We report on measurements of the dc and ac magnetic susceptibility, (155)Gd Mössbauer spectra, and specific heat of the 1/1 approximant Ag(50)In(36)Gd(14), and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag(50)In(36)Gd(14). These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag(50)In(36)Gd(14), spin freezing occurs at T(f) = 4.3 K, and the frequency dependence of T(f) is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag(50)In(36)Gd(14) occurs in two stages: at T(f(1)) = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T(f(2)) = 2.4 K. The frequency dependences of T(f(1)) and T(f(2)) can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The (155)Gd Mössbauer spectra of the 1/1 approximant Ag(50)In(36)Gd(14) confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T(f(1)), but the temperature derivative of the magnetic entropy peaks at T(f(1)). The Debye temperature of the 1/1 approximant Ag(50)In(36)Gd(14) is 199(1) K as determined from the Mössbauer data, and 205(2) K as determined from the specific heat data.

The results of x-ray diffraction, dc magnetization, and 61 Ni Mössbauer spectroscopy studies of the ternary arsenide CrNiAs are reported. This compound crystallizes in the orthorhombic Fe 2 P-type structure (space group P62m) with the lattice parameters a = 6.1128(2)Å and c = 3.6585(1)Å. CrNiAs is a mean-field ferromagnet with Curie temperature T C = 171.9(1) K and the critical exponents β = 0.514(18), γ = 1.010(16), and δ = 2.922(10). The temperature dependence of the magnetic susceptibility above T C follows the modified Curie-Weiss law with a paramagnetic Curie temperature of 176.0(3) K and effective magnetic moment per transition metal atom of 2.42(1) μ B. The magnetic moment per formula unit at 4.2 K is found to be 1.114(33) μ B. The hyperfine magnetic field at 61 Ni nuclei at 4.2 K of 41.5(1.0) kOe implies that the Ni atoms carry a magnetic moment of 0.15(3) μ B , and that the moment carried by the Cr atoms is 0.95(6) μ B. The Debye temperature of CrNiAs is 221(1) K.

The results of x-ray diffraction, dc magnetization, and 61 Ni Mössbauer spectroscopy studies of the ternary phosphide CrNiP are reported. This compound crystallizes in the orthorhombic Co 2 P-type structure (space group Pnma) with the lattice parameters a = 5.7965(1) Å, b = 3.5337(1) Å, and c = 6.8123(2) Å. NiCrP is a ferromagnet with Curie temperature T C = 135.1(1) K. The ferromagnetic-to-paramagnetic transition is characterized by the critical exponents β = 0.355(22), γ = 1.241(18), and δ = 4.585 (20). Their values are close to those of a 3D Heisenberg ferromagnet. The temperature dependence of the magnetic susceptibility above T C follows the modified Curie-Weiss law with a paramagnetic Curie temperature of 142.9(6) K and effective magnetic moment per transition-metal atom of 1.70(2) μ B . The magnetic moment per formula unit at 4.2 K is found to be 0.816(13) μ B . The hyperfine magnetic field at 61 Ni nuclei at 4.2 K of 32.3(1.3) kOe implies that the Ni atoms carry a magnetic moment of 0.14(8) μ B , and that the moment carried by the Cr atoms is 0.68(9) μ B . The Debye temperature of NiCrP is 261(3) K.