Molecular-field-theory fits to magnetic susceptibilities of antiferromagnetic GdCu2Si2, CuO, LiCrO2, and alpha-CaCr2O4 single crystals below their Neel temperatures

Abstract

A molecular field theory (MFT) developed by the author [Phys. Rev. Lett. 109, 077201 (2012); Phys. Rev. B 91, 064427 (2015)] has been used in the past to fit single-crystal magnetic susceptibility χ versus temperature T data below the antiferromagnetic ordering temperature TN for a variety of collinear and coplanar noncollinear Heisenberg antiferromagnets. The spins in the system are assumed to interact by Heisenberg exchange and to be identical and crystallographically equivalent. The fitting parameters for χ(T ) of collinear antiferromagnets are measurable quantities: the Weiss temperature θp in the Curie-Weiss law, TN, χ(TN), and the spin S. For coplanar noncollinear helix and cycloid structures, an additional fitting parameter is the turn angle between layers of ferromagnetically-aligned spins. Here MFT fits to anisotropic χ(T ) data from the literature for single crystals of the collinear antiferromagnet CuO and the noncollinear antiferromagnets LiCrO2 with a 120 • cycloidal structure and α-CaCr2O4 with a 120 • helical structure below their respective Néel temperatures are presented. The MFT fit to the anisotropic χ(T ≤ TN) data for CuO is poor, whereas the fits to the data for LiCrO2 and α-CaCr2O4 are quite good. The magnetic contribution to the zero-field heat capacity of the collinear antiferromagnet GdCu2Si2 is also fitted by the MFT.

Magnetic Li–M (M = Ni, Ni0.8Cu0.2, Cr) layered oxides nanoparticles for Li-ion batteries electrodes

“…The kink at about 300 K could represent instead a signal of the possible presence of Cr 2 O 3 , which is a canted (or frustrated) antiferromagnet with a Néel temperature T N = 306 K, although its contribution is expected to be hindered by the overwhelming role of the ferromagnetic phase. As regards the transition at low temperature, it can be ascribed to LiCrO 2 , which is an antiferromagnet with a Néel temperature reported at T N = 64 K [39] or T N = 62 K [40]. The steep increase of the low-field magnetization below 50 K could be due to the contribution of another (unknown) paramagnetic phase: the M(H) curve at 10 K (figure 6(b)) displays indeed a linear behavior, typical of a paramagnet.…”