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The effects of a combined substitution of Nd by Y and Fe by Si in Nd2−xYxFe17−ySiy compounds (0⩽x⩽1.5,0⩽y⩽3.0) on structural and magnetic properties have been investigated by means of x-ray diffraction, neutron diffraction, and magnetic measurements. The investigated samples crystallize in Th2Zn17-type structure with only small amounts of alpha-Fe. The unit cell volume decreases with increasing Y content or Si content. Neutron diffraction analysis indicates that substitution of Y for Nd induces a decrease of Si occupancy in 18h sites and increases in 9d sites and 18f sites. With the substitution of Y for Nd, the average site bond lengths in 6c, 9d, 18f, and 18h sites all decrease, but the distances of all Fe-Fe pairs do not change negatively. The TC of Nd2−xYxFe17−ySiy increases significantly with increasing Si substitution (y⩽3.0), but it changes slightly with increasing Y substitution. Similar to the case of Si substitution, the Ms also first increases and then decreases with increasing Y substitution. The highest TC of 535K and the highest Ms of 121.1emu∕g were observed in Nd1.5Y0.5Fe14.0Si3.0 and Nd1.5Y0.5Fe15.0Si2.0, respectively, which indicates that the combined substitution of Nd by Y and Fe by Si can have a strongly cooperative effect on the improvements of magnetic properties.

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