- Email: [email protected]
Magnetic character of us with fission damage
Journal of the Less-Common
307
Metals, 121 (1986) 307 - 311
MAGNETIC CHARACTER OF US WITH FISSION DAMAGE* HISAYUKI MATSUI, KENJI KATORI, MASAYOSHI TAMAKI and TOM00 Department of Nuclear Engineering, Chikueaku, Nagoya 464 (Japan)
Faculty of Engineering,
KIRIHARA
Nagoya University, Furocho,
summary Effects of neutron irradiation (fission damage) and successive annealing on the magnetic character of ferromagnetic uranium monosulphide (US) are examined. Fission-induced defects reduce drastically the magnetization of US in the ordered state, accompanied with a remarkable increase in the electrical resistivity due to magnetic disordering. The magnetic parameters also changed with fission damage. Successive annealing showed a recovery in all the magnetic parameters and the disordered magnetization and resistivity, in accordance with an annealing of fission damage.
1. Introduction There have so far been few studies of the effect of neutron irradiation on the actinide compounds. Recent studies on the effect of neutron irradiation (fission damage) on the magnetic property of an antiferromagnetic uranium mononitride (UN, TN = 52 K) have shown a reduction in the magnetic parameters [ 11 and an increase in the electrical resistivity [ 21. These effects are strongly dependent on the neutron fluence (fission dose). As uranium monosulphide (US, Tc = 180 K) is a ferromagnetic substance, it is also expected that the magnetic character is changed by fission-induced defects. In previous papers [ 3, 41 we reported neutron-irradiation effects on the electrical resistivity of US and the lattice parameter measured at room temperature. These features are quite similar in both materials, UN [l] and us [3]. In the present paper, therefore, we focus on the low temperature magnetic measurement of the neutron-irradiated US. The magnetization showed a drastic reduction, while a remarkable increase occurred in the electrical resistivity [ 31, in accordance with an increase in fission damage. On successive annealing up to 1200 ‘C, however, the induced changes in the magnetic properties and also in the lattice parameter recovered to their original values. It is suggested that an introduction of the short-range magnetic disorder and pinning of the magnetic domain walls contribute to the change in the magnetic character of neutron-irradiated US. *Paper presented at Actinides 85, Aix en Provence, September 2 - 6, 1985. 0022-5088/86/$3.50
0 EIsevier Sequoia/Printed in The Netherlands
308
2. Experimentals details The same specimens were used as in previous studies [3, 41. The neutron fluence (fission dose, fissions cm-‘) of the specimens are listed in Table 1, together with the changes in some of the physical properties, including the well-known magnetic parameters. Measurement of the magnetization was performed using a torsion balance (Faraday method). In the present study, the specimens were cooled before applying the magnetic field (“zero field cooling”). Because of the comparatively high magnetic transition temperature of the ferromagnetic US, the measurement was mainly done between 77 K and room temperature. In some cases, however, the measurements were carried out in “field cooling” and from 4.2 K. An HP-9825T microcomputer was used to compile all the data and to analyse them after the measurement.
3. Results and discussions 3.1. Effects of fission damage Temperature dependence of the magnetization of neutron-irradiated US was measured at various magnetic fields below 0.5 T (5 kOe). In original (non-irradiated) specimens, a broad maximum (“cusp”) of the magnetization was always found at magnetic fields less than 0.1 T. Whereas the magnetization of the irradiated specimens was reduced in the magnetically ordered state, especially in the lower temperature region, resulting in the appearance of a cusp even at higher magnetic fields. The cusp became sharper and reduced in height with increasing fission dose. At the highest irradiation dose (2.4 X 101’ fissions cmd3), only a small cusp was observed whatever the magnetic field. The temperature dependence of the magnetization at 0.4 T of US irradiated with various fission doses is shown in Fig. l(a). In the measurement with field cooling, however, no cusp was observed and the temperaturedependent magnetization of alI US showed typical ferromagnetic behaviour, but again with reduced magnetization in the ordered state. An increase in the magnetization with increase in temperature might be attributed to a movement of magnetic domain walls which were pinned up by the irradiation-induced defects. A reduction in the field-dependent magnetization (at 77 K) with increasing fission dose was also remarkable, as shown in Fig. l(b) . In nonirradiated US a rapid increase and saturation of the magnetization occurred at about 0.05 and 0.4 T respectively. This behaviour is generally interpreted as a movement of the magnetic domain walls in the ferromagnetic substance. With increasing fission damage, however, the sudden change and the saturation appeared at higher magnetic fields and finally disappeared at the highest irradiation dose. At liquid helium temperature, much lower magnetization was found in the irradiated US. Therefore, it is concluded that the higher the fission dose, the lower the magnetization at lower temperature. The size of
1.8 0.9 0.7 2.9
;.: 7:3 6.0 174.8
180.2 179.8 179.6 179.4 178.9 179.1 178.4 177.5 176.0 -
!f’cWY Magnetic 180.0 180.3 179.5 179.9 179.1 179.4 178.1 176.5 175.0 174.3 174.3
Electrical
aFractionai change in lattice parameter (aa = 0.54904 nm for non-irradiated US). bFractional change in resistivity po = 250 k 10 ~$2 cm at 285 K for original US). Vurie points obtained from magnetic and electric measurements. dDisordered magnetization (extrapolated to 0 K) in 0.4 T (zero field cooling). eDisordered electrical resistivity (extrapolated to 0 K).
