High-pressure synthesis of giant magnetostrictive PrxTb 1-xFe1.9alloys

Article abstract of DOI:10.1063/1.2387865

Prx Tb1-x Fe1.9 (0≤x≤1) magnetostrictive alloys with cubic Laves phase have been synthesized by a high-pressure synthesis method. Crystal structure, magnetic properties, magnetocrystalline anisotropy, and the magnetostriction of Prx Tb1-x Fe1.9 (0≤x≤1) alloys are investigated. Composition anisotropy compensation is realized in Pr0.9 Tb0.1 Fe1.9 alloy, which shows low magnetocrystalline anisotropy and a large magnetostriction value (λ∥ - λ⊥ =1497 ppm) at 13 kOe at room temperature. These characters suggest that Pr0.9 Tb0.1 Fe1.9 alloy may be a promising candidate for magnetostriction application.

Full text of DOI:10.1063/1.2387865

High-pressure synthesis of giant magnetostrictive Pr x Tb 1 − x Fe 1.9 alloys
Y. G. Shi, S. L. Tang, R. L. Wang, H. L. Su, Z. D. Han, L. Y. Lv, and Y. W. Du
Citation: Applied Physics Letters 89, 202503 (2006); doi: 10.1063/1.2387865
View online: http://dx.doi.org/10.1063/1.2387865
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/89/20?ver=pdfcov
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APPLIED PHYSICS LETTERS 89, 202503 ͑2006͒
High-pressure synthesis of giant magnetostrictive PrxTb1−xFe1.9 alloys
Y. G. Shi, S. L. Tang,a͒ R. L. Wang, H. L. Su, Z. D. Han, L. Y. Lv, and Y. W. Du
National Laboratory of Solid State Microstructures, Nanjing university, Nanjing 210093, China and
Department of Physics, Nanjing University, Nanjing 210093, China
͑Received 19 May 2006; accepted 26 September 2006; published online 13 November 2006͒
PrxTb1−xFe1.9 ͑0ഛxഛ1͒ magnetostrictive alloys with cubic Laves phase have been synthesized by
a high-pressure synthesis method. Crystal structure, magnetic properties, magnetocrystalline
anisotropy, and the magnetostriction of PrxTb1−xFe1.9 ͑0ഛxഛ1͒ alloys are investigated.
Composition anisotropy compensation is realized in Pr0.9Tb0.1Fe1.9 alloy, which shows low
magnetocrystalline anisotropy and a large magnetostriction value ͑␭ʈ −␭Ќ=1497 ppm͒ at 13 kOe at
room temperature. These characters suggest that Pr0.9Tb0.1Fe1.9 alloy may be a promising candidate
for magnetostriction application. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2387865͔
REFe2 ͑RE=rare earths͒ giant magnetostrictive com-
pounds, such as Terfenol-D ͑Tb0.27Dy0.73Fe2͒, have been
widely applied in acoustic transducers, sensors, actuators,
etc.1,2 According to the single-ion model,3 PrFe2 should gen-
erate a larger magnetostriction than TbFe2 and DyFe2 at 0 K
and it has the opposite anisotropy sign to TbFe2, so the
pseudobinary compounds PrxTb1−xFe2 should be an accept-
able compensating system. Owing to the small magnetocrys-
talline anisotropy of PrFe2,3 the anisotropy compensation in
PrxTb1−xFe2 system requires a high Pr concentration. In most
previous work, an unanticipated noncubic structure appeared
when the composition of Pr was beyond 20% ͑Ref. 3͒ or
25% ͑Ref. 4͒ and, therefore, the anisotropy compensating
could not be reached in the PrxTb1−xFe2 system under ambi-
ent condition. In the past several years, much attention has
been paid to enhance the cheaper rare earth Pr content in
magnetostrictive materials.5–8 As an example, progress was
made when boron atoms were introduced in the ͑Pr, RE͒ Fe2
system; however, the Pr content should not exceed 30 at.%
in order to obtain single Laves phase.8 So far, a good method
to prepare high Pr content of magnetostrictive materials is
still desired. In this letter, PrxTb1−xFe1.9 ͑0ഛxഛ1͒ polycrys-
talline alloys with cubic Laves phase are synthesized by a
high-pressure synthesis method and the anisotropy composi-
tion compensation is realized at x=0.9.
fields up to 65 kOe. The linear magnetostriction was mea-
sured using standard strain-gauge technique in directions
parallel ͑␭ ͒ or perpendicular ͑␭ ͒ to applied magnetic fields
ʈ
Ќ
up to 13 kOe at room temperature.
Figure 1 shows XRD patterns for PrxTb1−xFe1.9 with dif-
ferent Pr concentrations. It is found that all the polycrystal-
line alloys consist predominantly of cubic Laves phase with
MgCu2-type structure, coexisting with a minor of impurity
phases, i.e., hcp-͑Pr, Tb͒. For the RE–Fe2, the ideal radius
ratio of RE and Fe for the formation of a Laves phase is
1.225.9 It is known that Pr is the largest atom among all the
lanthanide elements except Ce. The large size of the Pr atom
precludes the ambient pressure synthesis of the PrxTb1−xFe1.9
alloys when the Pr concentration exceeds about 0.2.
The dependence of the lattice parameter ͑a͒ on the Pr
concentration obtained from the XRD data is shown in Fig.
2͑a͒. An approximate linear increase with stoichiometric Pr
concentration from 0.0 to 1.0 is found, as expected from
Vegard’s law:
a = xa1 + ͑1 − x͒a2,
where a1 and a2 are the lattice parameters of PrFe1.9 and
TbFe1.9, respectively. The lattice parameter increases slowly
with increasing Pr concentration in PrxTb1−xFe1.9 system due
to the fact that Pr has a larger ionic radius than Tb.
Ingots with PrxTb1−xFe1.9 ͑0ഛxഛ1͒ stoichiometric com-
position were prepared by melting the constituent metals in a
magnetocontrolled arc furnace in a high-purity argon atmo-
sphere. The purities of the constituents are 99.9% for Tb and
Pr and 99.8% for Fe. The as-cast ingots ͑about 10 mm in
diameter and 2 mm in thickness͒ were wrapped in tantalum
foils and pressed into a graphite pipe heater with the shape of
cylinder. The heater was then pressed to 6 GPa by a Hall-
type hexahedral anvil press and heated to 1173 K for 30 min.
Then the samples were annealed between 623 and 723 K for
120 h in vacuum quartz capsules. Conventional x-ray dif-
fraction ͑XRD͒ analysis was carried out using Cu K␣ radia-
tion with a Rigaku D/Max-gA diffractometer. The Curie tem-
peratures were measured by
a
quantum design
superconducting quantum interference device ͑SQUID͒ mag-
netometer at fields of 1 kOe. Magnetization curves at room
temperature were measured by a SQUID magnetometer at
a͒
Electronic mail: tangsl@nju.edu.cn
FIG. 1. XRD patterns of the PrxTb1−xFe1.9 alloys with different x.
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0003-6951/2006/89͑20͒/202503/3/$23.00 89, 202503-1 © 2006 American Institute of Physics
202.28.191.34 On: Sat, 20 Dec 2014 10:59:39

