Effect of Preparation Condition on Magnetic Properties of ${\rm Nd-Fe-B}/\alpha-{\rm Fe}$ Multi-Layered Thick Film-Magnets Prepared by PLD Method

${\rm Nd-Fe-B}/\alpha-{\rm Fe}$
multi-layered thick film-magnets were synthesized by pulse laser deposition (PLD) method from a
${\rm Nd}_{2.4}{\rm Fe}_{14}{\rm B}/\alpha$
-Fe composite target. In order to improve magnetic properties and their reproducibility, effects of the stacking period of
${\rm Nd-Fe-B}/\alpha-{\rm Fe}$
layers,
$t_{\rm p}$
, the target-substrate distance,
$D_{\rm TS}$
, and the laser beam energy on a target,
$E_{\rm L}$
, on them were studied. The reproducibility of magnetic properties was improved significantly by decreasing
$E_{\rm L}$
. In particular, the standard deviation of the Nd content was suppressed within 3%, when
$E_{\rm L}$
was reduced from a value higher than 200
${\rm mJ/mm}^{2}$
to 25
${\rm mJ/mm}^{2}$
. An increase in
$D_{\rm TS}$
and selection of a suitable
$t_{\rm p}$
value improved the maximum energy product
$(BH)_{\max}$
. The largest
$(BH)_{\rm max}$
value obtained in this investigation was 112
${\rm kJ/m}^{3}$
, which is higher than the values reported previously for isotropic film-magnets thicker than 10
$\mu{\rm m}$
. Origins of superior magnetic properties were discussed from the viewpoints of suitable interlayer exchange interaction between Nd-Fe-B and
$\alpha$
-Fe layers and morphology of prepared film-magnets.