[Host: Jongsoo Yoon]
LnBaCo2O5.5 (Ln=Gd, Eu) and Sr3Ru2O7 are examples of weakly magnetic systems of 3d
and 4d transition metal oxides, respectively. The former is nonmetallic and exhibits magnetic
properties of two sublattice magnetic systems with an in-plane ferromagnetic interaction and a
relatively weak temperature dependent inter-plane magnetic coupling. The latter is a paramagnetic
metal with strongly correlated electrons near a magnetic instability.
The magnetization, resistivity and magnetoresistance (MR) of single crystals of
GdBaCo2O5.5 and EuBaCo2O5.5 are measured over a wide range of dc magnetic fields (up to 30 T)
and temperature. The data suggest an equal ratio of low spin (S=0) and intermediate spin (S=1)
Co3+ ions below TMI, with no indication of additional spin state transitions. The low field
magnetization shows a transition to a highly anisotropic ferromagnetic phase, followed by another
magnetic transition to an antiferromagnetic phase at a slightly lower temperature. Significant
anisotropy between the a-b plane and c axis was observed in magnetic and magnetotransport
properties for both compounds.
The specific heat and electrical resistivity of Sr3Ru2O7 single crystals are measured in
several magnetic fields applied along the c-axis for temperatures below 2 K and at fields up to 17
T. Near the critical metamagnetic field at B1
*~7.8 T, the electronic specific heat divided by
temperature increases logarithmically as the temperature decreases, over a large range of T, before
saturating below a certain T* (which is sample dependent). This crossover from a non-Fermi
Liquid to a Fermi Liquid state is also observed in the resistivity data near the critical metamagnetic
field for I || c and B || c. At the lowest temperatures, a Schottky-like upturn with decreasing
temperature is observed.
Condensed Matter Seminar
Thursday, November 11, 2004
Physics Building, Room 204
Note special time.
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