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David Sellmyer Publications Research Papers in Physics and Astronomy
May 2000
Magnetic and structural properties of SmCoMagnetic and structural properties of SmCo
7-x7-x
CuCu
xx
alloys alloys
I.A. Al-Omari
University of Nebraska - Lincoln
Y. Yeshurun
Institute of Superconductivity and Department of Physics, Bar-Ilan University, Ramat Gan 52900, Israel
Jian Zhou
University of Nebraska - Lincoln
David J. Sellmyer
University of Nebraska-Lincoln
, dsellmyer@unl.edu
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Al-Omari, I.A.; Yeshurun, Y.; Zhou, Jian; and Sellmyer, David J., "Magnetic and structural properties of
SmCo
7-x
Cu
x
alloys" (2000).
David Sellmyer Publications
. 60.
https://digitalcommons.unl.edu/physicssellmyer/60
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Magnetic and structural properties of SmCo
7À
x
Cu
x
alloys
I. A. Al-Omari
a)
Behlen Laboratory of Physics and Center for Materials Research and Analysis, University of Nebraska,
Lincoln, Nebraska 68588-0111
Y. Yeshurun
Institute of Superconductivity and Department of Physics, Bar-Ilan University, Ramat Gan 52900, Israel
J. Zhou and D. J. Sellmyer
Behlen Laboratory of Physics and Center for Materials Research and Analysis, University of Nebraska,
Lincoln, Nebraska 68588-0111
We report the structural and magnetic properties of SmCo
7⫺ x
Cu
x
, where x⫽ 0, 0.1, 0.2, 0.3, 0.4,
0.5, and 0.7. X-ray diffraction shows that these alloys from the disordered hexagonal TbCu
7
-type
structure. For large values of x(x⭓0.8) the hexagonal TbCu
7
-type structure cannot be formed.
X-ray diffraction on magnetically aligned samples show that these samples have uniaxial
anisotropy. The lattice parameters 共a and c兲 are dependent on the Cu concentration, and the unit cell
volume is found to increase with x. The saturation magnetization decreases with x at both room
temperature and 25 K. The Curie temperature increases with x for small values of x while it
decreases with x for large values of x. A maximum value of T
C
⫽ 852 °C is found in these alloys.
© 2000 American Institute of Physics. 关S0021-8979共00兲95108-9兴
I. INTRODUCTION
In the last 30 years, there has been an intensive search
for new iron-rich or cobalt-rich rare-earth intermetallic com-
pounds for magnetic applications including materials for
room temperature permanent magnets, high temperature per-
manent magnets, magnetic recording, etc. The compounds
(R
x
Fe
y
Co
z
) include materials with atomic ratios of rare-earth
to iron and cobalt 1:5, 1:7, 1:12, and 2:17 with different
types of structure. Most of the R–Fe compounds have low
Curie temperature (T
C
), relatively low saturation magnetiza-
tion (M
s
), small magnetic anisotropy, in-plane anisotropy,
and are unstable at high temperature which lowers their po-
tential as materials for high temperature applications.
1–7
The
disordered TbCu
7
-type or so-called 1:7 structure shows in-
teresting magnetic properties when Co or other elements are
substituted for Fe.
The metastable TbCu
7
-type structure of Sm共Fe, Ti兲
7
or
Sm共Fe, V兲
7
can be formed under certain preparation condi-
tions. Saito et al.
8
studied SmFe
11
Ti alloy ribbons and found
that the structure changes from a tetragonal ThMn
12
-type
structure to a hexagonal TbCu
7
-type structure by changing
the roller velocity. They also found that ribbons with a
ThMn
12
-type structure give the maximum hard magnetic
properties. Xiao et al.
9
studied the Sm–Fe–Ti system and
found that this system crystallizes in the metastable
TbCu
7
-type structure with an easy in-plane magnetization
and has a T
C
of 243 °C. The metastable TbCu
7
-type structure
transforms to a ThMn
12
structure 共with T
C
⫽ 305 °C and easy
in-plane magnetization兲 at an annealing temperature higher
than 740 °C. Katter et al.
10
studied Sm–Fe–N and found that
Sm
10.6
Fe
89.4
N
y
forms the TbCu
7
-type structure with a coer-
civity of 6.0 kOe, a remanence of 684 emu/cm
3
, and an en-
ergy product (BH)
max
of 8.74 MGOe, while Sm
12
Fe
88
crys-
tallizes in the rhombohedral Th
2
Zn
17
structure. This study
also showed that T
C
and M
s
change from 200 °C and 987
emu/cm
3
for Sm
10.6
Fe
89.4
to 470 °C and 1114 emu/cm
3
for
Sm
10.6
Fe
89.4
N
y
. A study of R–Cu compounds by Buschow
and Van Der Gast
11
showed that for R⫽Gd, Tb, Dy, and Y a
compound of the approximate composition RCu
7
can be
formed with the TbCu
7
structure and these compounds de-
compose with annealing at low temperatures into RCu
5
and
elementary Cu. They also found that c/a is about 0.84 for
RCu
7
compounds while it is about 0.80 for RCu
5
com-
pounds. Huang et al.
