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Magnetostriction in the ferromagnetic state of UGa2
Physica B 312–313 (2002) 904–905
Magnetostriction in the ferromagnetic state of UGa2 Tetsuo Honmaa,*, Tetsuya Takeuchib, Keitaro Kuwaharac, Abdul Hannanc, Masahumi Kohgic, Satoshi Tsutsuid, Yoshinori Hagad, Masami Nakadad, f,1 % Saburo Nasue,1, Yoshichika Onuki a
Japan Synchrotron Radiation Research Institute, Mikazuki, Hyogo 679-5198, Japan b Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan c Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan d Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan e Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan f Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
Abstract X-ray diffraction study of ferromagnetic UGa2 indicated that a lattice distortion occurs below a Curie temperature of TC ¼ 123 K. We also observed the distortion in the sound velocity and thermal expansion measurements in the ferromagnetic state. We performed the thermal expansion in the magnetic field of 20 kOe along the magnetic easy axis . and X-ray diffraction using a single crystal, and 238 U Mossbauer measurements using its powder in order to investigate the relationships between the ferromagnetic order and the lattice distortion. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Magnetostriction; X-ray diffraction; Quadrupole splitting; UGa2
The lattice distortion of ferromagnetic UGa2 occurs below a Curie temperature TC ¼ 123 K from the hexagonal (P6/mmm) to the orthorhombic (Cmmm) structure, which was clarified from the measurement of the lattice parameters by Andreev et al. [1]. This was also observed by the thermal expansion and sound velocity measurements by Honma et al. [2]. In a zero magnetic field, the thermal expansion coefficient along the [1 1 2% 0] direction a½1 1 2% 0 exhibits the l-type anomaly at TC : The abrupt softening based on the lattice distortion in the basal plane below TC is also reflected in the elastic constant c11 and (c11 –c12 )/2 modes. Furthermore, the other lattice distortion a½1 1 2% 0 exhibited a sharp anomaly at T n ¼ 100 K and a broad peak at about 50 K. In the magnetic field of 20 kOe *Corresponding author. Tel.: (+81)791-58-0802; fax: (+81)791-58-0948. E-mail address: [email protected] (T. Honma). 1 % Y. Onuki and S. Nasu are supported financially by a Grantin- Aid for COE Research (10CE2004) from the Ministry of Education, Science, Sports and Culture.
along the magnetic easy axis [1 1 2% 0] direction, the softening by the growth of the magnetic moment was observed in the (c11 –c12 )/2 mode. The echo is extremely dampened between about 70 and 90 K, which suggests lattice distortion in the basal plane. To further clarify the relation between the ferromagnetic order and the lattice distortion, we directly investigated the lattice distortion in the single domain structure, which was induced by reconstructing three magnetic domains under the magnetic field along the magnetic easy axis [1 1 2% 0], by thermal expansion measurements, together with X-ray diffraction and 238 U . Mossbauer measurements. We measured the temperature dependence of the lattice constant by X-ray diffraction using a high-quality single crystal of RRR ¼ 300 in a zero magnetic field. The experimental result of the lattice distortion below TC was almost the same as the previous one [1]. We also observed the three domains in the ferromagnetic phase. Within the bounds of experimental error, there was no anomaly found at T n : Figs. 1(a) and (b) show the temperature dependence of the thermal expansion coefficient að¼ dðDl=lÞ=dT)
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 2 7 1 - 6
40
UGa2
20
100 010
H = 20 kOe
(a)
0
−20 [010]
∆1/1 (x10−3)
4
0
[100]
0
50 100 Temperature (K)
50 100 Temperature (K)
150
Fig. 2. Temperature dependence of quadrupole splitting(QS) e2 qQ:
1 0
UGa2
0
(b)
3 2
905
50 e 2qQ ( mm s-1 )
α (x10−6 K−1)
T. Honma et al. / Physica B 312–313 (2002) 904–905
150
Fig. 1. (a) Temperature dependence of the thermal expansion coefficients for the [1 1 2% 0] and [1 0 1% 0] directions under an applied field of 20 kOe along the magnetic easy axis [1 1 2% 0] in UGa2 : (b) Temperature dependence of the thermal expansions in the (0 0 1) plane.
