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Signatures of a Spin-12 Cooperative Paramagnet in the Diluted Triangular Lattice of Y2CuTiO6

S. Kundu, Akmal Hossain, Pranava Keerthi S., Ranjan Das, M. Baenitz, Peter J. Baker, Jean-Christophe Orain, D. C. Joshi, Roland Mathieu, Priya Mahadevan, Sumiran Pujari, Subhro Bhattacharjee, A. V. Mahajan, and D. D. Sarma
Phys. Rev. Lett. 125, 117206 – Published 9 September 2020
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    Abstract

    We present a combination of thermodynamic and dynamic experimental signatures of a disorder driven dynamic cooperative paramagnet in a 50% site diluted triangular lattice spin-12 system: Y2CuTiO6. Magnetic ordering and spin freezing are absent down to 50 mK, far below the Curie-Weiss scale (−θCW) of ∼134  K. We observe scaling collapses of the magnetic field and temperature dependent magnetic heat capacity and magnetization data, respectively, in conformity with expectations from the random singlet physics. Our experiments establish the suppression of any freezing scale, if at all present, by more than 3 orders of magnitude, opening a plethora of interesting possibilities such as disorder stabilized long range quantum entangled ground states.

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    • Received 19 March 2020
    • Revised 11 June 2020
    • Accepted 4 August 2020

    DOI:https://doi.org/10.1103/PhysRevLett.125.117206

    © 2020 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Frustrated magnetismParamagnetism
    1. Physical Systems
    2-dimensional systemsMott insulators
    1. Techniques
    AC susceptibility measurementsDC susceptibility measurementsMuon spin relaxation & rotationSpecific heat measurements
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    S. Kundu1,‡, Akmal Hossain2,‡, Pranava Keerthi S.2, Ranjan Das2, M. Baenitz3, Peter J. Baker4, Jean-Christophe Orain5, D. C. Joshi6, Roland Mathieu6, Priya Mahadevan7, Sumiran Pujari1, Subhro Bhattacharjee8, A. V. Mahajan1,*, and D. D. Sarma2,†

    • 1Department of Physics, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India
    • 2Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
    • 3Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
    • 4ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX110QX, United Kingdom
    • 5Paul Scherrer Institute, Bulk MUSR group, LMU 5232 Villigen PSI, Switzerland
    • 6Department of Engineering Sciences, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
    • 7S. N. Bose National Center for Basic Sciences, Block-JD, Salt Lake, Kolkata-700106, India
    • 8International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru 560089, India

    • *Corresponding author. mahajan@phy.iitb.ac.in
    • †Corresponding author. sarma@iisc.ac.in
    • ‡These authors contributed equally to this work

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    Vol. 125, Iss. 11 — 11 September 2020

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    • Figure 1
      Figure 1

      Double perovskite structure with one unit cell of Y2CuTiO6 and corner-shared polyhedra of (Cu/Ti)O5 connected via oxygen atoms in the ab plane. The Cu2+/Ti4+ ions form edge-shared triangles.

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    • Figure 2
      Figure 2

      The left y axis shows χ(T) (open blue circles) of Y2CuTiO6 and the right y axis shows the inverse susceptibility (open pink triangles) free from χ0. The Curie-Weiss fit is shown in the T range 200–400 K with a solid line. The intercept on the x axis gives a θCW of about −134  K. Inset “I” shows the ac susceptibility for different frequencies till 2 K. Inset “II” shows the absence of any bifurcation in the ZFC/FC data in 50 Oe down to 500 mK.

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    • Figure 3
      Figure 3

      (a) Muon depolarization with time shown for various temperatures at zero fields. Solid lines are fits as described in the text. The inset shows the variation of the obtained muon relaxation rate with temperature. (b) Muon depolarization for various longitudinal fields at 0.5 K. The corresponding inset shows the variation of the obtained muon relaxation rate with field.

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    • Figure 4
      Figure 4

      (a) The change in the spin entropy ΔS as a function of temperature between 350 mK and 20 K. In the presence of a magnetic field, marginally more entropy is released, indicating a possible partial lifting of frustration by the Zeeman field, another canonical signature of cooperative magnets such as spin ice [67]. The inset shows the spin contributions to the specific heat (Cs=Cp−Clat)/T vs T over the same range. (b) The scaled magnetic heat capacity HγCm/T of YCTO is plotted against the scaled temperature T/H for various applied fields H. The data collapse in the low temperature regime is consistent with the q=0 form of the universal function of Ref. [27], which is expected in absence of spin-orbit coupling. The inset shows the Cm of YCTO after deduction of the lattice and Schottky contributions. (c) The M(H) isotherm has been scaled in the form of MT−α vs H/T.

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