- Email: [email protected]
Magnetic structure of rare-earth intermetallic compound, DyNiSn1
Journal of Magnetism and Magnetic Materials 182 (1998) 393—395
Magnetic structure of rare-earth intermetallic compound, DyNiSn1 S. Kawano!,*, Y. Andoh", M. Kurisu# ! Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka 590-04, Japan " Faculty of Education, Tottori University, Tottori 680, Japan # Japan Advanced Institute of Science and Technology, Ishikawa 923-12, Japan Received 16 September 1997
Abstract Single-crystal neutron diffraction studies have been performed on the rare-earth ternary compound, DyNiSn. Magnetic peaks at 1.5 K were analyzed by the propagation vector k"(0.641, 0.340, 0) and its third harmonics, and the magnetic structure was concluded to be approximated as a squared incommensurate one with the Ne´el temperature of 6.5 K. ( 1998 Elsevier Science B.V. All rights reserved. Keywords: Magnetic structure — modulated; Neutron diffraction; Rare-earth ternary compounds; Rare-earth—transition metal compounds
Ternary equiatomic rare-earth compounds, RNiSn (R"rare-earths) crystallize in the orthorhombic (Pnma) TiNiSi-type structure, and only the rare-earth ion bears the magnetic moment. Routsi et al. [1] have reported magnetic characteristics of RNiSn with R"heavy rare-earths and Y. DyNiSn was reported to be an antiferromagnet with the Ne´el temperature ¹ "8.2 K. On the other hand, N Kurisu et al. [2] have shown that DyNiSn has two magnetic transition points of ¹ "5.5 K and 1
* Corresponding author. Tel.: #81 724 51 2435; fax: #81 724 51 2620; e-mail: [email protected]. 1 Part of this paper was presented at ICM’97 in Cairns, Australia.
¹ "7.6 K from electrical resistivity and magnetic N susceptibility measurements. Furthermore, they have revealed that the b-axis magnetization increases metamagnetically in three steps in magnetic fields up to 5 T. Recently, neutron diffraction studies on TbNiSn [3—5] and HoNiSn [6] have elucidated that their magnetic structures are modulated only at low temperatures. However, for DyNiSn no information about any spin configuration has been reported up to the present, because Dy is much more absorbent for neutrons. The aim of the present work is to investigate magnetic structural properties of DyNiSn by single-crystal neutron diffraction. Single crystals of DyNiSn were prepared by a Czochralski method using a tri-arc furnace.
0304-8853/98/$19.00 ( 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 1 0 3 8 - X
394
S. Kawano et al. / Journal of Magnetism and Magnetic Materials 182 (1998) 393—395
Fig. 1. Magnetic satellite reflections at 1.5 K observed around (0,0,1), scanning along the a*-axis, where the nuclear (0 0 1) reflection is forbidden.
Purity of starting materials was 99.9% for Dy, 99.99% for Ni and 99.999% for Sn. The crystals were cut in a pillar-like shape of about 1] 1]7 mm3 along the b-axis. Neutron diffraction measurements were performed in the a*—c*, a*—b* and b*—c* reciprocal planes with a triple-axis spectrometer using neutrons of wavelength 2.445 A_ , installed at the ¹ — beam hole of the JRR-3M 11 reactor of JAERI in Tokai, Japan, in a double-axis mode at temperatures down to 1.5 K. Most of step scans in the reciprocal planes were carried out in 0.005 reciprocal unit step, and magnetic Bragg peak positions were determined with least-squares fitting. Fig. 1 gives a neutron diffraction pattern at 1.5 K around the (0 0 1) reflection scanning along the a* direction, where the nuclear (0 0 1) reflection is absent. We found out magnetic Bragg reflections of (h$q , 0, l) with q "0.92a* for h#l"even in 1 1 the a*—c* reciprocal plane, but there is no magnetic reflection on the a*-axis. These magnetic reflections decrease with increasing temperature and disappear around 6.5 K. As shown in Fig. 2a, this distribution of the magnetic reflections, absent on the a*-axis in the reciprocal plane implies that the magnetic moment is aligned parallel or antiparallel along the a*-axis and amplitude-modulated. On the other hand, strong magnetic reflections and their third harmonics were observed in the a*—b* reciprocal plane, as shown in Fig. 2b. In this plane, the magnetic wave is expressed by the two-component wave vector k"(q , q , 0) with x y
Fig. 2. Magnetic reflections at 1.5 K in the a*—c* reciprocal plane and in the a*—b* reciprocal plane. (a) a*—c* plane, (b) a*—b* plane, (L) magnetic reflections, (v) nuclear reflections.