x x x x x x x x 0.45 0.10 1.68 2.61 3.81 4.39 4.26 3.70
2:4 4.9 9.8 1.5 2.9 5.9 1.2 2.4
1015 1o15 10” 1o16 10’6 10’6 10” 1017
0
APIPC? x10-2
0.53 -
0 4.9
Non-irradiated 5104 5105 5106 5107 5095 5094 5093 5096 5157 5158
Aa/a$ X10P4
x 1o14 98x 1014
Fission dose (fissions cmm3)
Specimen
Fission dose and changes in some physical and magnetic properties of US
TABLE 1
2.51 2.49 2.47 2.45 2.49 2.44 2.32 2.32 2.26 2.12 2.17
(PB)
%ff
-
0.12 0.14 0.17 0.22 0.28 0.44 0.41 0.57 -
(‘I’)
F1;:
0
1.3 3.0 5.5 16.5 18.3 18.9 19.0 19.1 19.2
-
M d (~~&l kg-l)
0 4.47 7.44 10.75 11.12 20.25 37.26 68.06 72.28 67.97
-
$!!ecm)
Fig. 1. Dependence of the magnetization (a) temperature and (b) magnetic field.
of
US irradiated with various fission doses on
Fig. 2. Dependence of magnetization of US irradiated to 2.4 successive annealings on (a) temperature and (b) magnetic field.
X
10”
fissions cm-j
in
the magnetic domains must be small and the domain walls hardly move in US with high fission doses, because of the pinning effect of the domain walls by many irradiation-induced defects. The magnetic transition point TC shifted to lower temperatures with increasing fission damage. The change in Tc is listed in Table 1, and compared with that obtained from the resistivity measurements [3]. The consistency is fairly good between the two procedures. According to the shift in Tc, the effective moment Izeff in the paramagnetic state was gradually reduced from 2.51 (non-irradiated) to 2.17 pa (at 2.4 X 1Or’ fissions cmm3)with increasing fission dose (see Table 1). These changes are consistent with those observed in the lattice parameter and electrical resitivity measured at room temperature. A variation in the magnetic parameters of US with fission damage indicates a local change in the ferromagnetic structure, probably a change in the interaction of the magnetic moments owing to the introduction of many defects and an elongation of the lattice spacing. 3.2. Effects of annealing The reduced magnetization was recovered by successive anneahngs up to 1200 “C. Figures 2(a) and 2(b) show the effects of annealing on the tempera-
311
ture and on the field-dependent magnetization of US irradiated to 2.4 X 10” fissions cmP3, respectively. At 1000 “C, the disordered magnetization and resistivity and all the magnetic parameters, such as Tc and neff, returned to their original values. But the recovery behaviours were different between light and heavy irradiations. A similar recovery process was found in the coercive force H,, obtained from the hysteresis curve at 77 K, which increases with fission damage (see Table 1). The recovery of these magnetic parameters showed few steps corresponding to annihilation of the fission-induced defects (or magnetic disorder). Therefore, it is concluded here that the fission-induced defects play an important role in the change of the magnetic character of US with fission damage.
4. Conclusions (1) A reduction in the magnetization with fission damage was observed in US, corresponding to an increase of the electrical resistivity. (2) The magnetic parameters, such as Tc, net f and H,, also changed with fission damage. (3) The induced changes in parameters were removed and recovered to the original values in a few annealing steps. (4) Two major contributions were suggested for the change in the magnetic character of US with fission damage: a short-range magnetic disorder and a pinning of the magnetic domain walls by the induced defects.
References 1 M. Tamaki, H. Matsui, A. Ohnuki, G. Matsumoto and T. Kirihara, Radiat. Eff., 91 (1985) 61. 2 M. Tamaki, A. Ohnuki, H. Matsui, G. Matsumoto and T. Kirihara, Physica B, 102 (1980) 282. 3 H. Matsui, S. Nakashima, K. Katori, M. Tamaki and T. Kirihara, J. Nucl. Mater., 110 (1982) 208. 4 H. Matsui, M. Tamaki, K. Katori, S. Nakashima and T. Kirihara, J. Magn. 1Magn. Mater., 31/34 (1983) 231.
