- Email: [email protected]
Magnetic properties and magnetocaloric effect in the R2PdSi3 (R = Gd, Dy and Er) compounds
Journal of Alloys and Compounds 626 (2015) 145–149
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Magnetic properties and magnetocaloric effect in the R2PdSi3 (R = Gd, Dy and Er) compounds Zhao Jun Mo a,b,⇑, Jun Shen b,⇑, Xin Qiang Gao b, Yao Liu c, Cheng Chun Tang d, Jian Feng Wu b, Feng Xia Hu c, Ji Rong Sun c, Bao Gen Shen c a
School of Material Science and Engineering, Tianjin University of Technology, Tianjin, China Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, China State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter, Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, China d School of Material Science and Engineering, Hebei University of Technology, Tianjin, China b c
a r t i c l e
i n f o
Article history: Received 4 November 2014 Received in revised form 27 November 2014 Accepted 28 November 2014 Available online 5 December 2014 Keywords: Magnetocaloric effect Magnetic entropy change Adiabatic temperature change Magnetic refrigeration
a b s t r a c t The magnetic properties and magnetocaloric effect in R2PdSi3 (R = Dy, Dy and Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Néel temperatures. And, it is found that the Dy2PdSi3 and Er2PdSi3 compounds undergo a spin-glass behavior below Néel temperature. Under the magnetic field change of 5 T, the values reach 11.8 J/kg K for Gd2PdSi3, 16.6 J/kg K for Dy2PdSi3 and 22 J/kg K for Er2PdSi3, respectively. of DSmax M in the Er2PdSi3 compound are 8 and 14.5 J/kg K for field change of 1 and Especially, the values of DSmax M 2 T, which is attributed to a field-induced metamagnetic transition from AFM to FM states. The large reversible DSM and large RC together with the absence of thermal and field hysteresis indicate that Er2PdSi3 compound could be a promising candidate for magnetic refrigeration at low temperatures. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Magnetic refrigeration based on the magnetocaloric effect (MCE) of materials has been extensively studied due to its higher energy-efficiency and lower environmental influence than conventional gas compression refrigeration [1–3]. Magnetic materials with large/giant MCE are studied experimentally and theoretically, not only due to understanding the fundamental properties of the materials but also for its potential application [4–11]. Usually, the magnitude of MCE can be characterized by magnetic entropy change (DSM) and/or adiabatic temperature change (DTad) upon the variation of magnetic field. Besides, refrigerant capacity (RC) is considered as another important parameter to quantify the heat transferred between the hot and cold sinks in an ideal refrigeration cycle. In 1997, Pecharsky et al. reported on a giant MCE of Gd5Si2 Ge2 near room temperature (TC = 276 K), which was attributed to a field induced first-order magnetic and structural transition [12]. On the other hand, the study of system with large MCE at low temperature is also important for their potential applications in special technological areas such as space science and liquefac⇑ Corresponding authors at: School of Material Science and Engineering, Tianjin University of Technology, Tianjin, China (Z.J. Mo). E-mail addresses: [email protected] (Z.J. Mo), [email protected] (J. Shen). http://dx.doi.org/10.1016/j.jallcom.2014.11.174 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.
tion of hydrogen in fuel industry [4,13]. In recent years, lots of rare earth based intermetallic compounds have been studied, and some of them have been found to possess not only large DSM but also a small hysteresis loss [14–18]. The series R2PdSi3 (R = rare earth) crystallizes in a high symmetrical AlB2 derived hexagonal structure (space group P6/mmm). The magnetic rare earth ions occupy the Al positions of the AlB2 structure while the non-magnetic Pd and Si atoms are assumed to be statistically distributed on the B positions [19]. Most of the R2PdSi3 (R = Ce, Gd, Tb, Dy, Ho, Er) compounds order antiferromagnetic (AFM) at TN between 3 K (Ce) and 25 K (Tb) with exception of the Nd compound which orders ferromagnetic (FM) at TC = 17 K [20,21]. The crystal-electric field (CEF) parameter B02 and the value of the two-ion interaction exchange integral J (Q = 0) are evaluated from the anisotropy of the AC-susceptibility measurements in the paramagnetic state in R2PdSi3 compounds (R = Tb, Dy, Ho, Er, and Tm) [22]. The anisotropic exchange interaction due to crystalline anisotropy and the anisotropy in the Fermi surface are responsible for the observed anisotropy in Gd2PdSi3 [23]. Though the magnetic properties and structures of these intermetallic compounds are extensively studied, to our knowledge, the magnetocaloric properties of R2PdSi3 are not to be particularity investigated [22–27]. In the present paper, we carry out a study on the magnetic and magnetocaloric properties of R2PdSi3 (R = Gd, Tb and Dy) compounds, especially Er2PdSi3 exhibit large MCE. The values of DSmax in the M
146
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149
Er2PdSi3 compound are 8, 14.5 and 22 J/kg K for field change of 1, 2 and 5 T. The values of RC are 111 and 381 J/kg for field change of 2 and 5 T. The large reversible MCE indicate that Er2PdSi3 compound could be a promising candidate for magnetic refrigeration at low temperatures. 2. Experiments The polycrystalline sample of R2PdSi3 (R = Gd, Tb and Dy) compounds were synthesized by arc melting of stoichiometric amounts of the elements R (99.9%), Pd (99.9%) and Si (99.9%) under a purified argon atmosphere. The content of Ho was 3% more than the theoretical value to compensate for the loss. The ingot was melted three times with the button being turned over after each melting to ensure the homogeneity. The sample was annealed at 1073 K for 7 days, and a subsequent quenching to room temperature was performed to obtain crystalline sample. Magnetizations were measured by employing a commercial superconducting quantum interference device (SQUID) magnetometer, model MPMS-7 from Quantum Design Inc. Heat capacity was measured by using a physical property measurement system (Quantum Design).
