Observation of unusual ferromagnetic cluster glass behavior in CrAlGe

We report on an experimental study on the structural and magnetic properties of the intermetallic compound CrAlGe. The material has been investigated in detail by x-ray diffraction, dc magnetization, ac susceptibility, and electrical resistivity measurements. X-ray diffraction and associated Rietveld analysis show that the compound crystallizes in the orthorhombic TiSi2-type structure, with lattice parameters a = 4.7531(1) A˚ ,b = 8.2182(1) A, ˚ and c = 8.6951(1) A. The magnetization measurements demonstrate that the alloy is ferromagnetic with a ˚ Curie temperature of TC ≈ 80 K. At 5 K the magnetization saturates at 50 kOe with a saturation moment of MS = 19 emu/g. Below TC, the ac susceptibility data exhibit two distinct frequency dependent peaks, which are also strongly dependent on ac field amplitude and dc magnetic fields. The experimental results strongly suggest the coexistence of ferromagnetic and reentrant spin glass type states in CrAlGe, which is due to the effect of the structural disorder in the 16f site (mixed Al/Ge occupation) on the crystallographically ordered 8a site of Cr. To our knowledge, CrAlGe is the first example where such unusual magnetic behavior is brought about not by structural disorder on the site occupied by the magnetic atom, but is due to the disorder in the atomic sites of the neighboring atoms.