DSpace at VNU: Magnetism and magnetocaloric effect in La1-yNdy(Fe0.88Si0.12)(13) compounds

Journal of Magnetism and Magnetic Materials 262 (2003) 427–431 Magnetism and magnetocaloric effect in La1ÀyNdy(Fe0.88Si0.12)13 compounds D.T Kim Anha, N.P Thuya,b, N.H Duca,*, T.T Nhiena, N.V Nongb a Cryogenic Laboratory, Faculty of Physics, College of Natural Science, Vietnam National University of Hanoi, Nguyen Trai, Thanh Xuan, Hanoi 334, Viet Nam b International Training Institute for Materials Science (ITIMS), Hanoi, Viet Nam Abstract Structural and magnetic properties of La1ÀyNdy(Fe0.88Si0.12)13 compounds have been investigated by means of X-ray diffraction and magnetization measurements The single-phase NaZn13-type cubic structure is stabilized for the compounds with y ¼ 0; 0.1, 0.3 and 0.4 All the synthesized compounds are ferromagnetic Their Curie temperature TC slightly increases with increasing Nd up to y ¼ 0:3: The most striking effect of the Nd substitution, however, is in their itinerant-electron metamagnetic behavior and the magnetocaloric effect in the vicinity of TC : The maximum entropy change decreases somewhat, but the relative cooling power increases with increasing Nd content (i.e for y ¼ 0:3) r 2003 Elsevier Science B.V All rights reserved PACS: 75.10.Lp; 75.30.Sg Keywords: Rare earth—transition metal intermetallic compounds; Itinerant-electron metamagnetism; Magnetocaloric effect Recently, the magnetic LaT13 (T=Fe and Co) compounds of the NaZn13-type cubic structure have been intensively studied It is, on the one hand, due to the fact that these compounds have the largest amount of transition metal in the crystalline formula unit among the rare-earth transition intermetallics [1,2] On the other hand, this is a novel composition that exhibits Femetamagnetism The cubic NaZn13-type structure is easily stabilized in the binary La–Co compound For the La–Fe, however, this structure can be formed only in pseudo-binary La(FexM1Àx)13 (M=Al, Si) compounds [3] The magnetic properties of these compounds are sensitive to the kind *Corresponding author E-mail address: duc@netnam.org.vn (N.H Duc) and the concentration of the M element The magnetic state in La(FexAl1Àx)13 compounds is ferromagnetic for 0:62oxp0:86; and antiferromagnetic for 0:86oxp0:92 [4] La(FexSi1Àx)13 compounds are ferromagnetic in the region 0:62oxp0:86: However, their Curie temperature TC decreases with increasing Fe concentration, whereas the saturation magnetic moment increases [1] For these La(FexSi1Àx)13 compounds, it was reported that in the high Fe concentration region, an itinerant-electron metamagnetic (IEMM) transition, i.e a field-induced first-order paramagneticferromagnetic transition, accompanied by a large negative lattice expansion, appeared just above the Curie temperature Finally, it is interesting to mention that the pseudo-binary La(FexM1Àx)13 compounds with M=Si and Al exhibit a giant 0304-8853/03/$ - see front matter r 2003 Elsevier Science B.V All rights reserved doi:10.1016/S0304-8853(03)00073-8 D.T Kim Anh et al / Journal of Magnetism and Magnetic Materials 262 (2003) 427–431 11.475 11.450 a (Å) magnetostriction effect, which is rather promising for applications [5,6] In order to enhance the ordering temperature and reduce the critical field of the 3d-metamagnetic transition, La was replaced partly by other magnetic rare-earth elements such as R=Pr, Nd and Gd La1ÀyRy(Fe0.88Si0.12)13 compounds [5] For these three rare-earth elements, the substitution is, however, limited up to y ¼ 0:2 only In addition, the influence of the 4f(R)–3d(Fe) exchange interactions on the TC is not so helpful