12
found c/a ratios of 0.82–0.83 for
Sm共Co, Zr兲
7
alloys and we also found the same ratios in our
Sm共Co, Ti兲
7
alloys.
13
Suzuki et al.
14
studied Sm
10
共Fe, V兲
90
N
y
and found that the substitution of vanadium for iron in
Sm
10
共Fe, V兲
90
alloys gives a great range of stability in the
TbCu
7
-type structure, where this structure can be formed for
5⬍ V⬍ 10. They also found that nitrogenation of the samples
improves the magnetic properties including a (BH)
max
value
of 8.0 MGOe and a T
C
value of 477 °C for
Sm
10
Fe
82.5
V
7.5
N
y
. Chen et al.
15
studied SmCo
x
alloys by
melt spinning and found that the alloys exhibit a single phase
SmCo
5
and Sm
2
Co
17
structure for x⫽ 5.0 and x⫽ 8.8,
respectively, while a three-phase structure
(Sm
2
Co
17
, SmCo
5
, SmCo
3
) appears for 5.0⬍ x⬍ 8.5. Re-
cently, studies by Lefever et al.
16,17
and by Huang et al.
12
showed that a small amount of Zr substitution could contrib-
ute to the stabilization of the hexagonal TbCu
7
structure and
improve the magnetic anisotropy in Sm–Co–Zr compounds.
An anisotropy field (H
A
) value of 180 kOe and a T
C
value of
750 °C for SmCo
6.5
Zr
0.5
have been reported by Huang
et al.
12
The TbCu
7
-type structure could be indexed according
to the CaCu
5
-type structure with significant deviation of the
lattice constants and x-ray peaks’ intensities.
a兲
Permanent address: Dept. of Applied Physical Sciences, Jordan University
of Science and Technology, PO Box 3030, Irbid, Jordan; electronic mail:
ialomari@hotmail.com
JOURNAL OF APPLIED PHYSICS VOLUME 87, NUMBER 9 1 MAY 2000
67100021-8979/2000/87(9)/6710/3/$17.00 © 2000 American Institute of Physics
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The aim of this article is to study the effect of Cu sub-
stitution for Co on the magnetic and structure properties of
SmCo
7⫺ x
Cu
x
alloys.
II. EXPERIMENTAL PROCEDURE
Bulk samples of SmCo
(7⫾
␦
)⫺ x
Cu
x
, where
␦
is between
0 and 2 and x⫽0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7, were pre-
pared by arc melting the elements of at least 99.9% purity in
a water-cooled copper boat in a flowing-argon gas atmo-
sphere. The alloys were melted four to five times to insure
homogeneity. The phase purity for all the samples was de-
termined by x-ray diffraction using Cu K
␣
radiation. The
magnetization of the alloys was measured by a supercon-
ducting quantum interference device 共SQUID兲 magnetometer
in the temperature range 25–300 K and in fields from 0 to 50
kOe. High temperature magnetic measurements were done
by a vibrating sample magnetometer 共VSM兲 in the tempera-
ture range 300–1273 K.
III. RESULTS AND DISCUSSION
Figure 1 shows a typical x-ray diffraction pattern for a
SmCo
6.7
Cu
0.3
alloy. From Fig. 1 we see that the sample crys-
tallizes in the hexagonal TbCu
7
-type structure. Samples with
different Sm to 共Co, Cu兲 atomic ratios showed different
structures. For example, if the Sm-to-共Co, Cu兲 atomic ratios
are more than 共1/7兲 a hexagonal CaCu
5
-type structure formed
and if the atomic ratio is less than 共1/7兲 a hexagonal
Th
2
Ni
17
-type structure formed. This is in agreement with
other observations by Khan
18,19
for RCo
5⫾x
. In this article
we are interested in alloys with the TbCu
7
-type structure;
therefore, we present the results for the samples with 1:7
composition. All the samples with the 1:7 composition
showed the TbCu
7
-type structure except for x⫽0 where a
minor 2:17-type structure appears. X-ray diffraction shows
that there is a shift in the peaks with increasing Cu concen-
tration, which is due to the difference in the atomic volume.
Table I summarizes the lattice parameters a and c obtained
from the x-ray diffraction patterns for different concentra-
tions. It can be seen that there is a small increase in a and c.
The c/a ratio for these compounds is about 0.81–0.82 which
is in agreement with other values of 0.82–0.83 by Huang
et al.
12
for Sm共Co, Zr兲
7
alloys and our same values for
Sm共Co, Ti兲
7
alloys.
13
The unit cell volume V obtained from
the lattice parameters a and c are listed in Table I. It can be
seen from the table that there is a volume expansion by sub-
stituting Cu for Co; this expansion is due to the larger atomic
volume of Cu, which is in agreement with our observations
for other alloys.
