B. Emre

Barocaloric effect in the magnetocaloric prototype Gd5Si2Ge2

We report on calorimetric measurements under hydrostatic pressure that enabled us to determine the barocaloric effect in Gd5Si2Ge2. The values for the entropy change for moderate pressures compare favourably to those corresponding to the magnetocaloric effect in this compound. Entropy data are complemented with direct measurements of the adiabatic pressure-induced temperature change.

Large reversible entropy change at the inverse magnetocaloric effect in Ni-Co-Mn-Ga-In magnetic shape memory alloys

Calorimetry under magnetic field has been used to study the inverse magnetocaloric effect in Ni-Co-Mn-Ga-In magnetic shape memory alloys. It is shown that the energy dissipated during a complete transformation loop only represents a small fraction (5% to 7%) of the latent heat of the martensitic transition. It is found that the entropy values obtained from isofield temperature scans agree well with those obtained from isothermal magnetic field scans. The reproducibility of the magnetocaloric effect has been studied from isothermal measurements. Reproducible entropy values under field cycling have been found within a temperature interval bounded by the start temperature of the forward transition at zero field and the start temperature of the reverse transition under applied field. Large reversible entropy changes around 11 J/kg K have been found for fields up to 6 T.

Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

The effect of Nb substitution for Ni in Ni45Co5Mn40Sn10 magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni45Co5Mn40Sn10 alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabati...

Accessibility investigation of large magnetic entropy change in CoMn1−xFexGe

The influence of Fe doping for Mn in CoMn1−xFexGe alloys on their structural and magnetic phase transitions was investigated. CoMn1−xFexGe alloys display a first-order magneto-structural transition from a high temperature paramagnetic hexagonal Ni2In-type crystal structure to a low temperature ferromagnetic orthorhombic TiNiSi-type structure. An entropy change of ΔSM = −32.8 J/kg K was measured and adiabatic temperature change of −8.0 K was computed for the x = 0.085 alloy under a magnetic field of 7 T in the vicinity of the phase transition at 317 K. With increasing Fe content, transition temperatures and magnetic entropy changes decrease. In addition to investigating the effect of replacing Mn with Fe, the accessibility of the giant measured entropy change was quantified by means of the minimum magnetic field required to start and to complete the magneto-structural phase transition.

Giant magnetocaloric effect in Tb5Ge2–xSi2–xMn2x compounds

The crystal structure, magnetic and magnetocaloric characteristics of the pseduo ternary compounds of Tb5Ge2–xSi2–xMn2x (0 ≤ 2x ≤ 0.1) were investigated by x-ray powder diffraction and magnetization measurements. The x-ray powder diffraction results show that all compounds preserve the monoclinic phase as the majority phase and all the synthesized compounds were observed to be ferromagnetic from magnetization measurements. Magnetic phase transitions were interpreted in terms of Landau theory. Maximum isothermal magnetic entropy change value (20.84 J kg−1 K−1) was found for Tb5Ge1.95Si1.95Mn0.1 at around 123 K in the magnetic field change of 5 T.

Inverse and conventional magnetic entropy change in La0.8Sm0.2Mn2Si2 and La0.775Gd0.225Mn2Si2 compounds

The magnetic and magnetocaloric properties of La0.8Sm0.2Mn2Si2 and La0.775Gd0.225Mn2Si2 compounds have been studied by temperature- and magnetic field-dependent magnetic measurements. Both compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. Both compounds exhibit reentrant magnetic phase transitions and field-induced transitions from antiferromagnetic to ferromagnetic or ferrimagnetic state. The isothermal magnetic entropy change is estimated by using the Maxwell relation and Landau theory. Both compounds show inverse and conventional magnetocaloric effects around transition temperatures. Application of Landau theory on magnetic transitions shows good agreement with the result obtained by Maxwell theory.