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Magnetic disorder in uranium compounds due to fission damage
237
Journal of Magnetism and Magnetic Materials 31-34 (1983) 237-239 MAGNETIC DISORDER IN URANIUM COMPOUNDS DUE TO FISSION DAMAGE H. M A T S U I , M. T A M A K I , K. K A T O R I , S. N A K A S H I M A a n d T. K I R I H A R A Dept. Nuclear Engineering, Faculty of Engineering, Nagoya University, Furocho, Chikusaku, Nagoya 464 Japan
Ferromagnetic US (T~ = 180 K) and antiferromagnetic UN (TN = 52 K), both with NaCl-type crystal structure, were examined with respect to the magnetic properties after neutron irradiation. Shifts of the magnetic transition point in both cases and a drastic reduction of the magnetization in US were accompanied with an increase of the lattice parameters due to fission damage. 1. Introduction
3. Results
Two fission fragments are produced in a fission event of 235-U with a thermal neutron. Because of the high energy of the fragments, a number of lattice atoms are displaced a n d / o r replaced. In a fissible material, it has been suggested that 105 lattice atoms are influenced by the single fission event. Therefore, a great number of defects are introduced by the fission (fragment) damage and the physical properties should be changed in uranium compounds. An aim of the present study is to examine effects of the fission damage on the magnetic properties of US, a ferromagnet below 180 K and UN, an antiferromagnet below 52 K.
Fig. 1. shows changes of the lattice parameter and the shift of the magnetic transition temperature of US and UN [1] after the neutron irradiations. With increasing fission dose, the lattice parameter increased and the Curie temperature (To) was reduced in US, while in UN, the shift of TN (N6el temperature) was accompanied by a reduction of the lattice expansion above 10 ]8 fission/era3. Typical examples of measurements of the magnetic property are illustrated in figs. 2 and 3. In fig. 2, we show the magnetizations of US with different doses as a function of temperature. A reduction of the low-temperature magnetization was revealed with increasing fission dose, as well as the corresponding increase found in the electrical resistivity [2] due to the magnetic disordering. The magnetic transition was determined using the "Arrot plot" from the low-temperature magnetization curves at a variety of magnetic fields, and was confirmed by the resisitivity measurements [2]. The irradiated UN, On the other hand, showed similar temperature dependences of the antiferromagnetism in the same way as the original
2. Experimental Sintered US and fused UN were used in the present study. Neutron irradiations were performed in the reactors, JRR-3 and JRR-4 with an irradiation temperature of about 50°C. Measurements of low-temperature magnetic susceptibility were performed before and after reactor irradiation, applying the Faraday method.
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Fig. I. Changes of lattice parameter and shifts of magnetic transition point for US (To) and UN (TN). 0 3 0 4 - 8 8 5 3 / 8 3 / 0 0 0 0 - 0 0 0 0 / $ 0 3 . 0 0 © 1983 N o r t h - H o l l a n d
238
H. Matsui et al. / Magnetic disorder in uranium compounds
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Fig. 2. Low-temperature magnetization of neutron irradiated US.
Fig. 3. Low-temperature magnetic susceptibility of neutron irradiated UN.
(non-irradiated) sample, as represented in fig. 3. The Shift of T~ and disordered magnetic susceptibility in the antiferromagnetic region were clearly discerned. It is noted here, however, that, in the highest irradiated UN (3.6 x 10 is fission/cm3), the TN was nearly identical to the original UN and that the susceptibility was reduced in comparison with other low irradiated samples. In table 1, we summarize the shifts of the magnetic transition temperature for US and UN irradiated to a variety of fission doses, together with changes of the lattice parameters and of n~t t (the effective number of the Bohr magneton in the paramagnetic region). The increased lattice parameters as a result of fission damage were recovered by thermal annealing both in US and UN. The transition temperatures and the other magnetic parameters returned to the original values at about 800°C, again apparently in accordance with the recovery of the lattice parameters.
4. Discussion The shift of the magnetic transition temperature due to the lattice expansion has been found in other magnetic substances, either in the ferromagnets or in the antiferromagnets. An interesting fact is that the shift (zaT~ and ATN) shows a roughly linear relation to the lattice expansion ( A a / a in cubic structure). On the contrary, reduced transition points have been found in both US [3] and UN [4] under hydrostatic pressure, where the lattice parameter might decrease. In either US or UN, the interaction between the magnetic spins play an important role for establishing the ordered state. In simple terms it is considered that the interactions should be weakened by an elongation of the distance between the magnetic spins on the uranium sublattice. In the magnetic ordered state, however, US has been found to show a distorted magnetic structure originated from the aligned ([111]) magnetic spins [5].
Table 1 Lattice expansion, magnetic transition temperature and neff for ferromagnetic US and antiferromagnetic UN for a variety of fission doses US
UN
Fission dose (f/cm3)
Aa / a
T~
( × 103)
(K)
Non-irrad.
0
9.8x 10~5
0.07
2.9 x 1016
0.75
5.9 X 10~6
0.66
2.4 X 1017
0.60
180.0 (180.2 a) 179.1 (179.4 a) 177.5 (176.5 a) 176.0 (175.0 a) 174.8 (174.3 a)
nett
Fision dose (f/cm 3)
Aa / a ( X 10 3)
2.51
Non-irrad.
