  Further property enhancement of alnico, an attractive near-term,
non-rare-earth permanent magnet alloy system, primarily composed of Al, Ni, Co,
and Fe, relies on improved morphology control and size refinement of its
complex spinodally decomposed nanostructure that forms during heat-treatment.
Using a combination of transmission electron microscopy and atom probe
tomography techniques, this study evaluates the magnetic properties and
microstructures of an isotropic 32.4Fe-38.1Co-12.9Ni-7.3Al-6.4Ti-3.0Cu
(wt.$\%$) alloy in terms of processing parameters such as annealing
temperature, annealing time, application of an external magnetic field, as well
as low-temperature "draw" annealing. Optimal spinodal morphology and spacing is
formed within a narrow temperature and time range ($\sim 840 \unicode{x2103}$
and 10 min during thermal-magnetic annealing (MA). The ideal morphology is a
mosaic structure consisting of periodically arrayed $\sim 40$ nm diameter
(Fe-Co)-rich rods ($\alpha_1$ phase) embedded in an (Al-Ni)-rich ($\alpha_2$
phase) matrix. A Cu-enriched phase with a size of $\sim$ 3-5 nm is located at
the corners of two adjacent $\{110\}$ facets of the $\alpha_1$ phase. The MA
process significantly increased remanence ($B_\text{r}$) ($\sim$ 40-70 $\%$) of
the alloy due to biased elongation of the $\alpha_1$ phase along the
$\langle100\rangle$ crystallographic direction, which is closest in orientation
to the applied magnetic field. The optimum magnetic properties of the alloy
with an intrinsic coercivity ($H_\text{cj}$) of 1845 Oe and a maximum energy
product ($BH_\text{max}$) of 5.9 MGOe were attributed to the uniformity of the
mosaic structure.
