Wagga Wagga CMM 2016

A ¹⁶¹Dy-Mössbauer spectroscopy investigation of DyCrO₄

Not scheduled

15m

Speakers

Dr Glen Stewart (UNSW Canberra)Prof. Sean Cadogan (UNSW Canberra)Dr Wayne Hutchison (UNSW Canberra)

Description

The rare earth (R) chromates RCrO₄ form with the tetragonal zircon type structure (space group I4₁/amd). They are of interest because of competing ferromagnetic and antiferromagnetic super-exchange interactions between the 3d (Cr⁵⁺) and 4f (R³⁺) sites, believed to be responsible for the giant magnetocaloric effect observed recently for R = Gd, Dy and Ho [1,2]. The ¹⁶¹Dy-Mössbauer spectroscopy measurements on DyCrO₄ reported here were prompted by earlier ¹⁶⁹Tm- and ¹⁵⁵Gd-Mössbauer spectroscopy results for TmCrO₄ [3] and GdCrO₄ [4], respectively. In both instances, it was necessary to interpret the Mössbauer spectra in terms of a superposition of two sub-spectra (approx. 80:20 intensity ratio) despite there being only a single crystallographic R(4a) site. In addition, the magnetic transitions exhibited first order character, which is contrary to bulk magnetic measurements. DyCrO₄ is reported to undergo a small crystal distortion to an orthorhombic (Imma) structure somewhere between 27 and 40 K and to order ferromagnetically at T_C = 22.4 K [5]. Our ¹⁶¹Dy-Mössbauer results show a simple magnetically-split spectrum at 5 K. Compared to the reference Dy metal spectrum there is a small increase in the line width. However, contrary to the earlier Mössbauer work [3,4], a second sub-spectral component is not immediately evident. The spectra are paramagnetic above T_C with the quadrupole splitting and Wegener relaxation broadening diminishing as the temperature increases to room temperature. This work was supported by AINSE, grant number 14547. [1] Midya A. et al. Appl. Phys. Lett. 103 (2013) 092402. [2] Midya A. et al. J. Appl. Phys. 115 (2014) 17E114. [3] Jiménez E. et al._J. Magn. Magn. Mater. 272 - 276 (2004) 568-570. [4] Jiménez-Melero E. et al. J Phys. Chem. Mater. 18 (2006) 7893-7904. [5] Long Y. et al. J. Magn. Magn. Mater. 322 (2010) 1912.