0
2.44
3.1 X 1016
0.74
2.32
3.7 X 1017
1.80
2.26
1.8 X 1018
0.35
2.04
3.6 X 1018
-- 0.20
a Measured by electrical resistivity. See ref. [1] and [2] for UN and US, respectively.
TN
neff
(K) 52 (51.6 a) 45 (48.2 a) 44 (_) 42 (37.4 a) 53 (48.6 ~)
2.75 2.49 2.07 1.93 2.64
H. Matsui et al. / Magnetic disorder in uranium compounds
As there were many defects induced by fission damage, the distortion might be more pronounced. This probably caused the reduction of the magnetization in the ferromagnetic US. Magnetic domain walls should also play a role in the reduced magnetization in US, because energy should be required to move the walls over imperfections. A crystallographic distortion of UN, on the other hand, is an open question in the antiferromagnetic ordered state [6,7]. Dislocation loops, both interstitialand vacancy-type loops, might be possible in neutron irradiated uranium compounds, and would play a role in the changes of the magnetic parameter, especially in the reduction of the effect of the magnetic properties of U N at higher fission doses. We are indebted to Dr Hi. Matzke (EUR, Karlsruhe) and Dr C.H. de Novion (CEN, Fontenay-aux-Roses)
239
for their discussions. Thanks are due to Dr H. Watanabe (JAERI, Tokai) for irradiations of the samples.
References [1] M. Tamaki, A. Ohnuki, H. Matsui, G. Matsumoto and T. Kirihara, Phys¢ia 102B (1980) 258. [2] H. Matsui, S. Nakashima, K. Katori, M. Tamaki and T. Kirihara, J. Nu¢i. Mater. 110 (1982) 282. [3] C.Y. Huang, R.J. Laskowski, C.E. Olsen and J. Smith, J. de Phys. 40-C4 (1979) C4-26. [4] J.M. Fournier, J. Beille and C.H. de Novion, J. de Phys. 40-C4 (1979) C4-32. [5] M. Allbutt, R.M. Dell, A.R. Junkison and J.A.C. Marples, J. Inorg, NucL Chem. 32 (1970) 2159. [6] H.W. Knott, G.H. Lander and M.H. Mueller, Phys. Rev. B21 (1980) 4159. [7] J.A.C. Marples, C.F. Sampson, F.A. Wedgwood and M. Kuznietz, J. Phys. C8 (1975) 708.
Journal of Magnetism and Magnetic Materials 31-34 (1983) 237-239 MAGNETIC DISORDER IN URANIUM COMPOUNDS DUE TO FISSION DAMAGE H. M A T S U I , M. T A M A K I , K. K A T O R I , S. N A K A S H I M A a n d T. K I R I H A R A Dept. Nuclear Engineering, Faculty of Engineering, Nagoya University, Furocho, Chikusaku, Nagoya 464 Japan
Ferromagnetic US (T~ = 180 K) and antiferromagnetic UN (TN = 52 K), both with NaCl-type crystal structure, were examined with respect to the magnetic properties after neutron irradiation. Shifts of the magnetic transition point in both cases and a drastic reduction of the magnetization in US were accompanied with an increase of the lattice parameters due to fission damage. 1. Introduction
3. Results
Two fission fragments are produced in a fission event of 235-U with a thermal neutron. Because of the high energy of the fragments, a number of lattice atoms are displaced a n d / o r replaced. In a fissible material, it has been suggested that 105 lattice atoms are influenced by the single fission event. Therefore, a great number of defects are introduced by the fission (fragment) damage and the physical properties should be changed in uranium compounds. An aim of the present study is to examine effects of the fission damage on the magnetic properties of US, a ferromagnet below 180 K and UN, an antiferromagnet below 52 K.
Fig. 1. shows changes of the lattice parameter and the shift of the magnetic transition temperature of US and UN [1] after the neutron irradiations. With increasing fission dose, the lattice parameter increased and the Curie temperature (To) was reduced in US, while in UN, the shift of TN (N6el temperature) was accompanied by a reduction of the lattice expansion above 10 ]8 fission/era3. Typical examples of measurements of the magnetic property are illustrated in figs. 2 and 3. In fig. 2, we show the magnetizations of US with different doses as a function of temperature. A reduction of the low-temperature magnetization was revealed with increasing fission dose, as well as the corresponding increase found in the electrical resistivity [2] due to the magnetic disordering. The magnetic transition was determined using the "Arrot plot" from the low-temperature magnetization curves at a variety of magnetic fields, and was confirmed by the resisitivity measurements [2]. The irradiated UN, On the other hand, showed similar temperature dependences of the antiferromagnetism in the same way as the original
2. Experimental Sintered US and fused UN were used in the present study. Neutron irradiations were performed in the reactors, JRR-3 and JRR-4 with an irradiation temperature of about 50°C. Measurements of low-temperature magnetic susceptibility were performed before and after reactor irradiation, applying the Faraday method.
