We have performed high-resolution neutron powder diffraction measurements on CeMn2Si2 and CeMn2Ge2 at temperatures between 12 and 550 K. Our measurements indicate that at high temperatures both compounds are paramagnetic. Below TN=380 K CeMn2Si2 becomes a collinear AF, with a structure similar to that reported by Siek et al. in which the magnetic propagation vector is τ=(0 0 1). CeMn2Ge2, on the other hand, exhibits two different magnetic transitions. At TN≊415 K there is a transition to a collinear AF phase characterized by the commensurate propagation wave vector τ=(1 0 1). At TC≊318 K there is a transition to a conical structure with a ferromagnetic component along the c axis and a helical component in the ab plane. The helical component is characterized by the incommensurate propagation vector τ=(1 0 1−qz), where qz is temperature dependent.

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Results of high-resolution small-angle neutron scattering (SANS) studies on amorphous alloys of composition FexZr100−x, x=90, 91, 92, show that ferromagnetic correlations exist below Tc, but that conventional long-range order is destroyed by competing exchange interactions. The transition temperatures drop with increasing iron concentration (Tc ≊226 K for Fe90Zr10 down to Tc ≊175 K for Fe92Zr8). Data taken at very low Q (0.008 Å−1<Q<0.02 Å−1) provide evidence of relatively large (≊200–≊400 Å) static spin clusters which do not disorder at Tc. Superposed on this is an ordering with a second shorter length scale which shows a cusp (not divergent) at the bulk Tc. The data were fitted to a combination of a Lorentzian and a power of a Lorentzian, the latter of which represents scattering from clusters with a Maxwellian distribution of sizes.

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Conventional phase transitions are well understood in terms of the order parameter, based on the Landau-Ginzburg-Wilson theory. However, unconventional magnetic orders have been observed in clean systems such as MnSi. The unconventional magnetic orders of conduction electrons in the metallic phase has been observed for high-temperature superconductors and heavy fermion compounds. However, these unconventional magnetic orders have been limited to relatively low temperatures as quantum phase transitions. Here high-temperature magnetic short-range order is observed as one of the unconventional magnetic orders at temperatures up to 720 K in a noncentrosymmetric intermetallic antiferromagnet Mn 3 RhSi with a well-ordered lattice. The magnetic Mn ions form a hyperkagome network of cornersharing triangles, where the spins are geometrically frustrated. The spin network is equivalent to that of a spin liquid and non-Fermi-liquid material, β-Mn. Our observation indicates that a metallic phase with magnetic short-range order exists at high temperatures.