Magnetovolume effects in manganese nitrides with antiperovskite structure

Abstract

Magnetostructural correlations in antiperovskite manganese nitrides were investigated systematically for stoichiometric and solid solution Mn3Cu1−xAxN (A = Co, Ni, Zn, Ga, Ge, Rh, Pd, Ag, In, Sn or Sb). This class of nitrides is attracting great attention because of their giant negative thermal expansion, which is achieved by doping Ge or Sn into the A site as a relaxant of the sharp volume contraction on heating (spontaneous volume magnetostriction ωs) because of the magnetovolume effects. The physical background of large ωs and mechanism of how the volume contraction becomes gradual with temperature are central concerns for the physics and applications of these nitrides. An entire dataset of thermal expansion, crystal structure and magnetization demonstrates that the cubic triangular antiferromagnetic state is crucial for large ωs. The intimate relationship between ωs and the magnetic structure is discussed in terms of geometrical frustration related to the Mn6N octahedron and magnetic stress concept. The results presented herein also show that ωs depends on the number of d electrons in the A atom, suggesting the important role of the d orbitals of the A atom. Not all the dopants in the A site, but the elements that disturb the cubic triangular antiferromagnetic state, are effective in broadening the volume change. This fact suggests that instability neighboring the phase boundary is related to the broadening. The relation between the gradual volume change and the local structure anomaly is suggested by recent microprobe studies.

Effect of composition on magnetocaloric properties of Mn3Ga(1−x)SnxC

“…This behavior points to the changing role of the A site ion in the magneto-structural transformation in antiperovskites. Such a crucial role of A site ions has also been highlighted in another family of Mn antiperovskites containing nitrogen [29]. Though both, Mn 3 GaC and Mn 3 SnC are isostructural compounds undergoing a volume discontinuous first order transformation, there are many dissimilarities between them.…”

“…Such a behavior indicates that Sn doping not only strengthens the ferromagnetic interactions but at the same time weakens the AFM state. Local interactions usually play a major role in metamagnetic transitions occurring in the vicinity of a first order transition [29]. Therefore it is quite intriguing to understand how Sn doping, beyond a critical concentration, changes the magnetic character of the compounds, increases the transformation temperature while completely destroying the AFM state.…”

“…The distortion of CMn 6 octahedra gives rise to shorter and longer Mn-Mn bond distances which critically affect the competition between nearest Mn-Mn antiferromagnetic interactions and next nearest Mn-Mn ferromagnetic interactions [29] and has been considered to be the reason for the change in the direction of magnetic propagation vector in Mn 3 SnC with respect to that in Mn 3 GaC. Such a distortion can also be used to explain the observed behavior of magnetocaloric effect and change in the first order magnetic transformation temperature.…”

“Entropics”: Science and engineering of caloric phenomena related to itinerant-electron magnetism and spin fluctuations

“…At the Neel temperature T N of about 290 K, the first-order phase transition appears and the paramagnetic (PM) state appears above T N [26]. A notable feature is volume shrinkage of about 1% accompanied by the AF-PM first-order transition at T N [26,27]. Attempts have been made to utilize this large volume change as new negative thermalexpansion materials, which alternate with conventional Invar alloys [28].…”

Effects of carbon deficiency on the magnetic interactions in GaCMn3, a critical behavior study

“…Although being similar to their perovskite oxides counterparts (i.e., manganites) in the crystal structure, the antiperovskite AXMn 3 compounds exhibit metallic conductivity and good thermal conductivity [8,20]. Owing to the metallic properties, it is has been widely adopted that magnetism in AXMn 3 is itinerant in nature [20,21]. Indeed, theoretical calculation reveals that the electronic density of state (DOS) at the Fermi energy (E F ) for AXMn 3 is mainly composed of the Mn 3d states which are strongly hybridized with the X 2p states, leading to a wide energy band [22,23].…”