Microstructures and magnetostrictive strains of Fe-Ga-Ni ferromagnetic shape memory alloys

Microstructures and magnetostrictive strains of Fe-Ga-Ni ferromagnetic

shape memory alloys

Yin-Chih Lin

Citation: J. Appl. Phys. 113, 17A303 (2013); doi: 10.1063/1.4793609 View online: http://dx.doi.org/10.1063/1.4793609

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Microstructures and magnetostrictive strains of Fe-Ga-Ni ferromagnetic

shape memory alloys

Yin-Chih Lina)

Department of Mold and Die Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, 807 Taiwan

(Presented 15 January 2013; received 5 October 2012; accepted 12 November 2012; published online 27 February 2013)

Transmission electron microscopy (TEM), a magnetostrictive-meter setup, and a superconducting quantum interference device magnetometer were used to investigate the microstructures, saturation magnetostriction, and magnetic properties of bulk Fe81Ga19and Fe73Ga19Ni8(at. %) ferromagnetic

shape memory alloys (FSMAs). In the Fe81Ga19FSMA, after solution treatment (ST) at 1100C

for 4 h and quenching in ice brine, the antiphase boundary segments of the D03 domain were

observed in the A2 (disordered) matrix. When the Fe81Ga19FSMA was solution treated and aged at

750C for 24 h and then furnace cooled (FC), the A2þ D03phase transformed into A2þ B2 þ D03

structures, accompanied by coarse B2þ D03precipitates in the A2 matrix. This result decreased

the saturation magnetostriction of the aged Fe81Ga19 FSMA. However, adding more Ni to the

Fe81xGa19Nix(x¼ 8 at. % Ni) FSMAs enhanced the formation of B2 þ D03structures, further

decreased the saturation magnetostriction, and destroyed the ferromagnetic shape memory effect in Fe73Ga19Ni8FSMA ST, aged at 750C for 24 h, and FC.VC 2013 American Institute of Physics.

[http://dx.doi.org/10.1063/1.4793609]

Magnetostriction, which is due mainly to spin-orbit cou-pling, is an important magnetic property of magnetic materials. In the Fe81Ga19alloy system, the increase in magnetostriction

is explained by an increase in the magnetoelastic coupling con-stant due to short-range ordering (SRO) between the Ga-Ga atoms in bcc a-Fe (A2 structure) with randomly substituted gallium (Ga) atoms.1,2

Figures 1(a)–1(d) present transmission electron micros-copy (TEM) images of the Fe81Ga19 (at. %) alloy solution

treatment (ST) at 1100C for 4 h and quenched in ice brine. Shown in Fig. 1(a) is the zone axis [111]D03//[313]A2

(hkl denotes SRO D03structure, which has a lattice

parame-ter ofa¼ 4.09 A˚ ; hkl denotes A2 disordered phase with a lat-tice parameter of a¼ 2.899 A˚ ). Figure 1(b) is a dark field (DF) image using the (101)A2 reflection corresponding to

Fig.1(a). In this image, the bright contrast is the disordered A2 structure. The smoothly curved antiphase boundary seg-ment (APBs) of the D03domains appears very sharp, as

indi-cated by the arrow in Fig. 1(b). It seems the antiphase domain structure of the D03phase appears first, after which

the ordered D03 structure develops along the APBs. A DF

image of the superlattice (112)D03reflection, corresponding

to Fig.1(a), is shown in Fig.1(c), in which the bright con-trast is an SRO D03 precipitate structure. Figure 1(d) is a

bright field (BF) image showing the A2þ D03structures.3–7

Figures 2(a)–2(f) present TEM micrographs of the Fe81Ga19 alloy ST, aged at 750C for 24 h, and furnace

cooled (FC). Figure 2(a) is a BF image that reveals the coarse B2þ D03precipitates (indicated by arrow) in the

dis-ordered A2 matrix.

