Magnetic Transitions in Perovskites Ca(Mn3−xCux)Mn4012

Abstract

A systematic study is made of the magnetic properties on perovskite‐like compounds Ca(Mn3−xCux)Mn4O12 in the temperature range (0.6 to 300) K. The occurrence of a succession of transitions with increasing temperature at × = 1: nonergodic ferrimagnetic—ferrimagnetic—par‐amagnetic is concluded. A magnetic phase transition perhaps due to a canted magnetic structure formation at 97 K is observed. A reentrant spin glass state is believed to realize with x = 0.8 at T = 0.6 K.

New Cubic Perovskite Na(Cu2.5Ti0.5)Ti4O12 with Square Planar Coordination of Ti4+

“…A typical substituent for Cu 2+ in this site is another Jahn-Teller ion, high-spin Mn 3+ . 15,16,[20][21][22] Although square planar coordination is characteristic for low-spin d 8 ions too, attempts to replace Cu 2+ with Pd 2+ have failed; 4 only partial substitution of Cu 3+ for Cu 2+ was found to be possible. 4,7,9 The most exotic and very rare substitution for the CaCu 3 -Ti 4 O 12 structure type is the incorporation of non-Jahn-Teller ions in the copper square planar site.…”

“…All these phases contain Cu 2+ in a square planar oxygen environment characteristic of the Jahn−Teller d 9 ion. A typical substituent for Cu 2+ in this site is another Jahn−Teller ion, high-spin Mn 3+ . ,,− Although square planar coordination is characteristic for low-spin d 8 ions too, attempts to replace Cu 2+ with Pd 2+ have failed; only partial substitution of Cu 3+ for Cu 2+ was found to be possible. ,, The most exotic and very rare substitution for the CaCu 3 Ti 4 O 12 structure type is the incorporation of non-Jahn−Teller ions in the copper square planar site. To our knowledge, only three examples of this kind of material were reported (i.e., high-pressure phase CaFe 3 Ti 4 O 12 , Li[Cu 3 - x Li x ][Ti 3 - x M 1+ x ]O 12 (M = Ta 5+ , Nb 5+ with x up to 0.33), and Sr 0.946 [Cu 2.946 Ti 0.054 ]Ti 4 O 12 ), although we noticed that the bond-valence sum for the copper site, obtained using structural data reported for the lithium compound, has a value of 2.06 which is much closer to the ideal value of 2.0 for a purely copper site than to the expected value of 1.89 and may indicate that the crystal structure has been determined incorrectly.…”