Spin–lattice instability to a fractional magnetization state in the spinel HgCr2O4

Magnetostructural Transitions in a Frustrated Magnet at High Fields

“…We evidenced novel effects, namely, plateaus in the sound velocity on the way towards the recovery of the lattice symmetry in the polarized state which are ascribed to different crystallographic phases with constant stiffness. In contrast to geometrically frustrated antiferromagnets ACr 2 O 4 (A= Zn, Cd, Hg) which reveal magnetization plateaus accompanied by lattice distortions [13,14,[26][27][28], the magnetization of bond-frustrated ZnCr 2 S 4 evolves continuously without any anomalies up to full polarization. Our study provides a new insight into the physics of bond-frustrated spinels which is clearly distinct from that of the geometrically frustrated oxides.…”

“…The ground-state properties of frustrated magnets are characterized by a large degeneracy and are highly susceptible to external perturbations. An external magnetic field can change the balance between the competing interactions, and unusual phenomena, such as magnetization plateaus at half or fractional saturation are observed [13,14].…”

“…The ground-state properties of frustrated magnets are characterized by a large degeneracy and are highly susceptible to external perturbations. An external magnetic field can change the balance between the competing interactions, and unusual phenomena, such as magnetization plateaus at half or fractional saturation are observed [13,14].In geometrically frustrated ACr 2 X 4 oxide (X=O) spinels the Cr ions forming a pyrochlore lattice of cornersharing tetrahedra are strongly coupled by direct antiferromagnetic (AFM) interactions of the order of 100 -400 K. Emerging phenomena in geometrically frustrated oxides are dominated by local "tetrahedron" physics [15,16]. In sulphide (X=S) and selenide (X=Se) spinels the direct AFM exchange is reduced due to the increasing distance between the magnetic ions and at the same time 90 o ferromagnetic (FM) exchange becomes important.…”

Néel to spin-glass-like phase transition versus dilution in geometrically frustratedZnCr2−2xGa2xLee1, Ratcliff2, Huang3 et al. 2008Phys. Rev. BSelf Cite

“…ACr 2 O 4 (A = Zn [1], Cd [25], Hg [26]) realizes the most frustrating Hamiltonian because the t 2g orbital of the Cr 3+ (3d 3 ) is half filled and the nearest neighbor interactions due to the direct overlap of the neighboring t 2g orbitals are dominant and spatially uniform. [27] In comparison, in the case of AV 2 O 4 where the V 2+ (3d 2 ) ion has an orbital degeneracy, a Jahn-Teller distortion can occur at low temperatures, which makes the vanadates effectively one-dimensional spin chain systems.…”

“…The novel three-dimensional spin-Peierls phase transition, i.e., the lattice instability driven by magnetic interactions, occurs and drives the system into a Neél state. The lattice distortion can occur in different forms, depending on details of the crystal environment: tetragonal I4m2 symmetry for ZnCr 2 O 4 [33], tetragonal I4 1 /amd for CdCr 2 O 4 [33], and orthorhombic F ddd for HgCr 2 O 4 [26,34]. When an external magnetic field is applied to the Neél state, the half-magnetization plateau states appear in CdCr 2 O 4 [35] and HgCr 2 O 4 [26,34] due to the field-induced lattice instability [36,37].…”