An extremely large magnetic entropy change has been discovered in $\mathrm{Gd}{}_{5}(\mathrm{Si}{}_{2}\mathrm{Ge}{}_{2})$ when subjected to a the field. It exceeds reversible (with respect an alternating field) magnetocaloric effect any known material by at least factor of 2, and it is due first order $[\mathrm{ferromagnetic}(\mathrm{I})\ensuremath{\leftrightarrow}\mathrm{ferromagnetic}(\mathrm{II})]$ phase transition 276 K its unique field dependence.

The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. MCE properties have compiled and correlations made comparing behaviours of different families magnetic materials which exhibit large or unusual values. These include: lanthanide (R) Laves phases (RM2, where M = Al, Co Ni), Gd5(Si1−xGex)4, Mn(As1−xSbx), MnFe(P1−xAsx), La(Fe13−xSix) their hydrides manganites (R1−xMxMnO3, R Ca, Sr Ba). potential for use these in refrigeration is discussed, including a comparison...

▪ Abstract In the last decade of twentieth century there has been a significant increase in research on more than 100-year old phenomenon—the magnetocaloric effect (MCE). As result, many new materials with large MCEs (and lesser values) have discovered, and much better understanding this magneto-thermal property resulted. review we briefly discuss principles magnetic cooling heating); measurement properties by direct indirect techniques; special problems that can arise; MCE 4f lanthanide...

A study of four Gd samples different purities using ac susceptibility, magnetization, heat capacity, and direct measurements the magnetocaloric effect in quasistatic pulse magnetic fields revealed that all techniques yield same value zero-field Curie temperature 294(1) K. The determined from inflection points experimental susceptibility capacity is excellent agreement with those obtained Arrot plots. Above 2 T this transition increases almost linearly field at a rate...

Accurate values for the magnetocaloric effect can be obtained from both magnetization and heat-capacity data. A reliable estimate of experimental errors in calculated made known measured physical properties. Attempts past to simplify basic thermodynamic relation allow calculation adiabatic temperature change heat capacity at constant field magnetic entropy data fail because assumption that is magnetic-field independent erroneous. suitable approach carry out these calculations combined suggested.

A giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x⩽0.5. For temperature range between ∼50 and ∼280 K it exceeds reversible (with respect to alternating magnetic field) ΔSmag for any known refrigerant material at corresponding Curie by a factor of 2–10. The two most striking features this alloy system are: (1) first order phase transformation, which brings about large Gd5(SixGe1−x)4, is with field, i.e., can be utilized an active...

A temperature-dependent, single crystal x-ray diffraction study of the giant magnetocaloric material, Gd5(Si2Ge2), across its Curie temperature (276 K) reveals that simultaneous orthorhombic to monoclinic transition occurs by a shear mechanism in which (Si, Ge)-(Si,Ge) dimers are richer Ge increase their distances 0.859(3) and lead twinning. The structural changes electronic structure, provides an atomic-level model for change magnetic behavior with Gd5(SixGe1-x)(4).

The relationship between the behavior of temperature-dependent heat capacity at constant pressure measured in different magnetic fields and magnetocaloric effect systems with without discontinuous change entropy is discussed. It shown that two are directly related to each other, if either property (i.e., or effect) known, general second one can be predicted. derived relationships illustrated using several sets experimental data model examples.

The efficient use of reversible thermal effects in magnetocaloric, electrocaloric, and elastocaloric materials is a promising avenue that can lead to substantially increased efficiency refrigeration heat pumping devices, most importantly, those used household commercial cooling applications near ambient temperature. A proliferation caloric material research has resulted wide array where only the isothermal change entropy response handful different field strengths over limited range...

Replacement of Dy and substitution Nd in NdFeB-based permanent magnets by Ce, the most abundant lowest cost rare earth element, is important because are costly critical elements. The Co co-doped alloys have excellent high-temperature magnetic properties with an intrinsic coercivity being highest known for T ≥ 453 K.

The appropriate heat treatment of the Gd5Si2Ge2 alloy prepared from high-purity Gd results in a considerable enhancement its magnetocaloric effect. maximum magnetic entropy change increases by ∼80% (from ∼20 to 36 J/kg K) and adiabatic temperature ∼55% ∼11 17 for field 0 50 kOe when compared as arc-melted material. ordering is slightly reduced ∼277 K material ∼272 fully homogenized annealed Gd5Si2Ge2. behavior isothermal magnetization function changes some extent, while capacity anomaly at...

A massive magnetic-field-induced structural transformation in Gd5Ge4, which occurs below 30 K, was imaged at the atomic level by uniquely coupling high-resolution x-ray powder diffraction with magnetic fields up to 35 kOe. In addition uncovering nature of field induced transition, our data demonstrate that giant magnetocaloric effect, observed low fields, arises from amplification a conventional entropy-driven mechanism difference entropies two phases, borne concomitant transformation.

The large shear displacements of atomic layers in Gd5(SixGe1–x)4 materials, coupled with the change crystallographic symmetry and magnetic order, characterizes these transformations as magnetic–martensitic, which are extremely rare. start end magnetic–martensitic transitions depends strongly on direction (i.e., increasing or decreasing) either both temperature field. These profound bonding, structural, electronic, changes, occur system, bring about some extreme changes materials' behavior...

The relationships between both extensive and intensive properties quantifying the magnetocaloric effect, i.e., isothermal entropy change adiabatic temperature change, respectively, have been analyzed. An measure of effect alone, without considering another important also thermodynamic property, heat capacity, may lead to biased conclusions about size and, consequently, applicability a magnetic material as refrigerant. near room colossal magnetoresistive manganites [(R1−xMx)MnO3, where...

We describe the nearly quantitative preparation of phosphorus ylides and Wittig reaction occurring in solid sate during high-energy mechanochemical processing. Initial insights into details discovered chemical transformations indicate that mechanical processing supports interaction reacting centers by breaking crystallinity reactants providing mass transfer without a solvent.