Nonequilibrium states and anomalies of Young’s modulus in rare-earth cobaltites RBaCo$_4$O$_7$ (R = Dy–Er, Y, Lu) caused by short-range magnetic order

The elastic properties of rare-earth cobaltites RBaCo$_4$O$_7$ (R = Dy, Ho, Er, Y, Lu) have been investigated experimentally. It has been found that the temperature dependences of the Young’s modulus exhibit significant hysteresis and irreversible effects over a wide range (80–280 K) between the structural and magnetic phase transition temperatures. These effects indicate that the short-range magnetic order in the Co sub-system of the studied rare-earth cobaltites gradually develops below the structural phase transition, when the distortion of the structure relieves the frustration of exchange interactions both in the Kagome lattice and in the triangular lattice of the cobalt subsystem. At the magnetic phase transition temperature, there are weak and smoothed anomalies of the Young’s modulus, which correlate with the low dimensionality and frustration of the exchange interactions in the Co subsystem of the studied rare-earth cobaltites.