The proton spin relaxation time in the antiferromagnetic single crystal of CuC12. 2H,O Was measured in the temperature region of liquid helium. A strong temperature dependence was found, the relaxation time increasing to a few seconds at 1.2ยฐK. Up to 2.5ยฐK the results can be described in terms of a simple model concerning the fluctuating magnetic moments of the Cu ions.
I. Introduction.
Previous experiments on the decomposed proton magnetic resonance line in single crystals of paramagnetic CuSO4.5H20 1) and CuC12. 2KC1.2H20 z) showed saturation effects for high RF amplitudes at the lowest temperatures (about 1.2ยฐK). During later measurements on the proton resonance in single crystals of antiferromagnetic CuCI~.2HzO 3), the same effects were observed. Various experiments have been carried out cn this crystal, resulting in detailed information about its magnetic properties.
To extend the data we carried out relaxation time measurements on the antiferromagnetic single crystal of CuC1,.2H,O. In the following we describe the temperature dependence of the proton magnetic relaxation time t 1 for one specified resonance line and at a certain fixed direction of the external field. Further experiments are being made in order to determine t 1 as a function of the direction of the external field to the crystal axes. Measurements on t 1 are also being carried out in the paramagnetic state for which the single crystal of CuClz. 2KCI. 2HzO is being used. In our theoretical discussion we assume that the major contribution to the relaxation originates from the time dependence of the interaction between the protons and their surrounding copper ions. Because ot the low temperatures involved, only the time variations of the electron spin coordinates are taken into account. In principle, the model for the rapidly fluctuating copper magnetic moment was already assumed in one of our earlier papers 4).
- Experimental arrangement. Several methods of determining ~1 were tried. As the oscillator method 3) 4) proved to be convenient in our previous --48 --