S. El-Khatib

Magnetic ordering in single-crystalline SrLaFeO4 and Sr1.1La0.9FeO4

We report on the magnetic properties of single-crystalline SrLaFeO4 and Sr1.1La0.9FeO4. Both compounds crystallize in the tetragonal K2NiF4 structure (I4∕mmm) with the La and Sr atoms randomly distributed over the 4e crystallographic sites of this structure. SrLaFeO4 orders antiferromagnetically below 350K, and Sr1.1La0.9FeO4, orders antiferromagnetically at about 150K. Both compounds exhibit magnetic structures described by orthorhombic Cmca-type symmetry and two magnetic propagation vectors q1=(12,12,0) and q2=(−12,12,0), representing the two possible magnetic domains. A collinear antiferromagnetic arrangement of the Fe3+ moments confined to the tetragonal basal plane is found. Bulk magnetic studies on SrLaFeO4 show that the properties of this compound are highly anisotropic, and there is evidence for additional magnetic transitions at lower temperatures (30 and 90K). Low-temperature neutron diffraction data were taken to gain some insight into the nature of these transitions.

Magnetic field effects in UNi1∕3Ru2∕3Al

We report on the electronic properties of a UNi1∕3Ru2∕3Al single crystal as a function of temperature and magnetic field. Our specific-heat, magnetization, and resistivity data provide strong evidence that the uranium 5f moments order ferromagnetically below TC=74K. Magnetic measurements reveal that the c axis is the easy magnetization direction with a saturation moment of about 0.78μB∕U-atom. Our neutron diffraction studies on UNi1∕3Ru2∕3Al provide strong evidence that Ni occupies the 1b (and Ru the 2c) positions of the ZrNiAl structure. We argue that such preferential occupation of Ni and Ru atoms is responsible for the observed ferromagnetic ground state.