3. Results and discussion The zero-field-cooling (ZFC) and field-cooling (FC) temperature dependence of magnetization for R2PdSi3 compounds under an applied magnetic field of 0.01 T is shown in Fig. 1. It exhibits magnetic transitions from paramagnetic (PM) to AFM at 21 K for Gd2 PdSi3 and 7 K for Dy2PdSi3 and Er2PdSi3, which agree with the previous reported [24,26]. In the Dy2PdSi3 and Er2PdSi3 compounds, the additional lower temperature (<2 K) magnetic transition is probably due to an evidence of spin glass phenomenon [27]. The ZFC and FC curves are well overlapped, indicating that there is no thermal hysteresis as usually observed in magnetic materials with a second-order magnetic transition. On the other hand, we also notice that the reciprocal magnetic susceptibility (v1 m ) of the R2PdSi3 compounds follow the CurieWeiss law v1 m = (Thp)/ Cm above 10 K as shown the inset of Fig. 1. Here hp is the PM Curie temperature and Cm is the Curie– Weiss constant. The dashed lines represent a Curie–Weiss fit used to yield the asymptotic paramagnetic Curie temperatures hp and
Fig. 1. Temperature dependences of ZFC and FC magnetizations for R2PdSi3 (R = Gd, Dy and Er) compounds under the magnetic fields of 0.01 T; inset: the temperature variation of the ZFC inverse susceptibility fitted to the Curie–Weiss law.
the effective magnetic moment leff can be obtained based on the value of Cm. The slopes of both inverse susceptibilities curves are equal resulting in an experimental paramagnetic moment of leff = 7.99lB for Gd2PdSi3 in good agreement with the theoretical free-ion value for Gd3+ (lth = 7.94lB). The effective magnetic moment of leff = 9.14lB for Dy2PdSi3 is smaller than the free-ion value for Dy3+ (lth = 10.64lB) and the leff = 9.18lB for Er2PdSi3 is insignificantly smaller than the free-ion value for Er3+ (lth = 9.58lB). The reduction in ordered state moment for Dy3+ and Er3+ might be attributed to the magnetic anisotropy and crystal field effects [28]. This fact implies the absence of localized magnetic moment on Pd atoms in R2PdSi3, which is in agreement with the result of other reports [22]. As mentioned above all investigated R2PdSi3 samples undergo an antiferromagnetic transition. The values of hp turn out to be the same for both geometries, with the same magnitude as that of TN, however, with a positive sign suggesting the existence of strong ferromagnetic correlations. It agrees with the positive values of hp for single crystals of R2PdSi3 compounds with the easy axis [24]. Frontzek et al. had been reported that ferromagnetic and antiferromagnetic exchange interaction as well as CEF effect is competing interactions in Dy2PdSi3 and Er2PdSi3 [22]. Gd3+ is an S-state ion and thus not susceptible to the CEF effect, the anisotropic exchange interaction along with the Fermi surface anisotropy may be responsible for that in Gd2PdSi3 [25]. Therefore, we consider that the polycrystalline samples of R2PdSi3 (R = Gd, Tb and Dy) compounds are more easily along the magnetic easy direction to crystal. Fig. 2 shows the magnetization data obtained for Gd2PdSi3 compound. The results show that the system orders antiferromagnetically below TN. The magnetic and electronic properties of Gd2PdSi3 have been already investigated with various methods on polycrystalline and single crystalline samples. Gd3+ is an S-state ion and thus not susceptible to the CEF effect, the anisotropic exchange interaction along with the Fermi surface anisotropy may be responsible for that in Gd2PdSi3 [25,29]. The magnetic properties in the ordered state are anisotropic. The isothermal magnetization (M) behavior at 2 K for increasing and decreasing magnetic fields (H) is shown in Fig. 2(a) for Gd2PdSi3. There are two step-like metamagnetic transitions, one around 4 kOe (Hc1) and the other around 9 kOe (Hc2). In the single crystal of Gd2PdSi3, the two step-like transitions seen in the measurement along c-direction, while the magnetization curve along the a-direction does not show step-like transitions. Evidently, there is a small hysteresis around these transitions, indicating the first-order nature of the transitions. The inset of Fig. 2(a) shows the isothermal magnetization curves as a function of magnetic field in a temperature range from 2 to 19 K. It can be seen that there exist intersections among the curves. The low temperature magnetization is smaller than the high temperature value in low fields. On the contrary, this condition reverses in higher fields. This agrees with the AFM ordering of the compound below TN [30]. Above TN, The isothermal curves show an appreciable nonlinearity, which indicate the existence of short-range correlations as shown in Fig. 2(b). Fig. 3 shows the isothermal magnetization curves of R2PdSi3 (Dy and Er) in applied fields of up to 5 T with a wide temperature range. In the Er2PdSi3 compound, the isothermal curves for T < TN show a rapid increase at considerably low fields, and tend to saturate in strong magnetic fields, which indicate the FM ground state nature. It indicates the occurrence of a field-induced AFM-FM transition below TN. The isotherms are far from linear even at temperatures above TN, which implies the existence of short-range FM correlations in the PM state. Fig. 4 shows the Arrott plots of R2PdSi3 (R = Gd, Dy, Er) compounds around the order temperature. As is well known, the negative slope of Arrott plot implies a first-order magnetic transition,
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149
147
Fig. 2. (a) Magnetic isotherms of Gd2PdSi3 compound measured with increasing field and decreasing field at 2 K; inset: the low field magnetization isotherms for Gd2PdSi3 at 2–19 K; (b) magnetization isotherms of collected in the temperature range of 21–54 K.