307
Metals, 121 (1986) 307 - 311
MAGNETIC CHARACTER OF US WITH FISSION DAMAGE* HISAYUKI MATSUI, KENJI KATORI, MASAYOSHI TAMAKI and TOM00 Department of Nuclear Engineering, Chikueaku, Nagoya 464 (Japan)
Faculty of Engineering,
KIRIHARA
Nagoya University, Furocho,
summary Effects of neutron irradiation (fission damage) and successive annealing on the magnetic character of ferromagnetic uranium monosulphide (US) are examined. Fission-induced defects reduce drastically the magnetization of US in the ordered state, accompanied with a remarkable increase in the electrical resistivity due to magnetic disordering. The magnetic parameters also changed with fission damage. Successive annealing showed a recovery in all the magnetic parameters and the disordered magnetization and resistivity, in accordance with an annealing of fission damage.
1. Introduction There have so far been few studies of the effect of neutron irradiation on the actinide compounds. Recent studies on the effect of neutron irradiation (fission damage) on the magnetic property of an antiferromagnetic uranium mononitride (UN, TN = 52 K) have shown a reduction in the magnetic parameters [ 11 and an increase in the electrical resistivity [ 21. These effects are strongly dependent on the neutron fluence (fission dose). As uranium monosulphide (US, Tc = 180 K) is a ferromagnetic substance, it is also expected that the magnetic character is changed by fission-induced defects. In previous papers [ 3, 41 we reported neutron-irradiation effects on the electrical resistivity of US and the lattice parameter measured at room temperature. These features are quite similar in both materials, UN [l] and us [3]. In the present paper, therefore, we focus on the low temperature magnetic measurement of the neutron-irradiated US. The magnetization showed a drastic reduction, while a remarkable increase occurred in the electrical resistivity [ 31, in accordance with an increase in fission damage. On successive annealing up to 1200 ‘C, however, the induced changes in the magnetic properties and also in the lattice parameter recovered to their original values. It is suggested that an introduction of the short-range magnetic disorder and pinning of the magnetic domain walls contribute to the change in the magnetic character of neutron-irradiated US. *Paper presented at Actinides 85, Aix en Provence, September 2 - 6, 1985. 0022-5088/86/$3.50
0 EIsevier Sequoia/Printed in The Netherlands
308
2. Experimentals details The same specimens were used as in previous studies [3, 41. The neutron fluence (fission dose, fissions cm-‘) of the specimens are listed in Table 1, together with the changes in some of the physical properties, including the well-known magnetic parameters. Measurement of the magnetization was performed using a torsion balance (Faraday method). In the present study, the specimens were cooled before applying the magnetic field (“zero field cooling”). Because of the comparatively high magnetic transition temperature of the ferromagnetic US, the measurement was mainly done between 77 K and room temperature. In some cases, however, the measurements were carried out in “field cooling” and from 4.2 K. An HP-9825T microcomputer was used to compile all the data and to analyse them after the measurement.
3. Results and discussions 3.1. Effects of fission damage Temperature dependence of the magnetization of neutron-irradiated US was measured at various magnetic fields below 0.5 T (5 kOe). In original (non-irradiated) specimens, a broad maximum (“cusp”) of the magnetization was always found at magnetic fields less than 0.1 T. Whereas the magnetization of the irradiated specimens was reduced in the magnetically ordered state, especially in the lower temperature region, resulting in the appearance of a cusp even at higher magnetic fields. The cusp became sharper and reduced in height with increasing fission dose. At the highest irradiation dose (2.4 X 101’ fissions cmd3), only a small cusp was observed whatever the magnetic field. The temperature dependence of the magnetization at 0.4 T of US irradiated with various fission doses is shown in Fig. l(a). In the measurement with field cooling, however, no cusp was observed and the temperaturedependent magnetization of alI US showed typical ferromagnetic behaviour, but again with reduced magnetization in the ordered state. An increase in the magnetization with increase in temperature might be attributed to a movement of magnetic domain walls which were pinned up by the irradiation-induced defects. A reduction in the field-dependent magnetization (at 77 K) with increasing fission dose was also remarkable, as shown in Fig. l(b) . In nonirradiated US a rapid increase and saturation of the magnetization occurred at about 0.05 and 0.4 T respectively. This behaviour is generally interpreted as a movement of the magnetic domain walls in the ferromagnetic substance. With increasing fission damage, however, the sudden change and the saturation appeared at higher magnetic fields and finally disappeared at the highest irradiation dose. At liquid helium temperature, much lower magnetization was found in the irradiated US. Therefore, it is concluded that the higher the fission dose, the lower the magnetization at lower temperature. The size of
1.8 0.9 0.7 2.9
;.: 7:3 6.0 174.8
180.2 179.8 179.6 179.4 178.9 179.1 178.4 177.5 176.0 -
!f’cWY Magnetic 180.0 180.3 179.5 179.9 179.1 179.4 178.1 176.5 175.0 174.3 174.3
Electrical
aFractionai change in lattice parameter (aa = 0.54904 nm for non-irradiated US). bFractional change in resistivity po = 250 k 10 ~$2 cm at 285 K for original US). Vurie points obtained from magnetic and electric measurements. dDisordered magnetization (extrapolated to 0 K) in 0.4 T (zero field cooling). eDisordered electrical resistivity (extrapolated to 0 K).
