A variable-frequency pulsed spectrometer was used to search for zero-field NMR lines in the two ferromagnetic compounds Fe2P and Fe3P. In Fe2P we observed spin echoes at 17.0, 20.5, 77.5, and 86.6 MHz. We deduce for the iron atoms hyperfine fields of 123 kOe (Fe II site) and 148 kOe (Fe I site). The phosphorus hyperfine fields are 45.0 kOe (P II site) and 50.2 kOe (P I site). The frequency shift under applied magnetic field indicates the phosphorus hyperfine fields are positive. The temperature dependence of the 31P NMR frequency was studied. In Fe3P a rather complicated NMR spectrum was observed. Tentatively we deduce hyperfine fields of 190, 260, and 300 kOe for the three iron sites and a phosphorus hyperfine field of 52.2 kOe. The calculated hyperfine fields for both compounds are in good agreement with previous Mössbauer data.

The spin-lattice relaxation of Co nuclei in an iron host has been studied in various applied magnetic fields using the technique of nuclear magnetic resonance on oriented nuclei. In this method the nuclei studied are those in the bulk of the domains. The measurements show that the relaxation rate is dependent on the state of magnetization of the sample; the rate in 0.4 kOe is nearly five times faster than that measured in 5.7 kOe. This result agrees with previous measurements using conventional nuclear magnetic resonance, and demonstrates unambiguously the existence of a relaxation process in multidomain transition-metal ferromagnets that has never been adequately explained by theory. The resonance linewidths measured in the experiments show a dependence on the applied field. At high fields, when the sample is magnetically saturated, the full width at half maximum is about 0.7 MHz, while in the lowest field employed this width is only 0.2 MHz. An explanation in terms of demagnetizing effects is offered.

NMR of oriented Mn in antiferromagnetic MnC12 4H20 has been studied by monitoring the change in y-ray intensity. The strongest line has frequency 500.4+0.1 MHz and weaker lines are observed at 503.5+0.1 and 507.0+0.5 MHz. The linewidth is 35+5 kHz. A value for the hyperfine interaction strength A = -203.8+0. 1 MHz is deduced. The 3.1-MHz splitting of the lines is due to second-order magnetic "pseudoquadrupole" interaction (2.7 MHz) and pure quadrupole interaction (0.4 MHz). Point-charge calculations agree fairly well with the latter value.

We have invented a new superheated superconducting granule detector which is a prime candidate for sensing dark matter and which could prove very useful for other applications. The sensor element is a planar array of spherical granules for which the spread in transition temperatures is nearly an order of magnitude smaller than that for a colloidal device. The detecting efficiency for low-energy deposition is thereby significantly increased. Preliminary results are described.

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