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Impact of nanostructuring on the magnetic and magnetocaloric properties of microscale phase-separated LaPrCaMnO manganites
N. S. Bingham, P. Lampen, M. H. Phan, T. D. Hoang, H. D. Chinh, C. L. Zhang, S. W. Cheong, and H. Srikanth
Phys. Rev. B 86, 064420 – Published 16 August 2012
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Abstract
Bulk manganites of the form LaPrCaMnO (LPCMO) exhibit a complex phase diagram due to coexisting charge-ordered antiferromagnetic (CO/AFM), charge-disordered paramagnetic (PM), and ferromagnetic (FM) phases. Because phase separation in LPCMO occurs on the microscale, reducing particle size to below this characteristic length is expected to have a strong impact on the magnetic properties of the system. Through a comparative study of the magnetic and magnetocaloric properties of single-crystalline (bulk) and nanocrystalline LPCMO (3/8) we show that the AFM, CO, and FM transitions seen in the single crystal can also be observed in the large particle sizes (400 and 150 nm), while only a single PM to FM transition is found for the small particles (55 nm). Magnetic and magnetocaloric measurements reveal that decreasing particle size affects the balance of competing phases in LPCMO and narrows the range of fields over which PM, FM, and CO phases coexist. The FM volume fraction increases with size reduction, until CO is suppressed below some critical size, ∼100 nm. With size reduction, the saturation magnetization and field sensitivity first increase as long-range CO is inhibited, then decrease as surface effects become increasingly important. The trend that the FM phase is stabilized on the nanoscale is contrasted with the stabilization of the charge-disordered PM phase occurring on the microscale, demonstrating that in terms of the characteristic phase separation length, a few microns and several hundred nanometers represent very different regimes in LPCMO.
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- Received 30 March 2012
DOI:https://doi.org/10.1103/PhysRevB.86.064420
©2012 American Physical Society
Authors & Affiliations
N. S. Bingham1, P. Lampen1, M. H. Phan1,*, T. D. Hoang2, H. D. Chinh2, C. L. Zhang3, S. W. Cheong3, and H. Srikanth1,†
- 1Department of Physics, University of South Florida, Tampa, Florida 33620, USA
- 2Department of Inorganic Chemistry, Hanoi University of Science and Technology, Hanoi, Vietnam
- 3Rutgers Center for Emergent Materials and Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- *phanm@usf.edu
- †sharihar@usf.edu
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Vol. 86, Iss. 6 — 1 August 2012
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Figure 1
X-ray diffraction patterns of LaPrCaMnO nanoparticles annealed at 650, 850, and 1050 °C. A representative TEM micrograph of the particles annealed at 850 °C is shown in the inset.Reuse & Permissions
Figure 2
Field cooled (FC) and zero field cooled (ZFC) temperature-dependent magnetization curves for (a) single-crystal, (b) 400 nm, (c) 150 nm, and (d) 55 nm LPCMO in an applied dc field of 100 Oe.Reuse & Permissions
Figure 3
Magnetization vs field isotherms from 10 to 300 K and 0 to 5 T for (a) single-crystal, (b) 400 nm, (c) 150 nm, and (d) 55 nm LPCMO.Reuse & Permissions
Figure 4
(a) Comparison of the field-dependent magnetization at 70 K up to 3 T. (b)–(e) represent the 1 T spin alignment within (b) the FM regions of the bulk sample and the FM particles in each nanocrystalline sample (c)–(e).Reuse & Permissions
Figure 5
Temperature-dependent magnetic entropy change (−Δ) for fields between 0.2 and 5 T.Reuse & Permissions
Figure 6
Magnetic field dependence of maximum magnetic entropy change () (a)–(c) and magnetization (d)–(f) near the charge ordering temperature. Phase coexistence occurs between , the field at which the CO phase begins to melt, and , the field at which the CO phase is fully converted to FM.Reuse & Permissions
Figure 7
Magnetic field dependence of maximum magnetic entropy change () (a) and magnetization (b) near for the 55 nm particles.Reuse & Permissions
Figure 8
Size and temperature effects on phase coexistence in LPCMO. Paramagnetic (PM, cream), charge-ordered (CO, red), and ferromagnetic (FM, black) coexist in the temperature range < < . In the bulk, microscale phase separation occurs between PM and CO (a); FM domains nucleate in the PM phase and grow slowly (b) then suddenly (c) as is lowered. The FM volume fraction increases on the nanoscale (d)–(i) due to surface effects and weakening of the CO. Large particles exhibit bulklike behavior, while CO is suppressed in the smallest particles.Reuse & Permissions
