Weakly(x=0)and randomly(x=0.033)coupled Ising antiferromagnetic planes in

David Vaknin

¹

,

J. Zarestky

²

,

J. E. Ostenson

³

et al.

Abstract

Neutron diffraction and magnetic susceptibility studies of (Li 1Ϫ3x Fe x )NiPO 4 (xϭ0 and xϭ0.033) compounds reveal remarkable differences between the magnetic properties of pure LiNiPO 4 and those of its lightly iron-doped derivative. The spin system associated with the Ni 2ϩ ions (Sϭ1) in the pure compound undergoes a collinear antiferromagnetic ordering at T N ϭ19.1Ϯ0.5 K, with the characteristics of weakly coupled twodimensional ͑2D͒ Ising square planes. By contrast, randomly intercalated iron spins ͑in Li sites͒ between Ni 2ϩ planes comprise a spin-glass-like subsystem which, despite their minute amount, drives the antiferromagnetic transition to higher temperatures T N ϭ25.2Ϯ0.5 K, and significantly modifies the critical behavior of the 2D Ni 2ϩ system. It is argued that the doped compound can serve as a model system for studying the randomly coupled planar Ising model. ͓S0163-1829͑99͒15425-0͔

Tweaking the spin-wave dispersion and suppressing the incommensurate phase inLiNiPO4by iron substitution

“…Magnetic-susceptibility studies of polycrystalline LiNiPO 4 showed a significant deviation from the CurieWeiss law in a temperature range much higher than T N , and neutron scattering from the same polycrystalline sample gave rise to diffuse scattering at the nominal position of the AFM Bragg reflection up to T Ϸ 2T N . 28 Recent magneticsusceptibility measurements of single-crystal LiNiPO 4 showed two features, one at T N = 20.8 K and one at T IC = 21.7 K associated with an AFM transition and an intermediate IC phase, 17 in agreement with the observed neutrondiffraction data. 16 …”

“…27 Neutron-scattering studies demonstrated that LiMPO 4 ͑M = Ni, Co, and Mn͒ exhibit properties between two dimensions ͑2D͒ and three dimensions ͑3D͒ with an interlayer coupling that is stronger relative to the coupling found in the cuprates, for instance. [19][20][21]28,29 These insulators also exhibit strong linear ME effects with the observed ME tensor components, ␣ xz , ␣ zx , for LiNiPO 4 , in agreement with the antiferromagnetic point groups mmЈm but with some anomalies. [30][31][32] In particular, the ME effect measurements of LiNiPO 4 as a function of temperature reveal a first-order AFM transition and an unusual decrease in the ME coefficient at temperatures below a maximum close to T N .…”

Spin-waves in antiferromagnetic single-crystalLiFePO4

“…Thus, the olivine family of LiMPO 4 exhibits highly anisotropic properties which are between those of two-(2D) and threedimensional (3D) systems [11,12].…”

“…Nearest-neighbor (NN) spins in the b-c plane are anti-parallel and the stacking along the a-axis is such that ferromagnetic * electronic mail: jiy@ameslab.gov † electronic mail: vaknin@ameslab.gov sheets perpendicular to the b-axis are formed; nearest neighbor sheets are anti-parallel giving rise to (010) fundamental magnetic reflection that, depending on the direction of the magnetic moment, can be intense or extinct. Earlier neutron diffraction studies of polycrystalline samples showed that the magnetic space group of LiFePO 4 and LiCoPO 4 is Pnma' with the spins oriented along b crystallographic direction (i.e., the (010) reflection is absent), and Pnm'a magnetic space group for LiNiPO 4 and LiMnPO 4 with the spins aligned parallel to the c-axis (i.e., strong intensity at the (010) reflection) [11,12,15,16,17,18]. Recent neutron diffraction measurements of single crystal LiCoPO 4 reported finite intensity at the (010) reflection, interpreted in terms of a ground state with a spin direction that is slightly rotated from the b-axis [12].…”

Antiferromagnetic order in Li(Ni1−xFex)PO4(Zimmermann1, Sondermann2, Li3 et al. 2013Phys. Rev. B2060View full textAdd to dashboardCite

“…4(a)). 42 Although the NN superexchange is strongest, the NNN interactions cannot be neglected and promote frustration. 35 The…”