Magnetisation reversal in Ca2PrCr2NbO9 and Ca2PrCr2TaO9

Abstract Polycrystalline samples of the perovskites Ca 2 PrCr 2 B O 9 ( B  = Nb, Ta) have been synthesised using the standard ceramic method and characterized by x-ray diffraction, neutron diffraction and magnetometry. Both crystallise in the orthorhombic space group Pnma and exhibit magnetisation reversal when field-cooled in an applied field of 100 Oe. The absolute value of the negative magnetisation at 2 K in an applied field of 100 Oe is an order of magnitude greater in Ca 2 PrCr 2 TaO 9 than it is for Ca 2 PrCr 2 NbO 9 . Magnetometry and powder neutron diffraction showed that the Cr 3+ cations in Ca 2 PrCr 2 NbO 9 and Ca 2 PrCr 2 TaO 9 order in a G y F z magnetic structure below 110 and 130 K, respectively. The Pr 3+ cations remain paramagnetic down to ~ 10 K and show no-long range order at 2 K. Both compounds show a large degree of hysteresis in M ( H ), with coercive fields of 3.79 kOe and 3.03 kOe at 2 K.