TR 288 - Elasto-Q-Mat: Research Data

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Browsing TR 288 - Elasto-Q-Mat: Research Data by Person "Tutsch, Ulrich"

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  • Research Data
    Field-induced effects in the spin liquid candidate PbCuTe2O6
    2023-06-16
    Tutsch, Ulrich 
    PbCuTe2O6 is considered to be one of the rare candidate materials for a three-dimensional quantum spin liquid (QSL). This assessment was based on the results of various magnetic experiments, performed mainly on polycrystalline material. More recent measurements on single crystals revealed an even more exotic behavior, yielding ferroelectric order below T_FE ≈ 1 K, accompanied by distinct lattice distortions, and a somewhat modified magnetic response which is still consistent with a QSL. Here we report on low-temperature measurements of various thermodynamic, magnetic, and dielectric properties of single-crystalline PbCuTe2O6 in magnetic fields B ≤ 14.5 T. The combination of these various probes allows us to construct a detailed B-T phase diagram including a ferroelectric phase for B ≤ 8 T and a B-induced magnetic phase at B ≥ 11 T. These phases are preceded by or coincide with a structural transition from a cubic high-temperature phase into a distorted noncubic low-temperature state. The phase diagram discloses a ferroelectric quantum critical point at B_c1 = 7.9 T, where the second-order phase transition line associated with ferroelectric order is suppressed to zero. In addition, a magnetic quantum phase transition is revealed at B_c2 = 11 T. The corresponding phase transition to a fieldinduced magnetic order at B > B_c2 is likely to be of first order. Field-induced lattice distortions, observed in the state at T > 1 K and which are assigned to the effect of spin-orbit interaction of the Cu2+ ions, are considered as the key mechanism by which the magnetic field couples to the dielectric degrees of freedom in this material.
      4  45
  • Research Data
    From magnetic order to valence-change crossover in EuPd2(Si1−xGex)2 using He-gas pressure
    2023-06-19
    Tutsch, Ulrich 
    We present results of magnetic susceptibility and thermal expansion measurements performed on high-quality single crystals of EuPd2(Si1−xGex )2 for 0 ≤ x ≤ 0.2 and temperatures 2 K ≤ T ≤ 300 K. Data were taken at ambient pressure and finite He-gas pressure p ≤ 0.5 GPa. For x = 0 and ambient pressure we observe a pronounced valence-change crossover centred around T′_V ≈ 160 K with a non-magnetic ground state. This valence-change crossover is characterized by an extraordinarily strong pressure dependence of dT′_V /dp = (80 ±10) K/GPa. We observe a shift of T′_V to lower temperatures with increasing Ge-concentration, reaching T′_V ≈ 90 K for x = 0.1, while still showing a non-magnetic ground state. Remarkably, on further increasing x to 0.2 we find a stable Eu(2+δ)+ valence with long-range antiferromagnetic order below T_N = (47.5 ± 0.1) K, reflecting a close competition between two energy scales in this system. In fact, by the application of hydrostatic pressure as small as 0.1 GPa, the ground state of this system can be changed from long-range antiferromagnetic order for p < 0.1 GPa to an intermediate-valence state for p ≥ 0.1 GPa.
      2  50
  • Research Data
    Pressure study on the interplay between magnetic order and valence crossover in EuPd2(Si1−xGex)2
    2023-06-30
    Tutsch, Ulrich 
    We present results of the magnetic susceptibility on high-quality single crystals of EuPd2(Si1−xGex )2 for Ge concentrations 0 ≤ x ≤ 0.105 performed under varying hydrostatic (He-gas) pressure 0 ≤ p ≤ 0.5 GPa. The work extends recent studies at ambient pressure demonstrating the drastic change in the magnetic response from valence-crossover behavior for x = 0 and 0.058, to long-range antiferromagnetic (AFM) order below T_N = 47 K for x = 0.105. The valence-crossover temperature T_V shows an extraordinarily strong pressure dependence of dT'_V/dp= +(80 ± 10) K/GPa. In contrast, a very small pressure dependence of dT_N/dp ≤ +(1 ± 0.5) K/GPa is found for the AFM order upon pressurizing the x = 0.105 crystal from p = 0 to 0.05 GPa. Remarkably, by further increasing the pressure to 0.1 GPa, a drastic change in the ground state from AFM order to valencecrossover behavior is observed. Estimates of the electronic entropy related to the Eu 4f electrons, derived from analyzing susceptibility data at varying pressures, indicate that the boundary between AFM order and valence crossover represents a first-order phase transition. Our results suggest a particular type of second-order critical end point of the first-order transition for x = 0.105 at p_cr ≈ 0.06 GPa and T_cr ≈ 39 K where intriguing strong-coupling effects between fluctuating charge, spin, and lattice degrees of freedom can be expected.
      53  4