A power inductor (270, 290, 300, 320, 340, 360, 380), comprising: a first magnetic core (272, 292, 302, 322, 342, 362, 382) that has first and second ends, an inner surface, and an outer surface, and that comprises a ferrite bead core material; a cavity (273, 293, 303, 323, 343, 363, 383) in the first magnetic core that extends from the first end to the second end; a slotted air gap (274, 294, 304, 324, 344, 364, 384) in the first magnetic core that extends from the first end to the second end and from the inner surface to the outer surface; a second magnetic core (276, 296, 306, 326, 346, 366, 386) that is located in the slotted air gap and extends from the inner surface to the outer surface through the slotted air gap; and a conductor that passes through the cavity, wherein the slotted air gap is arranged in the first magnetic core in a direction that is parallel to the conductor, wherein the first magnetic core and the second magnetic core are selflocking in at least two orthogonal planes, wherein the second magnetic core has a permeability that is lower than the first magnetic core, characterised in that at least one of: opposing walls of the first magnetic core (322, 362) that are adjacent to the slotted air gap are "V"-shaped; the second magnetic core is "T"-shaped and extends along an inner wall of the first magnetic core; and the second magnetic core is "H"-shaped and extends partially along inner and outer walls of the first magnetic core. a first magnetic core (272, 292, 302, 322, 342, 362, 382) that has first and second ends, an inner surface, and an outer surface, and that comprises a ferrite bead core material; a cavity (273, 293, 303, 323, 343, 363, 383) in the first magnetic core that extends from the first end to the second end; a slotted air gap (274, 294, 304, 324, 344, 364, 384) in the first magnetic core that extends from the first end to the second end and from the inner surface to the outer surface; a second magnetic core (276, 296, 306, 326, 346, 366, 386) that is located in the slotted air gap and extends from the inner surface to the outer surface through the slotted air gap; and a conductor that passes through the cavity, wherein the slotted air gap is arranged in the first magnetic core in a direction that is parallel to the conductor, wherein the first magnetic core and the second magnetic core are selflocking in at least two orthogonal planes, wherein the second magnetic core has a permeability that is lower than the first magnetic core, characterised in that at least one of: opposing walls of the first magnetic core (322, 362) that are adjacent to the slotted air gap are "V"-shaped; the second magnetic core is "T"-shaped and extends along an inner wall of the first magnetic core; and the second magnetic core is "H"-shaped and extends partially along inner and outer walls of the first magnetic core. opposing walls of the first magnetic core (322, 362) that are adjacent to the slotted air gap are "V"-shaped; the second magnetic core is "T"-shaped and extends along an inner wall of the first magnetic core; and the second magnetic core is "H"-shaped and extends partially along inner and outer walls of the first magnetic core.