Unusual magnetism of Er0.75Dy0.25Al2

dc magnetization, ac magnetic susceptibility, magnetic relaxation, electrical resistivity and x-ray powder-diffraction studies of Er0.75Dy0.25Al2 compound have been carried out in the temperature range of 5-300 K. The compound orders ferromagnetically at similar to 25 K, followed by another transition at similar to 10 K. This transition at 10 K is marked by a significant hysteresis in low applied fields in zero-field-cooled and field-cooled magnetization data. The saturation magnetic moment is 8.24 mu(B)/R3+ at 2 K in a 70 kOe field, indicating the presence of strong crystalline electric fields. A signature of weak glassy behavior is observed below 25 K in frequency dependent ac magnetic susceptibility measurements. This observation is attributed to competing single-ion anisotropies of Dy3+ and Er3+ ions that are statistically distributed in the lattice, thus creating large positional entropy. The paramagnetic phase of this compound includes a narrow region of Griffiths-phase-like behavior, signified by the presence of short-range ferromagnetic correlations. A long-time logarithmic relaxation of magnetization has been observed in the ferromagnetically ordered state. The electrical resistivity shows a slope change near 25 K and also a drop at 10 K. The electrical resistivity in the ferromagnetic state follows T-2 law, indicating the dominant role of magnon scattering. The magnetoresistance is similar to 13% at 25 K in a 30 kOe field. The role of quadrupolar interactions and magnetoelastic coupling in producing a possible structural distortion at 10 K has been considered and x-ray-diffraction studies were carried out down to 5 K. No structural change has been detected at 10 K, and hence the quadrupolar coupling between the rare-earth ions via the lattice should be weak, whereas direct higher-order Coulombic interactions may prevail.