Research Of Negative Thermal Expansion And Magnetic Properties Of Nb Doped Antiperovskite Mn₃AgN

Perovskite oxides have attracted numerous attentions since their discovery because of the various physical properties and promising applications, such as ferroelectric, colossal magnetoresistance, and superconductivity, etc. In recent years, antiperovskite compounds, with the similar crystal structure to that of perovskites, have been intensively investigated owing to their novel properties including negative thermal expansion, magnetocaloric effect, giant magnetoresistance, and near zero temperature coefficient of resistance. In this work, we synthesized the antiperovskite Mn3Ag1-xNbxN and studied its negative thermal expansion, magnetic, and transport properties, further, the intrinsic correlation between crystal structure and thermal expansion were also discussed.It is shown that Nb substitution of Ag could alter the negative thermal expansion in Mn3Ag1-xNbxN. Nb doping resulted in the broadening of temperature window of negative thermal expansion, in which the linear thermal expansion coefficient decreased, while the onset of negative thermal expansion shifts to lower temperature. Specifically, pure Mn3 AgN exhibits negative thermal expansion from 270.1 K to 288.7 K(ΔT = 18.6 K) with-22.43 ppm/K, while the linear thermal expansion coefficient of Mn3Ag0.9Nb0.1N decrease to-18.2 ppm/K in temperature section from 260.1 K to 284.8 K.The magnetic measurement shows that parent material Mn3 AgN has an antiferromagnetic-to-paramagnetic transition at 278.6 K, and the introduction of Nb into host Mn3AgN(Mn3Ag0.96Nb0.04 N sample) can realize a lower Neel temperature of 271.3 K. Notably, with the temperature decreasing, Mn3Ag1-xNbxN exhibits a spin – glass behavior, with the freezing temperature shift from 74 K(undoped Mn3AgN) to 129 K(Mn3Ag0.96Nb0.04N), implying an enhanced magnetic exchange interaction of Mn-Mn induced by Nb doping.The transport property demonstrates that near zero temperature coefficient of resistance exists in above magnetic transition temperature of Nb doped Mn3 AgN, in which the temperature coefficient of resistance decreased gradually with increasing the concentration of Nb in system. Partial Nb doping at Ag site induced the contraction of lattice and variation of electric structure, therefore the density of state of electrons reconstructed at Fermi level.Comparing the negative thermal expansion, Neel temperature, and onset of near zero temperature coefficient of resistance, it can be found that Mn3Ag1-xNbxN is a strongly internal correlated system in lattice, spin, and charge. Nb doping in host material leads to an obvious variation in lattice and induces enhancement of magnetic exchange mechanism simultaneously. In addition, transport property is affected by various factors such as electric structure, lattice scattering and magnetic scattering. The above experimental results show that physical properties of antiperovskites could be ameliorated by altering the species of the atoms located in corner of unit cell.