Polaron Formation in Colossal Magnetoresistive Oxides 

The magnetic properties of the lanthanum manganese oxide class of materials have attracted tremendous interest recently because of the dramatic increase in conductivity these systems exhibit when the magnetic moments order ferromagnetically, either by lowering the temperature or applying a magnetic field.  This huge increase in the carrier mobility, which has been given the name "Colossal MagnetoResistivity" (CMR), is both of scientific and technological interest.  In particular, it is anticipated that the "half-metallic" behavior these materials exhibit could provide fully spin polarized electrons for use in “spintronics” applications, for sensors in a variety of applications such as in the automotive industry, and may also provide the next generation of read/write heads for the magnetic data storage industry. 

The CMR originates from a magnetically driven insulator-metal transition, where the magnetic, electronic, and structural degrees of freedom are intimately intertwined.  Neutron scattering measurements have been used to discover that the transition from the low temperature ferromagnetic-metallic state to the paramagnetic-insulator state is caused by the formation of combined structural/magnetic polarons, which have a size of about one nanometer.  The formation of these nanoscale polarons truncates the ferromagnetic phase, and thus explains the first-order nature of the transition.  These polarons form a well defined thermodynamic glass phase above the ferromagnetic ordering temperature, which then melts into a polaron fluid at higher temperatures as shown in the figures below.

There is a strong similarity between these nanoscale polarons observed in the CMR materials, the polar nanoregions that cause the dramatic piezoelectric response of relaxor ferroelectrics, and the formation of stripes in the high temperature superconducting cuprates.  Recent progress in our understanding of these intrinsic nanoscale structures has enabled a deeper understanding of the fundamental properties and shared concepts of all these perovskite-based materials.

polaron mountains    graphgraph

"Polaron Mountains" shown on the left were discovered in the colossal magnetoresistive oxide materials.  They "pop up" as we go from the metallic ferromagnetic state at low temperature to the paramagnetic polaron state at high temperatures, whereas a magnetic field suppresses the polarons.  Thus the development of ferromagnetic order, either by lowering the temperature or increasing the magnetic field, is detrimental to polaron formation.

To understand the structure and dynamics of this ferromagnetic-metallic to paramagnetic-insulating transition, as the paramagnetic state is entered the purely elastic component to the structural polaron scattering signals the development of the correlated polaron glass phase.  This elastic scattering is accompanied by dynamic correlations are also peak at the same wave vector.  The dynamic polaron correlation length in this phase is also around a nanometer.  The strength of the elastic scattering diminishes with increasing temperature until the static polarons disappear at a higher temperature T*. The correlations remain above this temperature, but are then purely dynamic in character. The statics and dynamics of this scattering bear a remarkable similarity to the magnetic fluctuation spectrum recently observed in underdoped cuprates, suggesting that the underlying behavior has a similar origin.

energy scatteringblock phase diagram

Left:  Energy dependence of the scattering at the wave vector position of the polaron scattering.  There are two components of the scattering evident, a purely elastic component, and inelastic scattering that peaks at E=0 (quasielastic scattering).  Right:  Schematic block phase diagram for La1-xCaxMnO3, where we have sketched  the proposed polaronic glass phase and how it evolves into the long-range ordered Jahn-Teller transition for the undoped compound.  Basic ferromagnetic-metallic to paramagnetic-insulating, ferromagnetic-insulating to paramagnetic insulating, and antiferromagnetic to paramagnetic phase transitions are from previous work of other authors and us.  Note that at lower x the transitions are also dependent on the oxygen concentration and hence the heat treatment of the samples.  The ferromagnetic-paramagnetic transitions are from our work as well as the work of other authors (see references given in Phys. Rev. B 76, 014437 (2007)), while above optimal doping the transition becomes second order.  The polaron glass phase is based on our recent work.

