Weak ferromagnetism in the antiferromagnetic magnetoelectric crystal LiCoPO4

Kharchenko, N. F.; Kharchenko, Yu. N.; Szymczak, R.; Baran, M.; Schmid, Hans

doi:10.1063/1.1414584

Cited by 35 publications

(32 citation statements)

References 14 publications

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“…But, as was shown by Mercier [47], the Pnma symmetry group of LiMnPO 4 forbids Dzyaloshinski-Moriya anti-symmetrical interactions [48]. Recently, an analogous conclusion has been drawn for isostructural LiCoPO 4 and LiNiPO 4 crystals, which also exhibit weak ferromagnetic moments [49].…”

Section: Magnetic Order Inmentioning

confidence: 84%

Some aspects of antiferromagnetic ordering in LiMnP0.85V0.15O4: Neutron diffraction and DC-magnetization studies

Келлерман

Chukalkin

Mukhina³

et al. 2012

Journal of Magnetism and Magnetic Materials

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Section: Magnetic Order Inmentioning

confidence: 84%

Some aspects of antiferromagnetic ordering in LiMnP0.85V0.15O4: Neutron diffraction and DC-magnetization studies

Келлерман

Chukalkin

Mukhina³

et al. 2012

Journal of Magnetism and Magnetic Materials

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“…Since no evidence for a structural incommensurability was found, we hypothesize that the IC phases (long-and short-range) originate from spindimensionality crossover, i.e., from a continuous Heisenberg (or XY) type model to an Ising-model. The ground state of the system is AF with no modulations, indicating a spin Hamiltonian that does not include strong terms that invoke an IC ground state (for instance, a Dzyaloshinsky-Moriya term), as recently suggested by Kharchenko et al [25]. Thus, the occurrence of intermediate magnetic incommensurate phases in LiNiPO 4 has all the characteristics of typical structural IC phases, which also manifest soft-phonon modes [8].…”

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confidence: 80%

Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single CrystalLiNiPO4

et al. 2004

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Neutron scattering studies of single-crystal LiNiPO4 reveal a spontaneous first-order commensurate-incommensurate magnetic phase transition. Short-and long-range incommensurate phases are intermediate between the high temperature paramagnetic and the low temperature antiferromagnetic phases. The modulated structure has a predominant antiferromagnetic component, giving rise to satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg reflection, and a ferromagnetic component giving rise to peaks at small momentum-transfers around the origin at (0, ±Q, 0). The wavelength of the modulated magnetic structure varies continuously with temperature. It is argued that the incommensurate short-and long-range phases are due to spindimensionality crossover from a continuous to the discrete Ising state. These observations explain the anomalous first-order transition seen in the magnetoelectric effect of this system. . There has been a continuous interest in the spontaneous and magnetic-field induced commensurate-incommensurate magnetic (C-IC) transition over the years [4,5,6]. For instance, in the semimetallic europium tri-arsenide (EuAs 3 ), the ground state of the system is commensurate and as temperature increases the system undergoes a C-IC transition [4]. In copper metaborate, on the other hand, the ground state is incommensurate and undergoes a continuous phase transition to a non-collinear commensurate antiferromagnetic state [7]. It has also been demonstrated that the C-IC transition can be induced by the application of an external magnetic field [5,6].Here, we report a novel C-IC magnetic phase transition in the weakly coupled antiferromagnetic planes of LiNiPO 4 (S=1, Ni 2+ ), its characteristics resemble IC structural phase transitions [8]. LiNiPO 4 is an antiferromagnetic (AF) insulator[9, 10] which belongs to the olivine family of lithium orthophosphates LiMPO 4 (M = Mn, Fe, Co, and Ni) [11]; space group is Pnma[12]. Neutron scattering studies demonstrated that LiMPO 4 (M =Ni, Co) exhibit properties between the two-dimensional (2D) and three-dimensional (3D) with an interlayer coupling that is relatively stronger than the coupling found in the cuprates, for instance [13,14]. These insulators also exhibit a strong linear magnetoelectric (ME) effect, with the observed ME tensor components, α xy , α yx , for LiCoPO 4 and, α xz , α zx , for LiNiPO 4 , in agreement with the antiferromagnetic point groups mmm' and mm'm, respectively, but with some anomalies [15,16,17]. In particular, the ME effect measurements of LiNiPO 4 as a function of temperature reveal a first-order AF transition, and an unusual decrease of the ME coefficient at temperatures below a maximum close to T N [18]. By contrast, the isostructural LiCoPO 4 , LiFePO 4 , and LiMnPO 4 exhibit continuous change of the ME coefficients, indicative of second-order transitions [15]. Magnetic susceptibility studies of polycrystalline LiNiPO 4 showed a significant deviation from the Curie-Weiss law in a temperature range much higher than T N , and...

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“…͑v͒ Recent measurements by means of a superconducting quantum interference device have clearly confirmed the existence of a very weak spontaneous magnetization along the b axis of LiCoPO 4 . 43 This means that the compound has a symmetry lower than that of the so-far-admitted fully compensated antiferromagnetic structure with point group m x m y m z Ј ͑magnetic space group PnmaЈ). For the true lower symmetry one can claim that its tensor components of the linear ME effect must be identical to those of point group m x m y m z Ј or contain the coefficients ␣ xy and ␣ yx in addition to other components.…”

Section: Magnetoelectric Effect and Symmetrymentioning

confidence: 99%

Weakly coupled antiferromagnetic planes in single-crystalLiCoPO4

et al. 2002

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Neutron-scattering and magnetic susceptibility studies of single-crystal LiCoPO 4 are reported. The neutrondiffraction results indicate that in the antiferromagnetic phase the moments are not strictly aligned along the b axis, as previously reported ͓R. P. Santoro et al., J. Phys. Chem. 27, 1192 ͑1996͔͒, but are uniformly rotated from this axis by a small angle (Ϸ4.6°). This rotation breaks the mirror symmetry along the orthorhombic b axis. Symmetry considerations based on this rotation, on the magnetoelectric effect, and on a recently observed weak spontaneous magnetization along the spin direction, implying a so-far-unknown ferrimagneticlike kind of weak ferromagnetism, allow one to postulate the monoclinic magnetic point group 2Ј. The diffraction data are analyzed in terms of weakly coupled two-dimensional Ising antiferromagnets. The large anisotropy in the susceptibility is explained in terms of the single-ion anisotropy and anisotropic exchange interactions. We argue that the alignment of the magnetic moments in the antiferromagnetic phase is determined by the singleion anisotropy even though the exchange along this direction is the weakest.

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Weak ferromagnetism in the antiferromagnetic magnetoelectric crystal LiCoPO4

Cited by 35 publications

References 14 publications

Some aspects of antiferromagnetic ordering in LiMnP0.85V0.15O4: Neutron diffraction and DC-magnetization studies

Some aspects of antiferromagnetic ordering in LiMnP0.85V0.15O4: Neutron diffraction and DC-magnetization studies

Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single CrystalLiNiPO4

Weakly coupled antiferromagnetic planes in single-crystalLiCoPO4

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