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Shi et al.
Appl. Phys. Lett. 89, 202503 ͑2006͒
FIG. 2. Lattice parameter a ͑a͒, the Curie temperature TC ͑K͒ ͑b͒, and the
saturation magnetization Ms ͑c͒ as a function of Pr concentration.
FIG. 4. Magnetization of PrxTb1−xFe1.9 alloys at 300 K up to a field of
65 kOe.
The thermomagnetic curves of the sample with x=0.9
are shown in Fig. 3. With temperature increasing the magne-
tization decreases sharply and to zero near 551 K where Tc is
the Curie temperature of the Pr0.9Tb0.1Fe1.9 phase, and then
the magnetization increases slowly from 650 K due to oxi-
dation of the alloy and the formation of a little amount of
␣-Fe with temperature increasing. As the temperature turns
back from 770 K, the magnetization goes up sharply from
550 K and coincides with heating process magnetization
curves, which indicates that the Pr0.9Tb0.1Fe1.9 phase does not
decompose below 770 K. Compared with the decomposed
temperature ͑681 K͒ of the PrFe1.9 phase in our experiment,
the Pr0.9Tb0.1Fe1.9 phase is more stable with increasing Tb
content. The decomposed temperatures of the PrxTb1−xFe1.9
with xഛ0.9 are all higher than 770 K. Figure 2͑b͒ shows the
variation of Curie temperature with the Pr concentration for
PrxTb1−xFe1.9 compounds. It is found that the Curie tempera-
ture decreases almost linearly with increasing Pr content.
The magnetization curves for PrxTb1−xFe1.9 with various
compositions are shown in Fig. 4. The saturation magnetiza-
tions were deduced from M/H vs M plots. The saturation
magnetizations ͑Ms͒ of PrxTb1−xFe1.9 compounds as a func-
tion of the Pr concentration are shown in Fig. 2͑c͒. It is
found that the saturation magnetization decreases with in-
creasing Pr concentration till x=0.4 and increases when x
ജ0.6. Since Fe couples ferromagnetically with Pr and
couples antiferromagnetically with Tb respectively, the mag-
netic moment of PrxTb1−xFe1.9 can be described as ␮s=͑1
−x͒␮Tb−1.9␮Fe−x␮Pr. Therefore, the substitution of Tb with
Pr leads to the decrease and subsequent increase in saturation
magnetization.
Vacuum annealing below the decomposed temperature
of the alloys is an effective procedure to improve the mag-
netostriction of the samples. Considering the different de-
composed temperature of PrxTb1−xFe1.9 alloys, PrFe1.9 and
Pr0.95Tb0.05Fe1.9 were annealed at 623 K and all the other
alloys were annealed at 723 K. The magnetostrictions of all
the samples were improved to different extent after anneal-
ing. As an example, the magnetostriction value ͑␭ʈ −␭ ͒ of
Ќ
Pr0.9Tb0.1Fe1.9 alloy increased from 1228 to 1497 ppm at a
magnetic field of 13 kOe. The increase of the magnetostric-
tion of the samples after annealing might be ascribed to the
partial removal of the stress in the alloys.
The dependence of magnetostriction ͑␭ʈ −␭ ͒ on the Pr
Ќ
concentration in PrxTb1−xFe2 alloys at various applied mag-
netic fields is shown in Fig. 5͑a͒. Its behavior is similar to the
magnetostriction of Tb1−xDyxFe2 alloys.3 Near x=0.9, the
magnetostrictions exhibit a peak at low fields, reflecting that
the PrxTb1−xFe1.9 system is an anisotropy compensation sys-
tem and the compensating point is just around this point,
FIG. 5. Magnetostriction at different fields for PrxTb1−xFe1.9 alloys ͑a͒ and
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field of 1 kOe. Pr0.9Tb0.1Fe1.9 ͑b͒.
202.28.191.34 On: Sat, 20 Dec 2014 10:59:39
FIG. 3. Magnetization of as Pr0.9Tb Fe a function of temperature at a
magnetostriction for Tb0.27Dy0.73Fe2 ͓reported by Wu et al. ͑Ref. 11͔͒ and