Figure2(b) is a nano beam diffraction pattern (NBDP) taken from Fig. 2(a), marked with a circle A, showing [101]D03//[101]B2, in which the D03 structure has a lattice

parameter of a¼ 4.09 A˚ , and the B2 phase has a lattice pa-rameter ofa¼ 2.045 A˚ . For confirmation that D03contained

the B2 phase, the second NBDP, taken from Fig. 2(a) and marked with a circle B, is shown in Fig. 2(c); it reveals [100]D03//[100]B2. Figure2(d)is a DF image of the (002)D03

reflection corresponding to Fig.2(c). In this image, the bright contrast is the ordered D03 structure, as indicated by the

arrow. Figure 2(e) is a high resolution TEM (HRTEM) image taken from Fig. 2(a) and marked with a circle A. Careful measurement of the lattice space reveals that the d spacing of the D03structure is 0.23 nm, with APBs existing

in the D03phase, as indicated by an arrow. In addition, thed

spacing of the disordered A2 matrix is 0.289 nm; therefore, the plane (Fig. 2(e)) can be reasonably inferred to be (111)D03and (100)A2. Shown in Fig.2(f)is another HRTEM

image taken from Fig.2(a), marked with a circle B. Careful measurement of the lattice space revealed that thed spacing of the ordered D03or B2 structure was 0.20 nm and that of

the disordered A2 matrix was 0.289 nm; therefore, the plane (Fig. 2(f)) can be reasonably inferred to be (002)D03 or

(001)B2, and (010)A2, respectively. The B2þ D03structures

exist in the aged Fe81Ga19 alloy, as confirmed consistently

by NBDP and HRTEM.3–7

The TEM images of the Fe73Ga19Ni8(at. %) alloy ST at

1100C for 4 h and quenched in ice brine are shown in Figs. 3(a)–3(d). Shown in Fig.3(a)is the zone axis [111]D03//[513]A2

(hkl denotes SRO D03structure, which has a lattice

parame-ter of a¼ 4.194 A˚ ; hkl denotes A2 disordered phase with a lattice parameter of a¼ 2.887 A˚ ). Comparing the selected area diffraction pattern (SADP) of Figs. 1(a) and3(a), it is a)_{Author to whom correspondence should be addressed. Electronic mail:}

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0021-8979/2013/113(17)/17A303/3/$30.00 113, 17A303-1 VC2013 American Institute of Physics

JOURNAL OF APPLIED PHYSICS 113, 17A303 (2013)

found that adding Ni (8 at. %) into the Fe81xGa19Nix

ferro-magnetic shape memory alloy (FSMA) systems decreases the lattice parameter of the A2 structure, which in turn degrades the saturation magnetostriction of the Fe73Ga19Ni8

alloy. Figure 3(b) is a DF image of the (112)A2 reflection

corresponding to Fig.3(a). In this image, the bright contrast is the disordered A2 structure. The DF image of the superlat-tice (011)D03reflection corresponding to Fig.3(a), is shown

in Fig.3(c), in which the bright contrast is an SRO D03

pre-cipitate structure. The BF image shown in Fig. 3(d) shows the A2þ D03structures.3–7

A series of TEM images of the Fe73Ga19Ni8alloy ST,

aged at 750C for 24 h, and FC are shown in Figs.4(a)–4(f). Figure4(a)is a BF image showing the B2þ D03precipitates

(indicated by arrow) in the A2 matrix. An SADP with the zone axis [101]D03//[101]B2//[353]A2 is shown in Fig. 4(b)

(hkl denotes ordered D03 structure; hkl denotes B2 phase

with lattice parameter of a¼ 2.097 A˚ ; hkl denotes A2 struc-ture). Shown in Fig. 4(c) is a DF image of the (202)D03

reflection corresponding to Fig.4(b). In this image, the bright contrast is the ordered D03 precipitates, as indicated by

arrows. Figures 4(d)and4(e)are low and higher magnifica-tions of B2þ D03precipitates in BF images, which

demon-strate that adding Ni (8 at. %) into the Fe73Ga19Ni8 alloy,

aging it at 750C for 24 h, and furnace cooling it enhanced the formation of B2þ D03precipitates, and that the

satura-tion magnetostricsatura-tion and magnetostrictive susceptibility were degraded. Shown in Fig.4(f)is a HRTEM image taken from Fig.4(e). Careful measurement of the latticed spacing (Fig.4(f)) reveals that thed spacing of the D03structure is

0.24 nm, and the that of the disordered A2 matrix is 0.2 nm; therefore, the plane (Fig.4(f)) can be reasonably inferred to be (111)D03and (101)A2, respectively.

