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Efficient Adiabatic Demagnetization Refrigeration to below 50 mK with Ultrahigh-Vacuum-Compatible Ytterbium Diphosphates AYbP2O7 (A=Na, K)

U. Arjun, K.M. Ranjith, A. Jesche, F. Hirschberger, D.D. Sarma, and P. Gegenwart
Phys. Rev. Applied 20, 014013 – Published 10 July 2023
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  • INTRODUCTION
  • METHODS
  • RESULTS
  • DISCUSSION
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    Attaining millikelvin (mK) temperatures is often a prerequisite for the study of quantum phenomena and the operation of quantum devices. Adiabatic demagnetization refrigeration (ADR) is an effective, easy, and sustainable alternative to evaporation or dilution cooling with the rare and superexpensive 3He. Paramagnetic salts, traditionally used for mK ADR, suffer from chemical instability related to water of crystallization. We report synthesis, characterization, as well as low-temperature magnetization and specific heat measurements of two alternative UHV-compatible candidate materials NaYbP2O7 and KYbP2O7. Utilizing the physical property measurement system at 2 K, the ADR of sintered pellets with Ag powder admixture starting at 5 T yields base temperatures (warm-up times) of 45 mK (55 min) and 37 mK (35 min) for NaYbP2O7 and KYbP2O7, respectively, slightly advantageous to KBaYb(BO3)2 (45 mK and 40 min) studied under similar conditions.

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    • Received 24 March 2023
    • Revised 26 May 2023
    • Accepted 12 June 2023

    DOI:https://doi.org/10.1103/PhysRevApplied.20.014013

    © 2023 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Cryogenic technologyDipolar interactionHeat transferMagnetocaloric effectQuantum spin liquidSpecific heat
    1. Physical Systems
    Magnetic refrigerationRare-earth magnetic materials
    Condensed Matter, Materials & Applied PhysicsEnergy Science & Technology

    Authors & Affiliations

    U. Arjun1,2,*, K.M. Ranjith3, A. Jesche2,†, F. Hirschberger2, D.D. Sarma1, and P. Gegenwart2,‡

    • 1Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
    • 2Experimental Physics VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, Augsburg 86135, Germany
    • 3Laboratoire National des Champs Magnétiques Intenses-EMFL, CNRS, Université Grenoble Alpes, Grenoble 38042, France

    • *arjunu@iisc.ac.in
    • †anton.jesche@physik.uni-augsburg.de
    • ‡philipp.gegenwart@physik.uni-augsburg.de

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    Vol. 20, Iss. 1 — July 2023

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    Images

    • Figure 1
      Figure 1

      Crystal structure of NaYbP2O7 in the a-b plane and along the c direction. The YbO6 octahedra are linked via PO4 tetrahedra and span a distorted triangular grid (left panel). One such triangular layer is highlighted by a rectangular box in the right panel. Different Yb-Yb distances are color coded.

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    • Figure 2
      Figure 2

      Crystal structure of KYbP2O7. The YbO6 octahedra are linked via PO4 tetrahedra forming uniform chains running along the c axis (highlighted by a rectangular box), which are interconnected by alternating chains running in the a-c plane (highlighted by an ellipse in the right panel). This forms a three-dimensional distorted hyperhoneycomblike network. Different Yb-Yb distances are color coded.

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    • Figure 3
      Figure 3

      Powder x-ray diffraction pattern (open red circles) for NaYbP2O7 (upper panel) and KYbP2O7 (lower panel) at room temperature. The solid line represents the Rietveld refinement, with the vertical bars showing the expected Bragg peak positions and the lower solid blue line representing the difference between observed and calculated intensities.

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    • Figure 4
      Figure 4

      Inverse magnetic susceptibility (1/χ) data measured at 1 T as a function of temperature (T) for NaYbP2O7 (upper panel) and KYbP2O7 (lower panel). The dashed and solid lines represent the fits by Eqs. (1) and (2), respectively.

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    • Figure 5
      Figure 5

      Isothermal magnetization M(H) measured at 0.4 K for NaYbP2O7 (a) and KYbP2O7 (b). Dashed lines represent linear contributions (see text). The insets show the low-temperature inverse magnetic susceptibility after subtracting χ0 along with the CW fit for NaYbP2O7 [inset of (a)] and KYbP2O7 [inset of (b)].

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    • Figure 6
      Figure 6

      Low-temperature magnetic specific heat (Cm) of NaYbP2O7 [upper panel of (a)] and KYbP2O7 [upper panel of (b)] at several external magnetic fields. Phonon contribution is subtracted from the raw data using a polynomial fit. Magnetic entropy (Sm) of NaYbP2O7 [lower panel of (a)] and KYbP2O7 [lower panel of (b)] calculated by integrating Cm/T. For fields below 2 T the entropy is vertically shifted to match the other curves at 20 K. Two arrows show the ADR process.

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    • Figure 7
      Figure 7

      ADR performance comparison of NaYbP2O7 (red), KYbP2O7 (green), and KBaYb(BO3)2 (brown) in the commercial physical property measurement system (PPMS). The sample is slowly cooled to T=2K at H=5T through the weak thermal link to the PPMS puck kept at 2 K and the ‘high-vacuum mode’ of the PPMS was employed in order to achieve thermal decoupling. Subsequently, magnetic field is swept from 5 T to zero at a rate of 0.15T min−1 and the temperature change with time t is recorded. The blue curve shows the respective magnetic field.

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