Dr Glen Stewart (UNSW Canberra)Prof. Sean Cadogan (UNSW Canberra)Dr Wayne Hutchison (UNSW Canberra)
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  and GdCrO4 , 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 TC = 22.4 K . 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 TC 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.  Midya A. et al. Appl. Phys. Lett. 103 (2013) 092402.  Midya A. et al. J. Appl. Phys. 115 (2014) 17E114.  Jiménez E. et al._J. Magn. Magn. Mater. 272 - 276 (2004) 568-570.  Jiménez-Melero E. et al. J Phys. Chem. Mater. 18 (2006) 7893-7904.  Long Y. et al. J. Magn. Magn. Mater. 322 (2010) 1912.
Dr Glen Stewart (UNSW Canberra)