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We describe magneto-, baro- and elastocaloric effects (MCEs, BCEs and eCEs) in materials which possess both discontinuous (first-order) and continuous (second-order) magnetic phase transitions. Our ab initio theory of the interacting electrons of materials in terms of disordered local moments (DLMs) has produced explicit mechanisms for the drivers of these transitions and here we study associated caloric effects in three case studies where both types of transition are evident. Our earlier work had described FeRh's magnetic phase diagram and large MCE. Here we present calculations of its substantial BCE and eCE. We describe the MCE of dysprosium and find very good agreement with experimental values for isothermal entropy ($\Delta S_{iso}$) and adiabatic temperature ($\Delta T_{ad}$) changes over a large temperature span and different applied magnetic field values. We examine the conditions for optimal values of both $\Delta S_{iso}$ and $\Delta T_{ad}$ that comply with a Clausius-Clapeyron analysis, which we use to propose a promising elastocaloric cooling cycle arising from the unusual dependence of the entropy on temperature and biaxial strain found in our third case study - the Mn$_3$GaN antiperovskite. We explain how both $\Delta S_{iso}$ and $\Delta T_{ad}$ can be kept large by exploiting the complex tensile strain-temperature magnetic phase diagram which we had earlier predicted for this material and also propose that hysteresis effects will be absent from half the caloric cycle. This rich and complex behavior stems from the frustrated nature of the interactions among the Mn local moments., Comment: 7 pages, 3 figures

We study the structural stability of crystalline Na 3OCl in terms of cohesive energies and phonon spectra through the tilting of Na 6O octahedra. We prove that the crystal Na 3OCl can be stabilized through octahedral tilts by comparing 14 tilted structures that are consistent with the Howard and Stokes’ group-theoretical analysis of the octahedral tilting in perovskites. We found that all the 14 tilted structures of Na 3OCl have lower energies than the cubic Pm 3 ¯m structure by about 11 to 16 meV per five-atom unit cell. The tilt angles along the pseudocubic [100], [010], and [001] directions vary in the range of 2.6 °–9.3 °. While the Pnma and P2 1/m structures of Na 3OCl are found as the two most stable ones, only the P2 1/m phase has stable phonon vibrations with a direct band gap of 3.38 eV at the Γ point.

Mn4-xGdxN films with x ranging from 0 to 0.48 have been grown by a plasma-assisted molecular beam epitaxy (PA-MBE) system. Analyses show that there is a competition between Kondo coupling and the Ruderman–Kittel–Kasuya–Yosida interaction in these films. The anomalous Hall effect (AHE) was investigated, and a multiple competing scattering mechanism was used to differentiate different contributions to the AHE. Fitting results using a multivariable scaling relation show that contribution of the skew-scattering mechanism to the AHE is suppressed and competition between different contributions is stronger in highly doped samples than that in undoped samples. Resistivity-temperature (ρ-T) curves in Gd-rich samples exhibit a typical behavior of heavy fermion (HF) materials. It shows a weak metal conducting behavior in a high temperature range, while Kondo coupling dominates the middle temperature range of 50 K–110 K. With a further decrease in the temperature to 5 K, a Fermi-liquid behavior is found in the range of 5 K–20 K. Comprehensive analyses indicate that Mn4-xGdxN with large x might be a new kind of HF material with room temperature ferromagnetism.

The density functional theory based total energy calculations are performed to examine the effect of charge neutral and fully charged intrinsic vacancy defects on the thermodynamic, electronic, and magnetic properties of Ca3SnO antiperovskite. The chemical stability of Ca3SnO is evaluated with respect to binary compounds CaO, CaSn, and Ca2Sn, and the limits of atomic chemical potentials of Ca, Sn, and O atoms for stable synthesis of Ca3SnO are determined within the generalized gradient approximation parametrization scheme. The electronic properties of the pristine and the non-stoichiometric forms of this compound have been explored and the influence of isolated intrinsic vacancy defects (Ca, Sn, and O) on the structural, bonding, and electronic properties of non-stoichiometric Ca3SnO are analyzed. We also predict the possibility of achieving stable ferromagnetism in non-stoichiometric Ca3SnO by means of charge neutral tin vacancies. From the calculated total energies and the valid ranges of atomic chemica...

