Heliox

Magnetotransport experiments were carried out in a PPMS-Dynacool (Quantum Design) in the temperature range from 2 K to 300 K and magnetic fields up to 9 T and in a 3-Helium cryostat (Heliox, Oxford Instruments) down to 0.3 K and fields up to 12 T. The resistance was measured with a low-frequency ac-technique in a 4-point configuration with small excitation currents, I, to prevent Joule heating (I = 0.5–1 mA in the PPMS and 100 μA in the Heliox experiments). The current was applied in the basal plane along the long direction of the sample. For in-situ measurements of the angular magnetoresistance the crystals were mounted on a mechanical rotator in the PPMS and a piezocrystal-based rotator (Attocube) in the Heliox. The samples were mounted such that the rotation angle corresponds to B ⊥ I. Care was taken to align the a-axis with the current direction, but a misorientation of several degrees can not be excluded.

Electric permittivity ε up to 9 T above 1.8 K was measured using an LCR meter (E4980A/B, Agilent) in a commercial cryostat equipped with a superconducting magnet (PPMS, Quantum Design). Two electrodes were attached to the large (100) surfaces of the polished thin plate crystals. To achieve low temperature down to 0.4 K in static fields, ³He refrigerator (Heliox, Oxford Instruments) was used, which was inserted into the cryostat equipped with a 12 T/14 T superconducting magnet. Magnetization M below 7 T was measured using a SQUID magnetometer (MPMS-XL, Quantum Design). The higher-field M and ε up to 50 T were simultaneously measured using a non-destructive pulsed magnet (36 ms duration) at the Institute for Solid State Physics (ISSP). M was measured by the conventional induction method using coaxial pickup coils. Capacitance was measured along the electric field direction (E∥a) by using a capacitance bridge (General Radio 1615-A) and converted to ε^{48 (link)}. Magnetostriction ΔL/L up to 44 T was measured by the optical fiber-Bragg-grating technique using the optical filter method in a non-destructive pulsed magnet (36 ms duration) at ISSP^{49 (link)}.

For the polarization measurements two contacts where applied with silver paint on opposing ends of the sample along the a axis. The resulting capacitive signal was measured with a Novocontrol Alpha-A Analyzer at frequencies up to 1 kHz in high ac electric fields, additional magneto- and pyro-current measurements where performed with a Keithley electrometer 6517B. The dielectric measurements where done in two cryostats, a Quantum Design PPMS and a top-loading dilution refrigerator (Oxford Instruments KELVINOX).
High-resolution measurements of the relative length changes ΔL(T, H)/L were performed in a home-built capacitance dilatometer that was attached to a³ He system (Oxford Instruments Heliox). The corresponding magnetostriction (λ) and thermal expansion (α) coefficients were then obtained via numerical differentiation $(\alpha ,\lambda )=\frac{1}{L_0}\frac{\partial \mathrm{\Delta }L}{\partial (T,{\mu }_{0}H)}$ .