Currently, M-type strontium and barium hexaferrites account for about 60% of the market of hard magnetic materials and are mainly used as permanent magnets and microwave resonators [1]. These compounds are characterized by one easy magnetization axis and a large magnetic crystalline anisotropy, which, in addition to their low cost and chemical inertness, makes them candidates for high-density magnetic storage media [2, 3]. One of the popular methods for preparing highly dispersed hexaferrite particles is crystallization of a glassy oxide precursor upon its heat treatment [4‐7]. This treatment leads to the formation of submicron single-domain hexaferrite particles characterized by a high coercive force. In this work, we pioneered the use of microwave heating to stimulate the crystallization of hexaferrites from their glasses. The SrO–Fe 2 O 3 –B 2 O 3 system was used as a glass-forming system. Previously, this system was studied as applied to the preparation of glass ceramics [4, 8]. To obtain a glass of the nominal composition SrFe 12 O 19 + 12Sr 2 B 2 O 5 , an initial mechanical mixture of iron oxide, strontium carbonate, and boric acid was preheated at 600–800°ë . Then, the precursor was melted in a platinum crucible with the use of an arc plasma torch for 2 min at about 1200°ë . The melt was quenched between copper plates.