Oxygen-defect-induced magnetism to 880 K in semiconducting anatase TiO_2−δfilms

Abstract

We demonstrate a semiconducting material, TiO 2−δ , with ferromagnetism up to 880 K, without the introduction of magnetic ions. The magnetism in these films stems from the controlled introduction of anion defects from both the filmsubstrate interface as well as processing under an oxygen-deficient atmosphere. The room-temperature carriers are n-type with n ∼ 3 × 10 17 cm −3 . The density of spins is ∼10 21 cm −3 . Magnetism scales with conductivity, suggesting that a double exchange interaction is active. This represents a new approach in the design and refinement of magnetic semiconductor materials for spintronics device applications.(Some figures in this article are in colour only in the electronic version)Recent research efforts on the growth of magnetically ordered semiconductor materials [1,2] have received great attention because of potential new applications in spintronics devices [3]. The rationale for this optimism is the plausibility of integrating properties of both magnetic and semiconductor materials in new devices [1] (e.g. spin diodes [3-6] and spin-FETs [7]). Recent research has focused on dilute magnetic semiconductors (DMS) which were synthesized by introducing magnetic ions (e.g. Mn, Co, Fe, and etc) into conventional III-V [1, 2] and II-VI type semiconductors [8,9] or wide bandgap semiconductors including ZnO and TiO 2 [8][9][10][11][12][13]. Also, ferromagnetism was induced in films of hafnium dioxide, HfO 2 , deposited by pulsed laser deposition (PLD) on sapphire substrates and attributed to defect doping [10][11][12]. Bulk HfO 2 is intrinsically non-magnetic and electrically insulating. This report has created intense

Defect-induced magnetism in undoped wide band gap oxides: Zinc vacancies in ZnO as an example

“…Thus, it is of paramount importance to investigate the roles of intrinsic defects in the onset of ferromagnetism because of their abundance in wide band gap oxides. [42][43][44] On the other hand, we should note that although there is no immediate danger of metal clustering in undoped oxides, extreme cares should still be taken to exclude the contribution of magnetic contaminations, which clearly entails deliberate experimental designs. Furthermore, although native defects have been recognized as important players influencing the electrical and optical properties of ZnO, it is a formidable task to quantitatively determine their concentrations as well as their exact contributions to the physical properties.…”

Magnetically active vacancy related defects in irradiated GaN layers

“…4 Rather surprisingly, the appearance of room temperature ferromagnetism in nonmagnetic electronic materials has been recently observed in many materials such as oxide and nitride dielectrics and semiconductors. [5][6][7][8][9] It has been proposed that defect, surface and localized states are the source of magnetic moments leading to high temperature ferromagnetism in nonmagnetic materials.…”

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

“…1,2,3,4,5,6,7,8,9,10 in reduced dimensional form such as nanoparticle and thin films. Observation of ferromagnetism in these undoped systems created more excitement and threw open a wider debate as to the origin of magnetism in these wide band gap semiconductors.…”