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Ferromagnetism of hydride GdFe2Hx
Journal of Magnetism and Magnetic Materials 140-144 (1995) 815-816
journalof magnetism ~ H and magnetic ~14 materials
ELSEVIER
Ferromagnetism of hydride GdFe2H x Satoshi Tokita *, Kazuo Kanematsu Physical Science Laboratories, Nihon University at Narashino, Funabashi, Chiba-ken 274, Japan
Abstract Magnetization measurements were performed on three types of hydrides: amorphous, and C15-type 3'- and 6-GdFe2H x, which were determined by isothermal hydrogen absorption experiments. The magnetizations of all three hydrides are 2.8/*B/GdFeaH x, and the Curie temperatures of the amorphous, 3'- and 6-hydrides are Tc = 340 ~ 440, 400-480 and 110 K, respectively.
I. Introduction The magnetic properties of three types of hydride GdFezH * are reported: a C15-type hydride GdFezH 4 with Curie temperature Tc = 388 K and magnetization n f = 4.10~B/f.u. [1]; a C15-type hydride GdFe2H4. 4 with Tc = 107 K which was prepared by hydrogen absorption at 373 K [2]; and an amorphous hydride GdFe2H3. 6 with Tc = 443 K which was prepared by hydrogen absorption at 423-523 K [2]. As the Curie temperatures of both C15-type hydrides are quite different, they are probably different hydrides. Therefore isothermal hydrogen absorption experiments were performed at 273-573 K. The hydrogen absorption isotherms show three types of hydrides: an amorphous hydride of 1.1 < x < 2, and two C15-type hydrides 3' of 2.6 < x < 3.5 and 6 of 4.2 < x. The magnetization measurements show that the Curie temperatures of 6- and 3'-GdFe2H ~ are Tc --110 and 400-480 K, respectively. The magnetizations were measured using a vibrating sample magnetometer in a magnetic field of 0.84 M A / m (10.5 kOe).
though the X-ray examination could not detect these inclusions. The formation of other hydrides and the decomposition can not be avoided in hydrogen absorption and desorption. The magnetization above 100 K is probably due to the 3' and amorphous hydrides. The abrupt increase in magnetization at 440 K is ascribed to GdFe 2 (Tc = 790 K) formed as a result of the desorption of hydrogen.
3. y-hydride A typical 3'-hydride GdFe2H2. 6 was prepared by hydrogen absorption at 373 K. The magnetization curve at 0 K estimated by extrapolating the thermomagnetic curve (Fig. 1) is 2.8/Xn/f.u. and Tc = 480 K. The X-ray diffraction lines are indexed as C15 structure with a = 0.7828 nm and there is no extra line. The magnetization measurements for the other ~/-hydrides show that the Curie temperatures are
3.0
2. 8-hydride
Z
A typical 6-hydride GdFe2H4. 6 was prepared by hydrogen absorption at 298 K. The thermomagnetic curve is shown in Fig 1. The magnetization at 0 K estimated by extrapolation is n f = 2 . 8 / z n / f . u . (GdFeeH4. 6) and the Curie temperature T c = 110 K. The X-ray diffraction lines consist of main lines indexed as C15 structure with a = 0.8048 nm, and weak lines suggesting a superstructure. This hydride may include a small amount of 3,-hydride, an amorphous hydride and decomposed GdH 2 + Fe, al-
cl
* Corresponding author.
2.0
1.O
0
I
I
I
I
I
I
I
100
200
300
400
500
600
700
"r0~) Fig. 1. Temperature dependence of magnetization of hydrides 6 GdFezH4. 6 and 'y-GdFezH2.6 measured in 0.84 MA/m (10.5 kOe). The increases in magnetization above 450 K were due to GdFe 2 formed by hydrogen desorption.
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI0304-8853(94)01021-8
816
S. Tokita et al. /Journal of Magnetism and Magnetic Materials 140-144 (1995) 815-816
the hydrogen causes the Curie temperature to increase in the amorphous hydrides.
2.0
- o5o5 °-.. ~
5. Effect of hydrogen
1.0
I 100
200
30O
40O
50O
T 0~)
600
700
Fig. 2. Temperature dependence of magnetization of amorphous hydride GdFe 2H I 6. The Curie temperature of the heating curve is Tc = 440 K and that of the cooling curve is Tc = 340 K.
on the range 4 0 0 - 4 8 0 K and decrease with increasing hydrogen concentration, which has little influence in the magnetization.
