Weak ferromagnetism and an intermediate incommensurate antiferromagnetic phase in LiNiPO4

Abstract

The temperature dependence of the magnetization of single-crystal LiNiPO4 is measured for magnetic-field orientations along the a, b, and c crystallographic axes. It is found that the value of the magnetization depends on the magnetic prehistory of the sample. The magnetic behavior of the antiferromagnetic sample is explained by the presence of weak ferromagnetism in LiNiPO4. At a temperature of 5 K the value of the spontaneous magnetic moment along the c axis is around 0.005 G. When the sample is heated to 20.8 K the magnetic moment decreases monotonically to zero. All of the magnetic susceptibility curves M(T)/H exhibit two features: a jump and a kink at temperatures T1 and T2, respectively. At a magnetic field of 10 kOe these temperatures are close to 20.84 and 21.86 K. The observed features indicate that in the establishment of the main antiferromagnetic order in the LiNiPO4 crystal, an intermediate antiferromagnetic phase is spontaneously formed in the temperature interval from TN1=20.8(5) K to TN2=21.8(5). The sequence of continuous and abrupt transitions at the boundary temperatures of its existence region indicate that the intermediate phase is most likely an incommensurate antiferromagnetic state.

Spin-waves in antiferromagnetic single-crystalLiFePO4

“…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]. Weak ferromagnetism has been reported for LiMnPO 4 [18] and LiNiPO 4 [19] at a temperature below T N .…”

“…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].…”

Probing magnetic order in LiMPO4(M=Ni, Co, Fe) and lithium diffusion in LiBaker1, Franke2, Pratt3 et al. 2011Phys. Rev. B446300View full textAdd to dashboardCite

“…On cooling LiNiPO 4 orders incommensurately at T N = 21.8 K, then orders commensurately at T IC−C = 20.7 K. 2,37 Neutron diffraction has characterized both the long-range ordered phases and found diffuse scattering well above T N . The trend in the magnetic order parameter approaching the breakup of collinear order was found to follow the dependence expected for a 2D Ising model; 38 an anomalous correlation between the spin wave spectrum and the incommensurate magnetic order 39 and coexisting short-and long-range incommensurate magnetic order were reported for the intermediate phase.…”

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

“…16 Here, it was found that LiNiPO 4 undergoes a first-order transition from the antiferromagnetic ground state to a long-range IC order at a Néel temperature, T N = 20.8 K ͑T N ϵ T C-IC ͒. As the temperature is increased, a second-order phase transition from the longrange incommensurate magnetic order to the paramagnetic state occurs at T IC = 21.7 K. 16,17 The incommensurate spin correlations gradually weaken and the spins are essentially PHYSICAL REVIEW B 79, 174435 ͑2009͒…”