Magnetic orderings and temperature dependence of the hysteresis loops of Nb 1-xFe 2+x

Investigations of the magnetic properties of NbFe ₂ were performed by measuring the temperature dependence of hysteresis loops, initial AC-susceptibility and zero field cooled (ZFC)-FC magnetizations in a wide field range of 50 Oe⩽ μ₀H⩽8000 Oe. Two well-defined peaks, at 4.8 and 21.4 K, were found in the AC-susceptibility curve, and only the first peak is sensible to a frequency change of the applied field. The peak changes to high temperature and its intensity decreases with increasing frequency, thus showing a relaxation phenomenon. In ZFC magnetization at 50 Oe, the peaks occur at 3.4 and 21.4 K. With increasing DC field, both peaks are shifted to low temperatures; however, the first peak disappears at fields higher than 100 Oe and a field higher than 1250 Oe suppresses the second peak. A third maximum merges from the magnetization curve at around 7 K in a field of 500 Oe, in which case, the maximum is suppressed by an external field higher than 4000 Oe. One can suggest that the ordered state of the stoichiometric NbFe ₂ is a spin density wave (SDW) and both ferro- and antiferromagnetic spin fluctuations coexist.