4. Amorphous hydride A typical amorphous hydride GdFe2H1. 6 was prepared by hydrogen absorption at 473 K. The temperature dependence of magnetization is N-type ferrimagnetism with a compensation point Tm = 60 K (Fig. 2). The magnetization at 0 K estimated by extrapolation is nearly same as those of the ",/- and 8-hydrides, and Tc = 440 K. After heating up to 600 K in the magnetization measurements, the cooling curve of magnetization shows that Tc = 340 K and the compensation temperature Tm = 40 K. The hydrogen concentration of the amorphous hydride on cooling is lower than that on heating because of hydrogen desorption caused by heating under reduced pressure. In consequence,
The magnetizations of all three hydrides at 0 K are 2.9/~B/f.u., which is smaller than our value of GdFe 2 (3.5/~n/f.u.). These values suggest that the magnetic moment of Gd (7~B) is antiparallel to those of Fe in GdFe 2 and GdFe2H x. The estimated values of Fe in GdFe 2 and GdFe2H x are 1.75 and 2.1/~B/Fe, respectively. The hydrogenation leads to an increase in the magnetic moment of Fe, which is almost independent of hydrogen concentration x, similar to YFe2H x [3]. The Curie temperatures of crystalline GdFe2H x decrease with increasing hydrogen concentration, similar to YFe2H x [3], but the Curie temperature of amorphous GdFe 2H x increases with increasing hydrogen concentration. These facts suggest that the formation of hydride determines the magnetic moment of Fe. and that the Curie temperature may be ascribed to the interatomic distance between Fe atoms, which is dependent on the hydrogen concentration. In the amorphous hydride, the interatomic distance between Fe atoms probably decreases with increasing hydrogen concentration, although there is no evidence for this. A decrease in volume due to hydrogenation has been observed in 13-YFe2H x (1.0 < x <
1.4). References [1] A.M. Diepen and K.H.J. Buschow, Solid State Commun. 22 (1977) 113. [2] K. Aoki, M. Nagano, A. Yanagitani and T. Masumoto, J. Appl. Phys. 62 (1987) 3314. [3] K. Kanematsu, Proc. 2nd Int. Conf. on Rare Earth Develop. Appl. (International Academic Publishers, 1991) p. 116.
journalof magnetism ~ H and magnetic ~14 materials
ELSEVIER
Ferromagnetism of hydride GdFe2H x Satoshi Tokita *, Kazuo Kanematsu Physical Science Laboratories, Nihon University at Narashino, Funabashi, Chiba-ken 274, Japan
Abstract Magnetization measurements were performed on three types of hydrides: amorphous, and C15-type 3'- and 6-GdFe2H x, which were determined by isothermal hydrogen absorption experiments. The magnetizations of all three hydrides are 2.8/*B/GdFeaH x, and the Curie temperatures of the amorphous, 3'- and 6-hydrides are Tc = 340 ~ 440, 400-480 and 110 K, respectively.
I. Introduction The magnetic properties of three types of hydride GdFezH * are reported: a C15-type hydride GdFezH 4 with Curie temperature Tc = 388 K and magnetization n f = 4.10~B/f.u. [1]; a C15-type hydride GdFe2H4. 4 with Tc = 107 K which was prepared by hydrogen absorption at 373 K [2]; and an amorphous hydride GdFe2H3. 6 with Tc = 443 K which was prepared by hydrogen absorption at 423-523 K [2]. As the Curie temperatures of both C15-type hydrides are quite different, they are probably different hydrides. Therefore isothermal hydrogen absorption experiments were performed at 273-573 K. The hydrogen absorption isotherms show three types of hydrides: an amorphous hydride of 1.1 < x < 2, and two C15-type hydrides 3' of 2.6 < x < 3.5 and 6 of 4.2 < x. The magnetization measurements show that the Curie temperatures of 6- and 3'-GdFe2H ~ are Tc --110 and 400-480 K, respectively. The magnetizations were measured using a vibrating sample magnetometer in a magnetic field of 0.84 M A / m (10.5 kOe).
though the X-ray examination could not detect these inclusions. The formation of other hydrides and the decomposition can not be avoided in hydrogen absorption and desorption. The magnetization above 100 K is probably due to the 3' and amorphous hydrides. The abrupt increase in magnetization at 440 K is ascribed to GdFe 2 (Tc = 790 K) formed as a result of the desorption of hydrogen.
