Fig. 2: γ-BaFe₂O₄ macroscopic measurements.

a ZFC and FCC magnetization measurements as a function of temperature collected at 2 T between 400 and 1000 K showing an anomaly at ~890 K in agreement with the neutron data. Please note the very small magnetic moment value in μB/f.u. excluding a ferro/ferrimagnetic transition. b Magnetic hysteresis loops measured at 300 K (blue curve), 800 K (red curve), and 1000 K (black curve) for a high purity sample of γ-BaFe₂O₄. The inset shows the low field regions of the loops showing the disappearing of the coercive field above 750 K indicating that is likely related to the presence of BaFe₁₂O₁₉ (T_C = 720 K) as impurity. The remaining ferromagnetic component in the 800 K data is likely related to other Fe-containing impurities, e.g., BaFe₄O₇ (T_N = 850 K). c Magnetic hysteresis loop collected at 320 K for a micrometric film of γ-BaFe₂O₄ deposited by pulsed electron deposition on a monocrystalline silicon substrate covered by a thin layer of thermal SiO₂. The measurement was corrected by subtracting the diamagnetic signal of the substrate, additional information and plots of the raw data can be retrieved in the Supporting Information. The linear behavior without hysteresis and null coercive field agree with the neutron data which indicate an antiferromagnetic structure without ferromagnetic component. d PN electric polarization loop collected at a frequency f = 100 Hz with triangular pulse of amplitude 1000 V. The inset shows the corresponding integrated current as a function of the applied voltage. The clear, symmetric current peaks reinforce the conclusion of a switchable polarization in the system.