A Novel Route for the Preparation of Nanocomposite Magnets

Abstract

Nanocomposite magnets are of importance because they are expected to provide a very high maximum‐energy product. Here is presented a route to α‐Fe/Sm2(Fe,Si)17Cx nanocomposite magnets with fine grain size below 10 nm. Annealing amorphous Sm8Fe85‐Si2C5 alloy under high pressure gives nanocomposite magnets (see Figure) with significantly increased coercivity and remnant magnetization.

Study of interface structure of α-Fe/Nd2Fe14B nanocomposite magnets

“…[3][4][5][6] More recently, we have successfully prepared the nanocomposite magnets with a grain size below 10 nm by annealing amorphous alloy under high pressure. [7][8][9] The maximum energy product of the magnets is, however, about 25 MGOe, 8 which is still much lower than the predicted one. This indicates clearly that, besides the grain size, some factors also have a large effect on the magnetic properties of the nanocomposite magnets.…”

Nanocomposite Magnets and their Preparation under High Pressure

“…[14] Further studies showed that high pressure can not only reduce the grain size of a-Fe/Sm 2 (Fe,Si) 17 C x magnets but also change the volume fraction ratio of the a-Fe phase to the Sm 2 (Fe,Si) 17 C x phase and even their crystallization sequence. [15,16] At low pressure, a-Fe crystallizes first, while at a high pressure of 6 GPa Sm 2 (Fe,Si) 17 C x crystallizes first. High pressure promotes the formation of the hard-magnetic phase, which can improve the uniformity of the microstructure of nanocomposite magnets.…”

Thermo-remnant magnetization assisted switching response

“…To meet the requirements of suitable memory media for thermally assisted recording, characteristics of significantly robust TRM across Néel temperature (T N ) in SmCrO 3 associated with ordering of Cr sub-lattices in canted antiferromagnetic phase are studied here. The candidature can be justified with the fact the value of energy product (M remnant x H coercive ) significantly changes by factor of ≈ 1000 in a very sharp thermal window (∆T w ) of 10 K across T N and, as a consequence, fully reversible bi-stability is realized either by sweeping the temperature across ∆T w or using magnetic field pulses ≥ 0.1 T. The high coercive fields in the vicinity of ordering temperature ensure the thermally stable scaling and consequently minimize the noise levels, whereas, low magneto-crystalline anisotropy and spontaneous magnetization ratio K U /M S for temperature values close to transition, keeps the required magnitude of writing field sufficiently low 8,9 . Evidently, understanding the origin and peculiar behavior of TRM in SmCrO 3 can serve as a recipe towards the goal of technologically feasible single phase TRM assisted recording base.…”