In this paper, we systematically studied the mechanical and electronic properties of a series of antiperovskite-type Ti-based ternary carbides and nitrides AXTi3 (A = Ba, Ca, In, Sn, Sr, Zn, Cu, Al, Ga, Cd, and La; X = C, N) from first-principles calculations. By calculating the formation energies, elastic constants, and other mechanical parameters, we predicted that 7 carbides ACTi3 and 7 nitrides ANTi3 compounds are stable among the 22 compounds. The predicted large Young's modulus and high hardness imply a good mechanical application prospect of AXTi3. Particularly, SnNTi3 was found to show ferromagnetic ground state. For the electronic structure, our results confirm that the compounds are metallic in nature, and the density of states near the Fermi energy is predominately contributed by Ti-3d states. The effect of A- and X-site atom doping on AXTi3 can be evaluated by rigid band approximation. Our prediction will be useful for the experimental exploration of the new antiperovskite compounds.

The magnetocaloric effect of Mn3GaC, which shows an antiferromagnetic to ferromagnetic transition at 165 K has been investigated. In this compound, magnetocaloric effect obtained at the transition is opposite to that of ordinary ferromagnetic systems, namely, negative magnetocaloric effect. It was found that a large magnetic entropy change, ΔSmag, of 15 J/kg K is obtained under an applied field of 2 T. The adiabatic temperature change, ΔTad, reaches 5.4 K in a field change of 2 T. At higher magnetic fields, both ΔSmag and ΔTad retain a large value over wide temperature range, exhibiting characteristic temperature dependence of a trapezoidal shape. These features are attributed to a sharp first-order transition retained in high magnetic fields as well as small magnetocrystalline anisotropy.

A large positive magnetic entropy change ΔSM is observed in the metallic antiperovskite Mn3GaC near its first-order metamagnetic transition temperature 159 K where the stoichiometric compound transforms from an antiferromagnetic to a canted ferromagnetic state accompanied by a discontinuous volume change of −0.46% without change of symmetry. The unusual field dependence of the ΔSM of Mn3GaC shows a very rapid linear increase from zero to a saturation value within a field interval smaller than 1 T. The broadening of the peak of ΔSM to low temperature with increasing field change creates an ΔSM plateau in the temperature dependence of the MCE, which is of significance for practical application of these materials in the Ericsson-cycle magnetic refrigerator.

Copper matrix composites containing antiperovskite manganese nitrides with negative thermal expansion (NTE) were formed using pulsed electric current sintering. Energy dispersive X-ray spectroscopy revealed that the chemically reacted region extends over 10 μm around the matrix–filler interfaces. The small-size filler was chemically deteriorated during formation of composites and it lost the NTE property. Therefore, we produced the composites using only the nitride particles having diameter larger than 50 μm. The large-size filler effectively suppressed the thermal expansion of copper and improved the conductivity of the composites to the level of pure aluminum. The present composites, having high thermal conductivity and low thermal expansion, are suitable for practical applications such as a heat radiation substrate for semiconductor devices.

Epitaxial bilayers of antiferromagnetic Mn3GaN/ferromagnetic Co3FeN with an antiperovskite structure were grown by reactive magnetron sputtering, and their structural, magnetic, and electrical properties were investigated. Exchange coupling with an exchange field Hex of 0.4 kOe at 4 K was observed for Mn3GaN (20 nm)/Co3FeN (5 nm) bilayers. Negative anisotropic magnetoresistance (AMR) effect in Co3FeN was observed and utilized to detect magnetization reversal in exchange-coupled Mn3GaN/Co3FeN bilayers. The AMR results showed evidence for current-induced spin transfer torque in antiferromagnetic Mn3GaN.