for yp0:2 [5] In this paper, we report a study of the magnetocaloric effect (MCE) in La1ÀyNdy(Fe0.88Si0.12)13 (y ¼ 0; 0.1, 0.3 and 0.4) pseudo-binary compounds The La1ÀyNdy(Fe0.88Si0.12)13 samples with y ¼ 0; 0.1, 0.3, 0.4 were prepared by arc-melting the appropriate amount of high purity (99.9% or better) constituent elements in an inert purified Ar atmosphere The arc-melted alloy buttons were turned over and re-melted several times to ensure homogeneity Subsequently, the samples were annealed for days at 1020 C in evacuated quartz tubes, followed by quenching in ice water X-ray powder diffraction showed that the samples well crystallize in the NaZn13-type structure However, an amount of a-Fe exists as a secondary phase The concentration dependence of the lattice parameter a of the NaZn13-type structure in the La1ÀyNdy(Fe0.88Si0.12)13 (y ¼ 0:0; 0.1, 0.3 and 0.4) compounds is shown in Fig A clear reduction of the lattice parameter with increasing Nd concentration is observed This is a good indication of the introduction of Nd atoms into the La–Fe phase The thermomagnetic curves MðTÞ were measured in an applied field of 0.1 T using a vibrating sample magnetometer (VSM) The results are illustrated in Fig for samples with y ¼ 0:0 and 0.3 Note that both investigated samples are ferromagnetic Their Curie temperature TC slightly increases with increasing y (see Fig 3) The observed enhancement of the ordering temperature may be attributed to the Nd–Nd intrasublattice and the Nd–Fe intersublattice exchange interactions Fig 4a displays the magnetization isotherms MðHÞ measured in pulsed fields up to T in a wide temperature range around TC for the sample 11.425 11.400 0.0 0.1 0.2 0.3 0.4 0.5 y Fig The concentration dependence of the lattice parameter a in the La1ÀyNdy(Fe0.88Si0.12)13 The dotted line is a guide to the eye 55 50 y = 0.3 45 y = 0.0 40 M (emu/g) 428 35 30 25 20 15 10 100 150 200 250 T (K) 300 350 Fig Thermal magnetization curves of La1ÀyNdy(Fe0.88Si0.12)13 with y ¼ 0:0 and 0.3 at a field of 0.1 T with y ¼ 0:0: Note that well below the TC ; the magnetization curves are saturated In the vicinity of TC ; however, we observed only a tendency toward saturation A similar result is also obtained for the sample with y ¼ 0:3 (Fig 4b) This behavior can be associated with an IEMM D.T Kim Anh et al / Journal of Magnetism and Magnetic Materials 262 (2003) 427–431 250 429 150 150 K 170 K 180 K 240 195 K 230 200 K 220 205 K 210 K 220 K M (A m2/kg) TC (K) 100 210 200 50 190 180 0.0 0.1 0.2 0.3 0.4 0.5 y transition as already evidenced by means of the magnetostriction measurements [5] Based on general thermodynamics principles [7], the magnetic entropy change for an isobaricisothermal process can be related to the temperature dependence of the magnetization, with one of the Maxwell relation, by     qS qM ¼ : qH T;p qT H;p 0 H (T) 150 180 K 195 K 205 K 210 K 215 K 220 K 225 K 230 K 240 K 255 K 265 K 275 K 100 From a collection of magnetization isotherms, the magnetic entropy change—DSM or the MCE can be calculated approximately by [8], X DSM ẳ Mi Miỵ1 ị DHi ; T iỵ1 Ti i where Mi and Miỵ1 are the magnetization values obtained at temperature Ti and Tiỵ1 in a eld H; respectively The plots of ÀDSM as a function of temperature in different magnetic fields are presented in Fig for La(Fe0.88Si0.12)13 and La0.7Nd0.3(Fe0.88Si0.12)13 In an applied field of T, the maximal ÀDSM (max) values of 12.6 and 9.7 J/kg K are found for La(Fe0.88Si0.12)13 and La0.7Nd0.3(Fe0.88Si0.12)13, respectively The magnitude of the magnetic entropy change of La0.7Nd0.3(Fe0.88Si0.12)13 is smaller than that of La(Fe0.88Si0.12)13 