TIME-DOMAlN ZERO-FIELD MAGNETIC RESONANCE WITH FIELD PULSE EXCITATION

The principal attraction of magnetic resonance in zero field is the isotropy of space which allows one to record high-resolution spectra even for powder samples. This extends the domain of magnetic resonance to systems of which large single crystals cannot be grown. Normally, senslhvlty considerations do not pernut direct observation of zero-field resonance and special high-sensltlvity procedures must be applied. Numerous procedures have been proposed to detect resonance indirectly by field cycling techniques [l-7] consisting of three phases: (1) prepolarization in high magnetic field, (ii) resonance in zero fieId, and (iii) observation in high field This scheme has led to lugh-sensitivity techniques for the detection of ICI -v-abundance nuclei. Field cycling has become one of the standard procedues for deuterium, mtrogen-14, and oxygen-17 quadrupole resonance [S-7] _ All these techniques are conceived as spectral methods dete mumng the zero-field spectrum point by point_ Recently an alternative real-tune Fourier technique has been introduced by Pines and co-workers [8,9] where the zero-field free induction decay IS indirectly sampled and Fourier-transformed to obtain the speG trum. This technique features hrgh resolution and high sensitivity. The procedure used so far employs a very fast jump to zero field in order to create a nonequilibrium state which precesses under the zero-field Hamiltonian. By the sudden application of a magnetic field, it is then possible to spin-lock part of the magnetization for the final detection in high -magnetic field. We propose in this Letter an alternative technique of zero-field resonance, employing an adiabatic transfer of spm order between high field and zero field and vice versa. The non-equilibrium state is created and sampled by a pau of short magnetic field pulses which set the time interval for free precession. The proposed technique has advantages insofar as the technical realization is simpler, and numerous vatits are feasible in view of further refinements of zero-field spectros