q "0.641a*, and q "0.340b* at 1.5 K. Both of the x y components of the wave vector are slightly temperature-dependent, and show a little increase with temperature. Fig. 3 gives the temperature dependence of the peak height intensity of the (0.650, 0.344, 0) magnetic reflection, which is the value for the peak position at 4.2 K, and together with the (0.08, 0, 1) magnetic reflection. An abrupt disappearance of intensities and a small thermal hysteresis were observed around 6.5 K, and this temperature was identified as the Ne´el temperature. Observation of the thermal hysteresis suggests that this magnetic transition would be accompanied with a lattice distortion. The second transition at ¹ "5.5 K, which was concluded from electrical 1 resistivity and magnetic susceptibility measurements by Kurisu et al. [2], was not observed in the present study. Further measurements in the b*—c* reciprocal plane showed no magnetic Bragg reflection. The small satellites observed in the a*—c* plane should be the third harmonic components
S. Kawano et al. / Journal of Magnetism and Magnetic Materials 182 (1998) 393—395
Fig. 3. Temperature dependence of the magnetic (0.650, 0.344, 0) and (0.08, 0, 1) peak height intensities on warming (L) and cooling (h) process.
from the main satellites in the a*—b* plane. For instance, the (0.08, 0, 0) reflection comes as the third harmonics of the (1.36, 0.66, 1) and the (1.36,! 0.66, 1) satellites. The temperature dependence of the (0, 0, 1) satellites, i.e. (0.08, 0, 1), shows very gradual decrease, as shown in Fig. 3b, which is the typical behavior of higher harmonic components. The spin structure is incommensurate with k"(0.641, 0.340, 0). For the sake of simplicity, however, in the magnetic structure consideration we will consider the nearest (long-period) commensurate propagation vector, namely k@"(2, 1, 0). 3 3 The actual structure will not be too far from this commensurate one. In the k@"(2, 1, 0) structure the 3 3 magnetic unit along the a-axis is formed in an antiphase-type sequence of ##!#!! by every six spins, and also along the b-axis an antiferromagnetic sequence of ###!!! is formed by every six spins. Furthermore, diffraction patterns have higher harmonic components, so that the modulation is squared. Thus, the spin configuration of this compound may be approximated as a squared incommensurate structure, as shown in Fig. 4, for example. A similar magnetic structure has been reported for TbNiSn [5] and DyNiGe [7], having the same TiNiSi-type structure.
395
Fig. 4. Approximated representation of a squared incommensurate magnetic structure at 1.5 K for DyNiSn. The numbers, 1, 2, 3 and 4 denote the Dy spins in the chemical unit cell.
Acknowledgement This work was partially supported by a Grantin-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (No. 07230252), and performed under the visiting research program at Japan Atomic Energy Research Institute through the Institute of Solid State Physics, University of Tokyo.
References [1] C. Routsi, J.K. Yakinthos, E. Gamari-Seale, J. Magn. Magn. Mater. 98 (1991) 257. [2] M. Kurisu, H. Hori, M. Furusawa, M. Miyake, Y. Andoh, I. Oguro, K. Kindo, T. Takeuchi, A. Yamagishi, Physica B 201 (1994) 107. [3] P.A. Kotsanidis, J.K. Yakinthos, E. Roudaut, J. Magn. Magn. Mater. 124 (1993) 51. [4] J.K. Yakinthos, C. Routsi, J. Magn. Magn. Mater. 149 (1995) 273. [5] Y. Andoh, M. Kurisu, S. Kawano, Physica B (1997), in press. [6] J.K. Yakinthos, C.D. Routsi, E. Roudaut, J. Magn. Magn. Mater. 136 (1994) 65. [7] G. Andre, F. Bouree, M. Colenda, A. Oles, A. Pacyna, M. Pinot, W. Sikora, A. Szytula, J. Magn. Magn. Mater. 116 (1992) 375.
