Orbital-fluctuation freezing and magnetic-nonmagnetic phase transition in α-TiBr3

Abstract

We present a detailed study on the structural phase transition in α-TiBr3, which is deeply connected with the lattice and orbital degree of freedoms. A chemical vapor transport method is adopted to synthesize the α-TiBr3 single crystal samples, and the structural phase transition at about 180 K is characterized by x-ray diffraction (XRD), magnetic susceptibility, and specific heat capacity. To further the understanding in the physical nature of this phase transition, a systematic Raman spectroscopic study is performed on α-TiBr3 crystals. With temperature decreasing, a large frequency blue shift and peak width narrowing are observed in the vibrational mode associated with Ti in-plane relative movement, which indicates the formation of Ti–Ti bonding and orbital-fluctuation freezing at low temperatures. These results are fully consistent with magnetic–nonmagnetic phase transition resolved by the measurement of magnetic susceptibility and lattice changes by XRD.

Two dimensional Janus Ti-trihalide monolayers with half-metallic characteristics, Mott insulator properties and tunable magnetic anisotropy

“…51,52 This may be due to metal dimerization. [53][54][55] Although this is neglected in this paper, it can be based on the hypothesis that the reduction of Ti-Ti bond length leads to an enhanced AFM of direct exchange interactions, making the system AFM or paramagnetic. Recently, some theoretical works predict that TiCl 3 and TiI 3 are ferromagnets with higher Curie temperatures than CrI 3 .…”

Metal–metal bonding, electronic excitations, and strong resonance Raman effect in 2D layered α-MoCl3

“…In this work we performed a detailed spectroscopic and computational analysis of α-MoCl 3 with particular focus on the Mo-Mo bonding. Intertwining of structural and electronic properties necessarily involves phonon degrees of freedom, making vibrational and especially Raman spectroscopy a powerful tool in such an endeavor [18,[27][28][29][30]. Varying the Raman excitation laser wavelengths, we found that Mo-Mo stretching undergoes strong resonant enhancement when excitation matches electronic transitions between σ-bonding and σ * -antibonding orbitals of Mo-Mo dimers.…”

“…The delocalization-localization balance in layered transition metal compounds and the propensity for dimerization are very ubiquitous phenomena, which have a dramatic influence on their physical properties [13][14][15]. Formation of dimers with metal-metal bonds in MX 3 group was observed in α-TiCl 3 [16,17], α-TiBr 3 [18,19], β-TcCl 3 [20,21], α-RuCl 3 [22,23], and α-MoCl 3 (figure 1) [24][25][26]. While dimerization in RuCl 3 happens only under increased pressure, other listed halides can support M-M bonds under ambient conditions.…”

Cation Dimerization in a 3d1 Honeycomb Lattice System

“…Cation dimerization in a honeycomb lattice system has been reported in some halides (α-TiCl 3 , 14,15 α-TiBr 3 , 15,16 β-TcCl 3 , 17 α-MoCl 3 , 18 and α-RuCl 3 ) 19 and some oxides (Li 2 RuO 3 , 20 α-Li 2 IrO 3 , 21 and Cu 2 IrO 3 ). 22 This transition occurred only under high-pressure conditions in α-RuCl 3 , 19 α-Li 2 IrO 3 , 21 and Cu 2 IrO 3 .…”