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57Fe Mossbauer spectroscopy under external magnetic fields of up to 72 kOe has been used to study the magnetic ordering in amorphous (FexMn1−x)75P16B6Al3 (0.25⩽x⩽1) at 4.2 K. From the behavior of the magnetic hyperfine fields one concludes that the Fe‐rich samples are soft ferromagnets and the Mn‐rich samples exhibit spin glass‐like properties. In the samples with intermediate Fe concentrations, a magnetic ordering where both ferromagnetic and spin glass‐like orderings coexist occurs.

Members of the R2Fe3Si5 series become either superconducting or magnetically ordered depending on whether the metal atom R( = rare earth, Y or Sc) is diamagnetic or paramagnetic respectively. We have taken Mossbauer effect and magnetization measurements to determine the magnetic state of the iron and the nature of the superconducting electrons. 57Fe Mossbauer measurements on the Sc, Dy and Er compounds all showed two partially resolved, quadrupole split spectra at all temperatures from 300 K to 1.5 K, indicating that there is no resolvable magnetic interaction at the iron site. No major change in the spectrum of Dy2Fe3Si5 was observed in passing through its antiferromagnetic ordering temperature of ∼4 K. Measurements in an applied field of 5.6 T set an upper limit of 0.03 μB for the iron moment in Sc2Fe3Si5. However, measurements at 4.2 K in fields up to 7 T for the Dy compound gave an internal field ∼9% smaller than the applied field and linear with applied field. This corresponds to an induced moment at the iron site of ∼0.07 μB at 7 T applied field. The 161Dy Mossbauer resonance clearly showed the onset of magnetic order around 4 K and the magnetic moment Dy at 1.5 K was found to be 7.0±0.2 μB consistent with the magnetization measurements. The nature of the superconducting electrons in the R2Fe3Si5 series is discussed in the light of available measurements.

A single phase stable hydride with nominal composition DyFe2H2 is shown to have the cubic C15 Laves structure with a 5% larger lattice constant. 57Fe Mossbauer spectra show two sites with nearly equal population and with different isomer shifts and hyperfine fields. Based on the average hyperfine field at 4.2 K, an Fe moment of approximately 1.6 μB is estimated. From the 161Dy data at 4.2 K, which show a single site, a nearly free‐ion moment of 9.8 μB is determined. Relaxation effects in the 161Dy spectra above 77 K, combined with a sharp decrease in the moment with increasing temperature, imply a weakening of the Dy‐Fe magnetic coupling induced by the presence of the hydrogen.

Paramagnetic iron ions with electronic spin relaxation times long compared to 10−7 seconds give the nuclear magnetic moment of 57Fe an opportunity to couple to the electron magnetic moment. This coupling between the nuclear and electronic moments may be broken by the application of an external magnetic field. This is accomplished by fields of the order of 100 Oe since the nucleus produces a field of about 10 Oe at the site of the electron. The effect of a small applied field is clearly exhibited in the Mossbauer spectra of several slowly relaxing paramagnetic iron materials with different electronic configurations. Examples to be presented include biological molecules, minerals, and inorganic salts. One can detect changes in the Mossbauer spectrum of a paramagnetic iron ion with applied fields as small as 10 Oe. Mossbauer spectra are calculated for various electronic configurations and compared with the appropriate experimental data.