Magnetic structure of rare-earth intermetallic compound, DyNiSn1 S. Kawano!,*, Y. Andoh", M. Kurisu# ! Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka 590-04, Japan " Faculty of Education, Tottori University, Tottori 680, Japan # Japan Advanced Institute of Science and Technology, Ishikawa 923-12, Japan Received 16 September 1997
Abstract Single-crystal neutron diffraction studies have been performed on the rare-earth ternary compound, DyNiSn. Magnetic peaks at 1.5 K were analyzed by the propagation vector k"(0.641, 0.340, 0) and its third harmonics, and the magnetic structure was concluded to be approximated as a squared incommensurate one with the Ne´el temperature of 6.5 K. ( 1998 Elsevier Science B.V. All rights reserved. Keywords: Magnetic structure — modulated; Neutron diffraction; Rare-earth ternary compounds; Rare-earth—transition metal compounds
Ternary equiatomic rare-earth compounds, RNiSn (R"rare-earths) crystallize in the orthorhombic (Pnma) TiNiSi-type structure, and only the rare-earth ion bears the magnetic moment. Routsi et al. [1] have reported magnetic characteristics of RNiSn with R"heavy rare-earths and Y. DyNiSn was reported to be an antiferromagnet with the Ne´el temperature ¹ "8.2 K. On the other hand, N Kurisu et al. [2] have shown that DyNiSn has two magnetic transition points of ¹ "5.5 K and 1
* Corresponding author. Tel.: #81 724 51 2435; fax: #81 724 51 2620; e-mail: [email protected]. 1 Part of this paper was presented at ICM’97 in Cairns, Australia.
¹ "7.6 K from electrical resistivity and magnetic N susceptibility measurements. Furthermore, they have revealed that the b-axis magnetization increases metamagnetically in three steps in magnetic fields up to 5 T. Recently, neutron diffraction studies on TbNiSn [3—5] and HoNiSn [6] have elucidated that their magnetic structures are modulated only at low temperatures. However, for DyNiSn no information about any spin configuration has been reported up to the present, because Dy is much more absorbent for neutrons. The aim of the present work is to investigate magnetic structural properties of DyNiSn by single-crystal neutron diffraction. Single crystals of DyNiSn were prepared by a Czochralski method using a tri-arc furnace.
0304-8853/98/$19.00 ( 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 1 0 3 8 - X
394
S. Kawano et al. / Journal of Magnetism and Magnetic Materials 182 (1998) 393—395
Fig. 1. Magnetic satellite reflections at 1.5 K observed around (0,0,1), scanning along the a*-axis, where the nuclear (0 0 1) reflection is forbidden.
Purity of starting materials was 99.9% for Dy, 99.99% for Ni and 99.999% for Sn. The crystals were cut in a pillar-like shape of about 1] 1]7 mm3 along the b-axis. Neutron diffraction measurements were performed in the a*—c*, a*—b* and b*—c* reciprocal planes with a triple-axis spectrometer using neutrons of wavelength 2.445 A_ , installed at the ¹ — beam hole of the JRR-3M 11 reactor of JAERI in Tokai, Japan, in a double-axis mode at temperatures down to 1.5 K. Most of step scans in the reciprocal planes were carried out in 0.005 reciprocal unit step, and magnetic Bragg peak positions were determined with least-squares fitting. Fig. 1 gives a neutron diffraction pattern at 1.5 K around the (0 0 1) reflection scanning along the a* direction, where the nuclear (0 0 1) reflection is absent. We found out magnetic Bragg reflections of (h$q , 0, l) with q "0.92a* for h#l"even in 1 1 the a*—c* reciprocal plane, but there is no magnetic reflection on the a*-axis. These magnetic reflections decrease with increasing temperature and disappear around 6.5 K. As shown in Fig. 2a, this distribution of the magnetic reflections, absent on the a*-axis in the reciprocal plane implies that the magnetic moment is aligned parallel or antiparallel along the a*-axis and amplitude-modulated. On the other hand, strong magnetic reflections and their third harmonics were observed in the a*—b* reciprocal plane, as shown in Fig. 2b. In this plane, the magnetic wave is expressed by the two-component wave vector k"(q , q , 0) with x y
Fig. 2. Magnetic reflections at 1.5 K in the a*—c* reciprocal plane and in the a*—b* reciprocal plane. (a) a*—c* plane, (b) a*—b* plane, (L) magnetic reflections, (v) nuclear reflections.
