The magnetocaloric performance in pure and mixed magnetic phase CoMnSi

Abstract

Here we study the influence of sample preparation on the magnetocaloric properties of CoMnSi. Slow cooling from the high temperature hexagonal phase of the melt to the room temperature orthorhombic phase encourages the formation of a homogeneous material with large entropy changes when the system undergoes a coincident first order structural and (meta)magnetic transition. Samples that were quenched directly after annealing show a compressed a axis lattice parameter. Hall probe imaging indicates that the quenched sample has spatially inhomogeneous magnetic properties, which we attribute to strain because within error neither x-ray diffraction nor energy dispersive x-ray analysis indicates a second compositional phase. Calorimetric methods and global magnetization are used to examine the entropy changes of the pure and mixed magnetic phase compounds and we make a direct comparison of these materials in terms of their refrigerant capacity.

Identifying the critical point of the weakly first-order itinerant magnet DyCo2with complementary magnetization and calorimetric measurements

“…33 CoMnSi (which is also thought to be a local moment system that undergoes a first order magnetoelastic phase transition) shows a change of C p at the AFM/FM transition of only 5%, accompanied by a large latent heat. 29 So it is reasonable to describe the change in C p in DyCo 2 as giant and it is interesting that it is similar in magnitude to a previously-studied IEM system: La(Fe 1-x Si x ) 13 . 6,8 The latent heat as measured by the adiabatic probe approaches the limit of its resolution.…”

“…We stress again that the ac technique employed does not sample L directly, and have demonstrated this for several systems previously. 8,28,28,29 The first observation is that the signature enhancement of C p of the order of 600% is similar to that seen in the La(Fe 1-x Si x ) 13 material system, 6 and it is quickly suppressed when 7 the magnetic field and temperature are increased. In contrast, Gd (a local moment system which undergoes a continuous phase transition) also shows a large lambda-like change in C p , but of the order of 100% only.…”

“…7,27,29 This peak will have a characteristic decay time of ~1 s. For polycrystalline samples with a correlation length (measure of the nucleation volume) of less than 100 μm the transition will manifest as a series of spikes distributed in field as successive regions undergo the transition. The noise floor of this measurement is of the order of 1 μV, equivalent to ~ 10 nJ.…”

Tuning the metamagnetic transition in the (Co, Fe)MnP system for magnetocaloric purposes

“…However, due to the large hysteresis generally observed in these compounds, it is still unclear if their MCE can really be used in a refrigeration cycle ; (iv) Finally, the last family is the silicates derived from CoMnSi. [15][16][17][18] Among the inverse MCE materials, the CoMnSi family appears to be one of the most promising. However, some features limit their MCE performances.…”

“…In order to restore a MCE, substitutions can be used, but that shifts the Neel temperature far below room temperature. 16 Following this unusual "inverse MCE" approach, attention has been paid during this study to others MnM'X alloys (with M'=3d and X=non-metal elements) that could present an inverse MCE. We especially focused on the phosphides Co 1-x Fe x MnP that have often been considered as archetypical examples of the AF-FM behavior in orthorhombic manganese alloys (Co 2 P-type) and which are anticipated to have both a normal MCE at T C and an inverse at T N .…”