Fig. 3. Magnetization isotherms of Dy2PdSi3 and Er2PdSi3 collected in the wide temperature range.
Fig. 4. The Arrott plots of R2PdSi3 (R = Gd, Dy and Er) compounds around the order temperature range.
while a positive slope indicates a second-order transition [31]. Herein the Arrott plot of R2PdSi3 (R = Gd, Dy, Er) compounds exhibit a negative slope below TN, which confirm a first-order magnetic transition from AFM to FM. The DSM value of R2PdSi3 compound calculated from the magnetization isotherms by using an integral version of Maxwell’s RH thermodynamic relation DSðT; HÞ ¼ 0 ð@M=@TÞH dH in which, T is the absolute temperature and H is the applied field [32]. Fig. 5 shows the values of DSM for different magnetic field changes as a function of temperature for different magnetic field changes.
The negative values of DSM for R2PdSi3 compounds were observed at low temperature, which also confirm the antiferromagnetic order below TN. The value of DSM is found to increase monotonically with applied magnetic field increasing. Under the magnetic field change from 0 to 5 T, the maximum values of DSM (DSmax M ) reach 11.8 J/kg K for Gd2PdSi3 at 26 K, 16.6 J/kg K for Dy2PdSi3 at 10 K and 22 J/kg K for Er2PdSi3 at 9.5 K, respectively. Especially, the DSM values of the Er2PdSi3 compound are 8 and 14.5 J/kg K at 7.5 K for field change of 1 and 2 T, which can be realized by a permanent magnet. In the Er2PdSi3 compound, the value
148
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149
Fig. 5. Temperature dependences of magnetic entropy change for R2PdSi3 (R = Gd, Dy and Er) compounds under different magnetic field changes.
Table 1 The magnetic order transition temperature (T), DSMmax and RC with the field change of 2 and 5 T for Er2PdSi3 and other MCE materials. Compounds
HoNi2B2C DyCuSi TmCuAl ErMn2Si2 ErRu2Si2 Er2PdSi3
T (K)
6.5 16 4 4.5 5.5 7
DSM (J/kg K)
RC (J/kg)
2T
5T
2T
5T
Refs.
7.3 10.5 17.2 20 11 14.5
19.2 24 24.3 25.2 17.6 22
62 – 129 130 55 111
290 381 372 365 262 381
[36] [34] [37] [38] [16] This paper
without thermal and field hysteresis loss for field changes of 5 T, respectively. A field-induced metamagnetic transition from AFM to FM states is observed in these compounds and the large reversible MCE is attributed to AFM-PM and FM-PM the transitions. Especially, for the magnetic field changes of 2 T, the value of DSmax is M 14.5 J/kg K and RC is 111 J/kg, respectively. The low magnetic field can be realized by permanent magnet. Therefore, the large reversible MCE and large RC make the Er2PdSi3 a promising candidate for magnetic refrigeration. Acknowledgement
of DSmax is much larger than most potential magnetic refrigerant M materials having similar transition temperatures and subjected to the same field changes (DH = 0–2 T), such as ErFeSi (14.2 J/kg K) [33], ErRu2Si2 (11 J/kg K) [16] and DyCuSi (10.5 J/kg K) [34]. Magnetic refrigerant capacity (RC) is considered to be another important requirement of a potential magnetic refrigerant. The RT RC, defined as a cooling capacity of RC ¼ T 12 jDSM jdT, is calculated by numerically integrating the area under the DSM–T curve, where T1 and T2 are the temperatures at half maximum of the peak taken as the integration limits [35]. The values of RC are evaluated to be 317 J/kg for Gd2PdSi3, 288 J/kg for Dy2PdSi3 and 381 J/kg for Er2PdSi3 under the magnetic field changes of 5 T, respectively. For comparison, the magnetocaloric properties of Er2PdSi3 and some other refrigerant materials with a magnetic ordering temperature around 10 K are listed in Table 1. Particularly, under the magnetic field changes of 2 T, value of RC is evaluated to be 111 J/kg for Er2PdSi3 compound. The large DSmax M and RC indicate that the Er2PdSi3 compound appears to be a very attractive candidate material for use in a magnetic refrigerator working in low temperature. 