The antiperovskite intermetallic compounds AgN1−xCxMn3 (0 ≤ x ≤ 0.15) have been synthesized. As x increases, the temperature coefficient of resistivity (TCR) above room temperature decreases monotonically and finally changes the sign from positive to negative above x = 0.1. Meanwhile, the temperature range is gradually broadened. For x = 0.07, TCR is ∼3.1 ppm/K between 280 K and 375 K. Both the resistivity and its slope are insensitive to the external magnetic field, indicating an insignificant contribution from magnetic scattering or short-range magnetic ordering to the observed low-TCR. As manifested by the Hall effect, the charge carrier density in the paramagnetic state for x = 0.15 is reduced by an order of magnitude in comparison with that for x = 0. The reduction of carrier density and the enhancive disorders when x increases was proposed to be responsible for the decrease in TCR and its sign switch.

We report a systematic study of the specific heat and dc magnetic susceptibility on the paramagnetic to ferrimagnetic transition (TC ∼ 141 K) in CuNMn3. A large magnetocaloric effect (MCE) at TC is observed with the entropy change of 3.49 J/kg K (6.38 J/kg K) for the field change of ΔH = 20 kOe (45 kOe). The analysis of the isothermal magnetizations, including the derived Arrott plots and magnetic entropy change, shows a second-order like transition at TC. However, the existence of latent heat around TC is unambiguously manifested by the reduced slope of the temperature-time relaxations recorded during the specific heat measurement, indicating the transition is in fact weakly first-order in nature. The large MCE comparable with those observed the antiperovskite manganese carbides suggests it is equivalently interesting to explore the MCE in the antiperovskite manganese nitrides as in the carbides.

We report detailed investigations of the structure, magnetic properties, electronic transport, and specific heat in Mn-based antiperovskite compounds Mn3Cu0.5Zn0.5N. Most strikingly, there are several fascinating features: (i) The magnetoresistance at 30 kOe (40 kOe) exceeds ∼1% (∼2%) over a temperature span of ∼70 K (∼25 K) from 5 to 140 K; (ii) magnetoresistance fluctuates at temperatures of 100–200 K, including an obvious sign reversal from negative to positive at ∼140 K. Analysis of the specific heat reveals that the magnetoresistance reversal may originate from the reconstruction of the Fermi surface accompanying an antiferromagnetic-ferromagnetic transition.

Substitution of Sb with Sn was achieved in ferrimagnetic antiperovskite Mn3SbN. The experimental results indicate that with an increase in Sn concentration, the magnetization continuously decreases and the crystal structure of Mn3Sb1-xSnxN changes from tetragonal to cubic phase at around x of 0.8. In the doping series, step-like anomaly in the isothermal magnetization was found and this behavior was highlighted at x = 0.4. The anomaly could be attributed to the magnetic frustration, resulting from competition between the multiple spin configurations in the antiperovskite lattice. Meantime, Hc of 18 kOe was observed at x = 0.3, which is probably the highest among those of manganese antiperovskite materials reported so far. With increasing Sn content, the abrupt change of resistivity and the sharp peak of heat capacity in Mn3SbN were gradually weakened. The crystal structure refinements indicate the weakened change at the magnetic transition is close related to the change of c/a ratio variation from tetrago...

The nuclear and magnetic structures of the cubic antiperovskite compound Mn3NiN are studied using neutron powder diffraction as a function of temperature and applied magnetic field. On cooling in zero field from the paramagnetic state, an anomalous lattice expansion abruptly occurs as the long range antiferromagnetic order first develops below TN = 262 K. The magnetic structure has lower symmetry than the crystal and can be conveniently described by a rhombohedral R-3 symmetry with dimension of √2ac × √2ac × √3ac, where ac is the chemical unit cell. In this description, the magnetic moment of the Mn is restricted to the a-b plane, but continuously rotates from 90° to around 38° as the temperature decreases to ≈120 K, below which the spin directions remain fixed. The combined magnetic and structural transition exhibits a very large magnetovolume effect with an entropy change of ΔS ≈ 54 J/kg K, but the application of a 6 T magnetic field has little effect on the magnetic structure or entropy change. The cry...

