Phys. Rev. Lett. 86, 3638).The compound LiNiO 2 which was first synthesized in 1958 [1] is known to be a good ionic conductor and therefore suitable as a material for rechargeable batteries. Despite its wide use as electrode material, its electronic and magnetic structures are not yet completely understood. Especially intriguing is the absence of any kind of long range magnetic or orbital order [2,3] at low temperature even in the purest samples synthesized up to now. That is especially remarkable since the isostructural compound NaNiO 2 shows orbital order and a collective Jahn-Teller transition at T o = 480 K from the trigonal high-temperature phase to the monoclinic low-temperature one, followed by an antiferromagnetic (AFM) order of ferromagnetic (FM) planes at the Néel temperature of T N = 20 K [4,5]. To explain the strange behavior of LiNiO 2 the proposal of an orbital liquid was pursued in terms of the SU(4) model [6,7,8]. There, a symmetry between orbital and spin degrees of freedom is assumed with equal amplitudes for the corresponding coupling terms. In reality, however, the energy scale for orbital interactions is one order of magnitude larger than those for spin exchange interactions as shown by experimental [3] and theoretical studies [9]. This is also indicated by the difference of T o and T N in NaNiO 2 . More in details, the magnetic susceptibility of LiNiO 2 shows a transition at T of = 400 K towards an orbitally frustrated state at low temperature. Given an orbital disorder that is frozen in, the magnetic properties at low temperature can be phenomenologically explained assuming FM exchange couplings between neighbouring orbitals of different kind (J do = (−6.2 ± 2) meV) and AFM couplings between identical ones (J so = (6.9 ± 2) meV) [3]. However, that contradicts seemingly the known Goodenough-Kanamori-Anderson (GKA) rules [10] which allow only FM couplings for the 90 degree Ni-O-Ni bond in LiNiO 2 [9].The trigonal (rhombohedral) crystal structure R3m of LiNiO 2 can be understood by starting from the cubic situation with oxygen and Ni/Li on the sites of the cubes, and with the cubic axesx,ỹ, andz. Perpendicular to the cube diagonal z =x +ỹ +z in fig. 1 one finds alternating planes of Li, Ni, and O. The electronically active NiO 2 layer (see fig. 1) contains a triangular lattice of the magnetic Ni ions. The O 2− ions have a completely filled 2p shell, whereas the Ni 3+ ion is in the low-spin electronic configuration (t 6 2g e 1 g ) with spin 1/2 [3]. The trigonal distortion changes the bond angle fro...

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Metamagnetism of NaNiO2

Cited by 53 publications

References 5 publications

Spin excitations in the antiferromagnetNaNiO2

Spin excitations in the antiferromagnetNaNiO2

Mean-Field Study of Charge, Spin, and Orbital Orderings in Triangular-Lattice CompoundsANiO₂(A= Na, Li, Ag)

Orbital and spin exchange in LiNiO ₂

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Metamagnetism of NaNiO2

Cited by 53 publications

References 5 publications

Spin excitations in the antiferromagnetNaNiO2

Spin excitations in the antiferromagnetNaNiO2

Mean-Field Study of Charge, Spin, and Orbital Orderings in Triangular-Lattice CompoundsANiO2(A= Na, Li, Ag)

Orbital and spin exchange in LiNiO 2

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Mean-Field Study of Charge, Spin, and Orbital Orderings in Triangular-Lattice CompoundsANiO₂(A= Na, Li, Ag)

Orbital and spin exchange in LiNiO ₂