Magnetic properties of amorphous (fe, ni)80B20, (fe, ni)80B19si1, and (fe, ni)80P14B6alloys

Magnetic measurements were performed on amorphous (Fe, Ni)
80
B
20
, (Fe, Ni)
80
B
19
Si
1
, and (Fe, Ni)
80
P
14
B
6
alloy ribbons to yield the values of the magnetic moment per transition metal atom at 0 K and the Curie temperature. A close fit to the moment data, obtained by allowing not only the moments on Ni and Fe atoms to vary with Fe concentration
x
, as revealed by neutron diffraction in crystalline alloys, but also the number of electrons per atom n
p
and n
b
that P and B atoms, respectively, donate to the transition metal
d
bands as described by the relations
n_{p} = 1.74 + 0.75 (1 - x)
and
n_{b} = 0.58 + 1.20 (1 - x)
, suggests a moment of 0 and
\sim0.13 \mu_{B}
per Ni atom in amorphous Ni
80
P
14
B
6
and Ni
80
B
20
alloys, respectively. The functional dependence of the Curie temperature on
x
, when followed closely for low Fe concentrations, gives the critical concentration x
c
above which ferromagnetism appears in amorphous Fe
x
Ni
80-x
B
20
and Fe
x
Ni
80-x
P
14
B
6
alloy series as
x_{c} \cong 5
and 8 at % Fe, respectively. The results of a theory based on coherent-potential approximation have been fitted to the measured values of Curie temperature in order to arrive at the Fe concentration dependence of the exchange interaction (J
NiNi
) between Ni-Ni pairs. The physical significance of the variation of J
NiNi
with
x
obtained thereby has been discussed.