ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 304 (2006) e325–e327 www.elsevier.com/locate/jmmm Structure, magnetic, magnetocaloric and magnetoresistance properties of Pr1ÀxPbxMnO3 perovskites D.T Hanh, N ChauÃ, N.H Luong, N.D Tho Center for Materials Science, College of Science, Vietnam National University, Hanoi, 334 Nguyen Trai Street, Hanoi, Vietnam Available online 28 February 2006 Abstract In our previous work, we have studied structure and properties of La1ÀxPbxMnO3 perovskites Variation of doping content leads to alternating structure and magnetic properties of materials In this paper, the investigation of structure, magnetic, magnetocaloric and magnetoresistance properties of family Pr1ÀxPbxMnO3 (x ¼ 0.1–0.5) is presented The grain size of samples increases with Pb content The FC and ZFC thermomagnetic curves measured at low field and low temperatures exhibit the spin-glass-like behavior The magnetic entropy changes, |DSm(T)|, were determined and showed belong to GMCE The resistance measurements indicated that first two samples exhibited semiconducting conductivity in the whole measured temperature range, whereas in the rest of samples there is insulator–metallic transition on R(T) curves Magnetoresistance measurements have also been performed r 2006 Elsevier B.V All rights reserved PACS: 75.47.Lx; 75.30.Sg; 75.47.Gk Keywords: Manganites; Magnetocaloric effect; Magnetoresistance Most recent papers aim to study the interplay between structure, magnetic and transport properties in perovskitetype manganites Ln1ÀxAxMnO3 (where Ln ¼ rare earth, A ¼ alkaline element) Magnetic and structural properties (as functions of ionic radius at A-site, A-site disorder, applied magnetic field, doping content and temperature) have revealed many interesting effects such as magnetoresistance, charge ordering, magnetocaloric, spin glass behavior, etc [1–3] It was pointed out that the mother compound LnMnO3 is an antiferromagnetic insulator, accounts of its A-type magnetic structure, where ferromagnetically aligned layers are coupled antiferromagnetically In this case, magnetic and transport properties are related to the Jahn–Teller distortion among Mn3+ ions When trivalent rare earth ions (La, Pr, Nd, Sm, etc.) are partly substituted by divalent ions, there is the mixedvalent state of Mn3+ and Mn4+ ions and that results in potential charge carriers for metallic conductivity ÃCorresponding author Tel.: +84 5582216; fax: +84 8589496 E-mail address: chau@cms.edu.vn (N Chau) 0304-8853/$ - see front matter r 2006 Elsevier B.V All rights reserved doi:10.1016/j.jmmm.2006.02.045 Recently, several authors have paid attention in holedoped manganites with A ¼ Pb [4–6] In our lab, overall investigation of properties of La1ÀxPbxMnO3 (x ¼ 0.1–0.5) has been performed [7] The results showed that the symmetry decreases from cubic x ẳ 0:5ị over rhombohedral x ẳ 0:4ị to triclinic x ẳ 0:3; 0:2; 0:1Þ, moreover the Curie temperature increases from 235 K for x ¼ 0:12310 K for x ¼ 0:2 and then remains almost constant with further increasing x Manganites Pr1ÀxPbxMnO3 (x ¼ 0.1–0.5) were prepared by conventional powder solid-state reaction technique The sintering temperature for all compositions was 1000 1C The microstructure was studied by a scanning electron microscope (SEM) 5410 LV Jeol Structure of samples was examined in a Bruker D5005 X-ray diffractometer The magnetic