Study of the first paramagnetic to ferromagnetic transition in as prepared samples of Mn–Fe–P–Si magnetocaloric compounds prepared by different synthesis routes

Abstract

Magnetocaloric materials with composition of Mn 1.3 Fe 0.65 P 0.5 Si 0.5 have been prepared by ball milling and solid-state reaction methods and consolidated using powder annealing, and conventional and spark plasma sintering. Magnetic and calorimetric measurements show remarkable differences upon first cooling, and slight differences on second and further coolings between the samples prepared by different synthesis routes. Further measurements using Hall probe imaging in high magnetic field have been also carried out. As-prepared samples have been cooled down just above the critical temperature, and the first phase transition has been induced by application of a magnetic field. Bulk samples show staircase isothermal magnetization curves whereas powders show smoother transition curves.

Hysteresis Design of Magnetocaloric Materials—From Basic Mechanisms to Applications

“…The magnetization curves of this compound at 0.2 and 2 T are shown in Figure a. The thermal hysteresis is determined from both inflection points of the heating and cooling curves and corresponds to approximately 7 K with a magnetization of 115 A m −2 kg −1 under a field of 2 T, which agrees well with literature values . The thermal hysteresis in this material is assumed to be related to the anisotropic lattice volume change of the sample, thereby resulting in only a minimal volume change .…”

“…Them agnetization curves of this compound at 0.2 and 2T are shown in Figure 22 a. Thet hermal hysteresis is determined from both inflection points of the heating andc ooling curves and correspondst oapproximately 7Kwith amagnetization of 115 Am À2 kg À1 under af ield of 2T ,w hich agrees well with literature values. [201] Thet hermal hysteresis in this material is assumed to be related to the anisotropic lattice volume change of the sample, therebyr esultingi no nly a minimalv olume change. [56] In Figure 22 bt he temperaturedependent adiabatic temperature change is shown for af ield changeo f1 .9 T, whichr esults in am aximum DT ad of 2.35 K measured on the cooling branch.T oj udge the cyclic magnetocaloric effect, the temperature change of the material is plottedv ersus time in the inset of Figure 22 b, undergoing a field cycle from 0t o1 .9 Tt o0to À1.9 Ta nd back to 0T , mimicking an application-relevant cooling cycle.D ue to the effect of thermal hysteresis explained above,t he cyclic and reversible adiabatic temperature change DT rev ad at ap eak temperature of 268 Ki sr educed by 24 %t oo nly 1.9 K.…”

Hysteresis of MnFePSi Spherical Powder Ensembles Studied by Magneto‐Optical Imaging

“…A SEM image is given in Figure 7a for comparison. The fragment size we observed for the MnFePSibased particles is in between a few microns to 100 mm, which is in agreement with previous investigations by Bartok et al [20] (several tens to hundreds of microns) and Fries et al [7] (several tens of microns). As can be seen in Figure 7, one consequence of the cracking is that even in individual MnFePSi particles with diameters of d ¼ 150 mm the magneto-elastic transition does occur in steps which are associated to the individual fragments.…”

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB0.03

“…Measurements of d Q /|d T | in sample #2 during the first cooling run reveal that the broad transition [Figure b] takes place in steps (heat Q was obtained after baseline subtraction, T is temperature). Both the broadness and step‐like character of the transition imply that the motion of phase boundaries was pinned via the formation of cracks, whose presence was confirmed in sample #3 using room‐temperature scanning electron microscopy after the first cooling run [Figure b inset].…”