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Zhao et al. Microstructures 2023;3:2023022 https://dx.doi.org/10.20517/microstructures.2022.46 Page 7 of 9

Table 1. Performance summary of several typical barocaloric materials
dT /dP -1 -1
Material T (K) (K GPa ) P (MPa) V/V (%) ΔS P →P (J kg K ) Ref.
t
-1
t
0
NPG 313 133 45 - 389 [24]
C B H 12 277 380 60 - 106.2 [44]
2 10
NH I 243 810 20 - 89 [45]
4
NH SCN 364 300 20 5 128.7 [46]
4
Fe Rh 310 60 250 1 12 [9,10]
49 51
MnNiSi 0.61 FeCoGe 0.39 311 70 260 - 44 [47]
Ni 0.95 Fe 0.05 S 274 75 100 2 39.6 [48]
Mn GaN 290 65 90 1 21.6 [28]
3
Mn NiN 262 13.5 280 0.4 35 [29]
3
Mn Pt 355 139 60 2.26* 13.79 This work
2.92 1.08
*determined for Mn Pt .
2.9
1.1
is not too small. The small entropy change at this first-order phase transition is due to unique magnetic
fluctuations in nature. Magnetic fluctuation refers to the fluctuation of magnetic (electron spin) moment in
[40]
magnetic systems . The interaction between the local moment and the itinerant electron matrix may
enhance spin fluctuation. Frustration structures are often accompanied by strong spin fluctuations [41,42] .
Neutron diffraction measurements suggest that the ordered moment is 3.3 µ /Mn atom in the colinear AFM
B
state, whereas 2.2 µ /Mn atom in the triangular AFM . The reduction in the latter should be attributed to
[37]
B
spin fluctuations due to geometric frustration. As a result, the triangle-lattice AFM state is magnetically less
ordered than the colinear AFM one, which leads to an increase of magnetic entropy across T. At the same
t
time, the crystal lattice shows a normal contraction, and a reduction of entropy of the lattice subsystem is
expected. We infer that the contributions of individuals to the total entropy change partially cancel each
other out, and the remaining entropy change represents the overall entropy change of the material.
According to the previous theoretic study, the system can be described by a nearest-neighboring exchange
interaction J and a next-nearest-neighboring exchange interaction J . J is always negative, but J can be
1
1
2
2
[31]
negative or positive, dependent on the interatomic distance between Mn atoms . At T, J just changes its
2
t
sign due to the shrinkage of the Mn-Mn distance. In this sense, such a picture is similar to the exchange
[43]
striction observed in NiMnIn alloys .
CONCLUSIONS
In summary, the first-order phase transitions of Mn Pt (x = 0.04, 0.08, 0.1, and 0.18) compounds have
1+x
3-x
been studied at varying temperatures, pressures, and magnetic fields. At the phase transitions, both
magnetizations and lattice constants showed abrupt drops as the temperature decreased. While the phase
transition temperatures decreased at lower Mn content, they increased at higher pressures. This system is
highly susceptible to pressure, and the pressure-induced entropy changes are saturated at 60 MPa, which is
the lowest among current intermetallics. This may be due to the intense geometric magnetic frustration.
DECLARATIONS
Authors’ contributions
Prepared the samples, collected the data, performed data analysis and contributed to the writing and
revisions: Zhao X
Conceived the study, designed the study, and contributed to the writing and revisions: Li B, Zhang K
Collected some of the data and provided technical support: Qi J, Liu P, Zhang Z (Zhang Zhao), Qu L