MAGNETIC STATES INSTABILITY OF Pt-Fe ALLOYS

Neutron-diffraction measurements have been used to 'determine the temperature and composition dependences of the ordered single crystals of Pt-Fe alloys containing 32, 30.5 and 28 at% of iron. A qualitative model for the complex antiferromagnetic ordering in the system based on the experimental data and band structure calculations has been proposed. The ordered Pt-Fe alloys with more than 36 at% of iron are ferromagnetic while the alloys with 25 at% of iron behave antiferromagnetically. Our previous studies of the magnetic and transport properties of Pt-Fe alloys over a wide range of temperatures and magnetic fields have enabled us to establish magnetic T-Cphase diagram of the intermediate concentration region, corresponding to the transition from antiferromagnetism (AF) to ferromagnetism (FM). In this system we have found the existence of the multiple magnetic phase transitions [I]. To understand better the types of the long range magnetic order we have performed neutron elastic scattering measurements of several ordered single crystals, containing 32, 30.5 and 28 at% of iron. The neutron-diffraction observations were made at the reactor in Budapest and neutrons of wavelength 1.06 A were used. In accordance with the magnetic data, in the alloy with 32 at% of iron the neutron diffraction measurements have revealed the existence of several magnetic structures in the region of 4.2-155 K, as may be seen from the temperature dependence of the neutron diffraction intensities of the reflexions shown in figure 1. fn this alloy at low temperatures only the mag1 netic (200) reflexions appear together with the weaker 1 3 reflections (1-0) and (-00). These reflexions are con2 2 -. sistent with AF structure with wavevector k =