Structural and magnetic properties of(Fe0.93Ni0.07)2P

Abstract

Structural and magnetic properties of(Fe0.93Ni0.07)2P havebeen investigated by means of powder x-ray and neutron diffraction, magnetization and paramagneticsusceptibility measurements over a temperature range of 10–500 K. The system crystallizes in theFe2P type hexagonal structure ( space group, Z = 3) in which the Ni atoms occupy the tetrahedralMI sites with total preference. Refined values of the cell parametersand bond distances are found slightly higher than those forFe2P and the atomic positional parameters are found quite close to those reported for the parent compoundFe2P. The temperature dependence of the magnetization shows a sharp magnetic phasetransition around 298(5) K. However there is difference of the zero-field cooled andfield cooled modes of the magnetization, which is indicative of the formation offerromagnetic clusters. The ferromagnetic to paramagnetic transition shifts towardsthe higher temperature side with increase in the applied magnetic field, whichindicates that the phase transition is a field induced type first-order magneticphase transition. There is no crystallographic structural transition associated withthe magnetic phase transition. The transition is caused by the change in thec/a ratio. The alloy retains the ferromagnetic order ofFe2P with the moments orienting along the [001] direction. The Rhodes–Wohlfarth ratio(µp/µs) of(Fe0.93Ni0.07)2P is foundto be 1.53 (>1), showing itinerant magnetism in this compound. At 297 K the magnetic moment at theMI site is found negligiblebut at the MII site itis ∼0.51 µB. The observednon-linearity above Tc in the χ−1–T curve gives clear evidence of the presence of short range magnetic order aboveTc. The momentsat the MII sites in the paramagnetic state and the exchange interactions are responsible forthe short range one-dimensional ferromagnetic chains along [001] well above theTc in(Fe0.93Ni0.07)2P.