Magnetic properties of the dipolar Heisenberg antiferromagnet Gd in GdBa{sub 2}Cu{sub 3}O{sub 6+{ital x}}
- Institut fuer Angewandte Physik, Universitaet Hamburg, Jungiusstrasse 11, D-20355 Hamburg (Germany)
The nuclear spin-lattice and spin-spin relaxation times ({ital T}{sub 1},{ital T}{sub 2}) and the rf-enhancement factor {eta} of {sup 63,65}Cu in GdBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} were investigated at low temperatures (1.3--4.2 K) and in magnetic fields up to 7 T. {ital T}{sub 1} and {ital T}{sub 2} of the Cu(1) and Cu(2) sites were measured in the whole temperature range for various oxygen concentrations. The phase transition of the Gd sublattice is well resolved with {ital T}{sub {ital N}}=2.19 K for {ital x}=0, decreasing slightly to {ital T}{sub {ital N}}=2.09 K for {ital x}=1. The temperature dependence of the Gd fluctuations is in good agreement with the two-dimensional (2D) Ising model, indicating a breaking of the expected Heisenberg symmetry for the {sup 8}{ital S}{sub 7/2} Gd spins by a uniaxial anisotropy. We propose that this is due to the dipolar interaction, similar to the behavior observed in the classical 2D dipolar Heisenberg antiferromagnets of the K{sub 2}MnF{sub 4} family. The critical field was determined for the semiconducting samples as a function of temperature by a maximum in {ital T}{sub 2}{sup {minus}1}. Extrapolation of the critical field to {ital T}=0 yields {mu}{sub 0}{ital H}{sub {ital c}}({ital T}=0)=3.1 T. Enhancement factors up to {eta}=15 were observed at the spin-flop field {mu}{sub 0}{ital H}{sub sf}=0.6 T in the nonsuperconducting samples. From the spin-flop and the critical field we find an in-plane exchange {ital J}/{ital k}{sub {ital B}}{approx}75 mK and an anisotropy field {mu}{sub 0}{ital H}{sub {ital a}}=0.1 T, which is in accord with the dipolar anisotropy calculated for the Gd sublattice.
- OSTI ID:
- 44575
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 51, Issue 18; Other Information: PBD: 1 May 1995
- Country of Publication:
- United States
- Language:
- English
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