Chemistry Reference
In-Depth Information
57
Fe Mössbauer spectra at 4.2 K for Fe (4.0 nm)/RE (3.0 nm) multilayers [
8
]
Fig. 5.3
temperatures. Thus, Fe/Mg multilayers are unique samples to investigate the
properties of ''pure'' amorphous Fe metal, although the thickness is limited to be
less than about 1 nm.
5.3.2 Fe/RE (Rare-Earth) Multilayers
Rare-earth (RE) metals have interesting magnetic properties, such as helical
magnetic spin structures and large magnetic anisotropies. However, the Curie
temperatures of RE metals are lower than room temperature and therefore only
intermetallic compounds and amorphous alloys between RE and 3d metals have
potentials for applications. Preparation of multilayers by combining 3d and RE
metals seems to be very interesting as a novel method to hybridize them. If 3d
metal layers (i.e. Fe or Co) and RE metal layers are alternately deposited and the
layer thicknesses are not too thin, high Curie temperatures of 3d metals and large
anisotropy of RE metals may coexist in the multilayers and novel magnetic fea-
tures may be resulted. In Fig.
5.3
, the Mössbauer absorption spectra of Fe
(4.0 nm)/RE (3.0 nm) multilayers measured at 4.2 K are shown [
8
]. All the spectra
have very sharp six lines and hyperfine field is the same as the bulk Fe value. This
result means that the Fe layers with the thickness of 4.0 nm in the Fe/RE multi-
layers have the bulk ferromagnetic properties. In most cases, the intensity ratio of
the six lines is 3:4:1:1:4:3, indicating that the magnetization is preferentially
oriented in the film plane. In Fe/Pr, Fe/Nd and Fe/Tb multilayers, however, the
relative intensities of No. 2 and 5 lines are remarkably smaller, indicating the easy
direction of magnetization is oriented toward film perpendicular. The spin direc-
tion of Fe layers is thus determined by the species of RE element. It is suggested
