A neutron scattering investigation of the magnetic phase diagram of FeI2

Half-magnetization plateau and the origin of threefold symmetry breaking in an electrically switchable triangular antiferromagnet

“…Such a plateau has been discussed theoretically [10,11] in triangular lattice antiferromagnets, appearing whenever there is a significant next nearest neighbor magnetic coupling [12]. As compared to plateaus occurring at one-third saturation magnetization [13][14][15][16][17][18][19], experimental realizations of a halfmagnetization plateau on a triangular lattice are relatively rare [15,20]. The implication from theory is that the same interactions that generate the plateau are also responsible for a threefold symmetry-breaking stripe phase in the ground state, for both quantum and classical models.…”

Instabilities of heavy magnons in an anisotropic magnet

“…At low temperature, the Fe 2+ ions bear effective S eff = 1 magnetic moments with an easy-axis anisotropy D ≈ 2 meV (26) along the crystallographic c axis. Magnetic exchange interactions are frustrated (27) with a ferromagnetic nearestneighbor coupling J 1 ≈ −0.1D competing with weaker antiferromagnetic further-neighbor exchanges that span up to third-neighbors within and between the triangular planes (24). This competition stabilizes a striped antiferromagnetic (AF) order below T N = 9.5 K (27,28), with rows of ferromagnetically aligned spins arranged in ↑↑↓↓ domains within the triangular layers, each with four magnetic sub-lattices.…”

“…Magnetic exchange interactions are frustrated (27) with a ferromagnetic nearestneighbor coupling J 1 ≈ −0.1D competing with weaker antiferromagnetic further-neighbor exchanges that span up to third-neighbors within and between the triangular planes (24). This competition stabilizes a striped antiferromagnetic (AF) order below T N = 9.5 K (27,28), with rows of ferromagnetically aligned spins arranged in ↑↑↓↓ domains within the triangular layers, each with four magnetic sub-lattices. At T = 1.8 K, the AF phase is stable up to a magnetic field of µ 0 H 1 = 4.8 T before evolving into a complex sequence of ferrimagnetic phases until reaching saturation at µ 0 H sat = 12.5 T (27).…”

“…This competition stabilizes a striped antiferromagnetic (AF) order below T N = 9.5 K (27,28), with rows of ferromagnetically aligned spins arranged in ↑↑↓↓ domains within the triangular layers, each with four magnetic sub-lattices. At T = 1.8 K, the AF phase is stable up to a magnetic field of µ 0 H 1 = 4.8 T before evolving into a complex sequence of ferrimagnetic phases until reaching saturation at µ 0 H sat = 12.5 T (27). Early neutron spectroscopy experiments (29) in the AF phase of FeI 2 elucidated that single-ion bound-states, previously identified by infrared spectroscopy (30), form quasiflat bands that lie below single-magnon excitations throughout the Brillouin zone.…”

Theory of orbital moment collapse under pressure inFeI2

“…In the layer above, this arrangement has been shifted by one atom along the chain and also one atom perpendicular to the direction of the chains, and the net repeat distance is four layers. The spin direction is along the hexagonal axis; in fact, a strong uniaxial anisotropy coefficient Dϭ26 K was established early on by Fujita et al 2 Neutron scattering in the presence of an applied field by Wiedenmann et al 3 of the simpler behavior of other ferrous halides mentioned above. For applied fields along ĉ up to 13 T, four other phases occur, separated by first-order phase boundaries.…”