measurements were performed on a vibrating sample magnetometer (VSM) DMS 880 in magnetic field up to 13.5 kOe The SEM pictures indicated that crystallites of the samples are quite homogeneous and their size increased from around 0.5 mm x ẳ 0:1ị to around 1.0 mm x ẳ 0:5ị The X-ray diffraction patterns showed that all studied ARTICLE IN PRESS D.T Hanh et al / Journal of Magnetism and Magnetic Materials 304 (2006) e325–e327 e326 Table Lattice parameters of Pr1ÀxPbxMnO3 perovskites (error of 70.1%) Sample a (A˚) b (A˚) c (A˚) V (A˚3) x ¼ 0:1 x ¼ 0:2 x ¼ 0:3 x ¼ 0:4 x ¼ 0:5 5.345 5.373 5.401 5.422 5.437 5.479 5.473 5.472 5.468 5.467 7.747 7.747 7.747 7.749 7.748 226.9 227.8 229.0 229.7 230.3 Pr0.9Pb0.1MnO3 FC Pr0.8Pb0.2MnO3 Pr0.7Pb0.3MnO3 FC M (emu/g) Pr0.6Pb0.4MnO3 ZFC ZFC ZFC ZFC DS m T; Hị ẳ ST; 0ị ST; Hị Z H max fqMT; Hị=qTgH dH, ẳ Pr0.5Pb0.5MnO3 FC FC Pb2+ for Pr3+ induces a mixed-valent state of Mn3+/ Mn4+ ions and enhances the FM–PM transition temperature due to double exchange interaction Moreover, with large average ionic radius at A-site cation, /rAS, the internal pressure increases yielding decrease the buckling of the MnO6 octahedra and then also enhancing TC To determine magnetic entropy change, DSm, as a function of temperature, M(H) isotherms have been measured for all samples at various temperatures around respective TC and in magnetic field up to 13.5 kOe Based on Maxwell’s thermodynamic relations, DSm can be calculated by the formula H = 20 Oe 100 125 150 175 200 225 250 275 300 325 350 Temperature (K) Fig Thermomagnetic field-cooled (FC) and zero-field-cooled (ZFC) curves of samples measured at 20 Oe Table Composition dependence of some parameters of Pr1ÀxPbxMnO3 manganites (error of 1%) Sample orA4(A˚) TC (K) Tf (K) |DSm|max (J/kg K) x ¼ 0:1 x ¼ 0:2 x ¼ 0:3 x ¼ 0:4 x ¼ 0:5 1.188 1.206 1.224 1.242 1.260 152 172 223 256 254 143 162 180 245 240 3.91 2.58 2.74 3.68 3.34 where SðT; 0Þ and SðT; HÞ are the entropy without and with applied magnetic field, respectively [8] Fig presents the dependence of |DSm| on temperature for studied samples The maximum magnetic entropy change, |DSm|max, of the samples is quite large, the lowest value is of 2.58 J/kg K for sample with x ¼ 0:2 and it reaches highest value of 3.91 J/kg K for sample Pr0.9Pb0.1MnO3 Our materials could be considered as giant magnetocaloric materials In the same magnetic field change (DH ¼ 13.5 kOe), the values of |DSm|max here are quite higher than those investigated in our previous reports for LaSr(Mn,Co)O3 [9,10], La1ÀxPbxMnO3 [7] and a little higher than that of La0.7Sr0.3MnO3 with small substitution of Ni for Mn [11] There should be attribution to magnetic spin of Pr3+ ions instead of nonmagnetic La3+ ions The temperature dependence of resistance of studied samples was determined by standard four-probe method The results indicated that while the two first compositions (x ¼ 0:1 and 0.2) exhibited semiconducting conductivity in the whole measured temperature range, the rest compositions (x ¼ 0:3, 0.4, and 0.5) established the metallic conductivity in the ferromagnetic state and semiconducting 4.5 (J/kg.K) 3.5 3.0 ∆ Sm samples are of single phase with orthorhombic structure Significant increase of lattice parameter a and volume of unit cell relates to the increase of Pb2+ content (with large ionic radius) substituted for Pr3+ (Table 1) For all