The structural and magnetic properties of nanoparticles of (LSMO) were studied using powder X-ray diffraction (XRD), transmission electron microscope (TEM), and magnetic measurements. The XRD refinement result indicates that samples crystallize in the rhombohedral structure with R-3C space group. The dc magnetization measurements revealed that samples exhibit no hysteretic behavior at room temperature, symptomatic of the superparamagnetic (SPM) behavior. The results of ac magnetic susceptibility measurements show that the susceptibility data are not in accordance with the Néel-Brown model for SPM relaxation but fit well with conventional critical slowing down model which indicates that the dipole-dipole interactions are strong enough to cause superspin-glass-like phase in LSMO samples. 1. Introduction Magnetic nanoparticles are currently the subject of intense research because of their potential applications in high density magnetic storage and biomedical applications [1–3]. The perovskite manganite with the formula ( , Ca, Ba, or vacancies) has attracted considerable attention due to the discovery of the phenomenon of colossal magnetoresistance (CMR) and its potential application [4–7]. The properties of these materials are explained by double exchange theory of Zener [7] and electron lattice interaction [8]. By varying the composition and consequently tuning the ratio, the compound reveals various electronic, magnetic, and structural phase transitions at different temperatures. These phase transitions have been attributed to strong coupling among spin, charge, orbital degree of freedom, and lattice vibrations. It is well known that the magnetic and transport properties of these materials strongly depend on the particle size, due to the influence of structural and magnetic disorders at the grain boundaries [9–13]. The size effects and the large surface area of magnetic nanoparticles intensely change some of the magnetic properties compared to bulk counter parts. Manganite nanoparticles display features like lower values of magnetization [14], higher values of low field magnetoresistance [15], exhibiting superparamagnetic (SPM) phenomena [16], and so forth. SPM nanoparticles with single domain microstructure have a high potential as carriers for biomedical applications. According to the Stoner-Wohlfarth theory, the magnetocrystalline anisotropy energy, , of a single-domain particle can be approximated by , where is the magnetocrystalline anisotropy constant, is the volume of the nanoparticle, and is the angle between the magnetization direction and the
References
[1]
M. Todorovic, S. Schuttz, J. Wong, and A. Scherer, “Writing and reading of single magnetic domain per bit perpendicular patterned media,” Applied Physics Letters, vol. 74, p. 2516, 1999.
[2]
T. D. Schladt, K. Schneider, H. Schild, and W. Tremel, “Synthesis and bio-functionalization of magnetic nanoparticles for medical diagnosis and treatment,” Dalton Transactions, vol. 40, no. 24, pp. 6315–6343, 2011.
[3]
L. Zhang and T. J. Webster, “Nanotechnology and nanomaterials: promises for improved tissue regeneration,” Nano Today, vol. 4, no. 1, pp. 66–80, 2009.
[4]
S. Jin, T. H. Tiefel, M. McCormack, R. A. Fastnacht, R. Ramesh, and L. H. Chen, “Thousandfold change in resistivity in magnetoresistive La-Ca-Mn-O films,” Science, vol. 264, no. 5157, pp. 413–415, 1994.
[5]
A. Asamitsu, Y. Moritomo, Y. Tomioka, T. Arima, and Y. Tokura, “A structural phase transition induced by an external magnetic field,” Nature, vol. 373, no. 6513, pp. 407–409, 1995.
[6]
Y. Tokura, Colossal Magnetoresistive Oxides, Gordon and Breach Science, Singapor, 2000.
[7]
C. Zener, “Interaction between the d-shells in the transition metals. II. Ferromagnetic compounds of manganese with perovskite structure,” Physical Review B, vol. 82, no. 3, pp. 403–405, 1951.
[8]
A. J. Millis and P. B. Shramin, “Double exchange alone does not explain the resistivity of La1？xSrxMnO3,” Physical Review Letters, vol. 74, no. 25, pp. 5144–5147, 1995.
[9]
R. D. Sánchez, J. Rivas, C. Vázquez et al., “Giant magnetoresistance in fine particle of La0.67Ca0.33MnO3 synthesized at low temperatures,” Applied Physics Letters, vol. 68, p. 134, 1996.
[10]
N. Zhang, W. Ding, W. Zhong, D. Xing, and Y. Du, “Tunnel-type giant magnetoresistance in the granular perovskite La0.85Sr0.15MnO3,” Physical Review B, vol. 56, p. 8138, 1997.
[11]
K. Wang, W. Song, T. Yu, B. Zhao, M. Pu, and Y. Sun, “Colossal magnetoresistance in fine particle of layered-perovskite La2-2xCa2+2xMn2O7 (x = 0.3) synthesized at low temperatures,” Physica Status Solidi A, vol. 171, no. 2, pp. 577–582, 1999.
