Magnetoelastic and thermal effects in the BiMn2O5 lattice: a high-resolution x-ray diffraction study

TL;DR

This study uses high-resolution x-ray diffraction to investigate magnetoelastic and thermal effects in BiMn2O5, revealing lattice anomalies linked to magnetic transitions and suggesting complex magnetic interactions and phase coexistence.

Contribution

It provides detailed insights into the magnetoelastic coupling and structural phase behavior of BiMn2O5 across magnetic transition temperatures using synchrotron x-ray diffraction.

Findings

Linear temperature dependence of unit cell volume between 38 K and 100 K.

Incipient magnetoelastic effects observed below 65 K.

Structural phase coexistence below T_N indicating competing magnetostructural states.

Abstract

High-resolution synchrotron x-ray diffraction measurements were performed on single crystalline and powder samples of BiMn2O5. A linear temperature dependence of the unit cell volume was found between T_{N}=38$ K and 100 K, suggesting that a low-energy lattice excitation may be responsible for the lattice expansion in this temperature range. Between T* ~ 65 K and T_{N}, all lattice parameters showed incipient magnetoelastic effects, due to short-range spin correlations. An anisotropic strain along the a-direction was also observed below T*. Below T_{N}, a relatively large contraction of the a-parameter following the square of the average sublattice magnetization of Mn was found, indicating that a second-order spin hamiltonian accounts for the magnetic interactions along this direction. On the other hand, the more complex behaviors found for $b$ and $c$ suggest additional magnetic transitions below T_{N} and perhaps higher-order terms in the spin hamiltonian. Polycrystalline samples grown by distinct routes and with nearly homogeneous crystal structure above T_{N} presented structural phase coexistence below T_{N}, indicating a close competition amongst distinct magnetostructural states in this compound.