Deterministic switching of ferromagnetism at room temperature using an electric field.

The technological appeal of multiferroics is the ability to control magnetism with electric field. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroic material exhibiting unambiguous magnetoelectric coupling at room temperature is BiFeO3 (refs 4 and 5). Its weak ferromagnetism arises from the canting of the antiferromagnetically aligned spins by the Dzyaloshinskii-Moriya (DM) interaction. Prior theory considered the symmetry of the thermodynamic ground state and concluded that direct 180-degree switching of the DM vector by the ferroelectric polarization was forbidden. Instead, we examined the kinetics of the switching process, something not considered previously in theoretical work. Here we show a deterministic reversal of the DM vector and canted moment using an electric field at room temperature. First-principles calculations reveal that the switching kinetics favours a two-step switching process. In each step the DM vector and polarization are coupled and 180-degree deterministic switching of magnetization hence becomes possible, in agreement with experimental observation. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching. Given that the DM interaction is fundamental to single-phase multiferroics and magnetoelectrics, our results suggest ways to engineer magnetoelectric switching and tailor technologically pertinent functionality for nanometre-scale, low-energy-consumption, non-volatile magnetoelectronics.

[Celioscopic gastrostomies and jejunostomies]. / Gastrostomies et jéjunostomies coelioscopiques.

The authors describe a technique of laparoscopic gastrostomy and jejunostomy, which has been used in 23 patients between May 1991 and August 1992: 13 laparoscopic gastrostomies (LG) and 10 laparoscopic jejunostomies (LJ), all performed under general anaesthesia. There were no operative deaths, one intraoperative complication and 3 postoperative complications. Twelve patients had died by the end of the study, 7 patients were still using their feeding tube and 4 patients ate normally. The mean duration of use of the feeding tubes was 4 months for LG and 43 days for LJ. The secondary complications consisted of 3 tube obstructions and one case of pyloric obstruction. Laparoscopic gastrostomy and jejunostomy, performed according to the method described, constitute an effective and reliable alternative to open operations. They can be performed in cases in which endoscopic gastrostomy is impossible. Due to its technical simplicity, laparoscopic jejunostomy should be preferred to gastrostomy whenever there is a risk of inhalation.

[Place of celioscopy in the diagnosis of invasiveness of digestive cancers]. / Place de la coelioscopie dans le diagnostic d'extension des cancers digestifs.

The adequate treatment of gastrointestinal tract carcinoma requires accurate preoperative staging. Laparoscopy has been advocated for this purpose. We reviewed the data of 12 patients and the literature to compare the results of laparoscopic staging to those of conventional imaging (ultrasonography-CT scan). Laparoscopy was more sensitive in the diagnosis of peritoneal and lives metastases. It was inadequate for the diagnosis of lymph node metastases. Laparoscopy was especially useful in patients with esophagus, stomach, pancreas and liver cancers. Laparoscopic ultrasonography improved the staging of pancreatic carcinoma and the diagnosis of liver metastases.