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(Gadolinium) Gd-doped antiperovskite compounds Mn 3 Cu 1−x Gd x N were synthesized by the conventional solid-state reaction. With increasing Gd concentration, two magnetic transitions appeared at a high Curie temperature (T C1 ) corresponding to paramagnetic (PM)-ferromagnetic (FM) transition and a low temperature (T C2 ) ascribed to the FM-antiferromagnetic (AFM) transition. The magnetic relaxation results show the formation of a magnetic metastable state after the FM-AFM transition at low temperature (lower than T C2 ), forming a novel magnetic-step feature in the process from AFM to FM under a certain magnetic field. [ABSTRACT FROM AUTHOR]

[Display omitted] • The limitation of scaling laws of the magnetocaloric effect. • The reliability of the Banerjee criterion in antiperovskite materials. • The temperature and field dependences of magnetic entropy changes. For materials with magnetic phase transition, researchers have tried to find a simple magnetic method that can replace the calorimetric technique for determining the type of phase transition. Recently, the researchers provide a quantitative characteristic of first-order magnetic phase transitions, which is believed to have wide application prospect. The maximum exponent n , calculated from field dependence of magnetic entropy change, is>2 only for first-order phase transitions. This method has been tested in Bean-Rodbell model and for various types of materials with first-order phase transitions from ferromagnetic to paramagnetic or antiferromagnetic to ferromagnetic state. However, in this work, the determination of the order of phase transitions based on field dependence of magnetic entropy change contradicts the results of calorimetric measurements in antiperovskite compounds Mn 3 SnC and MnCu 0.97 N. This discrepancy may be associated with a first-order magnetic transition from ferrimagnetic to paramagnetic state in antiperovskite materials. [ABSTRACT FROM AUTHOR]

Antiferromagnetic antiperovskites, of the form Mn 3 B N (B = Ni, Cu, Zn, Sn, Ir, and Pt), have shown an outstanding behavior in which, giant negative thermal expansion and chiral magnetic structures are intertwined. As such, aiming to shed light on the magnetostructural behavior, related to the magnetic ordering and crystalline structure of this type of materials, we studied theoretically, based-on first-principles calculations, the lattice dynamics and spin–phonon coupling in the Manganese-based antiperovskite Mn 3 NiN, as a prototype in the Mn 3 B N family. We found a strong spin–lattice coupling by means of the understanding of the phonon-dispersion curves obtained when including the chiral noncollinear magnetic structures. To do so, we highlight the importance of the exchange–correlation scheme selected and its influence on the structural, electronic, magnetic, and vibrational degrees of freedom. Finally, we found two unstable vibrational modes at the M - and R -points when the magnetic ordering is switched to ferromagnetic from the chiral Γ 4 g and Γ 5 g. These octahedral-associated modes with spin–phonon coupling parameters, λ , as large as 10.74 cm−1 and −2.53 cm−1 for the R 5 − , and M 2 + , respectively. The latter coupling is observed as a key signature of the strong spin–lattice interaction. [ABSTRACT FROM AUTHOR]

We report a comparison study of the critical behavior near the ferromagnetic (FM) transition ( T C ) for stoichiometric GaCMn 3 and carbon deficient GaC 0.8 Mn 3 . For GaCMn 3 , the obtained critical exponent β that describes the ferromagnetic (FM) coupling below T C is slightly reduced compared with the Mean Field (MF) value. In GaC 0.8 Mn 3 , the value of β is further decreased towards the anticipated value of the 3D Heisenberg model. However, another critical exponent γ relevant to the paramagnetic behavior is slightly larger than the MF magnitude and insensitive to the carbon deficiency. The change in critical behavior accords with the modification of the electronic structure, i.e., the carbon deficiency weakens the Mn 3 d -C 2 p hybridization and thus increases the localization of Mn 3 d states. Consistently, the specific heat study shows an enhancement of density of state at the Fermi level in GaC 0.8 Mn 3 compared with GaCMn 3 , which further confirms the weakening of Mn 3 d -C 2 p hybridization due to carbon vacancies. [ABSTRACT FROM AUTHOR]