We controlled thermal expansion of metal matrix composites (MMCs) that had been blended using antiperovskite manganese nitrides with giant negative thermal expansion (NTE). The NTE of the manganese nitrides, which is isotopic, is greater than −30 ppm K−1 in α (coefficient of linear thermal expansion), which is several or ten times as large as that of conventional NTE materials. These advantages of nitrides are desirable for practical application as a thermal-expansion compensator, which can suppress thermal expansion of various materials including metals and even plastics. Powder metallurgy using pulsed electric current sintering enables us to reduce temperatures and times for fabrication of MMCs. Consequently, chemical reactions between matrix (Al, Ti, Cu) and filler can be controlled and even high-melting-point metals can be used as a matrix. Thermal expansion of these MMCs is tunable across widely various α values, even negative ones, with high reproducibility. These composites retain a certain amount ...

We report the magnetic phase diagram of antiperovskite compounds Zn1−xSnxCFe3 (0 ≤ x ≤ 1). The effects of the ratio of Zn/Sn on the structure, magnetic and electrical transport properties have been investigated systematically. With increasing the Sn content x, the lattice constant increases while both the Curie temperature (TC) and the saturated magnetization decrease gradually. All the resistivity curves of Zn1−xSnxCFe3 show a metal-like behavior in measured temperature range (2–350 K). In particular, the T2-power-law dependence of the electrical resistivity is obtained at low temperatures for all samples with x ≤ 0.3. It is noteworthy that, for x = 0.1, the TC is tuned just at the room temperature (∼300 K). Around TC, the magnetocaloric effect is considerably large with a magnetic entropy change of 2.78 J/kg K (ΔH = 45 kOe) as well as a relative cooling power (RCP) of 320 J/kg (ΔH = 45 kOe). Considering the considerably large RCP, suitable working temperature, inexpensive and innoxious raw materials, Zn...

The antiperovskite functional compound CuNMn3 exhibits magnetostriction below the non-collinear ferromagnetic (FM)-paramagnetic (PM) transition (accompanied by a martensitic transformation). After the substitution of Mn for Cu, martensitic transformation is decoupled from FM transition. Meanwhile, the tetragonality of the martensitic phase and the magnetostriction are weakened. The combined analysis indicates that the spin, charge, and lattice are closely coupled around martensitic transformation temperature (TMS). The low-temperature martensitic phase is associated with a metastable magnetic state characterized by small magnetocrystalline anisotropy. Additionally, the depression of TMS with introducing the Mn dopant is revelatory for the development of low-temperature negative thermal expansion material.

Giant negative thermal expansion in antiperovskite manganese nitrides Mn3AN (A = Zn, Ga, etc.) is achieved by substituting Ge for A as a “relaxant” to the sharp volume change associated with the magnetic transition. We have studied the effects of nitrogen deficiency on the broadening of volume change. Although the broadening increases with decreasing nitrogen content for Mn3Cu0.5Ge0.5N1-δ, the sharp volume change is robust against nitrogen deficiency in Ge-free Mn3GaN1-δ. Nitrogen deficiency probably does not broaden the volume change by itself; rather it probably assists the broadening in conjunction with the Ge dopant. The origin of the broadening is discussed in terms of local lattice distortion of the Mn6N octahedra.

The discovery of giant magnetostriction exceeding 2000 ppm in Mn3CuN has stimulated the research of manganese antiperovskites from the perspective of forced magnetostriction. We discovered that Mn3SbN exhibits a large magnetostriction of up to 450 ppm in the tetragonally distorted ferromagnetic phase below the Curie temperature TC = 360 K. The magnitude of magnetostriction is enhanced by up to 1000 ppm without reduction of TC by partial replacement of the constituent elements. The present results are examined in terms of ferromagnetic shape memory effects.

The recently discovered low temperature coefficient of resistance (low TCR) in Mn3Ag1-xCuxN exemplifies the peculiar magnetic and electronic states of this class of manganites. Despite its overall metallic character, a broad maximum appears in the temperature–resistivity curve in the paramagnetic region, and extremely low TCR is achieved over a temperature window that includes room temperature. The peak temperature can be tuned via Cu content x. It is apparently related to the magnetic transition temperature. These peculiar behaviors are possibly a result of the collapse of coherent quasiparticle states by strong magnetic scattering. We discuss the interplay between magnetism and charge transport in terms of magnetoresistance.