Figures 5(a)–5(d) show the saturation magnetostriction (ks) vs. magnetic field (H) curves, or ks H curves, measured

at RT, of the Fe81Ga19and Fe73Ga19Ni8alloys ST, and the ST

samples aged at 750C for 24 h and FC. The saturation mag-netostriction ksis evaluated as ks¼ (2/3)  [(kk)–(k?)], where

kk (k?) is the magnetostriction in the longitudinal direction

with a magnetic field parallel (perpendicular) to the sample’s

FIG. 3. TEM images of the Fe73Ga19Ni8alloy ST at 1100C for 4 h and

quenched in ice brine: (a) SADP of zone axis [111]D03//[513]A2(hkl denotes

SRO D03reflection; hkl denotes disordered A2 structure); (b) DF image

of (112)A2 reflection corresponding to (a); (c) DF image of superlattice

(011)D03reflection corresponding to (a); and (d) BF image.

FIG. 1. TEM images of the Fe81Ga19(at. %) alloy ST at 1100C for 4 h

and quenched in ice brine: (a) SADP of zone axis [111]D03//[313]A2

(hkl denotes SRO D03reflection; hkl denotes disordered A2 structure); (b)

DF image of (101)A2reflection corresponding to (a); (c) DF image of

super-lattice (112)D03reflection corresponding to (a); and (d) BF image.

FIG. 2. TEM micrographs of the Fe81Ga19alloy ST, aged at 750C for 24 h,

and FC: (a) BF image of the coarse B2þ D03precipitates, indicated by arrow;

(b) NBDP of zone axis [101]D03//[101]B2(hkl denotes ordered D03reflection;

hkl denotes ordered B2 structure); (c) NBDP of zone axis [100]D03//[100]B2;

(d) DF image of (002)D03reflection corresponding to (c); (e) HRTEM image

showingd spacing of the (111)D03and (100)A2; (f) HRTEM image showing

d spacing of the (002)D03or (001)B2, and (010)A2, respectively.

17A303-2 Yin-Chih Lin J. Appl. Phys. 113, 17A303 (2013)

length. It can be seen in Figs.5(a)and5(b)that the saturation magnetostriction of the ST Fe81Ga19 alloy (53.3 106) is

larger than that of the ST Fe73Ga19Ni8alloy (20.7 106).

In Fig. 5(b), the saturation magnetostriction of the ST Fe73Ga19Ni8alloy reveals that adding Ni (8 at. %) into the

Fe81xGa19Nixalloy lowers the saturation magnetostriction.

The reason is that adding more Ni into the Fe81xGa19Nix

(x¼ 8 at. % Ni) FSMAs enhances the formation of B2 þ D03

structures. Figures5(c)and5(d)reveal the saturation magne-tostriction of the Fe81Ga19and Fe73Ga19Ni8alloys ST, aged

at 750C for 24 h, and FC. Both aged alloys have a lower saturation magnetostriction (20.7 106); (12.7 106) and decreased magnetostrictive susceptibility (Dks/DH). The

rea-son is that 750C/24 h aging treatment causes the A2þ D03

phase to transform into the A2þ B2 þ D03 structures,

accompanied by precipitation of coarse B2þ D03structures

in the A2 matrix. This study reveals that adding Ni into the Fe81xGa19Nix (x¼ 8 at. % Ni) FSMA system drastically

decreases the saturation magnetostriction of the Fe73Ga19Ni8

alloy due to the presence of large scale A2þ B2 þ D03

pre-cipitates.8–10

In Fe81Ga19FSMA ST at 1100C for 4 h and quenched

in ice brine, the APBs of the D03domain were observed in

the A2 (disordered) matrix. The A2 disordered phase had a

lattice parameter of a¼ 2.899 A˚ . After the alloy was ST, aged at 750C for 24 h, and FC, coarse B2þ D03

precipi-tates in the A2 matrix were observed by TEM. The D03

structure has a lattice parameter of a¼ 4.09 A˚ , and the B2 structure has a lattice parameter of a¼ 2.045 A˚ . This study reveals that adding Ni into the Fe81xGa19Nix(x¼ 8 at. %

