Magnetoresistivity As A Probe To The Field-induced Change Of Magnetic Entropy In R Al2 Compounds (r=pr,nd,tb,dy,ho,er)

The heat capacity CP (T) of the ferromagnetic compounds R Al2 (R=Pr,Nd,Tb,Dy,Ho,Er) was measured at zero and applied magnetic field of 5 T in the temperature interval from 2 to 200 K. From these results are calculated the magnetic component of the entropy change, -Δ Smag (T) =S (0,T) -S (H,T). From resistivity measurements, ρ (H,T), from 2 to 300 K in the same compounds, we calculated the resistivity change due to the applied magnetic field, -Δ ρmag (T) = [ρmag (0,T) - ρmag (H,T)]. The results are compared and we observed a similar dependence between -Δ ρmag (T) and (T/ TC) m Δ Smag (T) with m=0 for T≥ TC and m=1 for T≤ TC. A simple model using a Hamiltonian considering molecular and crystalline electric fields, in a mean field approximation, is adopted for the calculus. Our results show that theory and experiment are in good agreement showing that the magnetoresistivity is a probe to the field-induced change of magnetic entropy in these compounds and can be extended to other materials. A model for the factor connecting both quantities, -Δ Smag (T) and -Δ ρmag (T), is developed. This factor contains mainly the effective exchange integral which is related to Fermi energy that in turn is related to the electron effective mass. © 2006 The American Physical Society.7413Ziman, M., (1972) Electrons and Phonons, , Oxford University Press, LondonPurwins, H.G., Leson, A., (1990) Adv. Phys., 39, p. 309. , ADPHAH 0001-8732 10.1080/00018739000101511Pecharsky, V.K., Gschneidner Jr., K.A., Pecharsky, A.O., Tishin, A.M., (2001) Phys. Rev. B, 64, p. 144406. , PRBMDO 0163-1829 10.1103/PhysRevB.64.144406Potter, H.H., (1932) Philos. Mag., Suppl., 13, p. 233. , ADPHAH 0001-8732Alexander, S., Helman, J.S., Balberg, I., (1976) Phys. Rev. B, 13, p. 304. , PLRBAQ 0556-2805 10.1103/PhysRevB.13.304Potter, H.H., (1931) Proc. R. Soc. London, Ser. a, 132, p. 560. , PRLAAZ 1364-5021Ravishankar, K., Sablik, M.J., Levy, P.M., Uffer, L.F., (1974) AIP Conf. Proc., 18, p. 923. , APCPCS 0094-243XVan Daal, H.J., Buschow, K.H.J., (1969) Solid State Commun., 7, p. 217. , SSCOA4 0038-1098Inoue, T., Sankar, S.G., Craig, R.S., Wallace, W.E., Gschneidner Jr., K.A., (1977) J. Phys. Chem. Solids, 38, p. 487. , JPCSAW 0022-3697Deenadas, C., Thompson, A.W., Craig, R.S., Wallace, W.E., (1971) J. Phys. Chem. Solids, 32, p. 1853. , JPCSAW 0022-3697Ibarra, M.R., Lee, E.W., Del Moral, A., Moze, O., (1985) Solid State Commun., 53, p. 183. , SSCOA4 0038-1098Ibarra, M.R., Moze, O., Algarabel, P.A., Arnaudas, J.I., Abell, J.S., Del Moral, A., (1988) J. Phys. C, 21, p. 2735. , JPSOAW 0022-3719Griffiths, R.B., (1969) Phys. Rev., 188, p. 942. , PHRVAO 0031-899X 10.1103/PhysRev.188.942Dekker, A.J., (1965) J. Appl. Phys., 36, p. 906. , JAPIAU 0021-8979 10.1063/1.1714260Von Ranke, P.J., Pecharsky, V.K., Gschneidner Jr., K.A., (1998) Phys. Rev. B, 58, p. 12110. , PRBMDO 0163-1829 10.1103/PhysRevB.58.12110Christen, M., (1980) Solid State Commun., 36, p. 571. , SSCOA4 0038-1098Sablik, M.J., Pureur, P., Creuzet, G., Fert, A., Levy, P.M., (1983) Phys. Rev. B, 28, p. 3890. , PRBMDO 0163-1829 10.1103/PhysRevB.28.3890Furrer, A., Purwins, H.G., (1977) Phys. Rev. B, 16, p. 2131. , PLRBAQ 0556-2805 10.1103/PhysRevB.16.2131Tsai, T.H., Sellmyer, D.J., (1979) Phys. Rev. B, 20, p. 4577. , PRBMDO 0163-1829 10.1103/PhysRevB.20.4577Milchberg, H.M., Freeman, R.R., Davey, S.C., More, R.M., (1988) Phys. Rev. Lett., 61, p. 2364. , PRLTAO 0031-9007 10.1103/PhysRevLett.61.2364Rawat, R., Das, I., (2001) J. Phys.: Condens. Matter, 13, p. 379. , JCOMEL 0953-8984 10.1088/0953-8984/13/19/104Das, I., Rawat, R., (2000) Solid State Commun., 115, p. 207. , SSCOA4 0038-1098Xiong, C.M., Sun, J.R., Chen, Y.F., Shen, B.G., Du, J., Li, Y.X., (2005) IEEE Trans. Magn., 41, p. 122. , IEMGAQ 0018-946