 

graph  graph

Chemical disorder can be a key factor in phase stabilization, and recently A-site ordered and disordered La1/2Ba1/2MnO3 samples have been synthesized.  The Curie temperature for the ordered sample is much higher than for the disordered sample, while the exchange interaction as determined from the low T spin waves is almost the same.  The spin dynamical data shown at the left/top demonstrate that the transition in the ordered sample (Tc=348.7 K) is continuous, while there is two-phase coexistence (right/bottom) for the disordered sample (Tc=297 K).  The results indicate that the energy for polaron formation is lower in the chemically disordered sample, which truncates the ferromagnetic state.
 

See link to Multiferroics 

 
Selected Publications

Unconventional Ferromagnetic Transition In La1-xCaxMnO3, J. W. Lynn, R. W. Erwin, J. A. Borchers, Q. Huang, A. Santoro, J. L. Peng, and Z. Y. Li, Phys. Rev. Lett. 76, 4046 (1996).

Magnetic, Structural, and Spin Dynamical Properties of La1-xCaxMnO3 , J. W. Lynn, R. W. Erwin, J. A. Borchers, Q. Huang, A. Santoro, J. L. Peng and R. L. Greene, J. Appl. Phys. 81, 5488 (1997).

Structure and Magnetic Order in Undoped Lanthanum Manganite, Q. Huang, A. Santoro, J. W. Lynn, R. W. Erwin, J. A. Borchers, J. L. Peng, and R. L. Greene, Phys. Rev. B 55, 14987 (1997).

Neutron Scattering Investigation of the Structure and Spin Dynamics in La0.85Ca0.15MnO3 , L. Vasiliu-Doloc, J. W. Lynn, A. H. Moudden, A. M. De Leon-Guevara and A. Revcolevschi, J. Appl. Phys. 81, 5491 (1997).

Structure and Spin Dynamics of La0.85Sr0.15MnO3, L. Vasiliu-Doloc, J. W. Lynn, A. H. Moudden, A. M. de Leon-Guevara, and A. Revcolevschi, Phys. Rev. B58, 14913 (1998).

Structure and Magnetic Order of La1-xCaxMnO3, Q. Huang, A. Santoro, J. W. Lynn, R. W. Erwin, J. A. Borchers, J. L. Peng, K. Ghosh, and R. L. Greene, Phys. Rev. B58, 2684 (1998)

Spin Dynamics of the Magnetoresistive Pyrochlore Tl2Mn2O7, J. W. Lynn, L. Vasiliu-Doloc, and M. A. Subramanian, Phys. Rev. Lett. 80, 4582 (1998).

Spin Dynamics of Strongly Doped La1-xSrxMnO3, L.Vasiliu-Doloc, J. W. Lynn, Y. M. Mukovskii, A. A. Arsenov, and D. A. Shulyatev, J. Appl. Phys. 83, 7342 (1998).

Magnetic Correlations in the Bilayer Manganite La1.2Sr1.8MnO3, S. Rosenkranz, R. Osborn, S. K. Sinha, K. E. Gray, J. F. Mitchell, L. Vasiliu-Doloc, J. W. Lynn, and D. Argyriou, J. Appl. Phys. 83, 7348 (1998).

Neutron Scattering Investigation of Magnetic Bilayer Correlations in La1.2Sr1.8Mn2O7, R. Osborn, S. Rosenkranz, D. N. Argyriou, L. Vasiliu-Doloc, J. W. Lynn, S. K. Sinha, J. F. Mitchell, K. E. Gray, and S. D. Bader, Phys. Rev. Lett. 81, 3964 (1998)

Charge Melting and Polaron Collapse in La1.2Sr1.8Mn2O7, L. Vasiliu-Doloc, S. Rosenkranz, R. Osborn, S. K. Sinha, J. W. Lynn, J. Mesot, O. Seeck, G. Preosti, A. J. Fedro, and J. F. Mitchell, Phys. Rev. Lett. 83, 4393 (1999)

Charge Ordering and Polaron Formation in La0.7Ca0.3MnO3, C. P. Adams, J. W. Lynn, Y. M. Mukovskii, A. A. Arsenov, and D. A. Shulyatev, Phys. Rev. Lett. 85, 3954 (2000).

