The determination of magnetic structures using low temperature nuclear orientation:166mHo-Ho

It is demonstrated that the low temperature nuclear orientation technique can be used to determine the axes of quantization in a multiaxial ordered ensemble of nuclear spins. Expressions for the anisotropic -ray intensity from particular geometries are derived for the case in which each subsystem has its own axial symmetry. The determination of the atomic magnetic structure in antiferromagnets is discussed and the results of recent experiments on helically ordered^166mHo-Ho are presented. In these experiments, the angular variation of the intensities of some of the more intense -rays were measured and compared to theory. A value of 80.4(1)°, not including systematic errors, was obtained for the semi-cone angle of the helix formed by the atomic magnets.     

Nuclear magnetic resonance of oriented54Mn nuclei in antiferromagnetic MnCl2 · 4H2O

Nuclear magnetic resonance of oriented⁵⁴Mn nuclei in antiferromagnetic MnCl₂ · 4H₂O has been observed. The first two lines of the sextuplet split by quadrupole interaction are at frequencies 500.4 and 514.7 MHz, implying a hyperfine field of 643(5) kG. The stronger line at 500.4 MHz has a half-width at half maximum of 60 kHz and is shifted downward and split in frequency on application of a magnetic field. The nuclear spin-lattice relaxation time is dependent both on the applied field and the size and/or quality of the crystal.     

Pulsed nuclear magnetic resonance of oriented nuclei in an insulating magnetic material:54Mn−MnCl2.4H2O

The first observation of pulsed nuclear magnetic resonance of oriented nuclei in an insulating magnetic material is reported. The system studied was the ordered antiferromagnet⁵⁴Mn−MnCl₂.4H₂O. The response of the⁵⁴Mn spins to a single pulse of variable length, the free induction decay, and Hahn spin-echo have all been observed. A discussion of the transverse decoherent relaxation timeT ₂ in MnCl₂.4H₂O is given.     

Pulsed NMRON measurements on insulators

Selective single and double quantum excitation pulsed NMRON has been utilized to obtain rotation patterns, free induction decays, and spin echoes in antiferromagnetic⁵⁴Mn−MnCl₂·4H₂O and the quasi-2 dimensional ferromagnet⁵⁴Mn−Mn(COOCH₃)₂·4H₂O. The pulsed technique is well suited to observing fast spin-lattice relaxation and T₁ values down to 100 ms have been measured in these systems. These short times may make magnetic insulators viable hosts for on-line experiments. The dependence on field and temperature of the⁵⁴Mn spin-lattice relaxation time T₁ has been investigated and a T₁ minimum at high fields observed in both systems. A spin-spin relaxation time T₂≈50 μs is measured in⁵⁴Mn−MnCl₂·4H₂O. The observation of NMRON in the paramagnetic phase of MnCl₂·4H₂O allows the resonant frequencies in the antiferromagnetic and paramagnetic phases to be compared, yielding a value for the zero point spin deviation in the former phase.