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Shi et al.
Appl. Phys. Lett. 89, 202503 ͑2006͒
which is consistent with the earlier prediction.10 In compari-
son with Tb0.27Dy0.73Fe2, the compensating point in
PrxTb1−xFe1.9 is at Tb=0.1 which results from the fact that
PrFe1.9 has a lower magnetocrystalline anisotropy than
TbFe2. We can note from Fig. 5͑b͒ that the magnetostriction
of Pr0.9Tb0.1Fe1.9 alloy approach to saturation at 13 kOe and
shows a large magnetostriction value ͑␭ʈ −␭Ќ=1497 ppm͒,
which is almost comparable to the magnetostriction of poly-
crystalline Tb0.27Dy0.73Fe2 alloy. Furthermore, this alloy,
which is near the anisotropy compensation point, should
have a small anisotropy similar to Tb0.27Dy0.73Fe2. Attention
should be paid to the Pr0.9Tb0.1Fe1.9 alloy that mainly con-
tains light rare earth Pr, which is much cheaper than
Tb0.27Dy0.73Fe2 alloy.
In conclusion, we have synthesized PrxTb1−xFe1.9 ͑0ഛx
ഛ1͒ magnetostrictive alloys with cubic Laves phase by a
high-pressure synthesis method. Pr0.9Tb0.1Fe1.9 alloy shows
low magnetocrystalline anisotropy and a large saturation
magnetostriction value at room temperature, which may be a
promising candidate for magnetostriction application. Con-
sidering the cheaper Pr and large magnetostriction of
Pr0.9Tb0.1Fe1.9 alloy, the present study may open an avenue in
the field of Pr-based magnetostrictive materials.
This work is supported by the Natural Sciences Founda-
tion of Jiangsu ͑Project No. BK2006125͒ and National Key
Project of Fundamental Research of China ͑Grant No.
2005CB623605͒.
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