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Page 2 of 9 Zhao et al. Microstructures 2023;3:2023022 https://dx.doi.org/10.20517/microstructures.2022.46

INTRODUCTION
Refrigeration technology is of great significance for both industry and everyday life. Current refrigeration
systems are mostly based on conventional vapor compression technology. Although highly optimized in
recent decades, they still have a considerable undesirable impact on the environment . Frequently used
[1]
refrigerants have thousand-time stronger global warming potentials compared to CO . To achieve carbon
2
neutrality, solid-state refrigeration technology based on the caloric effects of solids has been proposed as an
alternative solution. Various phase transitions caused by some calorimeter materials under external fields
are accompanied by huge latent heat, which can be utilized for cooling purposes through designated
thermodynamic cycles. Magnetocaloric effects (MCEs) is one of the most studied caloric effects, which is
usually linked to magnetic-field-induced first-order transitions. Barocaloric effects (BCEs), as the
counterpart and extension of the (MCEs), is defined as the change in the isothermal entropy or adiabatic
temperature of the material during the application or withdrawal of the external pressure field. Materials
with first-order phase transition are more likely to be the most potential barocaloric effect materials due to
the sensitivity of the lattice to pressure.

Initially observed around 2,000 years, BCEs has been found in Pr La NiO and CeSb . Subsequent
[3]
[2]
1-x
3
x
studies of magneto-elastically coupled materials for MCEs have revealed larger BCEs, such as in
magnetic shape memory alloys including NiMnIn , La(Fe,Si) 13 [5,6] , Gd Si Ge , MnCoGe In 0.01 [8] ,
[4]
[7]
2
2
0.99
5
FeRh [9,10] , and others. These materials exhibit a strong coupling between magnetic and lattice degrees of
freedom. Usually, there is a magnetic phase with a larger volume and a magnetic phase with a smaller
volume. The application of a sufficiently large hydrostatic pressure induces a change of the system from
the large-volume to the small-volume phase, and simultaneously the magnetic phase transition takes place.
Typically, the required driving pressures in these systems are as high as several hundred MPa, and a
comparable pressure-induced entropy change to that induced by a magnetic field can be obtained.
In recent years, a great variety of materials have been reported with larger BCEs, such as AgI , organic-
[11]
[12]
inorganic hybrid chalcogenide [TPrA][Mn(dca) ] , ferroelectric (NH ) SO 4 [13,14] , spin-crossover
4 2
3
complexes [15-18] , and even natural rubber [19,20] . First-principles calculations also predicted sizable BCEs for
[23]
[21]
lithium-ion conductor materials , fluorine ion conductor materials , and graphene . In plastic crystals,
[22]
the extensive molecular orientation disorder in plastic crystals leads to huge entropy changes larger than
100 J kg K , and the driving pressures have been significantly reduced down to below 100 MPa, for which
-1
-1
they are termed as colossal barocaloric effects [24-26] .
Antiferromagnetic materials are effective in releasing their entropy change by pressure in addition to the
magnetic field [10,27] , with remarkably reduced driving pressures, especially in frustrated antiferromagnets.
Recent research has found that larger BCEs are observed at phase transitions from frustrated
antiferromagnetic (AFM) to paramagnetic states in nitrides (Mn GaN , Mn NiN ) with an anti-
[29]
[28]
3
3
perovskite structure. This indicates that even small hydrostatic pressures (as low as 90 MPa in plastic
crystals) can effectively act on the AFM system. In this work, we report on the barocaloric properties of
Mn Pt alloys at first-order phase transitions from low-temperature triangle-lattice frustrated to high-
1+x
3-x
temperature colinear AFM states. The composition-dependent phase transition temperature (T) is about
t
331 K for the Mn Pt . The pressure-dependent calorimetric measurements suggest that entropy changes
2.82
1.18
are saturated at around 60 MPa.
EXPERIMENTS
Polycrystalline samples of Mn Pt with different Mn contents (x = 0.04, 0.08, 0.1, and 0.18) were prepared
3-x
1+x
by arc-melting the high-purity (99.9%) elements under an Ar atmosphere. The true composition was