Structural and magnetic properties of „ Fe
1 x
Mn
x
…
3
P „ x < 0.25…
A. Broddefalk
Department of Materials Science, Uppsala University, Box 534 SE-715 21, Uppsala, Sweden
P. James
Department of Physics, Uppsala University, Box 530 SE-751 21, Uppsala, Sweden
Hui-Ping Liu
Department of Inorganic Chemistry, Uppsala University, Box 538 SE-751, Uppsala, Sweden
B. Kalska
Department of Physics, Uppsala University, Box 530 SE-751 21, Uppsala, Sweden
and The Soltan Institute for Nuclear Studies, 05-400 Otwock-Swierk, Poland
Y. Andersson
Department of Inorganic Chemistry, Uppsala University, Box 538 SE-751, Uppsala, Sweden
P. Granberg and P. Nordblad
Department of Materials Science, Uppsala University, Box 534 SE-715 21, Uppsala, Sweden
L. Ha
¨
ggstro
¨
m and O. Eriksson
Department of Physics, Uppsala University, Box 530 SE-751 21, Uppsala, Sweden
Received 10 June 1999
Structural and magnetic properties of (Fe
1-x
Mn
x
)
3
P compounds have been investigated by means of x-ray
and neutron diffraction experiments, magnetization measurements, Mo ¨ssbauer experiments, and first principles
calculations. The Curie temperature of the system decreases linearly and rapidly with increasing Mn content.
The zero temperature saturation magnetization, the local magnetic moments, as well as the hyperfine fields on
the different metal positions of the system all decrease with increasing Mn content. The theoretical calcula-
tions, on the other hand, predict an increasing magnetic moment on the metal positions with increasing Mn
content. This apparent discrepancy is discussed in the light of a good agreement between experimental and
theoretical results for the Co-substituted sister compounds (Fe
1-x
Co
x
)
3
P.
I. INTRODUCTION
The magnetic properties of Fe
3
P and substitutions of 3d
elements for the Fe atoms are of considerable interest.
1–7
Fe
3
P is a ferromagnetic compound with a Curie temperature
of 692 K Ref. 5 and a saturation magnetization of
1.70
B
/Fe atom at room temperature
1,4
and 1.89
B
/Fe
atom at 10 K.
5
The crystal structure is tetragonal space
group I 4
¯
) with three different Fe sites denoted I, II, and
III. The combination of a tetragonal structure and the intro-
duction of P produces a large magnetocrystalline
anisotropy.
6,7
The three different Fe sites have different mag-
netic moments. At room temperature, neutron diffraction ex-
periments revealed moments of 2.12, 1.25, and 1.83
B
/atom, for site I, II, and III, respectively.
6
Interestingly,
one can substitute for the Fe atoms, 3 d elements with addi-
tional or less valence electrons, i.e., Cr, Mn, Co, and Ni, up
to a certain limit, without changing the crystal structure.
4
This enables studies of the magnetic properties of one class
of isostructural materials with the controlling parameter be-
ing the filling of electrons in the valence band. Recently, a
detailed experimental and theoretical study of the
(Fe
1 -x
Co
x
)
3
P compounds
5
has been published, where it was
found that the introduction of Co decreases the magnetic
moment in the entire range of solid solution (0 x 0.37).
The Co atoms were found to preferentially substitute Fe on
atomic sites III and II.
The magnetic properties of (Fe
1 -x
Co
x
)
3
P are well under-
stood from a delocalized electron picture, with the 3 d elec-
trons occupying band states, and it can be understood that the
decreasing magnetic moment of the alloy as a function of Co
concentration is due to a so called strong ferromagnetic or-
dering. This means that the exchange splitting of the material
is large so that additional valence electrons enter states of
only one of the spin channels. In (Fe
1 -x
Co
x
)
3
P there are
about 6.5–7.5 3 d electrons per metal atom depending on Co
concentration and consequently additional valence electrons
provided by alloying of Co enter the spin down band causing
a reduction of magnetic moment, which is consistent with
observations. With this in mind one can speculate that re-
placing Fe for Mn which has one less valence electron com-
pared to Fe should increase the magnetic moment of the
alloy due to the same band arguments. A decrease, on the
other hand, would possibly reflect a different magnetic cou-
pling between Mn and neighboring metal atoms Fe or Mn
than ferromagnetic or alternatively a reduction of the ex-
change splitting.
PHYSICAL REVIEW B 1 JANUARY 2000-I VOLUME 61, NUMBER 1
PRB 61 0163-1829/2000/611/4139/$15.00 413 ©2000 The American Physical Society