4. Conclusion In summary, the R2PdSi3 (R = Gd, Dy and Er) intermetallic compounds with the AlB2 derived hexagonal structure have been prepared and the magnetic and magnetocaloric properties of this system have been studied experimentally. All these compounds possess an AFM-PM transition around their respective Neel temperatures. The Dy2PdSi3 and Er2PdSi3 compounds undergo a spinglass behavior below Neel temperature. Gd2PdSi3 compound exhibits two-step first-order-like metamagnetic transitions for the magnetic field. The calculation of magnetic entropy change shows that the R2PdSi3 compounds, under the magnetic field change of 5 T, the values of DSmax reach 11.8 J/kg K for Gd2PdSi3, M 16.6 J/kg K for Dy2PdSi3. Especially, ErCu2Si2 exhibits large MCEs, the value of DSmax (22 J/kg K) and RC (381 J/kg) are obtained M
This work was supported by the National Natural Science Foundation of China (Grant Nos. 51271192, 11104337, 11274357). References [1] K.A. Gschneidner Jr., V.K. Pecharsky, A.O. Tsoko, Rep. Prog. Phys. 68 (2005) 1479. [2] M.H. Phan, S.C. Yu, J. Magn. Magn. Mater. 308 (2007) 325. [3] B.G. Shen, J.R. Sun, F.X. Hu, H.W. Zhang, Z.H. Cheng, Adv. Mater. 21 (2009) 4545. [4] N.A. de Oliveira, P.J. von Ranke, Phys. Rep. 489 (2010) 89. [5] O. Gutfleisch, M.A. Willard, E. Bruck, C.H. Chen, S.G. Sankar, J. Ping, Liu, Adv. Mater. 23 (2011) 821. [6] V. Franco, J.S. Blazquez, B. Ingale, A. Conde, Annu. Rev. Mater. Res. 42 (2012) 305. [7] Z.J. Mo, J. Shen, L.Q. Yan, C.C. Tang, J. Lin, J.F. Wu, J.R. Sun, L.C. Wang, X.Q. Zheng, B.G. Shen, Appl. Phys. Lett. 103 (2013) 052409. [8] J. Liu, T. Gottschall, K.P. Skokov, J.D. Moore, O. Gutfleisch, Nat. Mater. 11 (2012) 620. [9] M.H. Phan, G.T. Woods, A. Chaturvedi, S. Stefanoski, G.S. Nolas, H. Srikanth, Appl. Phys. Lett. 93 (2008) 252505. [10] L. Li, K. Nishimura, Appl. Phys. Lett. 95 (2009) 132505. [11] J.L. Wang, L. Caron, S.J. Campbell, S.J. Kennedy, M. Hofmann, Z.X. Cheng, M.F. Md Din, A.J. Studer, E. Br €uck, S.X. Dou, Phys. Rev. Lett. 110 (2013) 217211. [12] V.K. Pecharsky, K.A. Gschneidner Jr., Phys. Rev. Lett. 78 (1997) 4494. [13] M. Balli, D. Fruchart, D. Gignoux, J. Alloys Comp. 509 (2011) 3907. [14] J.L. Wang, S.J. Campbell, J.M. Cadogan, A.J. Studer, R. Zeng, S.X. Dou, Appl. Phys. Lett. 98 (2011) 232509. [15] Q.Y. Dong, J. Chen, J. Shen, J.R. Sun, B.G. Shen, Appl. Phys. Lett. 99 (2011) 132504. [16] Tapas Samanta, I. Das, S. Banerjee, Appl. Phys. Lett. 91 (2007) 152506. [17] L.W. Li, T. Namiki, D.X. Huo, Z.H. Qian, K. Nishimura, Appl. Phys. Lett. 103 (2013) 222405. [18] L.W. Li, O. Niehaus, M. Kersting, R. Pöttgen, Appl. Phys. Lett. 104 (2014) 092416. [19] R. Mallik, E.V. Sampathkumaran, M. Strecker, G. Wortmann, P.L. Paulose, Y. Ueda, J. Magn. Magn. Mater. 185 (1998) L135. [20] A. Szytula, M. Hofmann, B. Penc, M. Slaski, S. Majumdar, E.V. Sampathkumaran, A. Zygmunt, J. Magn. Magn. Mater. 202 (1999) 365. [21] P.A. Kotsanidis, J.K. Yakinthos, E. Gamari-Seale, J. Magn. Magn. Mater. 87 (1990) 199. [22] M. Frontzek, A. Kreyssig, M. Doerr, M. Rotter, G. Behr, W. Löser, I. Mazilu, M. Loewenhaupt, J. Magn. Magn. Mater. 301 (2006) 398–406. [23] S.R. Saha, H. Sugawara, T.D. Matsuda, Y. Aoki, H. Sato, E.V. Sampathkumaran, Physica B 281–282 (2000) 116–117.
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149 [24] E.V. Sampathkumaran, H. Bitterlich, K.K. Iyer, W. Löser, G. Behr, Phys. Rev. B 66 (2002) 052409. [25] M. Frontzek, F. Tang, P. Link, A. Schneidewind, J.U. Hoffman, J.M. Mignot, M. Loewenhaupt, Phys. Rev. B 82 (2010) 174401. [26] E.V. Sampathkumaran, I. Das, R. Rawat, Subham Majumdar, Appl. Phys. Lett. 77 (2000) 418. [27] M. Frontzek, A. Kreyssig, M. Doerr, A. Schneidewind, J.U. Hoffman, M. Loewenhaupt, J. Phys.: Condens. Matter 19 (2007) 145276. [28] S. Baran, D. Kaczorowski, A. Arulraj, B. Penc, A. Szytuła, J. Magn. Magn. Mater. 323 (2011) 833–837. [29] R. Mallik, E.V. Sampathkumaran, M. Strecker, G. Wortmann, Eur. Phys. Lett. 41 (3) (1998) 315–320. [30] N.K. Singh, K.G. Suresh, R. Nirmala, A.K. Nigam, S.K. Malik, J. Magn. Magn. Mater. 302 (2006) 302.
