Carlos Frontera

Room-temperature antiferromagnetic memory resistor.

The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.

Selective spin-state switch and metal-insulator transition in GdBaCo2O5.5

Ultrahigh resolution synchrotron diffraction data for GdBaCo 2 O 5 . 5 throw new light on the metal-insulator transition of Co 3 + Ba-cobaltites. An anomalous expansion of CoO 6 octahedra is observed at the phase transitionon heating, while CoO 5 pyramids show the normal shrinking at the closing of the gap. The insulator-to-metal transition is attributed to a sudden excitation of some electrons in the octahedra (t 6 2 g state) into the Co e g band (final t 4 2 g e 2 g state). The t 5 2 g e 1 g state in the pyramids does not change and the structural study also rules out a d 3 x 2 r 2 /d 3 y 2 - r 2 orbital ordering at T M I .

New crystal structure and characterization of lanthanum tungstate “La6WO12” prepared by freeze-drying synthesis

Lanthanum tungstates with a La/W atomic ratio between 6 and 4.8 have been synthesized as polycrystalline materials using the freeze-drying wet-chemical precursor method. Our results show that a single phase material is obtained when the La/W ratio is between 5.3 and 5.7 (T = 1500 degrees C). Outside this compositional range, segregation of either La(2)O(3) (La/W > or = 5.8) or La(6)W(2)O(15) (La/W < or = 5.2) are found. We have solved the crystal structure for the composition with a La/W nominal atomic ratio of 5.6 by combining powder X-ray and powder neutron diffraction techniques. This structure substantially differs from that previously reported for Ln(6)WO(12) (Ln = Y, Ho). The main differences between the two structure types are the crystal symmetry, the different coordination environment of the cations and the formula unit. The formula unit can be written as La(6.63)W(1.17)O(13.43) (Z = 4; calculated density = 6.395 g/cm(3)), well in accordance with the diffraction techniques, He-pycnometry and electron probe microanalysis. These materials can be described as a face centred cubic structure with space group F43m. Lattice parameters vary between 11.173 and 11.188 A, depending on composition. Dense ceramic materials are obtained at 1400 degrees C, and microanalyses measurements indicate that no significant tungsten evaporation occurs compared to the nominal values. Compositions with La(2)O(3) segregation show similar conductivity values as the single phase ones, but those containing segregation of W-rich phases show a considerable drop in conductivity with increasing content of the secondary phase.

Effect of band filling and structural distortions on the Curie temperature of Fe-Mo double perovskites

By means of high resolution neutron powder diffraction at low temperature we have characterized the structural details of

Elastocaloric and magnetocaloric effects in Ni-Mn-Sn(Cu) shape-memory alloy

{\mathrm{La}}_{x}{\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{FeMoO}}_{6}

Magnetocaloric effect in the low hysteresis Ni-Mn-In metamagnetic shape-memory Heusler alloy

(0l~\mathrm{x}l~0.5)

Enhanced ferromagnetic interactions in electron doped NdxSr2?xFeMoO6 double perovskites

and

Strain-induced nonsymmorphic symmetry breaking and removal of Dirac semimetallic nodal line in an orthoperovskite iridate

{\mathrm{Ca}}_{x}{\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{FeMoO}}_{6}