3. y-hydride A typical 3'-hydride GdFe2H2. 6 was prepared by hydrogen absorption at 373 K. The magnetization curve at 0 K estimated by extrapolating the thermomagnetic curve (Fig. 1) is 2.8/Xn/f.u. and Tc = 480 K. The X-ray diffraction lines are indexed as C15 structure with a = 0.7828 nm and there is no extra line. The magnetization measurements for the other ~/-hydrides show that the Curie temperatures are
3.0
2. 8-hydride
Z
A typical 6-hydride GdFe2H4. 6 was prepared by hydrogen absorption at 298 K. The thermomagnetic curve is shown in Fig 1. The magnetization at 0 K estimated by extrapolation is n f = 2 . 8 / z n / f . u . (GdFeeH4. 6) and the Curie temperature T c = 110 K. The X-ray diffraction lines consist of main lines indexed as C15 structure with a = 0.8048 nm, and weak lines suggesting a superstructure. This hydride may include a small amount of 3,-hydride, an amorphous hydride and decomposed GdH 2 + Fe, al-
cl
* Corresponding author.
2.0
1.O
0
I
I
I
I
I
I
I
100
200
300
400
500
600
700
"r0~) Fig. 1. Temperature dependence of magnetization of hydrides 6 GdFezH4. 6 and 'y-GdFezH2.6 measured in 0.84 MA/m (10.5 kOe). The increases in magnetization above 450 K were due to GdFe 2 formed by hydrogen desorption.
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI0304-8853(94)01021-8
816
S. Tokita et al. /Journal of Magnetism and Magnetic Materials 140-144 (1995) 815-816
the hydrogen causes the Curie temperature to increase in the amorphous hydrides.
2.0
- o5o5 °-.. ~
5. Effect of hydrogen
1.0
I 100
200
30O
40O
50O
T 0~)
600
700
Fig. 2. Temperature dependence of magnetization of amorphous hydride GdFe 2H I 6. The Curie temperature of the heating curve is Tc = 440 K and that of the cooling curve is Tc = 340 K.
on the range 4 0 0 - 4 8 0 K and decrease with increasing hydrogen concentration, which has little influence in the magnetization.
4. Amorphous hydride A typical amorphous hydride GdFe2H1. 6 was prepared by hydrogen absorption at 473 K. The temperature dependence of magnetization is N-type ferrimagnetism with a compensation point Tm = 60 K (Fig. 2). The magnetization at 0 K estimated by extrapolation is nearly same as those of the ",/- and 8-hydrides, and Tc = 440 K. After heating up to 600 K in the magnetization measurements, the cooling curve of magnetization shows that Tc = 340 K and the compensation temperature Tm = 40 K. The hydrogen concentration of the amorphous hydride on cooling is lower than that on heating because of hydrogen desorption caused by heating under reduced pressure. In consequence,
The magnetizations of all three hydrides at 0 K are 2.9/~B/f.u., which is smaller than our value of GdFe 2 (3.5/~n/f.u.). These values suggest that the magnetic moment of Gd (7~B) is antiparallel to those of Fe in GdFe 2 and GdFe2H x. The estimated values of Fe in GdFe 2 and GdFe2H x are 1.75 and 2.1/~B/Fe, respectively. The hydrogenation leads to an increase in the magnetic moment of Fe, which is almost independent of hydrogen concentration x, similar to YFe2H x [3]. The Curie temperatures of crystalline GdFe2H x decrease with increasing hydrogen concentration, similar to YFe2H x [3], but the Curie temperature of amorphous GdFe 2H x increases with increasing hydrogen concentration. These facts suggest that the formation of hydride determines the magnetic moment of Fe. and that the Curie temperature may be ascribed to the interatomic distance between Fe atoms, which is dependent on the hydrogen concentration. In the amorphous hydride, the interatomic distance between Fe atoms probably decreases with increasing hydrogen concentration, although there is no evidence for this. A decrease in volume due to hydrogenation has been observed in 13-YFe2H x (1.0 < x <
1.4). References [1] A.M. Diepen and K.H.J. Buschow, Solid State Commun. 22 (1977) 113. [2] K. Aoki, M. Nagano, A. Yanagitani and T. Masumoto, J. Appl. Phys. 62 (1987) 3314. [3] K. Kanematsu, Proc. 2nd Int. Conf. on Rare Earth Develop. Appl. (International Academic Publishers, 1991) p. 116.