149
[31] S.K. Banerjee, Phys. Lett. 12 (1964) 16. [32] V.K. Pecharsky, K.A. Gschneidner Jr., J. Appl. Phys. 86 (1999) 565. [33] H. Zhang, B.G. Shen, Z.Y. Xu, J. Shen, F.X. Hu, J.R. Sun, Y. Long, Appl. Phys. Lett. 102 (2013) 092401. [34] J. Chen, B.G. Shen, Q.Y. Dong, J.R. Sun, Solid State Commun. 150 (2010) 1429– 1431. [35] K.A. Gschneidner Jr., V.K. Pecharsky, A.O. Pecharsky, C.B. Zimm, Mater. Sci. Forum 315 (1999) 69. [36] L. Li, K. Nishimura, D. Huo, M. Kadonaga, T. Namiki, Z. Qian, Appl. Phys. Exp. 4 (2011) 093101. [37] Z.J. Mo, J. Shen, L.Q. Yan, J.F. Wu, L.C. Wang, C.C. Tang, B.G. Shen, Appl. Phys. Lett. 102 (2013) 192407. [38] L. Li, K. Nishimura, W.D. Hutchison, Z. Qian, D. Huo, T. Namiki, Appl. Phys. Lett. 100 (2012) 152403.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Magnetic properties and magnetocaloric effect in the R2PdSi3 (R = Gd, Dy and Er) compounds Zhao Jun Mo a,b,⇑, Jun Shen b,⇑, Xin Qiang Gao b, Yao Liu c, Cheng Chun Tang d, Jian Feng Wu b, Feng Xia Hu c, Ji Rong Sun c, Bao Gen Shen c a
School of Material Science and Engineering, Tianjin University of Technology, Tianjin, China Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, China State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter, Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, China d School of Material Science and Engineering, Hebei University of Technology, Tianjin, China b c
a r t i c l e
i n f o
Article history: Received 4 November 2014 Received in revised form 27 November 2014 Accepted 28 November 2014 Available online 5 December 2014 Keywords: Magnetocaloric effect Magnetic entropy change Adiabatic temperature change Magnetic refrigeration
a b s t r a c t The magnetic properties and magnetocaloric effect in R2PdSi3 (R = Dy, Dy and Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Néel temperatures. And, it is found that the Dy2PdSi3 and Er2PdSi3 compounds undergo a spin-glass behavior below Néel temperature. Under the magnetic field change of 5 T, the values reach 11.8 J/kg K for Gd2PdSi3, 16.6 J/kg K for Dy2PdSi3 and 22 J/kg K for Er2PdSi3, respectively. of DSmax M in the Er2PdSi3 compound are 8 and 14.5 J/kg K for field change of 1 and Especially, the values of DSmax M 2 T, which is attributed to a field-induced metamagnetic transition from AFM to FM states. The large reversible DSM and large RC together with the absence of thermal and field hysteresis indicate that Er2PdSi3 compound could be a promising candidate for magnetic refrigeration at low temperatures. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Magnetic refrigeration based on the magnetocaloric effect (MCE) of materials has been extensively studied due to its higher energy-efficiency and lower environmental influence than conventional gas compression refrigeration [1–3]. Magnetic materials with large/giant MCE are studied experimentally and theoretically, not only due to understanding the fundamental properties of the materials but also for its potential application [4–11]. Usually, the magnitude of MCE can be characterized by magnetic entropy change (DSM) and/or adiabatic temperature change (DTad) upon the variation of magnetic field. Besides, refrigerant capacity (RC) is considered as another important parameter to quantify the heat transferred between the hot and cold sinks in an ideal refrigeration cycle. In 1997, Pecharsky et al. reported on a giant MCE of Gd5Si2 Ge2 near room temperature (TC = 276 K), which was attributed to a field induced first-order magnetic and structural transition [12]. On the other hand, the study of system with large MCE at low temperature is also important for their potential applications in special technological areas such as space science and liquefac⇑ Corresponding authors at: School of Material Science and Engineering, Tianjin University of Technology, Tianjin, China (Z.J. Mo). E-mail addresses: [email protected] (Z.J. Mo), [email protected] (J. Shen). http://dx.doi.org/10.1016/j.jallcom.2014.11.174 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.
tion of hydrogen in fuel industry [4,13]. In recent years, lots of rare earth based intermetallic compounds have been studied, and some of them have been found to possess not only large DSM but also a small hysteresis loss [14–18]. The series R2PdSi3 (R = rare earth) crystallizes in a high symmetrical AlB2 derived hexagonal structure (space group P6/mmm). The magnetic rare earth ions occupy the Al positions of the AlB2 structure while the non-magnetic Pd and Si atoms are assumed to be statistically distributed on the B positions [19]. Most of the R2PdSi3 (R = Ce, Gd, Tb, Dy, Ho, Er) compounds order antiferromagnetic (AFM) at TN between 3 K (Ce) and 25 K (Tb) with exception of the Nd compound which orders ferromagnetic (FM) at TC = 17 K [20,21]. The crystal-electric field (CEF) parameter B02 and the value of the two-ion interaction exchange integral J (Q = 0) are evaluated from the anisotropy of the AC-susceptibility measurements in the paramagnetic state in R2PdSi3 compounds (R = Tb, Dy, Ho, Er, and Tm) [22]. The anisotropic exchange interaction due to crystalline anisotropy and the anisotropy in the Fermi surface are responsible for the observed anisotropy in Gd2PdSi3 [23]. Though the magnetic properties and structures of these intermetallic compounds are extensively studied, to our knowledge, the magnetocaloric properties of R2PdSi3 are not to be particularity investigated [22–27]. In the present paper, we carry out a study on the magnetic and magnetocaloric properties of R2PdSi3 (R = Gd, Tb and Dy) compounds, especially Er2PdSi3 exhibit large MCE. The values of DSmax in the M
146
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149
Er2PdSi3 compound are 8, 14.5 and 22 J/kg K for field change of 1, 2 and 5 T. The values of RC are 111 and 381 J/kg for field change of 2 and 5 T. The large reversible MCE indicate that Er2PdSi3 compound could be a promising candidate for magnetic refrigeration at low temperatures. 2. Experiments The polycrystalline sample of R2PdSi3 (R = Gd, Tb and Dy) compounds were synthesized by arc melting of stoichiometric amounts of the elements R (99.9%), Pd (99.9%) and Si (99.9%) under a purified argon atmosphere. The content of Ho was 3% more than the theoretical value to compensate for the loss. The ingot was melted three times with the button being turned over after each melting to ensure the homogeneity. The sample was annealed at 1073 K for 7 days, and a subsequent quenching to room temperature was performed to obtain crystalline sample. Magnetizations were measured by employing a commercial superconducting quantum interference device (SQUID) magnetometer, model MPMS-7 from Quantum Design Inc. Heat capacity was measured by using a physical property measurement system (Quantum Design).
