Thermodynamic and magnetic properties of the layered triangular magnetNaNiO2

Abstract

We report muon-spin rotation, heat capacity, magnetization, and ac magnetic susceptibility measurements of the magnetic properties of the layered spin-1 / 2 antiferromagnet NaNiO 2 . These show the onset of long-range magnetic order below T N = 19.5 K. Rapid muon depolarization, persisting from T N to about 5 K above T N , is consistent with the presence of short-range magnetic order. The temperature and frequency dependence of the ac susceptibility suggests that magnetic clusters persist above 25 K and that their volume fraction decreases with increasing temperature. A frequency dependent peak in the ac magnetic susceptibility at T sf =3 K is observed, consistent with a slowing of spin fluctuations at this temperature. A partial magnetic phase diagram is deduced.

Unusual bidirectional frequency dependence of dynamical susceptibility in hexagonal intermetallic Pr2Ni0.95Si2.95

“…However, surprisingly, the frequency dependence of the low temperature peak appear to be in the reverse direction than that expected in case of glassy transitions. This is a highly unusual behaviour, and only a very few oxide compounds have been reported to exhibit such behaviour in literatures 26–29 . However, it may be noted here that so far, only one work has been reported in the literature with bidirectional frequency dependence, that too on an oxide compound NaNiO 2 which follows superexchange mechanism 26 .…”

Static magnetic order in the triangular lattice ofLixNiO2(x≤1Sugiyama1, Mukai2, Ikedo3 et al. 2008Phys. Rev. B290230View full textAdd to dashboardCite

“…15 This value is two or three times higher than those for Li x NiO 2 , while eff is comparable to that for LiNiO 2 ͑ϳ2.0 B ͒. This means that either ord for LiNiO 2 is smaller than that for NaNiO 2 ͑0.97 B ͒ or that the angle between ord and c H plane for LiNiO 2 is smaller than that for NaNiO 2 ͑ϳ100°͒.…”

“…[21][22][23][24][25] That is, NaNiO 2 exhibits two transitions at T JT ϳ 480 K and T N = 20 K. The former is a cooperative Jahn-Teller ͑JT͒ transition from a high-T rhombohedral phase to a low-T monoclinic phase, while the latter is a transition into an A-type AF phase, since ND and + SR experiments have shown ferromagnetic ͑FM͒ order in the NiO 2 plane but AF order between adjacent NiO 2 planes. [13][14][15] In contrast, AgNiO 2 lacks a cooperative JT transition but has a long-range commensurate ͑C͒ AF ordered state with T N = 21 K caused by slight spatial deviation of the O 2− ions, as was recently found by ND and + SR measurements. 17,18 For ͑Ag 2 ͒ + Ni 3+ O 2 , which also keeps a rhombohedral symmetry down to 2 K, static AF order, likely the formation of an incommensurate spindensity wave ͑IC-SDW͒ structure in the NiO 2 plane, was observed below T N = 56 K by a recent + SR experiment.…”

“…The Ni ions in the Li layer, however, naturally hinder the formation of long-range order, which would be detectable by ND and/or NMR whether the additional interplane interaction is FM or AF. 15 On the other hand, since muons mainly sense the local magnetic field generated by the nearest neighboring moments, + SR has provided information on static but short-range magnetic order for Li x NiO 2 with 3 / 5 Յ x Յ 1. This conclusion is, therefore, consistent with the ground state for LiNiO 2 proposed by NMR, i.e., a spin-liquid state with short-range FM correlations.…”

“…30͒ and NaNiO 2 . 15 This also excludes the possibility that the two magnetically different muon sites coexist in the LiNiO 2 lattice. On the other hand, concerning the possibility of an intrinsic phase separation at low T, there are no evidences in past NMR measurements.…”