The structure and magnetic properties of boron-oxide-encapsulated magnetic nanocapsules fabricated by arc discharge in diborane $\left({\mathrm{B}}_2{\mathrm{H}}_6\right)$ atmosphere have been investigated. The structure of boron-oxide-coated Fe(B) nanocapsules is different from that of carbon-coated nanocapsules. In contrast to carbon-coated nanocapsules consisting of a crystalline shell of graphite and a core of α-Fe and/or ${\mathrm{Fe}}_3\mathrm{C},$ boron-oxide-coated Fe nanocapsules show an amorphous surface layer and a core of α-Fe [and α-Fe(B) solid solution], γ-Fe, FeB, and/or ${\mathrm{Fe}}_3\mathrm{B}$ phases. The loop shift in the hysteresis loop indicates the existence of the exchange bias between ferromagnetic and antiferromagnetic components at room temperature. The ${\mathrm{Fe}}_3{\mathrm{O}}_4$ phase contributes to the exchange bias as antiferromagnetic components. A very wide energy barrier distribution exists in the Fe(B) nanocapsules.

The increasing addition of Tb in the system Bi _1−x Tb _x FeO ₃ produces a progressive modification of the crystal structure from rhombohedral R 3 c to orthorhombic Pnma which results in the appearance and enhancement of the net magnetization, with the composition x ≈ 0.15–0.20 being a promising candidate for magnetoelectric applications.