Experimental And Theoretical Analyses Of Pr Al2 And Nd Al2 Composite For Use As An Active Magnetic Regenerator

We report the theoretical and experimental investigations on the magnetocaloric effect in the Pr Al2 and Nd Al2 compounds and a composite of these compounds for use as an active magnetic regenerator. The theoretical calculations were performed considering the crystalline electrical field anisotropy and the magnetocaloric potentials were calculated in the three main crystallographic directions. The experimental data, obtained for the polycrystalline samples, are in good agreement with the theoretical results. Also, an optimum molar fraction of the Pr Al2 and Nd Al2 composite was determined theoretically and experimentally and discussed in the framework of the optimum regeneration Ericsson cycle. © 2005 American Institute of Physics.978Brown, G.V., (1976) J. Appl. Phys., 47, p. 3673Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494Tegus, O., Bruck, E., Buschow, K.H.J., De Boer, F.R., (2002) Nature (London), 415, p. 150Wada, H., Taniguchi, K., Tanabe, Y., (2002) Mater. Trans., JIM, 43, p. 73Wada, H., Tanabe, Y., (2001) Appl. Phys. Lett., 79, p. 3302Von Ranke, P.J., Nobrega, E.P., De Oliveira, I.G., Gomes, A.M., Sarthour, R.S., (2001) Phys. Rev. B, 63, p. 184406Von Ranke, P.J., De Oliveira, N.A., Tovar Costa, M.V., Caldas, A., De Oliveira, I.G., Nobrega, E.P., (2001) J. Magn. Magn. Mater., 226, p. 990Von Ranke, P.J., Pecharsky, V.K., Gschneidner Jr., K.A., (1998) Phys. Rev. B, 58, p. 12110Von Ranke, P.J., De Oliveira, I.G., Guimarães, A.P., Da Silva, X.A., (2000) Phys. Rev. B, 61, p. 447Williams, H.J., Wernick, J.H., Nesbit, E.A., Sherwood, R.C., (1962) J. Phys. Soc. Jpn., 17, p. 91Swift, W.M., Wallace, W.E., (1968) J. Phys. Chem. Solids, 29, p. 2053Mader, K.H., Segal, E., Wallace, W.E., (1969) J. Phys. Chem. Solids, 30, p. 1Nereson, N., Olsen, C., Arnold, G., (1968) J. Appl. Phys., 39, p. 4605Nereson, N., Olsen, C., Arnold, G., (1966) J. Appl. Phys., 37, p. 4575Rossignol, M.F., (1980), University of GrenoblePurwins, H.G., Leson, A., (1990) Adv. Phys., 39, p. 309Lima, A.L., Oliveira, I.S., Gomes, A.M., Von Ranke, P.J., (2002) Phys. Rev. B, 65, p. 172411Hashimoto, T., Kuzuhara, T., Sahashi, M., Inomata, K., Tomokiyo, A., Yayama, H., (1991) J. Appl. Phys., 70, p. 1911Yan, Z., Chen, J., (1992) J. Appl. Phys., 72, p. 1Smaïli, A., Chahine, R., (1996) Adv. Cryog. Eng., 42, p. 445Dai, W., (1992) J. Appl. Phys., 71, p. 527

