Acoustic study of dynamical molecular-spin state without magnetic phase transition in spin-frustratedZnFe2O4

Abstract

Ultrasound velocity measurements were performed on a single crystal of spin-frustrated ferrite spinel ZnFe2O4 from 300 K down to 2 K. In this cubic crystal, all the symmetrically-independent elastic moduli exhibit softening with a characteristic minimum with decreasing temperature below ∼100 K. This elastic anomaly suggests a coupling between dynamical lattice deformations and molecular-spin excitations. In contrast, the elastic anomalies, normally driven by the magnetostructural phase transition and its precursor, are absent in ZnFe2O4, suggesting that the spin-lattice coupling cannot play a role in relieving frustration within this compound. The present study infers that, for ZnFe2O4, the dynamical molecular-spin state evolves at low temperatures without undergoing precursor spin-lattice fluctuations and spin-lattice ordering. It is expected that ZnFe2O4 provides the unique dynamical spin-lattice liquid-like system, where not only the spin molecules but also the cubic lattice fluctuate spatially and temporally.

Role of defects on the magnetic behaviour of the geometrically frustrated spinel ZnFe2O4

“…interactions [4,6], and ii) the slight degree of inversion of these samples which gives rise to modified first nearest-neighbor J 1 ' AF interactions that compete with also modified thirdneighbor J 3 ' ones both now involving Fe 3+ at (A) and [B] sites [5,30]. On the other hand, χ´ measurements down to 2 K (see S. I. and Fig.…”

“…this compound intrinsically displays a long-range order (LRO) or it is driven by the presence of defects [3][4][5]. While the susceptibility shows a peak near T N , its positive Curie-Weiss temperature Θ CW ~ +120 K (or higher) and the lack of evidence of a LRO at least down to 1.5 K for high-purity single-crystal of ZnFe 2 O 4 suggest the existence of a strong spin frustration [4,6]. Actually, ZnFe 2 O 4 can be modeled as a Heisenberg 3D-geometrical frustrated system where the B-sites form a network of corner-sharing tetrahedra (pyrochlore-type) from neighboring BO 6 octahedra [3,4,7].…”

“…Actually, ZnFe 2 O 4 can be modeled as a Heisenberg 3D-geometrical frustrated system where the B-sites form a network of corner-sharing tetrahedra (pyrochlore-type) from neighboring BO 6 octahedra [3,4,7]. Therefore, its unusual magnetic behavior has been interpreted as driven by the third-neighbor antiferromagnetic (AF) interactions J 3 (paths B-O-B-O-B and B-O-A-O-B) that compete with the temperature-dependent first-neighbor ferromagnetic (FM) interactions J 1 (B-O-B) [6,8,9].…”

On the deviation from a Curie–Weiss behavior of the ZnFe2O4 susceptibility: A combined ab-initio and Monte-Carlo approach

“…The underlying magnetism of the spinel ferrite ZnFe 2 O 4 has been of interest over the last three decades in the condensed matter community [1], [2], [3], [4], [5]. ZnFe 2 O 4 in its normal structure (i.e., with Fe 3+ and Zn 2+ ions at octahedral B and tetrahedral A -sites, respectively) is widely identified as an antiferromagnet insulator with a Néel temperature (TN) around 10 K and a band gap of 0.2 eV [1], [6].…”

Valence of Ti cations and its effect on magnetic properties of spinel ferrites TixM1−xFe2O4(M = Co, Mn)

“…Spinel ferrites have received much attention in recent years because of their application in spintronics and multiferroics. [1][2][3][4][5][6][7] In a (A)[B] 2 O 4 spinel ferrite, each unit cell contains eight formula units, in which the 32 larger oxygen anions form a close-packed face-centered-cubic structure with the 24 smaller metal cations occupying two types of interstitial position: the tetrahedral (8a) or (A) sites and the octahedral (16d) or [B] sites, [8][9][10][11] which form the (A) and [B] sublattices.…”