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Quantum Critical Scaling in the Disordered Itinerant Ferromagnet UCo1−xFexGe

K. Huang, S. Eley, P. F. S. Rosa, L. Civale, E. D. Bauer, R. E. Baumbach, M. B. Maple, and M. Janoschek
Phys. Rev. Lett. 117, 237202 – Published 30 November 2016
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    Abstract

    The Belitz-Kirkpatrick-Vojta (BKV) theory shows in excellent agreement with experiment that ferromagnetic quantum phase transitions (QPTs) in clean metals are generally first order due to the coupling of the magnetization to electronic soft modes, in contrast to the classical analogue that is an archetypical second-order phase transition. For disordered metals the BKV theory predicts that the second-order nature of the QPT is restored because the electronic soft modes change their nature from ballistic to diffusive. Our low-temperature magnetization study identifies the ferromagnetic QPT in the disordered metal UCo1−xFexGe as the first clear example that exhibits the associated critical exponents predicted by the BKV theory.

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    • Received 2 August 2016

    DOI:https://doi.org/10.1103/PhysRevLett.117.237202

    © 2016 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Magnetic phase transitionsQuantum criticality
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    K. Huang1,2, S. Eley1, P. F. S. Rosa1, L. Civale1, E. D. Bauer1, R. E. Baumbach1,*, M. B. Maple2, and M. Janoschek1,†

    • 1Condensed Matter and Magnet Science, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
    • 2Department of Physics, University of California, San Diego, La Jolla, California 92093, USA

    • *Present address: Condensed Matter Group, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA.
    • †Corresponding author. mjanoschek@lanl.gov

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    Vol. 117, Iss. 23 — 2 December 2016

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    Images

    • Figure 1
      Figure 1

      Isotherms of the magnetization M(T,H) of UCo1−xFexGe as a function of magnetic field H for Fe concentrations x=0.22 (a), 0.23 (b), and 0.24 (c) displayed in a log-log plot. Because M(T,H) ∝H1/δ the slope of each curves describes 1/δ. In panels (d)–(f), the temperature dependence of 1/δ is shown for each concentration. Because for H≦0.1  T scaling is not expected due to domain effects, the corresponding data were omitted for the determination of 1/δ [22]. The blue dashed lines in panels (d) and (e) are guides to the eye. The horizontal dashed black line denotes δ=3/2. The red solid curves are the partial derivative ∂(1/δ)/∂T with respect to T.

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    • Figure 2
      Figure 2

      Scaling of the magnetization M of UCo1−xFexGe as function of magnetic field H and temperature T. (a)–(c) M/TβT vs H/TγT+βT for the Fe concentrations x=0.22, 0.23, and 0.24, respectively. The respective critical exponents βT, γT, and δ are denoted in each plot (see the main text). (d)–(f) The corresponding adjusted R2 value that describes the goodness of fit for the scaling of M in panels (a)–(c) (R2=1 is the best agreement between the data and fit) for a wide range of combinations of the critical exponents (βT, γT) for each x. The details of how to calculate the adjusted R2 value are provided in the Supplemental Material [20]. The black and white dashed lines denote the Widom relationship γT=βT(δ−1) that relates the critical exponents βT and γT with the exponent δ determined from Fig. 1. Here, the black and white lines use the asymptotic and preasymptotic values of δ, respectively (see the text and Table 1). The blue dashed lines denote the values of (βT, γT) used for the modified scaling plots of M in panels (a)–(c).

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    • Figure 3
      Figure 3

      The Curie temperature TC of UCo1−xFexGe as a function of (x−xcr). Here, x is the Fe concentration and xcr denotes the concentration at which TC is suppressed to zero temperature. The black line is a fit to TC=(x−xcr)zmν with zmν=4/5 for xcr=0.24. The red circles, blue diamonds, and green triangles denote TC determined from the magnetization M(T), specific heat C(T), and electrical resistivity ρ(T) from Ref. [19].

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