Multiple magnetic phases ofLa2CoMnO6−δ

Abstract

Transport and magnetic properties of polycrystalline La 2 CoMnO 6Ϫ␦ , 0р␦р0.05, have revealed the existence of two distinguishable monoclinic ferromagnetic phases separated by a two-phase domain 0.02р␦ р0.05 and a pseudotetragonal (c/aϽ&) phase with ␦ у0.05 that was prepared at 600°C. A nearly oxygenstoichiometric sample having a magnetization M (5 K, 50 kOe)ϭ5.78 B /f.u. with a Curie temperature T c Ϸ226 K is identified as atomically ordered La 2 Co 2ϩ Mn 4ϩ O 6 containing about 1.8% antiferromagnetic spins at antisites. This ferromagnetic phase is an n-type polaronic conductor that progressively traps mobile electrons at the oxygen vacancies that introduced them on lowering the temperature. Although the x-ray-diffraction pattern can be indexed in orthorhombic ͑Pbnm͒ or monoclinic ( P2 1 /n) symmetry with ␤Ϸ90°, atomic order identifies the space group as P2 1 /n. A second monoclinic, ferromagnetic phase with T c Ͻ150 K and ␦ Ϸ0.05 has a large, positive thermoelectric power that increases progressively with decreasing temperature. Quenching a ␦ Ϸ0.02 sample from 1350°C into liquid N 2 gave a single phase with T c ϭ134 K and ␦ Ϸ0.05. A sample with ␦ у0.05 that was synthesized at 600°C was pseudotetragonal (c/aϽ&) and had a paramagnetic Weiss constant ϽT c Ϸ225 K as well as a significantly smaller magnetization, but its magnetization curve M (T) showed no evidence of spin-glass behavior; its large, positive thermoelectric power was characteristic of polaronic conduction without trapping of mobile charge carriers at lower temperatures. Interpretation of the two phases with ␦Ϸ0.05 is based on the hypothesis that introduction of high-spin Mn 3ϩ by the oxygen vacancies creates around it additional Mn 3ϩ and intermediate-spin Co 3ϩ at neighboring sites; the resulting gain in elastic energy from cooperative, dynamic Jahn-Teller deformations at these ions must be sufficient to overcome the cost of about 0.2 eV for the electron transfer from a Co 2ϩ ion to a Mn 4ϩ ion.

Ferromagnetism and magnetodielectric effect in insulating LaBiMn4∕3Co2∕3O6 thin films

“…[4][5][6] The spin-glass behavior of the low temperature magnetic phase has been reported previously in the bulk. 10 Figure 3 shows the dielectric measurements carried out at 1 MHz in the temperature range of 10 to 300K, both for bulk and thin film samples.…”

Electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with cationic ordering

“…19 Either in the form of bulk or films, local Co/Mn or Ni/Mn disorder has been observed which results in the coexistence of multi phases with various behaviors. [3][4][5][6][7][8][9][10] The distinct disorder effects in LNMO and LCMO thus call for the first-principle investigation for effect of cation ordering, but such kind of calculation does not exist. Furthermore, due to recent developments of molecular beam epitaxy (MBE) technology, perovskite oxides superlattices can be grown layer by layer with very high quality.…”

“…It is different from Mn 3þ /Ni 3þ or Mn 3þ /Co 3þ pairs expected in disorder phase. 8,9,16 According to Goodenough-Kanamori rules, 26 while Mn 3þ -O-Ni 3þ or Mn 3þ -O-Co 3þ has AFM exchange interaction. For the middle valence state, our calculations reveal that Mn (…”

“…1,2 Double perovskite La 2 NiMnO 6 (LNMO) and La 2 CoMnO 6 (LCMO) are attractive due to their impressive properties and potential on industrial applications. [3][4][5][6][7][8][9][10][11][12][13] LNMO is a ferromagnetic semiconductor with high critical temperature of T c % 280 K, which may be used in commercial solid-state thermoelectric (Peltier) coolers. 3 LCMO is also a ferromagnetic semiconductor with critical temperature T c % 230 K. 4,9 Several crystal structures have been identified, and it is confirmed that the ferromagnetic semiconductors LNMO and LCMO with high T c are P21/n monoclinic structure, in which octahedra with Ni (or Co) and Mn centers alternately stacking along (111).…”

Stabilization and functional properties of La3NiAlMnO9 and La3CoAlMnO9 magnetoelectric triple perovskites

“…and A = La) represent an alternative avenue to search for such innovative materials [4][5][6][7][8][9][10][11][12][13][14][15] .…”