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Fig. I. Changes of lattice parameter and shifts of magnetic transition point for US (To) and UN (TN). 0 3 0 4 - 8 8 5 3 / 8 3 / 0 0 0 0 - 0 0 0 0 / $ 0 3 . 0 0 © 1983 N o r t h - H o l l a n d
238
H. Matsui et al. / Magnetic disorder in uranium compounds
20 1 Non-irr~d. 2 49x10,s ,/cm3
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K
Fig. 2. Low-temperature magnetization of neutron irradiated US.
Fig. 3. Low-temperature magnetic susceptibility of neutron irradiated UN.
(non-irradiated) sample, as represented in fig. 3. The Shift of T~ and disordered magnetic susceptibility in the antiferromagnetic region were clearly discerned. It is noted here, however, that, in the highest irradiated UN (3.6 x 10 is fission/cm3), the TN was nearly identical to the original UN and that the susceptibility was reduced in comparison with other low irradiated samples. In table 1, we summarize the shifts of the magnetic transition temperature for US and UN irradiated to a variety of fission doses, together with changes of the lattice parameters and of n~t t (the effective number of the Bohr magneton in the paramagnetic region). The increased lattice parameters as a result of fission damage were recovered by thermal annealing both in US and UN. The transition temperatures and the other magnetic parameters returned to the original values at about 800°C, again apparently in accordance with the recovery of the lattice parameters.
4. Discussion The shift of the magnetic transition temperature due to the lattice expansion has been found in other magnetic substances, either in the ferromagnets or in the antiferromagnets. An interesting fact is that the shift (zaT~ and ATN) shows a roughly linear relation to the lattice expansion ( A a / a in cubic structure). On the contrary, reduced transition points have been found in both US [3] and UN [4] under hydrostatic pressure, where the lattice parameter might decrease. In either US or UN, the interaction between the magnetic spins play an important role for establishing the ordered state. In simple terms it is considered that the interactions should be weakened by an elongation of the distance between the magnetic spins on the uranium sublattice. In the magnetic ordered state, however, US has been found to show a distorted magnetic structure originated from the aligned ([111]) magnetic spins [5].
Table 1 Lattice expansion, magnetic transition temperature and neff for ferromagnetic US and antiferromagnetic UN for a variety of fission doses US
UN
Fission dose (f/cm3)
Aa / a
T~
( × 103)
(K)
Non-irrad.
0
9.8x 10~5
0.07
2.9 x 1016
0.75
5.9 X 10~6
0.66
2.4 X 1017
0.60
180.0 (180.2 a) 179.1 (179.4 a) 177.5 (176.5 a) 176.0 (175.0 a) 174.8 (174.3 a)
nett
Fision dose (f/cm 3)
Aa / a ( X 10 3)
2.51
Non-irrad.
0
2.44
3.1 X 1016
0.74
2.32
3.7 X 1017
1.80
2.26
1.8 X 1018
0.35
2.04
3.6 X 1018
-- 0.20
a Measured by electrical resistivity. See ref. [1] and [2] for UN and US, respectively.
TN
neff
(K) 52 (51.6 a) 45 (48.2 a) 44 (_) 42 (37.4 a) 53 (48.6 ~)
2.75 2.49 2.07 1.93 2.64
H. Matsui et al. / Magnetic disorder in uranium compounds
As there were many defects induced by fission damage, the distortion might be more pronounced. This probably caused the reduction of the magnetization in the ferromagnetic US. Magnetic domain walls should also play a role in the reduced magnetization in US, because energy should be required to move the walls over imperfections. A crystallographic distortion of UN, on the other hand, is an open question in the antiferromagnetic ordered state [6,7]. Dislocation loops, both interstitialand vacancy-type loops, might be possible in neutron irradiated uranium compounds, and would play a role in the changes of the magnetic parameter, especially in the reduction of the effect of the magnetic properties of U N at higher fission doses. We are indebted to Dr Hi. Matzke (EUR, Karlsruhe) and Dr C.H. de Novion (CEN, Fontenay-aux-Roses)
239
for their discussions. Thanks are due to Dr H. Watanabe (JAERI, Tokai) for irradiations of the samples.
References [1] M. Tamaki, A. Ohnuki, H. Matsui, G. Matsumoto and T. Kirihara, Phys¢ia 102B (1980) 258. [2] H. Matsui, S. Nakashima, K. Katori, M. Tamaki and T. Kirihara, J. Nu¢i. Mater. 110 (1982) 282. [3] C.Y. Huang, R.J. Laskowski, C.E. Olsen and J. Smith, J. de Phys. 40-C4 (1979) C4-26. [4] J.M. Fournier, J. Beille and C.H. de Novion, J. de Phys. 40-C4 (1979) C4-32. [5] M. Allbutt, R.M. Dell, A.R. Junkison and J.A.C. Marples, J. Inorg, NucL Chem. 32 (1970) 2159. [6] H.W. Knott, G.H. Lander and M.H. Mueller, Phys. Rev. B21 (1980) 4159. [7] J.A.C. Marples, C.F. Sampson, F.A. Wedgwood and M. Kuznietz, J. Phys. C8 (1975) 708.