Intrinsic Ferromagnetism in Insulating Cobalt Doped AnataseTiO2

Abstract

Using complementary experiments we show that the room temperature ferromagnetism observed in anatase Co:TiO(2) films is not carrier mediated, but coexists with the dielectric state. TEM and x-ray absorption spectroscopy reveal a solid solution of Co in anatase, where Co is not metallic but in the +2 state substituting for Ti. Measurements at 300 K yield a M(S) of 1.1 mu(B)/Co atom, while all films are highly insulating. The evidence of intrinsic ferromagnetism in the dielectric ground state of Co:TiO(2) leads to new considerations for the origin of ferromagnetism in transition metal doped oxides.

Superexchange in dilute magnetic dielectrics: Application to(Ti,Co)O2

“…As was mentioned above, the room temperature ferromagnetic order was detected in Cr and Co doped anatase TiO 2 , and in both cases native defects are involved in formation of the ferromagnetic order. 9,10 In the latter case these defects are apparently oxygen vacancies. Below, we adapt our theory 3 for vacancy mediated indirect exchange.…”

“…Since no spin-flip occurs in the course of the exchange, the spin index may be omitted in the Hamiltonian (5), (8), (9). This energy gain is given by the following equation 3,25 …”

“…In this paper we construct a model of insulating oxide, which considers intrinsic non-magnetic defects as an integral part of the ordering mechanism. We concentrate mainly on the superexchange between magnetic ions mediated by oxygen vacancies, which is believed to be the source of ferromagnetic order in TiO 2 diluted with Co. 9 …”

“…9 It means that we need now to find an exchange mechanism, which works in the case of really insulating oxides. In this paper we construct a model of insulating oxide, which considers intrinsic non-magnetic defects as an integral part of the ordering mechanism.…”

X-ray anomalous scattering of diluted magnetic oxide semiconductors: Possible evidence of lattice deformation for high temperature ferromagnetism

“…In addition, rutile Ti 1−x Co x O 2−δ has already been functionalized as a spin tunneling junction working up to 180 K. 15 Other studies that focus on this issue are mainly based on spectroscopic measurements such as x-ray absorption fine structure (XAFS) for samples in which no Co segregation was recognized by imaging probes such as scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscopy (TEM). 16,17,18,19 In these spectroscopic measurements, the spectral line shapes differ from that of Co metal. They state that the local structure of the Co site is close to those of Co oxides such as CoTiO 3 , in which the Co ion is surrounded by six oxygen atoms, forming a CoO 6 cluster, and that the valence state of Co is divalent.…”