Magnetocaloric Effect: Overcoming The Magnetic Limit

We have studied anomalous peaks observed in magnetocaloric -ΔS(T) curves for systems that undergo first-order magnetostructural transitions. The origin of those peaks, which can exceed the conventional magnetic limit, R ln(2J+1), is discussed on thermodynamic bases by introducing an additional-exchange contribution (due to exchange constant variation arising from magnetostructural transition). We also applied a semiphenomenological model to include this additional-exchange contribution in Gd 5Si 2Ge 2- and MnAs-based systems, obtaining excellent results for the observed magnetocaloric effect. © 2008 Elsevier B.V. All rights reserved.3215446449Sahashi, M., Niu, H., Tohkai, Y., Inomata, K., Hashimoto, T., Kuzuhara, T., Tomokiyo, A., Yayama, H., (1987) IEEE Trans. Magn., MAG-23, p. 2853Wada, H., Tomekawa, S., Shiga, M., (1999) Cryogenics, 39, p. 915Fujita, A., Fujieda, S., Hasegawa, Y., Fukamichi, K., (2003) Phys. Rev. B, 67, p. 104416Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 494Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Appl. Phys. Lett., 70, p. 3299Tegus, O., Brück, E., Buschow, K.H.J., de Boer, F.R., (2002) Nature, 415, p. 150Wada, H., Taniguchi, K., Tanabe, Y., (2002) Mater. Trans., 43, p. 73Wada, H., Tanabe, Y., (2001) Appl. Phys. Lett., 79, p. 3302Pecharsky, V.K., Holm, A.P., Gschneidner Jr., K.A., Rink, R., (2003) Phys. Rev. Lett., 91, p. 197204Morellon, L., Arnold, Z., Magen, C., Ritter, C., Prokhnenko, O., Skorokhod, Y., Algarabel, P.A., Kamarad, J., (2004) Phys. Rev. Lett., 93, p. 137201Tishin, A.M., (1997) J. Alloys Compd., 250, p. 635von Ranke, P.J., Nóbrega, E.P., de Oliveira, I.G., Gomes, A.M., Sarthour, R.S., (2001) Phys. Rev. B, 63, p. 184406Gama, S., Coelho, A.A., de Campos, A., Carvalho, A.M.G., Gandra, F.C.G., von Ranke, P.J., de Oliveira, N.I., (2004) Phys. Rev. Lett., 93, p. 237202von Ranke, P.J., Gama, S., Coelho, A.A., de Campos, A., Carvalho, A.M.G., Gandra, F.C.G., de Oliveira, N.A., (2006) Phys. Rev. B, 73, p. 014415The magnetic entropy change can be obtained from experimental M(H, T) data through Maxwell's relation using either -ΔS=∫(-∂M/∂T)dH or equivalently -ΔS=(∫ΔMdH)/ΔTPecharsky, V.K., Gschneidner Jr., K.A., (1999) J. Appl. Phys., 86, p. 6315Amaral, J.S., Silva, M.J.O., Amaral, V.S., (2007) Appl. Phys. Lett., 91, p. 172503Liu, G.J., Sun, J.R., Shen, J., Gao, B., Zhang, H.W., Hu, F.X., Shen, B.G., (2007) Appl. Phys. Lett., 90, p. 032507Plaza, E.J.R., Campoy, J.C.P., (2007) Phys. Rev. B, 75, p. 174419Carvalho, A.M.G., Alves, C.S., de Campos, A., Coelho, A.A., Gama, S., Gandra, F.C.G., von Ranke, P.J., Oliveira, N.A., (2005) J. Appl. Phys., 97, pp. 10M320de Campos, A., Rocco, D.L., Carvalho, A.M.G., Caron, L., Coelho, A.A., Gama, S., da Silva, L.M., de Oliveira, N.A., (2006) Nat. Mater., 5, p. 82Bean, C.P., Rodbell, D.S., (1962) Phys. Rev., 126, p. 104Spichkin, Y.I., Tishin, A.M., (2005) J. Magn. Magn. Mater., 290-291, p. 700Paudyal, D., Pecharsky, V.K., Gschneidner Jr., K.A., Harmon, B.N., (2006) Phys. Rev. B, 73, p. 144406Chernenko, V.A., Wee, L., McCormick, P.G., Street, R., (1999) J. Appl. Phys., 85, p. 7833Mira, J., Rivadulla, F., Rivas, J., Fondado, A., Guidi, T., Caciuffo, R., Carsughi, F., Goodenough, J.B., (2003) Phys. Rev. Lett., 90, p. 097203Liu, G.J., Sun, J.R., Lin, J., Xie, Y.W., Zhao, T.Y., Zhang, H.W., Shen, B.G., (2006) Appl. Phys. Lett., 88, p. 21250

