Magnetic phase diagram of ${\mathrm{Fe}}_{80-x}{\mathrm{Ni}}_x{\mathrm{Cr}}_{20}$ ($10\le x\le 30$) alloys

Detailed magnetic measurements and a few neutron-diffraction experiments were performed on polycrystalline ${\mathrm{Fe}}_{80-x}{\mathrm{Ni}}_x{\mathrm{Cr}}_{20}$ alloys, with $x=30,26,23,21,19,17,14\mathrm{}$, and $10$. All the alloys are fcc except the one with $x=10\mathrm{}$, which is a mixture of fcc and bcc phases. The system is ferromagnetic for $x=30\mathrm{}$. The alloys with $x=26\mathrm{}$ and $23$ make transitions from a ferromagnetic to a Gabay-Toulouse ferromagnetic—spin-glass mixed phase at a lower temperature. Clear evidence of the presence of a spontaneous ferromagnetic bulk magnetization in this mixed phase supports recent theories predicting $Z$ ferromagnetism and $X-Y$ spin-glass freezing. For $x=21\mathrm{}$ and $19$ there is a spin-glass phase in low fields with some evidence of a field-induced ferromagnetism at high fields. Long-range antiferromagnetism takes over for the alloys with $x=17,14\mathrm{}$, and $10$. This sequence of compositional phase transition is due to competing ferromagnetic and antiferromagnetic interactions present in this system.