Lattice dynamics of antiperovskite manganese nitrides exhibiting large negative and positive thermal expansion*

Antiperovskite manganese nitrides Mn₃AN (where A is a metal or semiconducting element) have strong charge-spin-lattice interactions resulting in magnetovolume effects such as large positive (PTE) and negative thermal expansion (NTE) over transitions between their ferrimagnetic, antiferromagnetic, and paramagnetic phases [1]. We grow films of Mn₃Cu_1-xGe_xN with x = 0.1 to 0.5, which exhibit tunable NTE coefficients over a 50 K region, occurring anywhere from around 100 K to around 400 K depending on x. We also grow films of Mn₃Cu_1-xNi_xN with x = 0.09 to 0.10, which have a first order hysteretic PTE of 1-1.5% near 100 K and exhibit NTE for a total lattice contraction of roughly 0.5% over a 25 K range around 175 K. These regions are linked to transitions in magnetic phases. To probe the coupling of the structure and magnetism, we have measured the X-ray diffraction following photoexcitation within and through the interesting regions at the Advanced Photon Source. We present the complex lattice dynamics and discuss the spin-lattice coupling driving their response.

[1] Takenaka, K., et al. Appl. Phys. Lett. 87, 261902 (2005).