Anisotropy of the magnetization discontinuity at the vortex-lattice melting in untwinned YBa{sub 2}Cu{sub 3}O{sub 7-delta}.
We measured the magnetic torque {tau} experienced by an untwinned YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} single crystal in external magnetic fields up to {mu}{sub 0}H=7 T below the critical temperature T{sub c}=93.3 K, as a function of {Theta}, the angle between H and the c axis of the crystal. At the vortex-lattice melting transition we observe discontinuities in both {tau} and ({partial_derivative}{tau}/{partial_derivative}H){sub {tau}} that are related to changes in the transverse components of the magnetization vector M and ({partial_derivative}M/{partial_derivative}H){sub {tau}} respectively. We use thermodynamic relationships to determine the direction of the vector {Delta}M in space, and show that {Delta}M is always directed parallel to M. The discontinuities in magnetization {Delta}M and in entropy {Delta}S vanish slightly below the temperature where the melting field H{sub m}(T) extrapolates to zero, which could indicate the existence of a lower critical point of the vortex-lattice melting line. From our ({partial_derivative}{tau}/{partial_derivative}H){sub {tau}} data are able to extract the differences in the reduced specific heat {Delta}C/T between the vortex-fluid and the vortex-solid phases, and we compare these results with corresponding thermal data. We finally examine the validity of standard angular scaling rules for anisotropic superconductors for the melting fields H{sub m}(T,{Theta}) at temperatures as high as T/T{sub c}=0.99.
- Research Organization:
- Argonne National Laboratory (ANL)
- Sponsoring Organization:
- SC; FOR
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 942731
- Report Number(s):
- ANL/MSD/JA-34085
- Journal Information:
- Phys. Rev. B, Journal Name: Phys. Rev. B Journal Issue: 5 ; Feb. 1, 2000 Vol. 61; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- ENGLISH
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