Rearrangement of van der Waals stacking and formation of a singlet state at T = 90 K in a cluster magnet

Abstract

Insulating Nb 3 Cl 8 is a layered chloride consisting of two-dimensional triangular layers of S e f f = 1/2 Nb 3 Cl 13 clusters at room temperature. Magnetic susceptibility measurement show a sharp, hysteretic drop to a temperature independent value below T = 90 K. Specific heat measurements show that the transition is first order, with ∆S ≈ 5 J · K −1 · mol f .u. −1 , and a low temperature T-linear contribution originating from defect spins. Neutron and X-ray diffraction show a lowering of symmetry from trigonal P3m1 to monoclinic C2/m symmetry, with a change in layer stacking from -AB-AB-to -AB ′ -BC ′ -CA ′ -and no observed magnetic order. This lowering of symmetry and rearrangement of successive layers evades geometric magnetic frustration to form a singlet ground state. It is the lowest temperature at which a change in stacking sequence is known to occur in a Van-der-Waals solid, occurs in the absence of orbital degeneracies, and suggests that designer 2-D heterostructures may be able to undergo similar phase transitions.

Chemical disorder and spin-liquid-like magnetism in the van der Waals layered 5d transition metal halide Os0.55Cl2

“…An interesting intersection between crystal chemistry in low dimensional structures and physics of magnetism with spin orbit coupling is realized in 4d and 5d transition metal halides. Often such compounds form layered crystal structures with pseudo-2D magnetic sublattices 1 , and interesting effects of metal-metal bonding and clustering are also known 2,3 . Much of the recent research in layered 3d transition metal halides is driven by interest in magnetic monolayer materials based on Cr and more recently V trihalides [4][5][6][7][8][9][10] , while recent study of heavier transition metal halides is focused on the Kitaev spin liquid candidate RuCl 3 , in which spin-orbit coupling plays a key role [11][12][13][14] .…”

Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides

“…Dihalides (MX 2 ) and trihalides (MX 3 ) represent the majority of layered binary transition metal halides. There are, however, other examples, including Nb 3 Cl 8 [30], in which interesting magnetic behavior has been noted recently [31,32].…”

Stable Continuously Variable Temperature Cryo-STEM to Understand the Structurally Driven Phase Transition in the 2D Layered Magnet Nb3Br8

“…Two-dimensional (2D) magnetic materials have recently emerged at the forefront of quantum materials research for their distinct thickness-dependent properties [1,2]. Niobium halides of form Nb3X8 are new class of 2D layered materials that exhibit a paramagnetic to non-magnetic transition upon cooling [3,4]. Loss of magnetism at low temperature in these geometrically frustrated materials has been coupled to a structural transition with re-stacking of the van der Waals layers from a 2-layer (α-phase, Fig.…”