Temperature dependence of magnetisation of intermetallic compound GdFe11Ti in different structural states

Article abstract of DOI:10.1016/S0304-8853(02)01138-1

The temperature dependence of magnetisation σ(T) and the structure of GdFe₁₁Ti intermetallic compound in coarse-grained, microcrystalline, and nanocrystalline states are investigated experimentally. It is found that thermal stability of GdFe₁₁Ti compound depends on grain size. The phase composition of the coarse-grained sample remains unchanged upon heating to 1100K. Microcrystalline powder with a grain size of ～1 μm undergoes partial decomposition and transformation into iron phase during grinding and upon heating in the temperature range 800-1100 K. By contrast, heating of bulk nanocrystalline sample up to 1100 K partially restores phase composition. 2001 Elsevier Science. All rights reserved

Full text of DOI:10.1016/S0304-8853(02)01138-1

Journal of Magnetism and Magnetic Materials 258–259 (2003) 545–547
Temperature dependence of magnetisation of intermetallic
compound GdFe Ti in different structural states
1
1
a,
Galia F. Korznikova *, Tomash Czeppe , Alexander V. Korznikov
b
a
a
Institute of Metals Superplasticity Problems, Russian Academy of Sciences, 39 Khalturin st., Ufa 450001, Russia
Institute of Metallurgy and Materials Sciences, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow, Poland
b
Abstract
The temperature dependence of magnetisation sðTÞ and the structure of GdFe Ti intermetallic compound in coarse-
1
1
grained, microcrystalline, and nanocrystalline states are investigated experimentally. It is found that thermal stability of
GdFe11Ti compound depends on grain size. The phase composition of the coarse-grained sample remains unchanged
upon heating to 1100 K. Microcrystalline powder with a grain size of B1 mm undergoes partial decomposition and
transformation into iron phase during grinding and upon heating in the temperature range 800–1100 K. By contrast,
heating of bulk nanocrystalline sample up to 1100 K partially restores phase composition. r 2001 Elsevier Science. All
rights reserved
r 2002 Elsevier Science B.V. All rights reserved.
Keywords: Magnetization; Nanocrystalline structure; Intermetallic compounds
1
. Introduction
2. Results and discussion
The intermetallic compounds RFe11Ti (ThMn12-type
Coarse-grained samples, prepared by induction melt-
ing under argon atmosphere were initial ones. Micro-
crystalline powder sample was produced by mechanical
attrition of coarse-grained specimen in protecting
environment. Nanocrystalline bulk sample was pro-
duced, by severe plastic deformation on Bridgman anvils
under a pressure of 8 GPa from the initial coarse-grained
sample, at room temperature. Scanning electron micro-
scopy (SEM Philips XL30 with EDX system was used)
of coarse-grained sample revealed multiphase, non-
homogeneous structure with phase area sizes in the
range of 10–200 mm, while nanocrystalline samples have
homogeneous structure and contain only one phase.
Microcrystalline powder consists of particles with mean
diameter value about 1 mm. Phase composition analysis
of the samples provided by X-ray diffraction techniques
(X-ray diffractometer Philips PW17/10 was applied)
lattice) were found to be promising, hard magnetic
materials, due to high magnetic crystalline anisotropy
and adequate Curie point. It is a matter of general
experience that magnetic properties of ferromagnets are
sensitive to their structure so it is important to study the
influence of the structure on both the magnetic proper-
ties and the thermal stability, in order to take advantage
of this potential. Presently it is known that an increase in
lattice parameters as a result of nitrogenation and
hydrogenation causes a rise of both magnetisation and
Curie point in RFe11Ti compounds [1]. The decrease of
the grain size leads to the change of spin reorientation
temperature in DyFe11Ti compound [2]. In the present
work, we report our recent research on temperature
dependence of magnetisation and structure of GdFe11Ti
samples. The samples investigated revealed three differ-
ent microstructures: coarse-grained, microcrystalline,
and nanocrystalline.
2
revealed impurities of a-Fe and Fe Ti in the coarse-
grained state (Fig. 1a) and only main GdFe11Ti phase in
microcrystalline and nanocrystalline (Fig. 1b) states.
Significant broadening of lines on X-ray pattern of
nanocrystalline sample is caused obviously by a small
*Corresponding author. Fax: +7-34-72-25-37-59.
E-mail address: korznikova@anrb.ru (G.F. Korznikova).
0304-8853/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 8 8 5 3 ( 0 2 ) 0 1 1 3 8 - 1

