In situ SQUID measurement

In situ magnetic measurement was carried out with a custom-built miniaturized Teflon electrochemical cell in a superconducting quantum interference device (SQUID, MPMS3) at room temperature. In the electrochemical cell, the SmCo₅ electrode, Pt foil and peuso Ag/AgCl electrode were the working, counter and reference electrodes, respectively. The electrolyte was 1 M KOH. The SmCo₅ electrode and the Pt foil were attached to the flat surface of a plastic rod, while the reference electrode was threading through a capillary. The magnetic measurements were performed at the sealed mode of SQUID. All magnetic measurements were performed with the applied magnetic field parallel to the surface of the Cu foil.

For the determination of magnetocrystalline anisotropy constant (K₁), the SmCo₅ particles were first aligned in a homogeneous magnetic field before the drying of the slurry/Cu foil composite. Other steps in the preparation of the SmCo₅ electrode were the same as those described earlier. Before the magnetic measurements in SQUID, the SmCo₅ electrode was demagnetized with the vibrating fields from a value of 7–0 T. The sample was first measured along the easy axis. Then, the sample was removed from the plastic rod and remounted in a perpendicular direction and measured again. According to ref. ³⁷, K₁ was calculated by integrating the area enclosed between the hard and easy axis magnetization curves. Since the applied magnetic field was way smaller than the anisotropy field of SmCo₅ (~40 T), these two curves were extrapolated until they met and then the enclosed area was calculated.