Temperature Dependence of Low-Lying Electronic Excitations of LaMnO3, M. A. Quijada, J. R. Simpson, H. D. Drew, J. W. Lynn, L. Vasiliu-Doloc, Y. M. Mukovskii, and S. G. Karabashev, Phys. Rev. B64, 224426 (2001).

Charge Correlations in La0.7Ca0.3MnO3, J. W. Lynn, C. P. Adams, Y. M. Mukovskii, A. A. Arsenov, and D. A. Shulyatev, J.  Appl. Phys. 89, 6846 (2001).

Glass Transition in the Polaron Dynamics in CMR Manganites, D. N. Argyriou, J. W. Lynn, R. Osborn, B. Campbell, J. F. Mitchell, U. Ruett, H. N. Bordallo, A. Wildes, and C. D. Ling, Phys. Rev. Lett. 89, 036401 (2002).

Structure of Nanoscale Polaron Correlations in a Colossal Magnetoresistive Manganite, B. J. Campbell, R. Osborn, D. N. Argyriou, L. Vasiliu-Doloc, J. F. Mitchell, S. K. Sinha, U. Ruett, C. D. Ling, Z. Islam, and J. W. Lynn, Phys. Rev. B65, 014427 (2002).

First-order Transition in the Itinerant Ferromagnet CoS1.9Se0.1, T. J. Sato, J. W. Lynn, Y.-S. Hor, and S.-W. Cheong, Phys. Rev. B68, 214411 (2003).

Inhomogeneous Magnetism in La-doped CaMnO3:  (I) Phase Separation due to Lattice-coupled Ferromagnetic Interactions, C. D. Ling, E. Granado, J. J. Neumeier, J. W. Lynn, and D. N. Argyriou, Phys. Rev. B68, 134439 (2003).

Inhomogeneous Magnetism in La-doped CaMnO3:  (II) Nanometric-scale Spin Clusters and Long-range Spin Canting, E. Granado, C. D. Ling, J. J. Neumeier, J. W. Lynn, and D. N. Argyriou, Phys. Rev. B68, 134440 (2003).

First-order Nature of the Ferromagnetic Phase Transition in (La-Ca)MnO3 near optimal doping, C. P. Adams, J. W. Lynn, V. N. Smolyaninova, A. Biswas, R. L. Greene, W. Ratcliff, II, S-W. Cheong, Y. M. Mukovski, and D. A. Shulyatev, Phys. Rev.B70, 134414 (2004).

Correlated and Uncorrelated Nanoscale Lattice Distortions in the Paramagnetic Phase of Magnetoresistive Manganites, V. Kiryukhin, A. Borissov, J. S. Ahn, Q. Huang, J. W. Lynn, and S-W. Cheong, Phys. Rev. B70, 214424 (2004).

Crystal Structures and Magnetic Order of La0.5+dA0.5-dMn0.5+eRu0.5-eO3 (A=Ca, Sr, Ba):  Possible Orbital Glass Ferromagnetic State, E. Granado, Q. Huang, J. W. Lynn, J. Gopalakrishnan, and K. Ramesha, Phys. Rev. B70, 214416 (2004).

Disorder-induced Polaron Formation in the Magnetoresistive Perovskite La0.54Ba0.46MnO3, T. J. Sato, J. W. Lynn, and B. Dabrowski, Phys. Rev. Lett. 93, 267204 (2004).

Field-induced Avalanche to the Ferromagnetic State in the Phase-separated Ground State of Manganites, F. M. Woodward, J. W. Lynn, M. B. Stone, R. Mahendiran, P. Schiffer, J. F. Mitchell, D. N. Argyriou, and L. C. Chapon, Phys. Rev. B70, 174433 (2004). 

