Comparison of the low-temperature specific heat of Fe- and Co-doped Ca( (M=Fe or Co): Anomolously enhanced electronic contribution due to Fe doping
- 1 April 1996
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 53 (13) , 8651-8657
- https://doi.org/10.1103/physrevb.53.8651
Abstract
Specific-heat data of Fe-doped Ca( in the range 2–20 K are presented for x=1, 2, 4, 6, and 8 %. The data are compared with our previous measurements on Co-doped bismuth-strontium-calcium-copper oxide superconductors of nominal composition (BISCO 2212). Both Fe and Co are magnetic substitutions with effective moments close to their free-ion value. In the normal state the magnetic susceptibility increases by more than a factor 2 over the doping range due to effective-mass enhancement. In the superconducting state both ions act as magnetic pair breakers. For Co doping the normal-state linear term γ is observed, enhanced due to the effective-mass increase. For Fe doping we observe a large anomalous contribution to the electronic specific heat starting near 15 K and leading at the lowest temperature to a linear term near =72 mJ/mole (1 mole=1 formula unit). The anomalous term is typical of heavy fermion behavior. Comparison with specific-heat data of Co-doped BISCO 2212 suggests that hybridization between 3d electrons of the dopant and the planar carriers is more effective for Fe doping than for Co doping. © 1996 The American Physical Society.
Keywords
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