Magnetism and magnetoresistance in the critical region of a dilute ferromagnet.

We present detailed experimental measurements and simulations of the field-dependent magnetization and magnetoresistance in the vicinity of the Curie temperature in the highly disordered dilute ferromagnetic semiconductor (Ga,Mn)As. The observed dependence of the magnetization on external magnetic field and temperature is consistent with three-dimensional Heisenberg equation of state calculations including a narrow distribution of critical temperatures. The magnetoresistance shows a peak at the Curie temperature due to the suppression of magnetic scattering in an applied magnetic field, which is well-described by considering changes in the square of the magnetization induced by the magnetic field.

Electrical switching of an antiferromagnet.

Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10(6) ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.

Agglutinins to anaerobic bacteria in Crohn's disease and in Indian patients with diarrhoea.

Agglutinins to certain species of Eubacterium and Peptostreptococcus have been reported in sera from a high proportion of patients with Crohn's disease. Because this might be a non-specific finding common to patients with diarrhoea associated with damaged intestinal mucosa, we have compared the incidence of such agglutinins in patients with Crohn's disease with that seen in patients in North-East India with acute or chronic diarrhoea. The incidence of agglutinins in Crohn's disease was 44%, compared with 11% in acute and 17% in chronic diarrhoea. These figures suggest that mucosal damage alone does not explain the high incidence of agglutinins in Crohn's disease.

Q fever in an urban area.

In the summer of 1981 29 patients living in Gwent, South Wales, had Q fever; 20 were diagnosed by routine clinical and laboratory services and 9 were discovered by active case-finding. The date of onset of symptoms spanned a 2-month period. The peak incidence was at the end of June. A case-control study showed an association with one area on the outskirts of Newport. Most patients had no direct contact with farms of farm animals and a common source of infection could not be identified. The most likely explanation of the outbreak was that farm vehicles had disseminated contaminated straw, manure, or dust in the area of Newport adjacent to farmland.