[12]
A. Rostamnejadi, H. Salamati, P. Kameli, and H. Ahmadvand, “Superparamagnetic behavior of La0.67Sr0.33MnO3 nanoparticles prepared via sol-gel method,” Journal of Magnetism and Magnetic Materials, vol. 321, no. 19, pp. 3126–3131, 2009.
[13]
S. Daengsakul, C. Thomas, C. Mongkolkachit, and S. Maensiri, “Effects of crystallite size on magnetic properties of thermal-hydro decomposition prepared La1？xSrxMnO3 nanocrystalline powders,” Solid State Sciences, vol. 14, no. 9, pp. 1306–1314, 2012.
[14]
P. Kameli, H. Salamati, and A. Aezami, “Effect of particle size on the structural and magnetic properties of la0.8Sr0.2MnO3,” Journal of Applied Physics, vol. 100, no. 5, Article ID 053914, 2006.
[15]
D. G. Kuberkar, R. R. Doshi, P. S. Solanki et al., “Grain morphology and size disorder effect on the transport and magnetotransport in sol-gel grown nanostructured manganites,” Applied Surface Science, vol. 258, no. 22, pp. 9041–9046, 2012.
[16]
A. Rostamnejadi, H. Salamati, and P. Kameli, “Magnetic properties of interacting La0.67Sr0.33MnO3 nanoparticles,” Journal of Superconductivity and Novel Magnetism, vol. 25, no. 4, pp. 1123–1132, 2012.
[17]
J. L. Dormann, D. Fiorani, and E. Tronc, “On the models for interparticle interactions in nanoparticle assemblies: comparison with experimental results,” Journal of Magnetism and Magnetic Materials, vol. 202, no. 1, pp. 251–267, 1999.
[18]
J. Rodríguez-Carvajal, “Recent advances in magnetic structure determination by neutron powder diffraction,” Physica B, vol. 192, no. 1-2, pp. 55–69, 1993.
[19]
K. P. Shinde, S. S. Pawar, and S. H. Pawar, “Influence of annealing temperature on morphological and magnetic properties of La0.9Sr0.1MnO3,” Applied Surface Science, vol. 257, no. 23, pp. 9996–9999, 2011.
[20]
J. L. Dormann, D. Fiorani, and E. Tronc, “Magnetic relaxation in fine-particle systems,” Advances in Chemical Physics, vol. 98, pp. 283–494, 1997.
[21]
M. Suzuki, S. I. Fullem, I. S. Suzuki, L. Wang, and C. Zhong, “Observation of superspin-glass behavior in Fe3O4 nanoparticles,” Physical Review B, vol. 79, no. 2, Article ID 024418, 7 pages, 2009.
[22]
B. Aslibeiki, P. Kameli, I. Manouchehri, and H. Salamati, “Strongly interacting superspins in Fe3O4 nanoparticles,” Current Applied Physics, vol. 12, no. 3, pp. 812–816, 2012.
[23]
M. Tadi？, V. Kusigerski, D. Markovi？, M. Panjan, I. Milo？evi？, and V. Spasojevi？, “Highly crystalline superparamagnetic iron oxide nanoparticles (SPION) in a silica matrix,” Journal of Alloys and Compounds, vol. 525, pp. 28–33, 2012.
[24]
B. Aslibeiki, P. Kameli, H. Salamati, M. Eshraghi, and T. Tahmasebi, “Superspin glass state in MnFe2O4 nanoparticles,” Journal of Magnetism and Magnetic Materials, vol. 322, no. 19, pp. 2929–2934, 2010.
[25]
J. Mydosh, “Disordered magnetism and spin glasses,” Journal of Magnetism and Magnetic Materials, vol. 157-158, pp. 606–610, 1996.
[26]
M. Thakur, M. Patra, S. Majumdar, and S. Giri, “Coexistence of superparamagnetic and superspin glass behaviors in Co50Ni50 nanoparticles embedded in the amorphous SiO2 host,” Journal of Applied Physics, vol. 105, no. 7, Article ID 073905, 2009.
[27]
D. Fiorani, A. M. Testa, F. Lucari, F. D'Orazio, and H. Romero, “Magnetic properties of maghemite nanoparticle systems: surface anisotropy and interparticle interaction effects,” Physica B: Condensed Matter, vol. 320, no. 1–4, pp. 122–126, 2002.
[28]
K. Parekh and R. V. Upadhyay, “Static and dynamic magnetic properties of monodispersed Mn0.5Zn0.5Fe2O4 nanomagnetic particles,” Journal of Applied Physics, vol. 107, no. 5, Article ID 053907, 2010.
