Magnetic behaviour of di-metal iron phosphide with a small substitution of iron by chromium, (Fe_0.97Cr_0.03)₂P, has been studied using SQUID magnetometry and powder neutron diffraction. It is paramagnetic at temperatures above ∼180 K with persisting short range ferromagnetic (FM) order. At lower temperatures three different regions of magnetic behaviour are identified. FM order evolves in the region 180 K-120 K but much more slowly and with much less magnetic moments than in Fe₂P. In the region 120 K-50 K negative exchange interactions gain some importance leading to a loss of FM order. Below 50 K FM interactions again dominate. Pinning centres influence the behaviour at low temperature up to ∼100 K.

DC magnetization measurements are reported in the temperature range 20–100 K on a poly-disperse nano-particle sample of the spinel ferrite Fe_2.9Zn_0.1O₄ with a log-normal size distribution of median diameter 43.6 Å and standard deviation 0.58. Outside a core of ordered spins, moments in surface layer are disordered. Results also show some similarities with conventional spin glasses. Blocking temperature exhibits a near linear variation with two-third power of the applied magnetic field and magnetizationM evolves nearly linearly with logarithm of timet. Magnetic anisotropy has been estimated by analysing theM-logt curve. Anisotropy values show a large increase over that of bulk particle samples. Major contribution to this enhancement comes from the disordered surface spins.

Crystal structure and magnetic behaviour of FeCrP have been investigated using magnetization and neutron diffraction measurements. FeCrP crystallizes in orthorhombic FeZrP type structure (P_nma space group,Z = 4) in which Cr atoms occupy the pyramidal site and Fe atoms occupy the tetrahedral site with total preference. Structural parameters including positional parameters have been refined. The refined values of positional parameters for Fe and Cr are quite different from those in FeZrP. The nature of magnetization-temperature curve is suggestive of antiferromagnetic nature withT_N = 280 (±10) K. Preliminary analysis of neutron diffraction pattern at 13 K is indicative of a rather complicated magnetic structure.

Magnetization and neutron diffraction measurements have been made on the title pseudo-binary of tetragonal anti-ferromagnets Fe₂ As and Cr₂ As. In this system antiferromagnetic (AFM) ordering appears below 310 K. The moments are confined in theab plane but unlike in the end members they are tilted off thea-axis. In addition to the AFM structure a weak ferromagnetic behaviour shows up below∼80 K with a rather low moment of ∼0.07 μB per formula unit at 5 K and under a field of 3 T.

Magnetization measurements are reported on a nano-particle sample of Znsubstituted spinel ferrite Fe_2.8Zn_0.2O₄ in the temperature range 20–300 K. Analysis of small-angle neutron scattering data shows the sample to have a log-normal particle size distribution of median diameter 64.4 Å and standard deviation 0.38. Magnetization evolves over a long period of timet going nearly linearly with logt. Magnetic anisotropy, estimated by fitting M-logt curve, shows many fold increase over that of bulk particle sample. Major enhancement owes to disordered moments in surface layer. In the nano-particle state as well increasing amount of Zn causes anisotropy to decrease.