samples, zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves were measured in magnetic field of 20 Oe From Fig we can see that they are separated from each other at below irreversibility temperature Tr and there is a cusp in ZFC curves at a so-called freezing or spinglass-like transition temperature, Tf These phenomena are specific features of spin-glass- or cluster-glass-like state The FM–PM transition temperature, TC (see Table 2), increases with increasing Pb content, from 152 K ðx ¼ 0:1Þ to 256 K ðx ¼ 0:4Þ and then becomes a little lower in the sample x ¼ 0:5 The doping content dependence of Tf has the same tendency (Table 2) Clearly, the substitution of Pr0.9Pb0.1MnO3 Pr0.8Pb0.2MnO3 Pr0.7Pb0.3MnO3 Pr0.6Pb0.4MnO3 Pr0.5Pb0.5MnO3 4.0 2.0 2.5 1.5 1.0 0.5 0.0 100 125 150 175 200 225 250 Temperature (K) 275 300 Fig Magnetic entropy change versus temperature, |DSm(T)|, of studied samples ARTICLE IN PRESS D.T Hanh et al / Journal of Magnetism and Magnetic Materials 304 (2006) e325–e327 The authors acknowledge the financial support from the Vietnam National Fundamental Research Program (Project 421004) 400 4.5 350 Pr0.5Pb0.5MnO3 e327 4.0 300 3.0 200 2.5 150 R (Ohm) R (Ohm) 3.5 250 2.0 100 Pr0.8Pb0.2MnO3 1.5 50 1.0 0 50 100 150 200 250 300 Temperature (K) Fig Resistance versus temperature for the samples x ¼ 0:2 and 0.5 conductivity in paramagnetic state Fig displays conducting behavior for samples with x ¼ 0:2 and 0.5 We suppose that only at high Pb content substituted for Pr ðxX0:3Þ, the double exchange is still strong enough to favor metallic conductivity Magnetoresistance MR as a function of magnetic field, defined as ½rH Fr0 =r0 , where r0 is the zero field resistance and rH is the resistance in 13 kOe, was measured and the highest MR has reached 20% for sample x ¼ 0:5 and this value belongs to CMR References [1] H.Y Hwang, S.-W Cheong, P.G Radaelli, M Marezio, B Batlogg, Phys Rev Lett 75 (1995) 914 [2] P.G Radaelli, D.E Cox, M Marezio, S.-W Cheong, P.E Schiffer, A.P Ramirez, Phys Rev Lett 75 (1995) 4488 [3] R Mahesh, R Mahendiran, A.K Raychaudhuri, C.N.R Rao, J Solid State Chem 120 (1995) 204 [4] S.L Young, Y.C Chen, L Horng, T.C Wu, H.Z Chen, J.B Shi, J Magn Magn Mater 289 (2000) 5576 [5] I.O Troyanchuk, D.D Khalyavin, H Szymczak, Mater Sci Bull 32 (1997) 1637 [6] T.S Wang, C.H Chen, M.F Tai, MRS Symp Proc 674 (2001) U.3.4.1 [7] C Nguyen, N.N Hoang, H.L Nguyen, L.M Dang, D.T Nguyen, N.C Nguyen, Physica B 327 (2003) 270 [8] A.M Tishin, J Magn Magn Mater 184 (1998) 62 [9] H.L Nguyen, C Nguyen, M.H Phan, L.M Dang, N.C Nguyen, T.C Bach, M Kurisu, J Magn Magn Mater 242–245 (2002) 760 [10] C Nguyen, Q.N Pham, N.N Hoang, H.L Nguyen, D.T Nguyen, Physica B 327 (2003) 214 [11] Md.A Choudhury, J.A Akhter, L.M Dang, D.T Nguyen, C Nguyen, J Magn Magn Mater 272–276 (2004) 1295 ... magnetization curves were measured in magnetic field of 20 Oe From Fig we can see that they are separated from each other at below irreversibility temperature Tr and there is a cusp in ZFC curves at. .. La1ÀxPbxMnO3 [7] and a little higher than that of La0.7Sr0.3MnO3 with small substitution of Ni for Mn [11] There should be attribution to magnetic spin of Pr3+ ions instead of nonmagnetic La3+... ions The temperature dependence of resistance of studied samples was determined by standard four-probe method The results indicated that while the two first compositions (x ¼ 0:1 and 0.2) exhibited