3. Results and discussion The zero-field-cooling (ZFC) and field-cooling (FC) temperature dependence of magnetization for R2PdSi3 compounds under an applied magnetic field of 0.01 T is shown in Fig. 1. It exhibits magnetic transitions from paramagnetic (PM) to AFM at 21 K for Gd2 PdSi3 and 7 K for Dy2PdSi3 and Er2PdSi3, which agree with the previous reported [24,26]. In the Dy2PdSi3 and Er2PdSi3 compounds, the additional lower temperature (<2 K) magnetic transition is probably due to an evidence of spin glass phenomenon [27]. The ZFC and FC curves are well overlapped, indicating that there is no thermal hysteresis as usually observed in magnetic materials with a second-order magnetic transition. On the other hand, we also notice that the reciprocal magnetic susceptibility (v1 m ) of the R2PdSi3 compounds follow the CurieWeiss law v1 m = (Thp)/ Cm above 10 K as shown the inset of Fig. 1. Here hp is the PM Curie temperature and Cm is the Curie– Weiss constant. The dashed lines represent a Curie–Weiss fit used to yield the asymptotic paramagnetic Curie temperatures hp and
Fig. 1. Temperature dependences of ZFC and FC magnetizations for R2PdSi3 (R = Gd, Dy and Er) compounds under the magnetic fields of 0.01 T; inset: the temperature variation of the ZFC inverse susceptibility fitted to the Curie–Weiss law.
the effective magnetic moment leff can be obtained based on the value of Cm. The slopes of both inverse susceptibilities curves are equal resulting in an experimental paramagnetic moment of leff = 7.99lB for Gd2PdSi3 in good agreement with the theoretical free-ion value for Gd3+ (lth = 7.94lB). The effective magnetic moment of leff = 9.14lB for Dy2PdSi3 is smaller than the free-ion value for Dy3+ (lth = 10.64lB) and the leff = 9.18lB for Er2PdSi3 is insignificantly smaller than the free-ion value for Er3+ (lth = 9.58lB). The reduction in ordered state moment for Dy3+ and Er3+ might be attributed to the magnetic anisotropy and crystal field effects [28]. This fact implies the absence of localized magnetic moment on Pd atoms in R2PdSi3, which is in agreement with the result of other reports [22]. As mentioned above all investigated R2PdSi3 samples undergo an antiferromagnetic transition. The values of hp turn out to be the same for both geometries, with the same magnitude as that of TN, however, with a positive sign suggesting the existence of strong ferromagnetic correlations. It agrees with the positive values of hp for single crystals of R2PdSi3 compounds with the easy axis [24]. Frontzek et al. had been reported that ferromagnetic and antiferromagnetic exchange interaction as well as CEF effect is competing interactions in Dy2PdSi3 and Er2PdSi3 [22]. Gd3+ is an S-state ion and thus not susceptible to the CEF effect, the anisotropic exchange interaction along with the Fermi surface anisotropy may be responsible for that in Gd2PdSi3 [25]. Therefore, we consider that the polycrystalline samples of R2PdSi3 (R = Gd, Tb and Dy) compounds are more easily along the magnetic easy direction to crystal. Fig. 2 shows the magnetization data obtained for Gd2PdSi3 compound. The results show that the system orders antiferromagnetically below TN. The magnetic and electronic properties of Gd2PdSi3 have been already investigated with various methods on polycrystalline and single crystalline samples. Gd3+ is an S-state ion and thus not susceptible to the CEF effect, the anisotropic exchange interaction along with the Fermi surface anisotropy may be responsible for that in Gd2PdSi3 [25,29]. The magnetic properties in the ordered state are anisotropic. The isothermal magnetization (M) behavior at 2 K for increasing and decreasing magnetic fields (H) is shown in Fig. 2(a) for Gd2PdSi3. There are two step-like metamagnetic transitions, one around 4 kOe (Hc1) and the other around 9 kOe (Hc2). In the single crystal of Gd2PdSi3, the two step-like transitions seen in the measurement along c-direction, while the magnetization curve along the a-direction does not show step-like transitions. Evidently, there is a small hysteresis around these transitions, indicating the first-order nature of the transitions. The inset of Fig. 2(a) shows the isothermal magnetization curves as a function of magnetic field in a temperature range from 2 to 19 K. It can be seen that there exist intersections among the curves. The low temperature magnetization is smaller than the high temperature value in low fields. On the contrary, this condition reverses in higher fields. This agrees with the AFM ordering of the compound below TN [30]. Above TN, The isothermal curves show an appreciable nonlinearity, which indicate the existence of short-range correlations as shown in Fig. 2(b). Fig. 3 shows the isothermal magnetization curves of R2PdSi3 (Dy and Er) in applied fields of up to 5 T with a wide temperature range. In the Er2PdSi3 compound, the isothermal curves for T < TN show a rapid increase at considerably low fields, and tend to saturate in strong magnetic fields, which indicate the FM ground state nature. It indicates the occurrence of a field-induced AFM-FM transition below TN. The isotherms are far from linear even at temperatures above TN, which implies the existence of short-range FM correlations in the PM state. Fig. 4 shows the Arrott plots of R2PdSi3 (R = Gd, Dy, Er) compounds around the order temperature. As is well known, the negative slope of Arrott plot implies a first-order magnetic transition,
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149
147
Fig. 2. (a) Magnetic isotherms of Gd2PdSi3 compound measured with increasing field and decreasing field at 2 K; inset: the low field magnetization isotherms for Gd2PdSi3 at 2–19 K; (b) magnetization isotherms of collected in the temperature range of 21–54 K.
Fig. 3. Magnetization isotherms of Dy2PdSi3 and Er2PdSi3 collected in the wide temperature range.
