Magnetic and magneto-optical properties of (Nd,Pr)-(Fe,Co) alloy amorphous films with huge perpendicular magnetic anisotropy

An extensive study of the magnetic and magneto-optical properties for Nd
x
Fe
100-x
, Pr
x
Fe
100-x
and Nd
40
- Fe
51
Co
6
Ti
3
amorphous films synthesized by r.f. sputtering onto heated substrates has been carried out. Both Nd-Fe and Pr-Fe alloy films exhibit the maximum values of the perpendicular magnetic anisotropy constant K
u
at 300K at about 40 at% of Nd and Pr elements. The strong thickness dependence of K
u
was found in both Nd
40
Fe
51
- Co
6
Ti
3
and Pr
40
Fe
60
films fabricated at the substrate deposition temperature
T_{s}=210 \sim 250\deg
C. The Kerr rotation angle θ
K
increases with decreasing wavelength in the range from 350 to 800 nm in those alloy films with Nd and Pr. This trend is in contrast to that of films with heavy rare earths. Together with observation by high resolution electron microscopy, it is proposed that a short range atomic ordering in a microcrystalline amorphous structure plays an important role in the perpendicular magnetic anisotropy mechanism.