and the thermal expansion Dl=l for the [1 1 2% 0] and [1 0 1% 0] directions under an applied magnetic field of 20 kOe along [1 1 2% 0]. Two anomalies are found at 70 and 120 K, as shown in Fig. 1(a). The temperature dependencies of Dl=l in Fig. 1(b) are similar to those of the lattice constants a for [1 0 0] and b=O3 for [0 1 0] directions in the orthorhombic structure, and are shown by X-ray diffraction in a zero field. With decreasing temperature, however, a shows a shoulder around 100 K and further decreases below about 100 K. The rate of the lattice distortion below TC changes around T n ¼ 100 K. We observed the induced nuclear quadrupole interaction in the ferromagnetic state of UGa2 : The
experimental result suggests that 5f-orbitals are elongated along the magnetic easy axis [3]. Fig. 2 shows the temperature dependence of the quadrupole splitting (QS ¼ e2 qQ). QS develops below TC : The temperature dependence of QS is not monotonous, but exhibits a shoulder around 100 K. However, the anomaly, accompanied by the lattice distortion, was not observed in the temperature dependence of the recoil-free fraction of at 238 U nuclei. In conclusion, the crossover phenomena at T n in the ferromagnetic state are not due to the reconstruction of the magnetic domains, but due to the change of the 5f electronic state which also causes the characteristic change of the magnetic anisotropy in the ferromagnetic state.
References [1] A.V. Andreev, et al., J. Phys. 40 (Suppl.) (1979) C4–82. [2] T. Honma, et al., J. Phys. Soc. Japan 69 (2000) 2647. [3] S. Tsutsui, et al., J. Phys. Soc. Japan A 70 (Suppl.) (2001) 34.
Magnetostriction in the ferromagnetic state of UGa2 Tetsuo Honmaa,*, Tetsuya Takeuchib, Keitaro Kuwaharac, Abdul Hannanc, Masahumi Kohgic, Satoshi Tsutsuid, Yoshinori Hagad, Masami Nakadad, f,1 % Saburo Nasue,1, Yoshichika Onuki a
Japan Synchrotron Radiation Research Institute, Mikazuki, Hyogo 679-5198, Japan b Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan c Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan d Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan e Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan f Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
Abstract X-ray diffraction study of ferromagnetic UGa2 indicated that a lattice distortion occurs below a Curie temperature of TC ¼ 123 K. We also observed the distortion in the sound velocity and thermal expansion measurements in the ferromagnetic state. We performed the thermal expansion in the magnetic field of 20 kOe along the magnetic easy axis . and X-ray diffraction using a single crystal, and 238 U Mossbauer measurements using its powder in order to investigate the relationships between the ferromagnetic order and the lattice distortion. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Magnetostriction; X-ray diffraction; Quadrupole splitting; UGa2
The lattice distortion of ferromagnetic UGa2 occurs below a Curie temperature TC ¼ 123 K from the hexagonal (P6/mmm) to the orthorhombic (Cmmm) structure, which was clarified from the measurement of the lattice parameters by Andreev et al. [1]. This was also observed by the thermal expansion and sound velocity measurements by Honma et al. [2]. In a zero magnetic field, the thermal expansion coefficient along the [1 1 2% 0] direction a½1 1 2% 0 exhibits the l-type anomaly at TC : The abrupt softening based on the lattice distortion in the basal plane below TC is also reflected in the elastic constant c11 and (c11 –c12 )/2 modes. Furthermore, the other lattice distortion a½1 1 2% 0 exhibited a sharp anomaly at T n ¼ 100 K and a broad peak at about 50 K. In the magnetic field of 20 kOe *Corresponding author. Tel.: (+81)791-58-0802; fax: (+81)791-58-0948. E-mail address: [email protected] (T. Honma). 1 % Y. Onuki and S. Nasu are supported financially by a Grantin- Aid for COE Research (10CE2004) from the Ministry of Education, Science, Sports and Culture.
