Preparation and properties of antiperovskite-type nitrides: InNNi3 and InNCo3

Two antiperovskite-type ternary nitrides of InNM₃ (M=Ni, Co) have been synthesized from In₂O₃ and Ni or Co powders under NH₃ atmosphere at 600 °C. InNCo₃ is a new ternary nitride whereas InNNi₃ was previously reported as InN_0.5Ni₃ with different nitrogen content. The lattice parameters refined by Rietveld method are 3.8445(1) Å for InNNi₃ and 3.8541(7) Å for InNCo₃, respectively. Both nitrides show metallic behaviors and below 70 K the T² temperature dependence of resistivity was observed indicative of a Fermi liquid behavior. The temperature dependence of the field-cooling (FC) and zero-field-cooling (ZFC) magnetization and time decay of thermoremanent magnetization indicate the spin-glass-like behavior in InNM₃ (M=Ni, Co). The freezing temperatures for this behavior, T_f, are about 300 K for InNNi₃ and 10 K for InNCo₃, respectively.     

Ab initio study of the structural,electronic and elastic properties of AgSbTe2, AgSbSe2, Pr3AlC,Ce3AlC,Ce3AlN,La3AlC and La3AlN compounds

In this paper, we study the structural, electronic and elastic properties of the ternary AgSbTe₂, AgSbSe₂, Pr₃AlC, Ce₃AlC, Ce₃AlN, La₃AlC and La₃AlN compounds using the full-potential linearized augmented plane wave (FP-LAPW) scheme and the pseudopotential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA). Results are given for the lattice parameters, bulk modulus, and its pressure derivative. The calculated lattice parameters are in good agreement with experimental results. We have determined the full set of first-order elastic constants, shear modulus, Young's modulus and Poisson's ratio of these compounds. Also, we have presented the results of the band structure, densities of states, it is found that this compounds metallic behavior, and a negative gap Г→R for Pr₃AlC. The analysis charge densities show that bonding is of covalent–ionic and ionic nature for AgSbSe₂ and AgSbTe₂ compounds.     

Lattice, magnetic and transport properties in antiperovskite compounds

The temperature-dependent magnetization, lattice, and transport properties of Mn₃Sn_1−xGe_xC (0≤x≤0.5) compounds are systematically investigated. The Mn–Mn atomic distance decreases as Ge content is increased, and the transition temperature from ferromagnetic (or ferrimagnetic) to paramagnetic state decreases too. Mn₃SnC has a large magnetovolume effect (MVE). However, Ge-doping in Mn₃SnC gradually reduces the MVE, till the MVE disappears. Whether there is an abnormal lattice change or not, there always exists an anomalous increase in resistivity near the magnetic phase transition point with decreasing temperature.     

Magnetic phase transitions of antiperovskite Mn3−xFexSnC (0.5≤x≤1.3)

The magnetization and electrical resistivity of Mn_3−xFe_xSnC (0.5≤x≤1.3) were measured to investigate the behavior of the complicated magnetic phase transitions and electronic transport properties from 5 to 300 K. The results obtained demonstrate that Fe doping at the Mn sites of Mn₃SnC induces a more complicated magnetic phase transition than that in its parent phase Mn₃SnC from a paramagnetic (PM) state to a ferrimagnetic (FI) state consisting of antiferromagnetic (AFM) and ferromagnetic (FM) components, while, with the change of Fe-doped content and magnetic field, there is a competition between the AFM component and FM component in the FI state. Both the Curie temperature (T_C) and the saturated magnetization M_s increase with increasing x. The FM component region becomes broader with further increasing Fe-doped content x. The external magnetic field easily creates a saturated FM state (and increased T_C) when . Fe doping quenches the negative thermal expansion (NTE) behavior from 200 to 250 K reported in Mn₃SnC.     

Magnetic properties and room-temperature magnetocaloric effect in the doped antipervoskite compounds Ga1−xAlxCMn3 (0≤x≤0.15)

We report the effects of Al doping on the structure, magnetic properties, and magnetocaloric effect of antiperovskite compounds Ga_1−xAl_xCMn₃ (0≤x≤0.15). Partial substitutions of Al for Ga enhance the Curie temperature (from 250 K for x=0.0 to 312 K 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 20 kOe, the RCP value tends to saturate at a high doping level (for x=0.12, 119 J/kg at 296 K). However, at 45 kOe, the RCP value increases quickly with increasing x (for x=0.15, 293 J/kg at 312 K). Considering the relatively large RCP and inexpensive raw materials, Ga_1−xAl_xCMn₃ may be alternative candidates for room-temperature magnetic refrigeration.     

Magnetic/structural diagram, chemical composition-dependent magnetocaloric effect in self-doped antipervoskite compounds Sn1−xCMn3+x (0≤x≤0.40)

The effects of Mn substitutions on the crystal structure, magnetic properties, and magnetocaloric effect (MCE) of antiperovskite Sn_1−xCMn_3+x (0≤x≤0.40) have been investigated detailedly. Both the Curie temperature (T_C) and the magnetizations at 40 kOe 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 ∼0.56 J/cm³ (∼75 J/kg) and ∼1.66 J/cm³ (∼221 J/kg) with the magnetic changes of 20 kOe and 48 kOe, respectively. Considering the large RCP, inexpensive, and innoxious raw materials, these serial samples Sn_1−xCMn_3+x are suggested to be potential room-temperature magnetic refrigerant materials.     

Forced volume magnetostriction in Mn3.3Sn0.7C compound at room temperature

The negative volume magnetostriction in the external magnetic field for antiperovskite Mn_3.3Sn_0.7C compound is discovered. Its magnetic transition temperature from paramagnetism to ferrimagnetism is 348 K. 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 1.5 T. The magnetization saturates basically at 1.5 T, however the volume magnetostriction should be higher with further increase in magnetic field.     

Magnetic/structural phase diagram and enhanced giant magnetoresistance in Zn-doped antiperovskite compound Ga1−xZnxCMn3

The structural, magnetic and electrical transport properties of Zn-doped antiperovskite compounds Ga_1−xZn_xCMn₃ (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 Ga_1−xZn_xCMn₃ 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 80 K at 50 kOe and displays the behavior of strongly depending on the magnetization history. The possible origins are discussed.     

Structural and elastic properties of antiperovskites XNBa3 (X=As, Sb) under pressure effect

First-principle calculations of structural, elastic and high pressure properties of antiperovskites XNBa₃ (X=As, Sb) are performed, using the full-potential linear muffin-tin orbital (FP-LMTO) method. The local density approximation (LDA) is used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus and its pressure derivatives. We have determined the elastic constants C₁₁, C₁₂ and C₄₄ and their pressure dependence. We derived shear moduli, Young's modulus, Poisson's ratio and Lamé's constants for ideal polycrystalline XNBa₃ aggregates. By analyzing the ratio of the bulk to shear moduli, we conclude that XNBa₃ compounds are brittle in nature. We estimated the Debye temperature of XNBa₃ from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNBa₃ and SbNBa₃ compounds, and it still awaits experimental confirmation.