AVS 52nd International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI-ThA

Invited Paper MI-ThA1
Doped Cobaltites: Phase Separation, Intergranular GMR, and Glassy Transport Phenomena

Thursday, November 3, 2005, 2:00 pm, Room 204

Session: Magnetic Oxides
Presenter: C. Leighton, University of Minnesota
Authors: C. Leighton, University of Minnesota
J. Wu, University of Minnesota
J. Lynn, NIST
C. Glinka, NIST
H. Zheng, Argonne National Laboratory
J. Mitchell, Argonne National Laboratory
W. Moulton, National High Magnetic Field Lab
M. Hoch, National High Magnetic Field Lab
P. Kuhns, National High Magnetic Field Lab
A. Reyes, National High Magnetic Field Lab
C. Perrey, University of Minnesota
C.B. Carter, University of Minnesota
Correspondent: Click to Email
Magneto-electronic phase separation, where a chemically homogeneous material displays spatial coexistence of multiple magnetic and electronic phases, is very common in perovskite oxides and is thought to play a key role in high temperature superconductivity and colossal magnetoresistance. We have used a battery of complementary experimental techniques to tackle the problem of magnetoelectronic phase separation in the perovskite cobaltite La1-xSrxCoO3. This is a material that offers many of the desirable attributes of a model system for investigating phase separation. Co and La NMR and small angle neutron scattering unequivocally demonstrate the existence of magnetoelectronic inhomogeneity in polycrystalline, single crystal and epitaxial thin film samples, which are chemically homogeneous on nm length scales. At low doping ferromagnetic metallic clusters form in an insulating matrix. These clusters coalesce with increasing doping, leading to a percolation transition and the onset of long-range ferromagnetic order. In single crystals, this formation of isolated clusters leads to a hysteretic negative MagnetoResistance (MR), which has field, temperature, and doping dependencies consistent with an intergranular Giant MagnetoResistance (GMR) effect. We argue that this system is a naturally forming analog to the artificial structures fabricated by depositing nanoscale ferromagnetic particles in a metallic or insulating matrix, i.e. this material displays an intergranular GMR effect without the deliberate introduction of chemical interfaces. The formation of nanoscopic F clusters also gives rise to glassy transport phenomena that are reminiscent of relaxor ferroelectrics. This is discussed in terms of the known phenomenology of the magnetic phase separation. Work supported by ACS PRF and NSF MRSEC.