x x x x x x x x 0.45 0.10 1.68 2.61 3.81 4.39 4.26 3.70
2:4 4.9 9.8 1.5 2.9 5.9 1.2 2.4
1015 1o15 10” 1o16 10’6 10’6 10” 1017
0
APIPC? x10-2
0.53 -
0 4.9
Non-irradiated 5104 5105 5106 5107 5095 5094 5093 5096 5157 5158
Aa/a$ X10P4
x 1o14 98x 1014
Fission dose (fissions cmm3)
Specimen
Fission dose and changes in some physical and magnetic properties of US
TABLE 1
2.51 2.49 2.47 2.45 2.49 2.44 2.32 2.32 2.26 2.12 2.17
(PB)
%ff
-
0.12 0.14 0.17 0.22 0.28 0.44 0.41 0.57 -
(‘I’)
F1;:
0
1.3 3.0 5.5 16.5 18.3 18.9 19.0 19.1 19.2
-
M d (~~&l kg-l)
0 4.47 7.44 10.75 11.12 20.25 37.26 68.06 72.28 67.97
-
$!!ecm)
Fig. 1. Dependence of the magnetization (a) temperature and (b) magnetic field.
of
US irradiated with various fission doses on
Fig. 2. Dependence of magnetization of US irradiated to 2.4 successive annealings on (a) temperature and (b) magnetic field.
X
10”
fissions cm-j
in
the magnetic domains must be small and the domain walls hardly move in US with high fission doses, because of the pinning effect of the domain walls by many irradiation-induced defects. The magnetic transition point TC shifted to lower temperatures with increasing fission damage. The change in Tc is listed in Table 1, and compared with that obtained from the resistivity measurements [3]. The consistency is fairly good between the two procedures. According to the shift in Tc, the effective moment Izeff in the paramagnetic state was gradually reduced from 2.51 (non-irradiated) to 2.17 pa (at 2.4 X 1Or’ fissions cmm3)with increasing fission dose (see Table 1). These changes are consistent with those observed in the lattice parameter and electrical resitivity measured at room temperature. A variation in the magnetic parameters of US with fission damage indicates a local change in the ferromagnetic structure, probably a change in the interaction of the magnetic moments owing to the introduction of many defects and an elongation of the lattice spacing. 3.2. Effects of annealing The reduced magnetization was recovered by successive anneahngs up to 1200 “C. Figures 2(a) and 2(b) show the effects of annealing on the tempera-
311
ture and on the field-dependent magnetization of US irradiated to 2.4 X 10” fissions cmP3, respectively. At 1000 “C, the disordered magnetization and resistivity and all the magnetic parameters, such as Tc and neff, returned to their original values. But the recovery behaviours were different between light and heavy irradiations. A similar recovery process was found in the coercive force H,, obtained from the hysteresis curve at 77 K, which increases with fission damage (see Table 1). The recovery of these magnetic parameters showed few steps corresponding to annihilation of the fission-induced defects (or magnetic disorder). Therefore, it is concluded here that the fission-induced defects play an important role in the change of the magnetic character of US with fission damage.
4. Conclusions (1) A reduction in the magnetization with fission damage was observed in US, corresponding to an increase of the electrical resistivity. (2) The magnetic parameters, such as Tc, net f and H,, also changed with fission damage. (3) The induced changes in parameters were removed and recovered to the original values in a few annealing steps. (4) Two major contributions were suggested for the change in the magnetic character of US with fission damage: a short-range magnetic disorder and a pinning of the magnetic domain walls by the induced defects.
References 1 M. Tamaki, H. Matsui, A. Ohnuki, G. Matsumoto and T. Kirihara, Radiat. Eff., 91 (1985) 61. 2 M. Tamaki, A. Ohnuki, H. Matsui, G. Matsumoto and T. Kirihara, Physica B, 102 (1980) 282. 3 H. Matsui, S. Nakashima, K. Katori, M. Tamaki and T. Kirihara, J. Nucl. Mater., 110 (1982) 208. 4 H. Matsui, M. Tamaki, K. Katori, S. Nakashima and T. Kirihara, J. Magn. 1Magn. Mater., 31/34 (1983) 231.