Fig. 4. The Arrott plots of R2PdSi3 (R = Gd, Dy and Er) compounds around the order temperature range.
while a positive slope indicates a second-order transition [31]. Herein the Arrott plot of R2PdSi3 (R = Gd, Dy, Er) compounds exhibit a negative slope below TN, which confirm a first-order magnetic transition from AFM to FM. The DSM value of R2PdSi3 compound calculated from the magnetization isotherms by using an integral version of Maxwell’s RH thermodynamic relation DSðT; HÞ ¼ 0 ð@M=@TÞH dH in which, T is the absolute temperature and H is the applied field [32]. Fig. 5 shows the values of DSM for different magnetic field changes as a function of temperature for different magnetic field changes.
The negative values of DSM for R2PdSi3 compounds were observed at low temperature, which also confirm the antiferromagnetic order below TN. The value of DSM is found to increase monotonically with applied magnetic field increasing. Under the magnetic field change from 0 to 5 T, the maximum values of DSM (DSmax M ) reach 11.8 J/kg K for Gd2PdSi3 at 26 K, 16.6 J/kg K for Dy2PdSi3 at 10 K and 22 J/kg K for Er2PdSi3 at 9.5 K, respectively. Especially, the DSM values of the Er2PdSi3 compound are 8 and 14.5 J/kg K at 7.5 K for field change of 1 and 2 T, which can be realized by a permanent magnet. In the Er2PdSi3 compound, the value
148
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149
Fig. 5. Temperature dependences of magnetic entropy change for R2PdSi3 (R = Gd, Dy and Er) compounds under different magnetic field changes.
Table 1 The magnetic order transition temperature (T), DSMmax and RC with the field change of 2 and 5 T for Er2PdSi3 and other MCE materials. Compounds
HoNi2B2C DyCuSi TmCuAl ErMn2Si2 ErRu2Si2 Er2PdSi3
T (K)
6.5 16 4 4.5 5.5 7
DSM (J/kg K)
RC (J/kg)
2T
5T
2T
5T
Refs.
7.3 10.5 17.2 20 11 14.5
19.2 24 24.3 25.2 17.6 22
62 – 129 130 55 111
290 381 372 365 262 381
[36] [34] [37] [38] [16] This paper
without thermal and field hysteresis loss for field changes of 5 T, respectively. A field-induced metamagnetic transition from AFM to FM states is observed in these compounds and the large reversible MCE is attributed to AFM-PM and FM-PM the transitions. Especially, for the magnetic field changes of 2 T, the value of DSmax is M 14.5 J/kg K and RC is 111 J/kg, respectively. The low magnetic field can be realized by permanent magnet. Therefore, the large reversible MCE and large RC make the Er2PdSi3 a promising candidate for magnetic refrigeration. Acknowledgement
of DSmax is much larger than most potential magnetic refrigerant M materials having similar transition temperatures and subjected to the same field changes (DH = 0–2 T), such as ErFeSi (14.2 J/kg K) [33], ErRu2Si2 (11 J/kg K) [16] and DyCuSi (10.5 J/kg K) [34]. Magnetic refrigerant capacity (RC) is considered to be another important requirement of a potential magnetic refrigerant. The RT RC, defined as a cooling capacity of RC ¼ T 12 jDSM jdT, is calculated by numerically integrating the area under the DSM–T curve, where T1 and T2 are the temperatures at half maximum of the peak taken as the integration limits [35]. The values of RC are evaluated to be 317 J/kg for Gd2PdSi3, 288 J/kg for Dy2PdSi3 and 381 J/kg for Er2PdSi3 under the magnetic field changes of 5 T, respectively. For comparison, the magnetocaloric properties of Er2PdSi3 and some other refrigerant materials with a magnetic ordering temperature around 10 K are listed in Table 1. Particularly, under the magnetic field changes of 2 T, value of RC is evaluated to be 111 J/kg for Er2PdSi3 compound. The large DSmax M and RC indicate that the Er2PdSi3 compound appears to be a very attractive candidate material for use in a magnetic refrigerator working in low temperature. 4. Conclusion In summary, the R2PdSi3 (R = Gd, Dy and Er) intermetallic compounds with the AlB2 derived hexagonal structure have been prepared and the magnetic and magnetocaloric properties of this system have been studied experimentally. All these compounds possess an AFM-PM transition around their respective Neel temperatures. The Dy2PdSi3 and Er2PdSi3 compounds undergo a spinglass behavior below Neel temperature. Gd2PdSi3 compound exhibits two-step first-order-like metamagnetic transitions for the magnetic field. The calculation of magnetic entropy change shows that the R2PdSi3 compounds, under the magnetic field change of 5 T, the values of DSmax reach 11.8 J/kg K for Gd2PdSi3, M 16.6 J/kg K for Dy2PdSi3. Especially, ErCu2Si2 exhibits large MCEs, the value of DSmax (22 J/kg K) and RC (381 J/kg) are obtained M