Synchrotron Radiation Multiple Diffraction In The Characterization Of The Pral2 Magnetocaloric Compound

X-ray multiple diffraction technique using synchrotron radiation is applied to characterize the PrAl2 magnetocaloric compound. Renninger scans (φ-scans) of the (002) primary reflection were measured in the Brazilian Synchrotron Laboratory (LNLS). The (5 3 3̄) (5 3 5) four-beam case provided a = 8.0277(5) Å and the sample surface polishing effect was clearly observed through the measurement of Bragg-surface diffraction (BSD) peak and the mapping (MBSD) of its multiple diffraction condition. © 2003 Elsevier B.V. All rights reserved.272-276III21542156Tishin, A.M., Magnetocaloric effect in the vicinity of phase transitions (1999) Handbook of Magnetic Materials, 4, p. 395. , K.H.J. Buschow (Ed.), Elsevier, AmsterdamVon Ranke Perlingeiro, P.J., Pecharsky, V.K., Gschneidner, K.A., (1998) Phys. Rev. B, 58, p. 12110Avanci, L.H., Cardoso, L.P., Girdwood, S.E., Pugh, D., Sherwood, J.N., Roberts, K.J., (1998) Phys. Rev. Lett., 81 (24), p. 5426Morelhão, S.L., Cardoso, L.P., (1996) J. Appl. Crystallogr., 29, p. 446Cole, H., Chambers, F.W., Dunn, H.M., (1962) Acta Crystallogr., 15, p. 138Appa Rao, B., Satyanarayana Murthy, K., Kistaiah, P., (1987) J. Phys. D, 20, p. 107

Co Doping Effects On The Magnetic And Magnetoresistance In Sm 0.35nd0.35pb0.30mn1-xco Xo3 (x = 0, 0.1, 0.2)

