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Magnetic coercivity, or coercive field, is the magnitude of the reverse magnetic field that must be applied to a magnetized material to reduce its magnetic induction—or magnetization—to zero after the material has been driven to saturation ^[1]. On the hysteresis loop, coercivity is measured as the field at which the B–H or M–H curve crosses the axis opposite to the original magnetization direction, and it quantifies the resistance of the material to demagnetization: a large coercivity means a strong reverse field is required to erase the magnetization, while a small coercivity means the material is readily demagnetized ^[2]. Coercivity is a microstructurally sensitive property that originates from the pinning of magnetic domain walls and from the energy barriers to reversal of magnetization, so its value reflects defects, inclusions, grain boundaries, and the shape and anisotropy of the material that impede domain-wall motion ^[1]. It is distinguished from remanence, which measures the magnetization retained at zero field, by measuring the field needed to remove that magnetization, and it is the parameter that separates magnetically hard materials, with high coercivity suitable for permanent magnets, from magnetically soft materials, with low coercivity suitable for cores ^[2]. Its defining meaning is the reverse field needed to annul magnetization ^[3].