実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report
課題番号 Project No. 2012B0002

提出日 Date of Report
May 15, 2013
装置責任者 Name of responsible person
Kazuya Aizawa

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Mechanism of a large elastic strain in Fe3Pt

TAKUMI/ BL19

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Takashi Fukuda

March 22 - March 25

所属 Affiliation
Osaka University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
The specimen used in this experiment was a single crystal of L12-type Fe3Pt (Fe-25at.%Pt alloy), which wasgrown by a floating zone method. A parallelepiped single crystal with dimensions of 9.8 mm x 2.5mm x 2.6 mm
was used for the present experiment. The single crystal was heat-treated for homogenization at 1373 K for 24hours followed by ordering heat-treatment at 923 K for 100 hours. The long range order parameter determinedby X-ray diffraction was 0.75. The martensitic transformation temperature of this specimen was approximately
90 K, which was measured by a SQUID magnetometer beforehand. The edges of the specimen was parallel to[001], [110] and [-110] directions.

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

The specimen was inserted in a dice with pistons, which are made of an aluminum alloy. Then the specimen
with dice and pistons are set into a compressing stage attached to a cold stage. The specimen is compressed inthe [001] direction in TAKUMI (BL19). We need to apply the minimum stress of -6 MPa to hold the specimen
for the measurements. Here the minus sign on stress means compressive stress is applied on the specimen. The
diffraction patterns with the scattering vector parallel to the [001] direction were detected by the SOUTH BANK
and those with scattering vector parallel to the [110] direction were detected by the NORTH BANK. We
measured the position and peak separation of (002) peak in the SOUTH BANK and (220) peak in the NORTHBANK. The slit condition used in TAKUMI was 3 mm in height and 5 mm in width.
(1) Temperature dependence of lattice parameters under -6 MPa and -100 MPa.
When the specimen was cooled under the stress of -6 MPa applied in the [001] direction, no peak separation wasobserved above 90 K and a clear peak separation due to the formation of the tetragonal martensite was observed
below 90 K. The volume of unit cell increased with decreasing temperature, which is characteristic feature of theInvar alloy. These results are consistent with previous experiments made under zero stress by x-ray diffraction.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
When the specimen was cooled or heated under -100 MPa applied in the [001] direction, no peak separation wasobserved in the whole examined temperature range (83 K to 264 K). Figure 1 shows temperature dependence oflattice parameters c and a obtained under -100 MPa. There is distinct difference between the lattice parameters aand c even above the transformation temperature of 90 K. The gradual deviation between a and c on cooling isdue to the lattice softening of this alloy. It should be noted that there is no discontinuous change in a and also in c
in the cooling process. This result implies that martensitic transformation in Fe3Pt probably disappears by theapplication of compressive stress of -100 MPa. The volume of unit cell (a2c) under -100 MPa showed negative
temperature dependence as that under -6 MPa.
(2) Stress dependence of lattice parameters
When the stress was applied at 90 K, the (002) peak in the south bank and (220) peak in the north bank were
essentially regarded as one peak in the stress range of -6 MPa and -280 MPa at 90 K. Figure 2 shows stressdependence of lattice parameters a and c obtained by the peak positions of the (002) and (220) peaks. The strain
in the [001] direction calculated form this lattice parameter coincides with the strain obtained by strain gageattached at the surface of the specimen. This means that the elastic strain of about 6%, which appears in thestress-strain curve of this alloy, is essentially caused by lattice strain. When the stress exceeds about -280 MPa,
there arises a large jump in lattice parameter. This jump is due to the martensitic transformation to the bct phase.
The tetragonality of the bct martensite is approximately 0.80. This tetragonality is consistent with the bct
martensite phase which forms in Fe3Pt with low degree of order.

0.42

0.380

a0.3750.370

c0.365Fe3Pt
 // [001] = -100 MPa

0.360
0.355

Lattice Parameter (nm)Lattice Parameter (nm)0.385100200Temperature (K)Figure 1 Temperature dependence
parameters of Fe3Pt under -100 MPa.

a0.380.36

c0.34
0.320.300300a (b.c.t.)

0.40

Fe3Pt
T = 90 K

100c (b.c.t.)
200300Stress, - (MPa)oflattice

Figure 2 Stress dependence of lattice parameters ofFe3Pt at 90 K.

(3) Temperature dependence of lattice parameter of the bct martensite
As the bct martensite phase was formed by the application of stress at 90 K, we measured temperaturedependence of the unit cell volume of of the bct martensite phase under -6 MPa. As a result, we found thatvolume increases with increasing temperature. That is, the Inver effect diminishes in the bct martensite phase.
In summary, we have confirmed by using TAKUMI (BL19) that Fe3Pt exhibits an extremely large elastic strainof approximately 6% appear at 90 K in Fe3Pt due to lattice distortion under compressive stress applied in the[001] direction. In addition, it is confirmed that the bct martensite appears when the strain exceeds about 6%.

2