We have investigated the magnetocaloric properties on the ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1-x}{\mathrm{A}}_x\mathrm{Ga}$ Heusler alloys with partial substitution of Mn by $A=\mathrm{Co}$ ($x=0.10$ , 0.20, and 0.30) and Cu ($x=0.15$ and 0.20) in the vicinity of the martensitic transition by measuring magnetization curves at magnetic field up to $20\mathrm{kOe}$ and in the temperature range of $250–300\mathrm{K}$ . The changes of the magnetic part of entropy dependence on magnetic field and temperature have been evaluated.

We have investigated the origin of the huge magnetocaloric effect in a manganite system with ferro–antiferromagnetic phase mixture at low temperatures. We carried out magnetic measurements in fields up to 100 kOe in order to show that both a high hysteretic behavior and a metamagnetic transition in the antiferromagnetic state are responsible for the large magnetic entropy change. The temperature where the maximum of the magnetic entropy change occurs can be tuned by varying the maximum value of the applied magnetic field to the system. This last procedure can open a new perspective for charge-ordered manganite applications to magnetic refrigeration at low temperatures.

We present a study of the substitution of Mn by Cu on the compound $\mathrm{N}{\mathrm{i}}_2$ $\mathrm{M}{\mathrm{n}}_{1-x}$ $\mathrm{C}{\mathrm{u}}_x$ $\mathrm{G}{\mathrm{a}}_{0.9}$ $\mathrm{A}{\mathrm{l}}_{0.1}$ , showing that the substitution of a small amount of Al on the Ga site does not affect the magnetic and magnetocaloric potential compared to $\mathrm{N}{\mathrm{i}}_2$ (Mn,Cu)Ga alloy. The samples were prepared with 10% substitution of Al and with Cu concentrations of x = 0.0, 0.2, and 0.3. Magnetization measurements as a function of temperature performed from 10 to 400 K, with an applied field of 0.02 T showed a ferromagnetic state, with critical temperature $T_c$ = 295 and 300 K for the samples with Cu, x = 0.2 and 0.3, respectively. For the sample without Cu, a complex behavior is observed at $T_c$ = 370 K, with martensitic transition at 220 K and a premartensitic at 250 K. Analysis of x-rays diffractograms at room temperature show a L $2_1$ structure for x = 0.0, while for x = 0.2 a mixture of L $2_1$ and martensitic is present, and the sample with x = 0.3 it is in a fully martensitic phase. Heat capacity measurements were performed in order to calculate magnetocaloric effect in the samples. The results indicate that in Ni(Mn,Cu)Ga alloys, a partial substitution of Ga by Al still produce a high refrigerant capacity while reducing the costs of fabrication.

The $\mathrm{La}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\right)}_{11.44}{\mathrm{Al}}_{1.56}$ system, with $x$ values of 0, 0.04, 0.08, and 0.12, was investigated for its magnetocaloric potential. For selected values of Co doping, it was possible to cover a wide magnetic ordering temperature range, from 200 up to $370\mathrm{K}$ , and reduce substantially the metamagnetic critical fields. At applied magnetic fields up to $5\mathrm{T}$ , the maximum magnetic entropy change approaches a nearly constant value of about $5\mathrm{J}∕\mathrm{kg}\mathrm{K}$ for Co-doped compounds, with $x$ varying from 0.04 to 0.12. The magnetic entropy change of a prototype composite was calculated in order to obtain a constant value in a wide temperature span. The results indicate that this material can be a good candidate for magnetic refrigeration using the Ericsson cycle.

Thermal hysteresis is recognized as one of the main drawbacks for cyclical applications of magnetocaloric and ferromagnetic shape memory materials with first-order transformations. As such, the challenge is to develop strategies that improve the compatibility between the phases involved in the transitions and study its influence on thermal hysteresis. With this purpose, we explore the thermal, structural, and magnetic properties of the ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1-x}{\mathrm{Cu}}_x{\mathrm{Ga}}_{0.84}{\mathrm{Al}}_{0.16}$ Heusler alloys. The alloys present a thermal hysteresis reduction of ∼60% when the Cu content in the compound varies from $x=0.10$ to $x=0.25$, with a minimum hysteresis width of 6 K being achieved. We applied the geometric nonlinear theory of martensite to address the phase compatibility, quantified by the parameter ${\lambda }_2$, the middle eigenvalue of the transformation stretch tensor, and found that the minimum of hysteresis is associated with a better crystallographic compatibility (${\lambda }_2$ closer to 1) between the austenite and martensite phases. In addition, we show that the valleylike properties of hysteresis found in the ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1-x}{\mathrm{Cu}}_x{\mathrm{Ga}}_{0.84}{\mathrm{Al}}_{0.16}$ compounds is present in several other alloys in the literature. These results provide pathways to understand as well as to master the phase compatibility and ultimately achieve a low thermal hysteresis in multifunctional Heusler alloys.

A 3D coordination polymer of Tb( iii ) of formula [Tb(bttb) _0.5 (2,5-pzdc) _0.5 ] _n , where two polycarboxylate ligands act as linkers, exhibits a maximum relative sensitivity of 0.76% K ⁻¹ at 295 K.