  Nanostructured permanent magnets are gaining increasing interest and
importance for applications such as generators and motors. Thermal management
is a key concern since performance of permanent magnets decreases with
temperature. We investigated the magnetic and thermal transport properties of
rare-earth free nanostructured SrFe12O19 magnets produced by the current
activated pressure assisted densification. The synthesized magnets have aligned
grains such that their magnetic easy axis is perpendicular to their largest
surface area to maximize their magnetic performance. The SrFe12O19 magnets have
fine grain sizes in the cross-plane direction and substantially larger grain
sizes in the in-plane direction. It was found that this microstructure results
in approximately a factor of two higher thermal conductivity in the in-plane
direction, providing an opportunity for effective cooling. The phonons are the
dominant heat carriers in this type of permanent magnets near room temperature.
Temperature and direction dependent thermal conductivity measurements indicate
that both Umklapp and grain boundary scattering are important in the in-plane
direction, where the characteristic grain size is relatively large, while grain
boundary scattering dominates the cross-plane thermal transport. The
investigated nano/microstructural design strategy should translate well to
other material systems and thus have important implications for thermal
management of nanostructured permanent magnets.