Polycrystalline samples of the Sm0.35Nd0.35Pb 0.3Mn1-xCoxO3 (x = 0, 0.1, 0.2) at low magnetic fields has been studied by AC susceptibility, and field cooled and zero field cooled magnetisation measurements. We conclude that a small amount of Co substitution tends to destroy the double exchange and broadens the coexistence region of the cluster-glass and ferromagnetic states. Also, the Co doping suppresses the large negative magnetoresistance and it becomes small for x = 0.2. © 2001 Published by Elsevier Science B.V.226-230PART I834836Martin, C., Maignan, A., Hervieu, M., Raveau, B., (1999) Phys. Rev. B, 60, p. 1219Coey, J.M.D., Viret, L., Von Moinar, S., (1999) Adv. Phys., 48, p. 167Blanco, J.J., Lezama, L., Insausti, M., Gutierrez, J., Barandiaran, J.M., Rojo, T., (1999) Chem. Mater., 11, p. 3464Peña, A., Blanco, J.J., Insausti, M., Lezama, L., Gutierrez, J., Barandiaran, J.M., Rojo, T., (1999) J. Magn. Magn. Mater., 196-197, p. 543Mukherjee, S., Ranganathan, R., Anikumar, P.S., Joy, P.A., (1996) Phys. Rev. B, 54, p. 9267Nam, D.N.H., Jonason, K., Nordblad, P., Khiem, N.V., Phuc, N.X., (1999) Phys. Rev. B, 59, p. 418

Magnetotransport Properties Of The Sm0.35nd0.35m0.3mn1-xfexo 3 (m = Pb, Cd; X = 0, 0.1) Manganites

Polycrystalline samples of the mixed-valence perovskite-type manganites Sm0.35Nd0.35M0.3Mn1-xFexO 3 (M = Pb, Cd; x = 0, 0.1) have been synthesised and their magnetic and transport properties studied. Magnetic measurements show that TC values decrease considerably with the presence of cadmium or iron. Colossal magnetoresistance has been shifted to lower temperatures. Values of magnetoresistance near to 40% have been obtained. The presence of defined maxima in the real part of ac susceptibility at the same temperature of the cusp in the zero field cooling curves corroborates cluster-glass behaviour.2201425428Von Helmolt, R., Wecker, J., Holzapfel, B., Schultz, L., Samwer, K., (1993) Phys. Rev. Lett., 71, p. 2331Jin, S., Tiefel, T.H., McCormack, M., Fastnacht, R.A., Ramesh, R., Chen, L.H., (1994) Science, 264, p. 413Tomioka, Y., Asamitsu, A., Moritomo, Y., Kuwahara, H., Tokura, Y., (1995) Phys. Rev. Lett., 74, p. 5108Zener, C., (1951) Phys. Rev., 82, p. 403Anderson, P.W., Hasegawa, H., (1955) Phys. Rev., 100, p. 675De Gennes, P.G., (1960) Phys. Rev., 118, p. 141Millis, A.J., Littlewood, P.B., Shraiman, B.I., (1995) Phys. Rev. Lett., 74, p. 5144Peña, A., Blanco, J.J., Insausti, M., Lezama, L., Gutiérrez, J., Barandiarán, J.M., Rojo, T., (1999) J. Magn. Magn. Mater., 196-197, p. 543Anil Kumar, P.S., Joy, P.A., Date, S.K., (1998) J. Phys.: Condensed Matter, 10, pp. L48

Crystallographic And 119sn And 155gd Mössbauer Analyses Of Gd5ge2(si1 - Xsnx)2 (x = 0.23 And X = 0.40)

