We determined the lattice location of Mn in ferromagnetic (Ga,Mn)As using the electron emission channeling technique. We show that interstitial Mn occupies the tetrahedral site with As nearest neighbors (T As ) both before and after thermal annealing at 200 °C, whereas the occupancy of the tetrahedral site with Ga nearest neighbors (T Ga ) is negligible. T As is therefore the energetically favorable site for interstitial Mn in isolated form as well as when forming complexes with substitutional Mn. These results shed new light on the long standing controversy regarding T As versus T Ga occupancy of interstitial Mn in (Ga,Mn)As.[http://dx.doi.org/10.1063/1.4905556] a lino.pereira@fys.kuleuven.be (Ga,Mn)As has become the model system, in which to explore the physics of carrier-mediated ferromagnetism in semiconductors and the associated spintronic phenomena. 1,2In particular, as the most widely studied dilute magnetic semiconductor (DMS), (Ga,Mn)As is the perfect example of how the magnetic behavior of DMS materials is strongly influenced by local structure. In typical high Curie temperature (T C ) (Ga,Mn)As thin films (several % Mn regime), the majority of the Mn atoms substitute for Ga (Mn s ), while a minority fraction (several % of all Mn) occupies interstitial sites (Mn i ).3,4 Mn s provides both the localized magnetic moment and the itinerant hole that mediates the magnetic coupling, whereas Mn i has a twofold compensating effect: (i) magnetically, as Mn i -Mn s pairs couple antiferromagnetically and (ii) electrically, since double donor Mn i compensates Mn s acceptors.3 For a given Mn s concentration, Mn i therefore determines the hole concentration, the Fermi level and the effective Mn s concentration (of non-compensated Mn s moments), all of which define the magneto-electronic behavior of (Ga,Mn)As. The existence of such a crucial role of Mn i is clearly reflected in the effect of the Mn i concentration on the two relevant figures of merit: T C and magnetization. 3−5 Despite this central role in the understanding of (Ga,Mn)As, and, consequently, of Mn-doped III-V DMS materials, interstitial Mn is far from being a well understood defect. The presence of Mn i in ferromagnetic (Ga,Mn)As was first reported based on ion channeling measurements. 6Although consistent with Mn i occupying tetrahedral (T) interstitial sites, the measurements did not allow to discriminate between the two nonequivalent T sites: coordinated by four Ga atoms (T Ga ) or by four As atoms (T As ). Transmission electron microscopy measurements using the (002) diffracted beam indicated that Mn i predominantly occupies the T As site.7 X-ray absorption fine structure (XAFS) techniques were later applied, suggesting T Ga occupancy (e.g., Refs. 8 and 9). However, XAFS is not well suited to distinguish neighboring elements with similar atomic numbers, as is the case for Ga and As, especially in such cases of multi-site occupancy (substitutional and interstitial), where the site to be identified is in fact the minority one (interstitial). In pi...

Summary Magnetocaloric refrigeration has been pointed out as the most promising alternative to the ubiquitous vapor‐compression refrigeration technology due to its high coefficient of performance. Nevertheless, the use of hydraulic components in current devices is, among other reasons, hindering their commercial widespread. Solid state thermally switchable components are alternatives to the use of fluids. Since current developed structures are not ideal, the refrigerator operation design must be optimized to reduce their strict requirements. Active magnetic regeneration in fully solid state systems has been recently shown to be possible by moving the magnetic field gradually at constant speed, i.e., in several isochronal steps. Here, we investigate the implications of different operating modes on the temperature span, where the motion of the magnetic field includes acceleration and deceleration. When the magnetic field is either applied in a single step or from the cold to the hot reservoirs with linear or decelerated motion and is removed with acceleration motion from the hot to the cold reservoirs, the resulted temperature span increases up to 20%. The implications of each operating mode on the optimum frequency is discussed.

We report on the lattice location of low-fluence ion implanted 124In in single-crystalline 3C-SiC by means of the emission channeling technique using radioactive isotopes produced at the ISOLDE/CERN facility. In the sample implanted at room temperature to a fluence of 4 × 1012 cm−2, 60(9)% of the In atoms were found slightly displaced (0.12–0.20 Å) from substitutional Si sites, with the remainder occupying sites of low crystallographic symmetry, the so-called random sites. For 800 °C implantation, the substitutional In fraction increased to 72(8)% and the displacements from ideal substitutional Si sites were reduced to those expected for the lattice vibrations. These results, in terms of lattice location and disorder, are compared to those on In implanted group IV semiconductors silicon and diamond.