Physical property measurement system (ppms)

Magnetization curves were measured for dilute (~0.1 vol. %) dispersions of core/shell in eicosane (melting point 42 °C), using a vibrating sample magnetometer (VSM). The magnetometry system used in this work is a from Quantum Design, Inc., physical property measurement system (PPMS) with vibrating sample magnetometry (VSM) option (Any mention of commercial products is for information only; it does not imply recommendation or endorsement by NIST). 9 T field-cooled hysteresis loops were recorded at 10 K to reveal evidence of exchange bias. Magnetization loops were measured at 5, 60, 200, and 300 K, at fields up to 9 T. The zero field-cooled magnetization was measured as a function of increasing temperature at 100 Oe. Dense assemblies were also measured, and were prepared by rapidly precipitating nanoparticles in gel capsules with the addition of 50% (by volume) ethanol. Ethanol and toluene were evaporated overnight leaving behind a dense assembly of particles. Due to rapid precipitation, these did now have the same long range stacking order (between particles) described below.

The electrical resistivity was measured at ambient and high pressure by the 4-terminal method using a Physical Property Measurement System (PPMS) from Quantum Design with the lowest temperature of about 1.8 K. The resistivity under pressure was measured using a piston cylinder cell to generate pressure up to ~2.5 GPa and daphne 7373 as a pressure medium in PPMS. The pressure value in the sample was determined from the superconducting transition temperature T_c of Pb under pressure, using the relation P = (7.20 − T_c)/0.365. Note that when the 4.8 C/cm² irradiated sample was set in the piston cell, even before pressure was applied, the resistivity value changed, probably due to cracks, so we have corrected it to the value before pressure was applied.

The temperature dependence of the DC electrical resistance, Seebeck coefficient and Hall resistivity of the Ce_yMnAsO_1-xF_x phases were recorded using a Quantum Design physical property measurement system (PPMS) between 4 and 300 K. The measurements were performed with both the 2-probe and 4-probe methods to ensure the transitions were not a result of instrumental error. From ∼20 K above T_II, data were also recorded every 0.25 K in order to obtain high quality and reliable data around the transition and to fully map out the transition. The temperature and frequency dependence of the AC transport of Ce_0.96MnAsO_0.95F_0.05, Ce_0.97MnAsO_0.95F_0.05 and CeMnAsO_0.0965F_0.035 were also recorded between 4 K and 300 K on the PPMS with selected frequencies between 1 Hz and 1000 Hz. Magnetisation measurements of all samples were recorded on a Quantum Design SQUID Magnetometer in an applied field of 100 Oe after zero field cooling (ZFC) and field cooling (FC) at temperatures between 2–400 K.

The purity and crystal structure of the samples were characterized by a PANalytical Empyrean Series 2 powder X-ray diffraction (XRD) diffractometer (Malvern Panalytical, Malvern, UK) with a Cu Kα source (λ = 1.54 Å). The morphology of the samples was observed by a TESCAN Vega3 SBH scanning electron microscope (SEM) (TESCAN, Brno, Czech Republic) and a ThermoFisher Scientific Talos L120C transmission electron microscope (TEM) (ThermoFisher Scientific, Waltham, MA, USA). The pellet sample was cut into a typical dimension of 0.5 × 0.5 × 6 mm for the thermal conductivity measurement. The density (ρ) of the pellet sample was determined to be 4.27 g cm⁻³. A Quantum Design Physical Property Measurement System (PPMS) (Quantum Design, San Diego, CA, USA) was employed to measure the thermal conductivity along the direction perpendicular to the cold-pressing direction. The specific heat of the sample from 2 to 300 K was measured with the PPMS. The room-temperature Raman measurement was carried out with a HORIBA LabRam (HORIBA, Kyoto, Japan) using a 532 nm laser.