Abnormal size-dependent coercivity in ternary Sm–Fe–N nanoparticles

•In present manuscript, the structure and magnetic properties were studied for the ternary Sm–Fe–N nanoparticles with different particle size.•The particles with average size of 750 nm, 36.5 nm, and 9.4 nm exhibit high coercivity of 12.4, 18.7, and 7.5 kOe, respectively.•The magnetic hardening mechanism of the particles was investigated by measurement and evaluation of their initial magnetization curves.•As the particle size decreases, the magnetization process switches from pinning to nucleation behavior, indicating that particle size plays a key role in determining the magnetic hardening mechanism of the Sm–Fe–N nanoparticles.•Our work opens a new avenue to manipulate the coercivity of Sm–Fe–N nanoparticles by controlling their particle size, and demonstrate the good potential of Sm–Fe–N nanoparticles in practical application.

Structure and magnetic properties were studied for Sm–Fe–N nanoparticles prepared by surfactant-aid high energy ball milling. Magnetic hardening mechanism of the particles was investigated by evaluating their initial magnetization curves. The particles with average size of 750 nm, 36.5 nm, and 9.4 nm exhibit high coercivity of 12.4, 18.7, and 7.5 kOe, respectively. As particle size decreases, the magnetization process switches from pinning to nucleation behavior, indicating that particle size plays a key role in determining the magnetic hardening mechanism of the nanoparticles.