along the magnetic easy axis [1 1 2% 0] direction, the softening by the growth of the magnetic moment was observed in the (c11 –c12 )/2 mode. The echo is extremely dampened between about 70 and 90 K, which suggests lattice distortion in the basal plane. To further clarify the relation between the ferromagnetic order and the lattice distortion, we directly investigated the lattice distortion in the single domain structure, which was induced by reconstructing three magnetic domains under the magnetic field along the magnetic easy axis [1 1 2% 0], by thermal expansion measurements, together with X-ray diffraction and 238 U . Mossbauer measurements. We measured the temperature dependence of the lattice constant by X-ray diffraction using a high-quality single crystal of RRR ¼ 300 in a zero magnetic field. The experimental result of the lattice distortion below TC was almost the same as the previous one [1]. We also observed the three domains in the ferromagnetic phase. Within the bounds of experimental error, there was no anomaly found at T n : Figs. 1(a) and (b) show the temperature dependence of the thermal expansion coefficient að¼ dðDl=lÞ=dT)
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 2 7 1 - 6
40
UGa2
20
100 010
H = 20 kOe
(a)
0
−20 [010]
∆1/1 (x10−3)
4
0
[100]
0
50 100 Temperature (K)
50 100 Temperature (K)
150
Fig. 2. Temperature dependence of quadrupole splitting(QS) e2 qQ:
1 0
UGa2
0
(b)
3 2
905
50 e 2qQ ( mm s-1 )
α (x10−6 K−1)
T. Honma et al. / Physica B 312–313 (2002) 904–905
150
Fig. 1. (a) Temperature dependence of the thermal expansion coefficients for the [1 1 2% 0] and [1 0 1% 0] directions under an applied field of 20 kOe along the magnetic easy axis [1 1 2% 0] in UGa2 : (b) Temperature dependence of the thermal expansions in the (0 0 1) plane.
and the thermal expansion Dl=l for the [1 1 2% 0] and [1 0 1% 0] directions under an applied magnetic field of 20 kOe along [1 1 2% 0]. Two anomalies are found at 70 and 120 K, as shown in Fig. 1(a). The temperature dependencies of Dl=l in Fig. 1(b) are similar to those of the lattice constants a for [1 0 0] and b=O3 for [0 1 0] directions in the orthorhombic structure, and are shown by X-ray diffraction in a zero field. With decreasing temperature, however, a shows a shoulder around 100 K and further decreases below about 100 K. The rate of the lattice distortion below TC changes around T n ¼ 100 K. We observed the induced nuclear quadrupole interaction in the ferromagnetic state of UGa2 : The
experimental result suggests that 5f-orbitals are elongated along the magnetic easy axis [3]. Fig. 2 shows the temperature dependence of the quadrupole splitting (QS ¼ e2 qQ). QS develops below TC : The temperature dependence of QS is not monotonous, but exhibits a shoulder around 100 K. However, the anomaly, accompanied by the lattice distortion, was not observed in the temperature dependence of the recoil-free fraction of at 238 U nuclei. In conclusion, the crossover phenomena at T n in the ferromagnetic state are not due to the reconstruction of the magnetic domains, but due to the change of the 5f electronic state which also causes the characteristic change of the magnetic anisotropy in the ferromagnetic state.
References [1] A.V. Andreev, et al., J. Phys. 40 (Suppl.) (1979) C4–82. [2] T. Honma, et al., J. Phys. Soc. Japan 69 (2000) 2647. [3] S. Tsutsui, et al., J. Phys. Soc. Japan A 70 (Suppl.) (2001) 34.