Theoretical study of the magnetic properties of BaNiF$$_4$$

Abstract

In this article we study the magnetic properties of the BaNiF 4 compound using ab-initio calculations and classical Monte-Carlo methods. We discuss the physical origin of the long range magnetic order. We show that the leading exchange interactions are those of a non-frustrated anisotropic two-dimensional Heisenberg system and that long range order and the experimentally observed preferential orientation of the magnetic moments along the b axis appear when local single-ion anisotropy contributions are added at first order. We also show that a canting of the magnetic moments appears at second order and can be written as an effective Dzyaloshinskii-Moriya interaction.

Ab initio investigation of the magnetic and ferroelectric properties of BaCuF4 under hydrostatic pressure

“…Such results agree with the ones of Garcia Castro et al [11]. It should be noticed that similar results were reported by Ederer et al [41] and Leveque et al [42] for BaNiF 4 , which is a S=1 system with Ni 2+ ions in a 3d 8 electronic configuration. Interestingly, in BaNiF 4 , the supplementary magnetic orbital is responsible for the apparition of an additional AFM interaction along the a direction (J 4 in Fig.…”

“…As a consequence, the magnetic exchange interaction related to J 4 , which is along the a direction (perpendicular to the magnetically active orbitals) is zero. It is interesting to note that in BaNiF 4 , where the Ni 2+ ions are in a 3d 8 electron configuration, the second magnetically active d z 2 orbital is responsible of a J 4 effective interaction which is indeed larger than J 1 [41,42] Similar values were obtained in Ref. [11], i.e.…”

“…In contrast, BaCuF 4 is essentially a 1D system where the anisotropy allows Ising-like AFM magnetic order at zero temperature with the magnetic moments oriented along the b axis. The small tilt associated with the canting is a consequence of the distortion of the Cmc2 1 polar phase and produces weak FM order along the c axis [11,41,42]. Interestingly, m z decreases with pressure and vanishes at P = P c (see Fig.…”