q "0.641a*, and q "0.340b* at 1.5 K. Both of the x y components of the wave vector are slightly temperature-dependent, and show a little increase with temperature. Fig. 3 gives the temperature dependence of the peak height intensity of the (0.650, 0.344, 0) magnetic reflection, which is the value for the peak position at 4.2 K, and together with the (0.08, 0, 1) magnetic reflection. An abrupt disappearance of intensities and a small thermal hysteresis were observed around 6.5 K, and this temperature was identified as the Ne´el temperature. Observation of the thermal hysteresis suggests that this magnetic transition would be accompanied with a lattice distortion. The second transition at ¹ "5.5 K, which was concluded from electrical 1 resistivity and magnetic susceptibility measurements by Kurisu et al. [2], was not observed in the present study. Further measurements in the b*—c* reciprocal plane showed no magnetic Bragg reflection. The small satellites observed in the a*—c* plane should be the third harmonic components
S. Kawano et al. / Journal of Magnetism and Magnetic Materials 182 (1998) 393—395
Fig. 3. Temperature dependence of the magnetic (0.650, 0.344, 0) and (0.08, 0, 1) peak height intensities on warming (L) and cooling (h) process.
from the main satellites in the a*—b* plane. For instance, the (0.08, 0, 0) reflection comes as the third harmonics of the (1.36, 0.66, 1) and the (1.36,! 0.66, 1) satellites. The temperature dependence of the (0, 0, 1) satellites, i.e. (0.08, 0, 1), shows very gradual decrease, as shown in Fig. 3b, which is the typical behavior of higher harmonic components. The spin structure is incommensurate with k"(0.641, 0.340, 0). For the sake of simplicity, however, in the magnetic structure consideration we will consider the nearest (long-period) commensurate propagation vector, namely k@"(2, 1, 0). 3 3 The actual structure will not be too far from this commensurate one. In the k@"(2, 1, 0) structure the 3 3 magnetic unit along the a-axis is formed in an antiphase-type sequence of ##!#!! by every six spins, and also along the b-axis an antiferromagnetic sequence of ###!!! is formed by every six spins. Furthermore, diffraction patterns have higher harmonic components, so that the modulation is squared. Thus, the spin configuration of this compound may be approximated as a squared incommensurate structure, as shown in Fig. 4, for example. A similar magnetic structure has been reported for TbNiSn [5] and DyNiGe [7], having the same TiNiSi-type structure.
395
Fig. 4. Approximated representation of a squared incommensurate magnetic structure at 1.5 K for DyNiSn. The numbers, 1, 2, 3 and 4 denote the Dy spins in the chemical unit cell.
Acknowledgement This work was partially supported by a Grantin-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (No. 07230252), and performed under the visiting research program at Japan Atomic Energy Research Institute through the Institute of Solid State Physics, University of Tokyo.
References [1] C. Routsi, J.K. Yakinthos, E. Gamari-Seale, J. Magn. Magn. Mater. 98 (1991) 257. [2] M. Kurisu, H. Hori, M. Furusawa, M. Miyake, Y. Andoh, I. Oguro, K. Kindo, T. Takeuchi, A. Yamagishi, Physica B 201 (1994) 107. [3] P.A. Kotsanidis, J.K. Yakinthos, E. Roudaut, J. Magn. Magn. Mater. 124 (1993) 51. [4] J.K. Yakinthos, C. Routsi, J. Magn. Magn. Mater. 149 (1995) 273. [5] Y. Andoh, M. Kurisu, S. Kawano, Physica B (1997), in press. [6] J.K. Yakinthos, C.D. Routsi, E. Roudaut, J. Magn. Magn. Mater. 136 (1994) 65. [7] G. Andre, F. Bouree, M. Colenda, A. Oles, A. Pacyna, M. Pinot, W. Sikora, A. Szytula, J. Magn. Magn. Mater. 116 (1992) 375.