[en] By means of ultra-high resolution synchrotron diffraction and calorimetry measurements we have studied the metal-insulator transition in GdBaCo₂O_5.5. The appearance of the metallic state is attributed to a sudden excitation of some electrons in the octahedra (t_2g⁶ state) into the Co e_g band (final t_2g⁴e_g² state). In contrast, the t_2g⁵e_g¹ state in the pyramids does not change at the transition. Calorimetry measurements show that the insulator-to-metal transition is first order and the entropy change estimated from the latent heat corroborates the pictured scheme

[en] Measurements of magnetic hysteresis loops performed at low temperatures on Cu-Al-Mn alloys with different Mn-content are presented. The loops are smooth and continuous above a certain temperature, while they exhibit a magnetization discontinuity below this temperature. Scaling analysis suggests that this system displays a disorder-induced phase transition line and allows determining the critical exponents (β=0.03±0.01 and βδ=13±3). Results indicate that by changing temperature, it is possible to tune the disorder responsible for the transition

[en] A study on the magnetocaloric effect in Ni-Mn-Ga shape-memory alloys has been carried out. It is shown that in addition to the (negative) contribution arising from microscopic spin-lattice coupling, a positive contribution originating from magnetostructural coupling takes place at the length scale of martensitic variants and magnetic domains. The latter contribution is dominant for low applied fields

[en] We present a comparative study of the magnetocaloric properties of Ni-Mn-X Heusler shape-memory alloys with X=Ga, Sn and In. In these materials, the magnetocaloric effect is a consequence of the magnetostructural coupling that enables the magnetic shape-memory properties. We show that inverse magnetocaloric effects can occur in these materials. The origin of this anomalous behavior is different in stoichiometric Ni₂MnGa and in Ni-Mn-Sn/In. In the former case it is related to the strong uniaxial magnetic anisotropy of the martensitic phase, while in the later it is an intrinsic effect associated with an incipient antiferromagnetism

[en] We report calorimetric and magnetization results showing that an increase in entropy is induced in a Ni-Mn-Sn ferromagnetic alloy by the application of a magnetic field, thus giving rise to an inverse magnetocaloric effect (MCE). The entropy change found for Ni-Mn-Sn is comparable to that reported for giant magnetocaloric materials but with opposite sign. This inverse MCE has the origin in a crystallographic phase change that modifies the magnetic exchange interactions through the change in the lattice parameters

[en] We have studied the lattice dynamics of a Ni₅₄Mn₂₃Al₂₃ (at.%) Heusler single-crystalline alloy by means of neutron scattering and ultrasonic techniques. Results show the existence of a number of precursor phenomena. We have found an anomaly (dip) in the low TA₂ phonon branch at the wave number ξ₀∼0.33 (in reciprocal lattice units) that becomes more pronounced (phonon softening) with decreasing temperature. We have also observed softening of the associated shear elastic constant (C^') with decreasing temperature. Ultrasonic measurements under applied magnetic field, both isothermally and varying the temperature show that the values of elastic constants depend on magnetic order thus evidencing magnetoelastic coupling

[en] The martensitic transformation temperature M_s depends linearly on the valence electron concentration for Ni-Mn-X Heusler systems where X is a group III-group V element. However, the slopes of the linearity are different for alloys with different X species and increases either as X changes from Al to In (isoelectronic) or from In to Sb (increase in number of p electrons). We discuss the features in the M_s vs e/a diagram and the relative stability of the various crystallographic phases of Ni-Mn based Heusler alloys