 Inter-granular Giant Magnetoresistance in a Spontaneously Phase Separated Perovskite Oxide, J. Wu, J. W. Lynn, C. J. Glinka, J. Burley, H. Zheng, J. F. Mitchell, and C. Leighton, Phys. Rev. Lett. 94, 037201 (2005).

Magnetic Order and Spin Dynamics in Ferroelectric HoMnO3, O. P. Vajk, M. Kenzelmann, J. W. Lynn, S. B. Kim and S.-W. Cheong, Phys. Rev. Lett. 94, 087601 (2005).

Magnetic Inversion Symmetry Breaking and Ferroelectricity in TbMnO3, M. Kenzelmann, A. B. Harris, S. Jonas, C. Broholm, J. Schefer, S. B. Kim, C. L. Zhang, S.-W. Cheong, O. P. Vajk and J. W. Lynn, Phys. Rev. Lett. 95, 087206 (2005).

Electronically Smectic Liquid-crystal Phase in a Nearly Half-doped Manganite, F. Ye, J. A. Fernandez-Baca, P, Dai, J. W. Lynn, H. Kawano-Furukawa, H. Yoshizawa, Y. Tomioka, and Y. Tokura, Phys. Rev. B72, 212404 (2005).

Evolution of Spin-Wave Excitations in Ferromagnetic Metallic Manganites, F. Ye, P. Dai, J. A. Fernandez-Baca, H. Sha, J. W. Lynn, H. Kawano-Furukawa, Y. Tomioka, Y. Tokura, and J. Zhang, Phys. Rev. Lett. 96, 047204 (2006).

Reentrant Orbital Order and the True Ground State of LaSr2Mn2O7, Qing’An Li, K. E. Gray, H. Zheng, H. Claus, S. Rosenkranz, S. Nyborg Ancona, R. Osborn and J. F. Mitchell, Y. Chen and J. W. Lynn, Phys. Rev. Lett. 98, 167201 (2007).

Effect of Antiferromagnetic Spin Correlations on Lattice Distortion and Charge Ordering in Pr0.5Ca1.5MnO4, S. Chi, F. Ye, P. Dai, J. A. Fernandez-Baca, Q. Huang, J. W. Lynn, E. W. Plummer, R. Mathieu, Y. Kaneko, and Y. Tokura, Proceedings of the National Academy of Sciences 104, 10796 (2007).

A “non-Griffiths-like” clustered phase above the Curie temperature of the doped perovskite cobaltite La1-xSrxCoO3, C. He, M.A. Torija, J. Wu, J.W. Lynn, H. Zheng, J.F. Mitchell and C. Leighton, Phys. Rev. B76, 014401 (2007).

Neutron Diffraction Study of Multiferroic Tb0.85Na0.15MnO3−y, T.S. Chan, R.S. Liu, C.C. Yang, W.-H. Li, Y.H. Lien, C.Y. Huang and J.W. Lynn, J. Mag. Mag. Materials 310, 1151 (2007).

Magnetic ordering of Mn and Ru in (La0.52Ba0.48) (Mn0.51Ru0.49)O3, S. Y. Wu, 1, W.-H. Li, C. C. Yang, J. W. Lynn, and R. S. Liu, Physica Stat. Sol. B 244, 2233 (2007).

Influence of Oxygen Defects on the Crystal Structure and Magnetic Properties of the (Tb1-xNax)MnO3-y (0 £ x £0.3) System, T. S. Chan,R. S. Liu, C. C. Yang, W.-H. Li, Y. H. Lien, C.Y. Huang, Jeff. W. Lynn, J. M. Chen, and H.-S. Sheu, Inorganic Chemistry 46, 4575 (2007).

Order and Dynamics of Intrinsic Nanoscale Inhomogeneities in Manganites, J. W. Lynn, D. N. Argyriou, Y. Ren, Y. M. Mukovskii, A. A. Arsenov, and D. A. Shulyatev, Phys. Rev. B 76, 014437 (2007).

 

 

 [please see Recent Publications list for full details to these references as well as additional ones]

Return to main page