546
G.F. Korznikova et al. / Journal of Magnetism and Magnetic Materials 258–259 (2003) 545–547
#[411 ][22 2]
25000
20000
15000
10000
αFe - *
Fe2Ti - +
Fe11GdTi - #
#[211 ]
#[721 ]
[
[
110] *
303] #
5000
#[310 ]
+
#[422 ],[521 ]
[622] #
+
*
[211]
+
+
+
+
*[200]
+
0
20
40
60
80
100
120
(a)
2Θ
*
[321] ,[202]
3
3
2
2
1
1
500
[
400 ]*
Fe11GdTi -*
*[330]
000
500
000
500
000
*
[301]
*[411],[222]
*[211]
[
710],[550]*
*[622]
[
422],[521]* [303 ]*
*[323]
*[404]
120
*[424]
500
20
40
60
80
100
(b)
2Θ
Fig. 1. X-ray diffraction profiles of coarse-grained (a) and nanocrystalline (b) samples of GdFe11Ti compound.
grain size. The small grain size was confirmed by
transmission electron microscopy (JEM 2000EX was
used) of nanocrystalline sample which revealed crystal-
lite size of about 50 nm.
nanocrystalline sample the curve corresponding to
cooling passes lower than the curve recorded during
heating, indicating some recovery and ordering of the
structure during heating, in the temperature range 1000–
1100 K (Fig. 2b). Microcrystalline powder sample ex-
hibits low thermal stability (Fig. 2c). Gradual increase of
magnetisation on heating above 800 K and high level of
magnetisation on cooling indicates on irreversible
decomposition of the initial compound and appearance
of pure iron.
Temperature dependence of magnetisation sðTÞ was
recorded by automated magnetic balance under the
ꢁ
2
vacuum of 1.3 ꢀ 10 Pa, for a field of 240 kA/m, in the
temperature range 293–1100 K. Two well-defined steps
on the curve sðTÞ for coarse-grained state, correspond-
ing to spin reorientation transition at 500 K and Curie
point at 600 K of GdFe11Ti compound, were observed
The reason for partial decomposition of microcrystal-
line sample is associated with an interaction of well-
developed powder surface with a residual gas. Similarly,
(Fig. 2a). On the similar curves sðTÞ for nanocrystalline
(Fig. 2b) and microcrystalline samples (Fig. 2c) the steps
are less pronounced and one more step appears near
050 K, which is close to the Curie point of pure iron,
2
detailed investigation of Er0.45Ho0.55Fe compound
1
powder during heating in the similar conditions revealed
increased reactivity of rare-earth metal ions and forma-
tion of oxides and nitrides in different valent states [3].
Under the same condition of measurements such a
decomposition was not observed neither in coarse-
grained nor in nanocrystalline samples of GdFe Ti.
which indicates partial decomposition of initial GdFe11-
Ti intermetallic compound. A comparison of sðTÞ
curves corresponding to heating and cooling of coarse-
grained sample reveals some retardation of magnetic
transitions. It should be noted that the decrease of the
applied field increases the retardation. In the case of
1
1
Thus, thermal stability of GdFe11Ti compound depends

G.F. Korznikova et al. / Journal of Magnetism and Magnetic Materials 258–259 (2003) 545–547
547
6
5
4
3
2
1
0
0
0
0
0
0
6
5
4
0
0
0
30
20
10
0
0
300
400
500
600
700
T,K
800
900
1000
1100
300
400
500
600
700
T,K
800
900
1000
1100
(a)
(b)
60
50
40
30
20
10
0
300
400
500
600
700
T,K
800
900
1000
1100
(c)
Fig. 2. The temperature dependence of magnetisation of GdFe11Ti compound in coarse-grained (a) nanocrystalline (b) and
submicrocrystalline (c) states.
on crystalline grain size and sample preparation
technique.
References
[
[
1] S.A. Nikitin, I.S. Tereshina, Yu. Scourski, V.N. Verbesky,
A.A. Salamova, Proceeding of the Moscow International
Symposium on Magnetism, part 1, 1999, p. 376.
Acknowledgements
2] G.F. Korznikova, Kh.Ya. Mulyukov, I.Z. Sharipov, S.A.
Nikitin, I.S. Tereshina, Phys. Solid State 44 (2002) 1646.
The work has been partially supported by RFBR
Grant No. 00-02-17723.
[3] Kh.Ya. Mulyukov, I.Z. Sharipov, G.F. Korznikova, Phys.
Solid State 44 (2002) 1060.