Abstract: Effect of carbon content on magnetostructural transformation in antiperovskites of the type Mn3GaC x (x=0.8, 1.0 and 1.05) has been investigated. It is found that increase in carbon content changes the ground state from ferromagnetic metallic (x=0.8) to antiferromagnetic semiconducting (x=1.05) type. This has been attributed to localization of itinerant Mn 3d electrons due to increased Mn3d – C2p hybridization. Such a hybridization strengthens Mn–C–Mn antiferromagnetic interactions over Mn–Mn ferromagnetic interactions. Further, magnetic field can be used as a tool to modulate the relative strengths of these ferromagnetic and antiferromagnetic interactions thereby affecting the nature and strength of magnetocaloric properties. [Copyright &y& Elsevier]

Abstract: We report the synthesis, crystal structure, magnetic, electrical/thermal transport properties and the magnetocaloric effect (MCE) of AlC1.1Fe3. With increase in the carbon concentration x, the single-phase AlC x Fe3 is obtained for x≥1.1 and the refined lattice constant is about 0.37802nm for AlC1.1Fe3. Magnetic measurements indicate that there exists a second-order ferromagnetic (FM)–paramagnetic (PM) phase transition around 292K. The electrical resistivity displays a good metallic behavior in the whole temperature range except for a broad slope change around the temperature of magnetic transition (∼292K). Meanwhile, a reversible MCE is observed around the FM–PM transition with the maximum value of magnetic entropy change () ∼1.61J/kgK (ΔH=45kOe) and the relative cooling power (RCP) of ∼126J/kg (∼281J/kg) under the magnetic field change ΔH=20kOe (45kOe). Furthermore, it is found that the dominant carriers in AlC1.1Fe3 are hole-type from the studies of thermoelectric power and Hall measurement. [Copyright &y& Elsevier]

Abstract: The effects of Mn substitutions on the crystal structure, magnetic properties, and magnetocaloric effect (MCE) of antiperovskite Sn1−x CMn3+x (0≤x≤0.40) have been investigated detailedly. Both the Curie temperature (T C ) and the magnetizations at 40kOe decrease with increasing x firstly for x≤0.10, and then increase with increasing x further. The type of magnetic transition changes from first-order to second-order around x=0.10 with increasing x. Chemical composition-dependent MCE is also studied around T C . With increasing x, the maximal magnetic entropy changes decrease and the magnetic phase transitions broaden. Accordingly, the relative cooling power (RCP) increases with increasing x, reaching the largest values of ∼0.56J/cm3 (∼75J/kg) and ∼1.66J/cm3 (∼221J/kg) with the magnetic changes of 20kOe and 48kOe, respectively. Considering the large RCP, inexpensive, and innoxious raw materials, these serial samples Sn1−x CMn3+x are suggested to be potential room-temperature magnetic refrigerant materials. [Copyright &y& Elsevier]

Abstract: The structural, magnetic and electrical transport properties of Zn-doped antiperovskite compounds Ga1−x Zn x CMn3 (0≤x≤0.30) have been investigated. After partial substitution of Zn for Ga, the Curie temperature increases monotonously and the ground antiferromagnetic (AFM)-ferromagnetic intermediate (FI) phase transition is gradually suppressed. With increasing the doping level x, the saturated magnetizations decreases gradually firstly for x≤0.20, then increases with increasing x. The electrical transport properties of Ga1−x Zn x CMn3 are studied at different magnetic fields. Enhanced giant magnetoresistance (GMR) was observed around the AFM-FI transition. With increasing x, the maximal values and peak widths of GMR increase. Particularly, for x=0.20, GMR reaches a maximum value of 75%, spanning a temperature range of 80K at 50kOe and displays the behavior of strongly depending on the magnetization history. The possible origins are discussed. [Copyright &y& Elsevier]