We verified the intimate relation between magnetism and volume in Mn3ZnN. The sample sintered at 900 °C is characterized by the Γ5g triangular antiferromagnetic (AF) state with larger volume below 170 K. However, for the sample sintered at 700 °C, the re-entrant phase transition appears at 80 K and the ground state is a different AF state with smaller volume. These results indicate that the ground state of Mn3ZnN is sensitive to the disorder in the N site and that the magnetic structure drastically alters magnetovolume effects. More detailed consideration is necessary beyond the conventional scheme, which incorporates only the amplitude of the magnetic moment.

With increasing the substitution of Sn for Cu in Cu0.8-xSnxMn0.2NMn3, the initial cubic-tetragonal structural phase transition disappears for the samples x ≥ 0.10 and is replaced by a discontinuous lattice expansion with a cubic structure which has been confirmed by the measurements of variable temperature x-ray diffractions and specific heat. The discontinuous lattice expansion broadens with increasing the doping level x and the negative thermal expansion coefficient up to −64.54 ppm/K between 190 K and 235 K is found for the sample x = 0.3. Detailed magnetic measurements indicate that the magnetic ground state is meta-stable for the lower-doping level and transforms into spin-glass-like state owing to the enhancement of antiferromagnetic interaction when x is up to 0.3. Furthermore, the magnetization curves M(T) display abnormal behaviors for lower-x. For the samples x = 0.1 and 0.2, the jump of field-cooled magnetization curve MFC (defined as ΔMFC/MFC) around the lower-temperature magnetic transition is suppressed with increasing the magnetic field. These abnormalities of magnetizations are also discussed based on a simple model.

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Giant magnetostriction of up to 2000 ppm was discovered in the tetragonally distorted ferromagnetic phase of antiperovskite Mn3CuN. This magnetostriction was associated with the rearrangement of thermoelastic martensite variants by the magnetic field, similar to that of Ni2MnGa Heusler alloy. The nitrogen-deficient Mn3CuN0.8 contracts, whereas the stoichiometric Mn3CuN expands, along the field direction. This implies a rotation of the easy axis from the longer a axis in Mn3CuN to the shorter c axis in Mn3CuN0.8. The drastic reduction of the operating magnetic field for magnetostriction in Mn3CuN0.8 suggests a possible supermagnetostriction around the compositional region of direction change in the easy axis.

Giant negative thermal expansion (NTE), over α = −30 × 10−6 K−1 (α: coefficient of linear thermal expansion), at room temperature can be achieved in Mn3ZnN-based antiperovskite manganese nitrides by simultaneous substitution of C and B for N as well as Sn for Zn. The developed NTE nitrides show larger negative α, although the width of the operating-temperature window is comparable to that of Mn3CuN-based materials developed to date. Such a large, isotropic, and high-stiffness NTE material can compensate for the large positive thermal expansion of, for example, even aluminum or plastic materials.

The magnetic structures of Mn3ZnN compound are theoretically studied, from which a new magnetic ground state (MGS) structure of Mn3ZnN is predicted. Comparison of the calculated volumes between different magnetic structures shows that the Mn3ZnN compound experiences a volume expansion from the high-temperature paramagnetic phase to the low-temperature antiferromagnetic phase Γ5g, and a volume contraction from the Γ5g phase to the MGS phase, in excellent agreement with the observation in experiment. Analysis of the exchange parameters between ions shows that the spin coupling between the Mn ions is responsible for the sudden expansion and contraction of the Mn3ZnN volume. Furthermore, we find that the existed N vacancies in the compound significantly lower the energy of Γ5g. When the concentration of N vacancies is large enough, Γ5g may become the ground state for the defective Mn3ZnN compound. This may be used to explain the experimental observation that the sudden change in volume of Mn3ZnN at about 127 ...