This work was supported by the National Natural Science Foundation of China (Grant Nos. 51271192, 11104337, 11274357). References [1] K.A. Gschneidner Jr., V.K. Pecharsky, A.O. Tsoko, Rep. Prog. Phys. 68 (2005) 1479. [2] M.H. Phan, S.C. Yu, J. Magn. Magn. Mater. 308 (2007) 325. [3] B.G. Shen, J.R. Sun, F.X. Hu, H.W. Zhang, Z.H. Cheng, Adv. Mater. 21 (2009) 4545. [4] N.A. de Oliveira, P.J. von Ranke, Phys. Rep. 489 (2010) 89. [5] O. Gutfleisch, M.A. Willard, E. Bruck, C.H. Chen, S.G. Sankar, J. Ping, Liu, Adv. Mater. 23 (2011) 821. [6] V. Franco, J.S. Blazquez, B. Ingale, A. Conde, Annu. Rev. Mater. Res. 42 (2012) 305. [7] Z.J. Mo, J. Shen, L.Q. Yan, C.C. Tang, J. Lin, J.F. Wu, J.R. Sun, L.C. Wang, X.Q. Zheng, B.G. Shen, Appl. Phys. Lett. 103 (2013) 052409. [8] J. Liu, T. Gottschall, K.P. Skokov, J.D. Moore, O. Gutfleisch, Nat. Mater. 11 (2012) 620. [9] M.H. Phan, G.T. Woods, A. Chaturvedi, S. Stefanoski, G.S. Nolas, H. Srikanth, Appl. Phys. Lett. 93 (2008) 252505. [10] L. Li, K. Nishimura, Appl. Phys. Lett. 95 (2009) 132505. [11] J.L. Wang, L. Caron, S.J. Campbell, S.J. Kennedy, M. Hofmann, Z.X. Cheng, M.F. Md Din, A.J. Studer, E. Br €uck, S.X. Dou, Phys. Rev. Lett. 110 (2013) 217211. [12] V.K. Pecharsky, K.A. Gschneidner Jr., Phys. Rev. Lett. 78 (1997) 4494. [13] M. Balli, D. Fruchart, D. Gignoux, J. Alloys Comp. 509 (2011) 3907. [14] J.L. Wang, S.J. Campbell, J.M. Cadogan, A.J. Studer, R. Zeng, S.X. Dou, Appl. Phys. Lett. 98 (2011) 232509. [15] Q.Y. Dong, J. Chen, J. Shen, J.R. Sun, B.G. Shen, Appl. Phys. Lett. 99 (2011) 132504. [16] Tapas Samanta, I. Das, S. Banerjee, Appl. Phys. Lett. 91 (2007) 152506. [17] L.W. Li, T. Namiki, D.X. Huo, Z.H. Qian, K. Nishimura, Appl. Phys. Lett. 103 (2013) 222405. [18] L.W. Li, O. Niehaus, M. Kersting, R. Pöttgen, Appl. Phys. Lett. 104 (2014) 092416. [19] R. Mallik, E.V. Sampathkumaran, M. Strecker, G. Wortmann, P.L. Paulose, Y. Ueda, J. Magn. Magn. Mater. 185 (1998) L135. [20] A. Szytula, M. Hofmann, B. Penc, M. Slaski, S. Majumdar, E.V. Sampathkumaran, A. Zygmunt, J. Magn. Magn. Mater. 202 (1999) 365. [21] P.A. Kotsanidis, J.K. Yakinthos, E. Gamari-Seale, J. Magn. Magn. Mater. 87 (1990) 199. [22] M. Frontzek, A. Kreyssig, M. Doerr, M. Rotter, G. Behr, W. Löser, I. Mazilu, M. Loewenhaupt, J. Magn. Magn. Mater. 301 (2006) 398–406. [23] S.R. Saha, H. Sugawara, T.D. Matsuda, Y. Aoki, H. Sato, E.V. Sampathkumaran, Physica B 281–282 (2000) 116–117.
Z.J. Mo et al. / Journal of Alloys and Compounds 626 (2015) 145–149 [24] E.V. Sampathkumaran, H. Bitterlich, K.K. Iyer, W. Löser, G. Behr, Phys. Rev. B 66 (2002) 052409. [25] M. Frontzek, F. Tang, P. Link, A. Schneidewind, J.U. Hoffman, J.M. Mignot, M. Loewenhaupt, Phys. Rev. B 82 (2010) 174401. [26] E.V. Sampathkumaran, I. Das, R. Rawat, Subham Majumdar, Appl. Phys. Lett. 77 (2000) 418. [27] M. Frontzek, A. Kreyssig, M. Doerr, A. Schneidewind, J.U. Hoffman, M. Loewenhaupt, J. Phys.: Condens. Matter 19 (2007) 145276. [28] S. Baran, D. Kaczorowski, A. Arulraj, B. Penc, A. Szytuła, J. Magn. Magn. Mater. 323 (2011) 833–837. [29] R. Mallik, E.V. Sampathkumaran, M. Strecker, G. Wortmann, Eur. Phys. Lett. 41 (3) (1998) 315–320. [30] N.K. Singh, K.G. Suresh, R. Nirmala, A.K. Nigam, S.K. Malik, J. Magn. Magn. Mater. 302 (2006) 302.
149
[31] S.K. Banerjee, Phys. Lett. 12 (1964) 16. [32] V.K. Pecharsky, K.A. Gschneidner Jr., J. Appl. Phys. 86 (1999) 565. [33] H. Zhang, B.G. Shen, Z.Y. Xu, J. Shen, F.X. Hu, J.R. Sun, Y. Long, Appl. Phys. Lett. 102 (2013) 092401. [34] J. Chen, B.G. Shen, Q.Y. Dong, J.R. Sun, Solid State Commun. 150 (2010) 1429– 1431. [35] K.A. Gschneidner Jr., V.K. Pecharsky, A.O. Pecharsky, C.B. Zimm, Mater. Sci. Forum 315 (1999) 69. [36] L. Li, K. Nishimura, D. Huo, M. Kadonaga, T. Namiki, Z. Qian, Appl. Phys. Exp. 4 (2011) 093101. [37] Z.J. Mo, J. Shen, L.Q. Yan, J.F. Wu, L.C. Wang, C.C. Tang, B.G. Shen, Appl. Phys. Lett. 102 (2013) 192407. [38] L. Li, K. Nishimura, W.D. Hutchison, Z. Qian, D. Huo, T. Namiki, Appl. Phys. Lett. 100 (2012) 152403.