Ni) FSMA systems drastically decreases the saturation mag-netostriction of the Fe73Ga19Ni8alloy due to the presence of

large scale A2þ B2 þ D03 precipitates, in which the

Fe73Ga19Ni8alloy has an A2 disordered phase with a lattice

parameter of a¼ 2.887 A˚ ; the ordered D03 structure has a

lattice parameter of a¼ 4.194 A˚ ; and the B2 structure has a lattice parameter of a¼ 2.097 A˚ . TEM SADP demonstrates that the orientation relationships of A2, D03, and B2 are:

[111]D03//[313]A2; [101]D03//[101]B2; [100]D03//[100]B2; and

[111]D03//[513]A2; [101]D03//[101]B2//[3 5 3]A2, respectively.

Neither A2þ D03 phases nor the phase mixture of A2

þ B2 þ D03 structures had any influence on the hysteresis

loops of the alloys at RT.

The author would like to express his sincere appreciation to the National Science Council of the ROC for supporting this study (under Grant-in-Aid for NSC-100-2221-E-151-020).

1

R. Gr€ossinger, R. Sato Turtelli, and N. Mehmood,IEEE Trans. Magn.44, 3001 (2008).

2_{Q. Xing, Y. Du, R. J. McQueeney, and T. A. Lograsso,Acta Mater.}

56, 4536 (2008).

3

C. B. Nunes, R. S. Turtelli, R. Gr€ossinger, H. M€uller, and H. Sassik,

J. Magn. Magn. Mater.322, 1605 (2010).

4_{Q. Xing and T. A. Lograsso,Appl. Phys. Lett.93, 182501 (2008).} 5

Q. Xing and T. A. Lograsso,Scr. Mater.65, 359 (2011).

6

J. Li, X. Gao, J. Zhu, J. Jia, and M. Zhang,Scr. Mater.61, 557 (2009).

7

A. Javed, T. Szumiata, N. A. Morley, and M. R. J. Gibbs,Acta Mater.58, 4003 (2010).

8

J. H. Li, X. X. Gao, J. Zhu, X. Q. Bao, T. Xia, and M. C. Zhang,

Scr. Mater.63, 246 (2010).

9

Q. Xing, D. Wu, and T. A. Lograsso,J. Appl. Phys.107, 09A911 (2010).

10_{Y. Du, M. Huang, S. Chang, D. L. Schlagel, T. A. Lograsso, and R. J.}

McQueeney,Phys. Rev. B.81, 054432 (2010).

FIG. 5. The linear saturation magnetostriction ks(106) vs. magnetic field

(H) ks–H curves measured at room temperature: (a) Fe81Ga19 and (b)

Fe73Ga19Ni8alloys 1100C/4 h ST and quenched in ice brine; (c) Fe81Ga19

and (d) Fe73Ga19Ni8alloys ST, aged at 750C for 24 h, and FC.

FIG. 4. TEM images of the Fe73Ga19Ni8alloy ST, aged at 750C for 24 h,

and FC: (a) BF images, the B2þ D03precipitates indicated by arrow; (b)

SADP of zone axis [101]D03//[101]B2//[353]A2 (hkl denotes ordered D03

reflection; hkl denotes ordered B2 structure; hkl denotes disordered A2 structure); (c) DF image of (202)D03reflection corresponding to (b); (d)–(e)

BF images showing B2þ D03 precipitates; (f) HRTEM image showingd

spacing of the (111)D03and (101)A2, respectively.

17A303-3 Yin-Chih Lin J. Appl. Phys. 113, 17A303 (2013)