Mpms xl

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)}.

The PFW crystals which we studied were grown from high temperature solution14 . Magnetization (M) of the crystal oriented along the [001] crystallographic direction was determined with a SQUID magnetometer (Quantum Design MPMS XL). Before each measurement the sample was heated up to 400 K without magnetic field. Magnetic moment was measured upon cooling with a field of H = 200 Oe (in FC experiments) or the sample was cooled down to 2 K without the field, and afterwards the moment was measured upon heating with H = 100 Oe (in ZFC experiments). The isothermal M(H) dependences were measured at different temperatures after cooling in zero field from 400 K. The ac magnetic susceptibility (χ_m) was measured under the ZFC mode with H = 5 Oe. Electric ac susceptibility (χ_e) was studied using a Novocontrol Alpha broadband dielectric spectrometer. The measured dependences were fitted to empirical formulae using nonlinear least squares method.

Transmission electron microscopy (TEM) analyses were performed with a LIBRA 120 PLUS Carl Zeiss SMT electron microscope (Germany) on ultrathin sections (50–70 nm) of the samples embedded in Embed 812 resin and deposited onto copper grids. For magnetoliposomes, drops were placed on copper grids with formvar film and they were stained using negative staining technique. In addition, electron energy loss spectroscopy (EELS) was used to characterize the presence of iron content inside the liposomes. The hydrodynamic particle size of the samples at pH 7 was measured by dynamic light scattering (DLS) using a Nano-ZS apparatus (Malvern Instruments, Worcestershire, UK). For the measurement of electrophoretic mobility, stock suspensions of BMLs and Oxa-BMLs were suspended in flasks containing oxygen-free NaClO₄ 10 mM (final volume of 10 mL/flask), and the pH was adjusted to 7.4. Samples were sonicated for 2 min, and the electrophoretic mobility was immediately measured. ζ-potential values were calculated from these measurements by using Malvern Zetasizer software (Malvern Instruments, UK). All measurements, done in triplicate for each sample, were carried out at 25 °C using disposable plastic cuvettes. Hysteresis cycles were carried out by using a superconducting quantum interference device (SQUID) 5 T magnetometer (Quantum Design MPMS XL, San Diego, CA, USA).

The morphologies of the samples were investigated by SEM (S4800, Japan), TEM (JEM-2100F, Japan), AFM (Veeco dimension V, USA), XRD (D8 Advance, Germany), UV-vis diffuse reflectance spectra (Shimadzu UV2550, Japan), XPS (Thermo ESCALAB 250, USA), inductively coupled plasma-atomic (ICP) mass spectrometry (Atomscan Advantage, Germany), superconducting quantum interference device (Quantum Design MPMS–XL, USA), X-ray absorption near-edge structure (Beamline of BL12B of Nation al Syncrotron Radiation Laboratory, China), Theoretical calculations (National Super Computing Centre in Jinan, China).

DC magnetization measurements were carried out on a superconducting quantum interference device magnetometer (MPMS XL, Quantum Design) equipped with oven. YBaCuFeO₅ pellets (m ∼ 20 mg, D ∼ 3 mm, H ∼ 1 mm) from the same batches as the samples used for the neutron and X-ray diffraction measurements were mounted in transparent drinking straws and cooled in zero field down to 1.8 K. The magnetization M of the sample was then measured in a magnetic field B=μ₀H=0.5 T up to 400 K by heating. For the high-temperature measurements (300–500 K) the samples were wrapped in Al foil as described in ref. 37 (link). After application of a magnetic field of 0.5 T the magnetization was measured by heating. The signal from the empty sample holders was separately measured in the same conditions and subtracted from the data. The magnetic susceptibility χ^DC=M/B was then calculated for all samples. The values of T_N1 and T_N2 mentioned in the text correspond to the maxima of the χ^DC vs temperature curves.