Design of magnetic spirals in layered perovskites: Extending the stability range far beyond room temperature

In insulating materials with ordered magnetic spiral phases, ferroelectricity can emerge owing to the breaking of inversion symmetry. This property is of both fundamental and practical interest, particularly with a view to exploiting it in low-power electronic devices. Advances toward technological applications have been hindered, however, by the relatively low ordering temperatures Tspiral of most magnetic spiral phases, which rarely exceed 100 K. We have recently established that the ordering temperature of a magnetic spiral can be increased up to 310 K by the introduction of chemical disorder. Here, we explore the design space opened up by this novel mechanism by combining it with a targeted lattice control of some magnetic interactions. In Cu-Fe layered perovskites, we obtain Tspiral values close to 400 K, comfortably far from room temperature and almost 100 K higher than using chemical disorder alone. Moreover, we reveal a linear relationship between the spiral’s wave vector and the onset temperature of the spiral phase. This linear law ends at a paramagnetic-collinear-spiral triple point, which defines the highest spiral ordering temperature that can be achieved in this class of materials. On the basis of these findings, we propose a general set of rules for designing magnetic spirals in layered perovskites using external pressure, chemical substitutions, and/or epitaxial strain, which should guide future efforts to engineer magnetic spiral phases with ordering temperatures suitable for technological applications.

A NEW MAGNETIC CONTROL METHOD FOR SPIRAL-TYPE WIRELESS CAPSULE ENDOSCOPE

In this paper, the authors propose a new magnetic control method for spiral-type wireless capsule endoscope (WCE). A cylindrical external permanent magnet (EPM) is used to generate rotational magnetic field to manipulate the synchronous rotation of a magnetic spiral-type WCE. To verify the feasibility of this method, a handheld actuator (HA) controlled by micro controller unit (MCU) was fabricated to drive the rotation of the EPM which is fixed on a step motor, and a magnetic spiral-type WCE along with a bracket were fabricated, too. Theoretical analysis and magnetic simulation about the control distance were performed. In ex vivo experiments were carried out in porcine small intestine, the control distance and control performances were evaluated. Experimental results indicate that this method can provide a maximum control distance up to 426.6[Formula: see text]mm with good control stability. Compared with Helmholtz coils method, this method is more cost-effective and the control region is broader. In addition, the estimated value of static friction torque (about 0.5694[Formula: see text]mN[Formula: see text][Formula: see text][Formula: see text]m) is obtained, which enriches the current research on friction issue in active control of the magnetic spiral-type WCE. This method has great potential to be applied in future clinical application.