20
Samples for magnetic anisotropy studies
were prepared by mixing a fine powder of diameter ⬍38
m
with 5-min epoxy on a glass sample holder and then aligning
in a magnetic field of 20 kOe for about 1 h. The inset of Fig.
1 shows a typical x-ray diffraction pattern for the
SmCo
6.7
Cu
0.3
alloy. From this figure we see that the sample,
after alignment, shows the 共002兲 peak only indicating a
uniaxial magnetocrystalline anisotropy. X-ray diffraction
measurements on other aligned samples showed the same
results. Magnetic measurements on aligned samples showed
that the magnetization in the direction parallel to the aligning
field is much higher than that along the direction perpendicu-
lar to the aligning field. Figure 2 shows a typical initial mag-
netization curve for SmCo
6.6
Cu
0.4
measured at a temperature
of 25 K using the SQUID magnetometer. This figure indi-
cates that the sample is magnetically ordered. Magnetic mea-
surements for other samples showed that all the samples
studied are magnetically ordered and the magnetization de-
pends on the Cu concentration. We find the saturation mag-
netization by using the law of approach to saturation, by
plotting M versus 1/H and extrapolating M to (1/H)⫽ 0. The
saturation magnetization values for the samples measured at
300 and 25 K are listed in Table I. It is clear from the table
that the saturation magnetization decreases with increasing
Cu concentration, 共x兲, which is due to the replacement of
magnetic element 共Co兲 by a nonmagnetic element 共Cu兲. The
deviation of the dependence of M
s
on x from linear depen-
dence can be due to experimental error and/or the estimation
of M
s
by extrapolation. The magnetization as a function of
temperature is measured with a VSM under an applied field
of 3 kOe for all the samples. Table I also gives the depen-
dence of T
C
on Cu concentration. The Curie temperature
increases with x reaching a maximum at x⫽ 0.2 (T
C
FIG. 1. Typical x-ray diffraction pattern for a SmCo
6.7
Cu
0.3
alloy. The inset
shows a typical x-ray diffraction pattern for the same sample after it has
been magnetically aligned.
TABLE I. Lattice parameters (a) and (c), unit cell volume (V), saturation
magnetization (M
s
)atT⫽ 300 and 25 K, and Curie temperature (T
c
)of
SmCo
7⫺ x
Cu
x
alloys as a function of copper concentration (x).
Xa共Å兲 C 共Å兲 V 共Å
3
兲
M
s
共emu/g兲
T⫽300 K
M
s
共emu/g兲
T⫽25 K T
c
共°C兲
0.0 4.935 4.010 84.576 102 103 770
0.1 4.967 4.003 85.538 85 86 850
0.2 4.968 4.060 85.606 84 84 852
0.3 4.974 4.060 85.817 82 83 828
0.4 4.975 4.009 85.939 71 72 769
0.5 4.978 4.010 86.045 61 63 758
0.7 4.981 4.011 86.159 57 58 760
6711J. Appl. Phys., Vol. 87, No. 9, 1 May 2000 Al-Omari
et al.
Downloaded 17 Nov 2006 to 129.93.16.206. Redistribution subject to AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp
⫽852 °C) then decreases with x as can be seen from the
table. The maxima in T
C
and c/a occur at the composition
x⫽ 0.2. The nonmonotonic dependence of T
C
and c/a on x
remains to be understood. This maximum value for T
C
is
higher than that of the SmCo
5
compound (T
C
⫽ 750°C).
IV. CONCLUSIONS
Samples of the form of SmCo
7⫺ x
Cu
x
共x⫽ 0, 0.1, 0.2,
0.3, 0.4, 0.5, and 0.7兲 have been prepared and studied. X-ray
diffraction shows that these alloys form the hexagonal
TbCu
7
-type structure. We find that the hexagonal
TbCu
7
-type structure cannot be formed at large values of
x(x⭓0.8). X-ray diffraction on magnetically aligned
samples show that these samples have uniaxial anisotropy.
The lattice parameters 共a and c兲 are dependent on the Cu
concentration. The unit cell volume is found to increase with
x. We find that the saturation magnetization decreases with x
at room temperature and at a temperature of 25 K. We find
that Curie temperature increases with x reaching a peak at
x⫽ 0.2 (T
C
⫽ 852 °C) then decreases with x. These properties
are promising for high temperature permanent-magnet appli-
cations.
ACKNOWLEDGMENTS
The authors would like to thank Jordan University of
Science and Technology, the US Department of Energy,
DARPA, US Air Force Office of Scientific Research, and the
Israeli Ministry of Infrastructure for financial support.
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FIG. 2. Typical initial magnetization curve for a SmCo
6.6
Cu
0.4
alloy mea-
sured at a temperature of 25 K.
6712 J. Appl. Phys., Vol. 87, No. 9, 1 May 2000 Al-Omari
et al.
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