Effects of Different Crystal Structures of Ta Underlayer on Magnetic Properties and Microstructures of Pr-Fe-B Thin Films

Pr-Fe-B/Ta bilayer films were sputtered on glass substrates in a high vacuum magnetron sputtering system. Before sputtering the magnetic Pr-Fe-B thin films, Ta underlayers with two different crystal structures, hexagonal close-packed HCP(0002) and body-centered cubic BCC(110), were prepared at substrate temperatures of 300 and 600 °C, respectively. With the Ta HCP(0002) underlayer, the Pr-Fe-B film showed significant in-plane oriented Pr
₂
Fe
₁₄
B phase and a small amount of perpendicular magnetic anisotropy (PMA) phases. The magnetic properties hence exhibited high nucleation field H
_n
, coercive field H
_c
, and large area in-plane hysteresis loop. Further replacing the Ta HCP(0002) underlayer with a Ta BCC(110) underlayer promoted the growth of columnar Pr-Fe-B grains. The typical hard Pr
₂
Fe
₁₄
B phase with PMA was obtained. Low H
_n
, H
_c
, and small area in-plane hysteresis loop were consequently obtained. The PMA of the Pr-Fe-B/Ta bilayer film was also improved. The mechanisms to enhance the PMA of Pr-Fe-B/Ta bilayer films could be attributed to a lattice mismatch between the magnetic Pr-Fe-B layer and the Ta underlayers, where the smaller lattice mismatch at Pr
₂
Fe
₁₄
B (00l)/Ta(110) interface promoted the (00l)-oriented Pr
₂
Fe
₁₄
B planes to epitaxially grow on the Ta BCC(110) underlayer. Replacing the Ta BCC(110) underlayer with a Ta HCP(0002) underlayer just reduced the epitaxial effects and increased the pinning sites in the Pr-Fe-B magnetic films.