Graded permanent magnets

Abstract

The effect of semihard magnetic phases and interfaces on the performance of nanostructured two-phase permanent magnets is investigated by model calculations. In addition to the trivial coercivity increase due to the replacement of soft regions by semihard regions, there is a coercivity enhancement even if the volume-averaged anisotropy is kept constant during the introduction of the semihard phase. A variational approach is used to derive analytical results for representative anisotropy profiles. The improvement is operative on length scales slightly larger than that of the soft phase in hard-soft composites, but the main challenge is to find semihard light or heavy transition metal phases with a high magnetization. There are several Fe-and Co-based phases, but most are thin-film systems and difficult to use in bulk magnets. Very hard nanostructured magnets may also be created from soft phases with negative but large anisotropy constants ͑hard-magnetic soft-soft magnets͒.

Advances in nanostructured permanent magnets research

“…The above results based on renewed modelling and experimental works have shown that a well-chosen soft phase and engineered interface will further enhance the energy product of a nanocomposite hard/soft magnet. Recent theoretical studies by Skomski [71], by Sato et al [72] and by Xia [73] on nanocomposite magnets have considered effects of 'semi-hard phase' and orientation of the grains on the interphase exchange coupling. Those factors were largely neglected in the early modelling work.…”

Magnet properties of Mn70Ga30 prepared by cold rolling and magnetic field annealing

“…Together with Mn-Al and Mn-Bi alloys, the Mn-Ga alloys are scrutinized for use as hard magnetic materials [9]. Having a low remanent magnetization and high material cost, Mn 3 Ga alone is not suitable for permanentmagnet applications, but it is a valid candidate for the hard component of an exchange spring magnet [10,11].…”

Unraveling the roles of thermal annealing and off-time duration in magnetic properties of pulsed electrodeposited NiCu nanowire arrays

“…Furthermore, from the application standpoints, we can consider functionalities for these arrays of NiCu ANWs in two-phase nanomagnets as well as the nanoscale MR and thermoelectric device applications. 27,48,49 On the other hand, thermal annealing leads to a decrease in the Hc FORC corresponding to the hard phase (from 900 to 800 Oe) as well as in the density of the soft phase from 1.88 Â 10 À6 to 1.40 Â 10 À6 (see Fig. 10).…”