We report the structural characterization of Gd5Ge2(Si1 - xSnx)2 (x = 0. 23 and x = 0. 40) compounds by means of 100 and 298 K-X-ray diffractometry (XRD) and 4 K-155Gd and 298 K-119Sn Mössbauer spectroscopy. These compounds order ferromagnetically at 218. 4 and 172. 7 K, respectively. At ∼100 K, it was identified the Gd5Si4-orthorhombic phase (type I) for both samples. At ∼298 K, it was identified a Gd5Si2Ge2-monoclinic phase, for x = 0. 23 and a Sm5Sn4-orthorhombic phase (type II), for x = 0. 40. The Rietveld analysis of XRD data suggests a first order magneto-structural transition at Curie temperature for both compositions. Mössbauer results are well consistent with the proposed crystallographic models for these systems. © Springer Science + Business Media B.V. 2009.1951191197Pecharsky, K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494Pecharsky, V.K., Gschneidner Jr., K.A., (1997) J. Magn. Magn. Mater., 167, pp. 179-184Pecharsky, A.O., Gschneidner Jr., K.A., Pecharsky, V.K., (2003) J. Appl. Phys., 93, p. 4722Pecharsky, A.O., Gschneidner Jr., K.A., Pecharsky, V.K., (2003) J. Magn. Magn. Mater., 267, p. 60Campoy, J.C.P., Plaza, E.J.R., Carvalho, A.M.G., Coelho, A.A., Gama, S., von Ranke, P.J., (2004) J. Magn. Magn. Mater., 272, p. 2375Li, J.Q., Sun, W.A., Jian, Y.X., Zhuang, Y.H., Huang, W.D., Liang, J.K., (2006) J. Appl. Phys., 100, p. 073904Campoy, J.C.P., Plaza, E.J.R., Nascimento, F.C., Coelho, A.A., Pereira, M.C., Fabris, J.D., Raposo, M.T., Gama, S., (2007) J. Magn. Magn. Mater., 316, p. 368Levin, E.M., Pecharsky, V.K., Gschneidner, K.A., Miller Jr., G.J., (2001) Phys. Rev. B, 64, p. 235103Pecharsky, V.K., Gschneidner, K.A., (1997) J. Alloys Compd., 260, p. 98Wang, H.B., Altounian, Z., Ryan, D.H., (2002) Phys. Rev. B, 66, p. 214413Raghavan, P., Table of nuclear moments (1989) At. Data Nucl. Data Tables, 42 (2), pp. 189-291Stevens, J.G., Dunlap, B.D., (1976) J. Phys. Chem. Ref. Data, 5, pp. 1093-1121Czjzek, G., Mössbauer spectroscopy of new materials containing gadolinium (1993) Mössbauer Spectroscopy Applied to Magnetism and Materials Science, 1, pp. 373-429. , G. J. Long and F. Grandjean (Eds.), New York: Plenu

Magnetocaloric Effect And Transport Properties Of Gd5ge2(si1-xsnx)2 (x=0.23 And 0.40) Compounds

We report a study about the structural properties of polycrystalline samples of nominal composition Gd5Ge2(Si1-xSnx)2 (x=0.23, 0.40) that closely influence their physical behavior particularly related to electric resistivity and magnetocaloric (MCE) effect. The samples were characterized by X-ray diffraction (XRD) using the Rietveld refinement method, metallographic analyses, 119Sn Mössbauer spectroscopy, DC magnetization and electrical transport measurements. It was identified a Gd5Si2Ge2-monoclinic phase for x=0.23 and a Sm5Sn4-orthorhombic phase (type II) for x=0.40, both with two non-equivalent crystallographic sites for the Sn ions. We were able to infer on the role of tin on the magnetic and transport properties in these compounds. © 2007 Elsevier B.V. All rights reserved.3162 SPEC. ISS.368371Campoy, J.C.P., Plaza, E.J.R., Carvalho, A.M.G., Coelho, A.A., Gama, S., von Ranke, P.J., (2004) J. Magn. Magn. Mater., 272, p. 2375Pecharsky, V.K., Gschneidner Jr., K.A., (1997) J. Alloys Compds., 260, p. 98Morellon, L., Blasco, J., Algarabel, P.A., Ibarra, M.R., (2000) Phys. Rev. B, 62, p. 1022Wang, H.B., Altounian, Z., Ryan, D.H., (2002) Phys. Rev. B, 66, p. 214413Greenwood, N.N., Perkins, P.G., Wall, D.H., (1967) Symp. Faraday Soc., 1, p. 51Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494Sousa, J.B., Braga, M.E., Correia, F.C., Carpinteiro, F., Morellon, L., Algarabel, P.A., Ibarra, M.R., (2003) Phys. Rev. B, 67, p. 134416Levin, E.M., (1999) Phys. Rev. B, 60, p. 7993Levin, E.M., (2001) Phys. Rev. B, 63, p. 064426Levin, E.M., (2000) J. Magn. Magn. Mater., 210, p. 18