Abstract: We report the effects of Al doping on the structure, magnetic properties, and magnetocaloric effect of antiperovskite compounds Ga1−x Al x CMn3 (0≤x≤0.15). Partial substitutions of Al for Ga enhance the Curie temperature (from 250K for x=0.0 to 312K for x=0.15) and the saturation magnetization. On increasing the doping level x, the maximum values of the magnetic entropy change (−ΔS M ) decreases while the temperature span of −ΔS M vs. T plot broadens. Furthermore, the relative cooling power (RCP) is also studied. For 20kOe, the RCP value tends to saturate at a high doping level (for x=0.12, 119J/kg at 296K). However, at 45kOe, the RCP value increases quickly with increasing x (for x=0.15, 293J/kg at 312K). Considering the relatively large RCP and inexpensive raw materials, Ga1−x Al x CMn3 may be alternative candidates for room-temperature magnetic refrigeration. [Copyright &y& Elsevier]

Abstract: The effects of Fe substitution on the structure, magnetic properties, magnetocaloric effect and positive magnetoresistance (MR) effect in antipervoskite compounds SnCMn3− x Fe x (x=0.05–0.20) have been investigated systematically. Partial substitution of Fe for Mn leads to the monotonic reduction in both the Curie temperature T C and saturated magnetization (MS ). It can be attributed to the reduction of electronic density of state at the Fermi energy by Fe-doping. The maximum values of magnetic entropy change (−ΔSM ) and positive MR gradually decrease as x increases, due to the broadening of magnetic phase transition. The refrigerant capacity increases initially with x≤0.05, then decreases gradually as x increases further, which is suggested to originate from the competition between the decreasing −ΔSM and broadening temperature span. Our result indicates that the chemical doping on Mn site is an effective method for manipulating the properties of antiperovskite compounds AXMn3. [Copyright &y& Elsevier]

Abstract: The character of the magnetic phase transitions in the metallic antiperovskite Mn3GaC1− δ (, 0.22) was analyzed to better evaluate the associated magnetic entropy changes under various field and temperature conditions. The stoichiometric Mn3GaC compound exhibits an abrupt magnetostructural transition at that produces a large entropy change with a plateau-like temperature dependence. A unique spike in of Mn3GaC at , associated with the abrupt magnetic transformation, is attributed to the interplay between the temperature- and field-induced transitions. The peak magnitude of this entropy change spike approaches 33J/kgK, over two times the averaged . It was observed that the field development of mimics the analogous magnetization behavior. An analytical phenomenological model based on the temperature and field dependence of the magnetization of this type of magnetic transition was developed to account for these results. [Copyright &y& Elsevier]

Abstract: The negative volume magnetostriction in the external magnetic field for antiperovskite Mn3.3Sn0.7C compound is discovered. Its magnetic transition temperature from paramagnetism to ferrimagnetism is 348K. The linear and volume magnetostrictions were investigated by measuring the change in length along the three-dimensional directions of the square samples at room temperature. Volume contraction was observed along all of the three directions throughout the whole magnetization. The value of volume magnetostriction is −44×10−6 at 1.5T. The magnetization saturates basically at 1.5T, however the volume magnetostriction should be higher with further increase in magnetic field. [Copyright &y& Elsevier]

• We have characterized the antiperovskite Fe 3.4 In 0.6 N systematically. • We find that Fe 3.4 In 0.6 N shows a second-order magnetic transition. • Critical exponents β , γ and δ are close to the theoretical prediction of the mean-field (MF) model. • Indium doping leads to the ferromagnetic and anti-ferromagnetic interactions, also the magnetic disorders. The critical behavior of the antiperovskite crystal Fe 3.4 In 0.6 N has been systematically studied in this paper. We have used a modified Arrott plot, the Kouvel-Fisher method, and critical isotherm analysis to obtain the critical exponents (β , γ and δ) which suggest that a long-range magnetic coupling described by mean-field (MF) theoretical model is dominant in Fe 3.4 In 0.6 N. The experimental M − T − H relations below and above Curie temperature (T c) collapse into two branches by the single scaling equation m = f ± (h) (m and h are renormalized magnetization and field), respectively. The critical exponents are confirmed by the Widom scaling law δ = 1 + γβ −1. In addition, it is suggested that the ferromagnetic (FM), anti-ferromagnetic (AFM) interactions and the magnetic disorders result to the exchange distance which is obtained just as J (r)∝ r - 4.4 . [ABSTRACT FROM AUTHOR]