Spin-liquid state with precursor ferromagnetic clusters interacting antiferromagnetically in frustrated glassy tetragonal spinel Zn0.8Cu0.2FeMnO4

S K Jena; M S Seehra; T Sarkar; M Reehuis; A Hoser; B Weise; S Thota

doi:10.1088/1361-648X/acdbfa

Spin-liquid state with precursor ferromagnetic clusters interacting antiferromagnetically in frustrated glassy tetragonal spinel Zn_0.8Cu_0.2FeMnO₄

J Phys Condens Matter. 2023 Jun 20;35(37). doi: 10.1088/1361-648X/acdbfa.

Authors

S K Jena¹, M S Seehra², T Sarkar³, M Reehuis⁴, A Hoser⁴, B Weise⁵, S Thota¹

Affiliations

¹ Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India.
² Department of Physics & Astronomy, West Virginia University, Morgantown, WV 26506, United States of America.
³ Department of Materials Science and Engineering, Uppsala University, Uppsala SE-75103, Sweden.
⁴ Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
⁵ Leibniz-IFW Dresden, Institute for Complex Materials, D-01069 Dresden, Germany.

PMID: 37279725
DOI: 10.1088/1361-648X/acdbfa

Abstract

Spinels (AB₂O₄) with magnetic ions occupying only the octahedralBsites have inherent magnetic frustration which inhibits magnetic long-range order (LRO) but may lead to exotic states. Here we report on the magnetic properties of the tetragonal spinel Zn_0.8Cu_0.2FeMnO₄, the tetragonality resulting from the Jahn-Teller active Mn³⁺ions. X-ray diffraction and x-ray photoelectron spectroscopy of the sample yielded the composition (Zn0.82+Cu0.22+)_A[Fe0.42+Fe0.63+Mn3+]_BO_4‒δ. Analysis of the temperature dependence of magnetization (M), ac magnetic susceptibilities (χ'andχ''), dc susceptibility (χ), heat capacityC_p, and neutron diffraction (ND) measurements show complex temperature-dependent short-range order (SRO) but without LRO. The data ofχ vs. Tfits the Curie-Weiss law:χ = C/(T ‒ θ) fromT= 250 K to 400 K withθ≃ 185 K signifying dominant ferromagnetic (FM) coupling with the FM exchange constantJ/k_B= 17 K, andC= 3.29 emu K mol^‒1Oe^‒1yielding an effective magnetic momentµ_eff= 5.13µ_Bresulting from the high-spin states of Cu²⁺(Asite) and Fe²⁺(Bsite), while theBsite trivalent ions Mn³⁺and Fe³⁺are in their low-spin states. The extrapolated saturation magnetization obtained from theM vs. Hdata atT= 2 K is explained using the spin arrangement (Cu²⁺↓)_A[Fe²⁺↑, Fe³⁺↓, Mn³⁺↑]_Bleading to FM clusters interact antiferromagnetically at low temperatures. Temperature dependence of d(χT)/dTshows the onset of ferrimagnetism below ∼100 K and peaks near 47 K and 24 K. The relaxation timeτobtained from temperature and frequency dependence ofχ″when fit to the power law and Vogel-Fulcher laws confirm the cluster spin-glass (SG) state. The magnetic field dependence of the SG temperatureTSGHfollows the equation:TSGH=TSG01-AH2/ϕwithT_SG(0) = 46.6 K,A= 8.6 × 10^‒3Oe^‒0.593andϕ= 3.37. The temperature dependence of hysteresis loops yields coercivityH_C∼ 3.8 kOe at 2 K without exchange-bias, butH_Cdecreases with increase inTbecoming zero above 24 K, theT_SG(H) forH= 800 Oe. Variations ofC_pvs. Tfrom 2 K to 200 K inH=0 andH=90 kOe do not show any peak characteristic of LRO. However, after correcting for the lattice contribution, a broad weak peak typically of SRO becomes evident centered around 40 K. ForT< 9 K,C_pvaries asT²; a typical signature of spin-liquids (SLs). Comparison of the ND measurements at 1.7 K and 79.4 K shows absence of LRO. Time dependence of thermo-remanent magnetizationM_TRM(t) studies below 9 K reveal weakening of the inter-cluster interaction with increase in temperature. A summary of these results is that in Zn_0.8Cu_0.2FeMnO₄, ferromagnetic clusters interact antiferromagnetically without LRO but producing a cluster SG state atT_SG(0) = 46.6 K, followed by SL behavior below 9 K.

Keywords: JahnTeller effect; pyrochlore; spin-glass; spin-liquids.