Carrier doping effect of magnetic and transport properties on the geometrically frustrated iridate Ca5Ir3O12

Abstract We show the carrier doping effect on magnetic and transport properties of Ca 5 Ir 3 O 12 , indicating semiconductivity and an antiferromagnetic ordering below Neel temperature T N = 7.8  K. The average valence of Ir ions in Ca 5 Ir 3 O 12 is +4.67. Carrier doping for 5 d electrons of Ir ions is achieved by substitution of Ca 2 + by Na + , La 3 + , and Bi 3 + ; Na substitution leads to hole doping, and La or Bi substitution leads to electron doping. The electrical resistivity decreases in both case of the hole doping or the electron doping. For La10% doped samples, T N does not change but Curie–Weiss temperature Θ CW becomes 3.5 times larger than 9.9 K for Ca 5 Ir 3 O 12 . For Bi10% doped samples, T N decreases to 5 K but Θ CW becomes 3 times larger than that of undoped compound. On the other hand, for Na10% doped samples, T N decreases to 4 K and Θ CW decreases to 8.3 K. The frustration index f which is defined by | Θ CW | / T N is enhanced by electron doping. The magnetic frustration becomes stronger with increase of filling of Ir 5 d electrons on the triangular lattice.