Influence of composition on the structure, electric and magnetic properties of Pd-Mn-P and Pd-Co-P amorphous alloys
<p> The influence of composition on the structure and on the electric and magnetic properties of amorphous Pd-Mn-P and Pd-Co-P prepared by rapid quenching techniques were investigated in terms of (1) the 3d band filling of the first transition metal group, (2) the phosphorus concentration...
| Summary: | <p> The influence of composition on the structure and on the electric
and magnetic properties of amorphous Pd-Mn-P and Pd-Co-P prepared
by rapid quenching techniques were investigated in terms of (1) the 3d
band filling of the first transition metal group, (2) the phosphorus
concentration effect which acts as an electron donor and (3) the transition metal concentration. </p>
<p> The structure is essentially characterized by a set of polyhedra
subunits essentially inverse to the packing of hard spheres in
real space. Examination of computer generated distribution functions
using Monte Carlo random statistical distribution of these polyhedra
entities demonstrated tile reproducibility of the experimentally calculated atomic distribution function. As a result, several possible
"structural parameters" are proposed such as: the number of nearest
neighbors, the metal-to-metal distance, the degree of short-range order
and the affinity between metal-metal and metal-metalloid. It is shown
that the degree of disorder increases from Ni to Mn. Similar behavior
is observed with increase in the phosphorus concentration.</p>
<p> The magnetic properties of Pd-Co-P alloys show that they are
ferromagnetic with a Curie temperature between 272 and 399°K as the
cobalt concentration increases from 15 to 50 at.%. Below 20 at.% Co the
short-range exchange interactions which produce the ferromagnetism are
unable to establish a long-range magnetic order and a peak in the
magnetization shows up at the lowest temperature range . The electric
resistivity measurements were performed from liquid helium temperatures
up to the vicinity of the melting point (900°K). The thermomagnetic
analysis was carried out under an applied field of 6.0 kOe. The
electrical resistivity of Pd-Co-P shows the coexistence of a Kondo-like
minimum with ferromagnetism. The minimum becomes less important
as the transition metal concentration increases and the coefficients
of ℓn T and T^2 become smaller and strongly temperature dependent.
The negative magnetoresistivity is a strong indication of the existence
of localized moment.</p>
<p> The temperature coefficient of resistivity which is positive
for Pd- Fe-P, Pd-Ni-P, and Pd-Co-P becomes negative for Pd-Mn-P. It is
possible to account for the negative temperature dependence by the
localized spin fluctuation model and the high density of states at the
Fermi energy which becomes maximum between Mn and Cr. The magnetization
curves for Pd-Mn-P are typical of those resulting from the interplay of different exchange forces. The established relationship between susceptibility and resistivity confirms the localized spin fluctuation model. The magnetoresistivity of Pd-Mn-P could be interpreted
in tenns of a short-range magnetic ordering that could arise
from the Rudennan-Kittel type interactions.</p>
|
|---|