for the same field change (a) M (A m2/kg) Fig The concentration dependence of the Curie temperature in the La1ÀyNdy(Fe0.88Si0.12)13 50 0 (b) H (T) Fig The magnetization isotherms of La1ÀyNdy(Fe0.88Si0.12)13 compounds: y ¼ (upper) and y ¼ 0:3 (lower) (DH ¼ T), although it is comparable to that of Gd metal (ÀDSM (max)E10 J/kg K) [9] This result is in good agreement with a previous report [10] For applications, however, it is interesting to consider the relative cooling power (RCP) based on the magnetic entropy change [10], i.e the D.T Kim Anh et al / Journal of Magnetism and Magnetic Materials 262 (2003) 427–431 430 14 14 H= H= H= H= 12 12 10 -∆SM (J/kg K) -∆SM (J/kg K) 10 5T 4T 3T 2T y = 0.0 y = 0.3 FWHM = 26 K FWHM = 40 K 4 2 0 140 160 180 200 220 240 260 280 T1 160 180 200 T2 220 240 260 280 T (K) T (K) (a) Fig The magnetic entropy change ÀDSM of La1ÀyNdy(Fe0.88Si0.12)13 with y ¼ 0:0 and 0.3, for DH from to T The full-width at half-maximum (FWHM) and the corresponding T1 and T2 are indicated 14 H= H= H= H= 12 10 -∆SM (J/kg K) 140 5T 4T 3T 2T parameter, whereas the Curie temperature TC slightly increases from 210 to 215 K In addition, the RCP increased in the La0.7Nd0.3(Fe0.88Si0.12)13 compounds Therefore, this alloy can be a candidate for magnetic refrigerant at the corresponding temperature range 140 (b) 160 180 200 220 240 260 280 This work was supported by the College of Natural Science, VNU, Hanoi under the Research Grants No TN-02.06 The authors would like to thank Mr N.N Phuoc for his help T (K) Fig The magnetic entropy change ÀDSM of La1ÀyNdy(Fe0.88Si0.12)13 with (a) y ¼ 0:0 and (b) 0.3 for the magnetic field changes of 0–2, 0–3, 0–4 and 0–5 T product of ÀDSM (max) Â dTFWHM ; where dTFWHM ¼ T2 À T1 is the full-width at half-maximum (FWHM) [11] As shown in Fig 6, the RCP equals 388 and 328 J/kg for La0.7Nd0.3(Fe0.88Si0.12)13 and La(Fe0.88Si0.12)13, respectively In summary, the Nd substitution in the La1ÀyNdy(Fe0.88Si0.12)13 decreases the lattice References [1] P.I Kripyakevich, O.S Zarechnyuk, E.I Gladyshevsky, O.I Bodak, Z Anorg Chem 358 (1968) 90 [2] T.T.M Palstra, J.A Mydosh, G.J Nieuwenhuys, A.M Van der Kraan, K.H.J Buschow, J Magn Magn Mater 36 (1983) 290 [3] T.T.M Palstra, G.J Nieuwenhuys, J.A Mydosh, K.H.J Buschow, J Appl Phys 55 (1984) 2367 [4] T.T.M Palstra, G.J Nieuwenhuys, J.A Mydosh, K.H.J Buschow, Phys Rev B 31 (1985) 4622 [5] A Fujita, K Fukamichi, IEEE Trans Magn 35 (1999) 1796 D.T Kim Anh et al / Journal of Magnetism and Magnetic Materials 262 (2003) 427–431 [6] Ye.V Shcherbakova, A.V Korolyov, S.M Podgornykh, J Magn Magn Mater 237 (1983) 147 [7] M Tishin, in: K.H.J Buschow (Ed.), Handbook of Magnetic Materials, Vol 12, Elsevier, New York, 1999, p 395 [8] X.X Zhang, G.H Wen, F.W Wang, W.H Wang, C.H Yu, G.H Wu, Appl Phys Lett 77 (2000) 3072 431 [9] V.K Pecharsky, K.A Gschneidner Jr., Phys Rev Lett 78 (1997) 4494 [10] F.X Hu, B.G Shen, J.R Sun, Z.H Cheng, G.H Rao, X.X Zhang, Appl Phys Lett 78 (2001) 3675 [11] V.K Pecharsky, K.A Gschneidner Jr., J Appl Phys 86 (1999) 565  ... slightly increases with increasing y (see Fig 3) The observed enhancement of the ordering temperature may be attributed to the Nd–Nd intrasublattice and the Nd–Fe intersublattice exchange interactions... T using a vibrating sample magnetometer (VSM) The results are illustrated in Fig for samples with y ¼ 0:0 and 0.3 Note that both investigated samples are ferromagnetic Their Curie temperature... of Magnetism and Magnetic Materials 262 (2003) 427–431 11.475 11.450 a (Å) magnetostriction effect, which is rather promising for applications [5,6] In order to enhance the ordering temperature