Metal–insulator transition in SrRuO3 induced by ion irradiation

Abstract

We have studied the effect of He ϩ irradiation on the electrical resistivity and Curie temperature of ferromagnetic SrRuO 3 thin films. An evolution from metallic to insulating behavior is observed when He ϩ ion fluence is increased, suggesting a metal-insulator transition. Damage by ion irradiation produces a strong decrease of the Curie temperature. On the other hand, no significant change in T c ͑ϳ160 K͒ takes place in fresh samples grown at different substrate temperatures. We discuss the possible correlation between structural changes induced by irradiation, which reflect in an increase of the pseudocubic lattice parameter, and the observed depression of T c . © 1998 American Institute of Physics. ͓S0003-6951͑98͒03349-X͔ SrRuO 3 is an orthorhombically distorted perovskite ͑space group Pbnm͒, and the only example of ferromagnetic ordering ͑with a Curie temperature T c , of 165 K͒ in conducting 4d transition-metal oxides. 1,2 This compound has a 4d 4 low spin configuration (Sϭ1) and is believed to have a narrow * band resulting from Ru t 2g and O 2 p orbitals, which governs magnetic ordering. 3,4 The actual nature of magnetism in this material, usually considered as an example of pure itinerant magnetism, 5 is not fully understood yet. This system can be included in the group of the so-called ''bad metals,'' 5,6 strongly correlated electron systems showing remarkable electrical and magnetic properties. A common feature of these materials is the high value of their roomtemperature electrical resistivities, close to the theoretical limit for the metallic state ͑Ioffe-Regel limit͒. From the point of view of possible technological applications, both the crystallographic structure ͑pseudocubic perovskite͒ and lattice parameters of this material, close to those of ͑YBCO͒, make it a promising candidate for the fabrication of ͑SNS͒ Josephson junctions of high-T c superconducting oxides. 7 In addition, its conducting character makes it a suitable material for electrodes in other types of devices based on perovskite oxides, as epitaxial conducting oxide-ferroelectric or superconduction-ferroelectric heterostructures. 8 Structural distortions are known to play a central role in the magnetic properties of SrRuO 3 . The absence of ferromagnetic ordering in the isostructural CaRuO 3 has been explained in terms of a stronger orthorhombical distortion in this compound which changes the sign of the magnetic interaction. 9 Both hydrostatic and chemical pressure resulting from the partial substitution of Sr 2ϩ ͑0.62 A͒ by the bigger Ca 2ϩ ͑1.06 A͒ give rise to a decrease of the Curie temperature, but the system remains metallic. This has been explained in terms of the magnetism of this compound being very sensitive to the Ru-Ru distance. 10 On the other hand, substitution of Ru by Ti up to 20% rapidly reduces the critical temperature and causes an increase of the resistivity which undergoes a crossover from metallic to semiconducting behavior at low temperatures. Once again, this has been proposed to occur as a result of local ...

Microstructure and Electrical Conductivity of Epitaxial SrRuO<SUB>3</SUB> Thin Films Prepared on (001), (110) and (111) SrTiO<SUB>3</SUB> Substrates by Laser Ablation

“…The epitaxial (001) SRO thin film exhibited the highest electrical conductivity of 2:4 Â 10 5 SÁm À1 at room temperature. It is reported that an expansion of c-axis induced by ion irradiation would cause the change of conduction behavior from metallic to semi-conductor like accompanying the decrease in T C from 160 K to 110 K. 20) Although the SRO thin films obtained in the present study showed the expansion of c-axis, no change of conduction behavior was observed. 4,[11][12][13][14]16,19,24) However, the T C of epitaxial SRO thin films were 10 K lower than that of single-crystals, ranging from 160 to 170 K. 5,27,28) This might be affected by lattice stress in the films.…”

“…[6][7][8][9][10] Since SRO has a good chemical stability and lattice matching to wide ranged oxides, epitaxial SRO thin films has been prepared on various single-crystal substrates such as SrTiO 3 (STO), 4,[11][12][13][14][15][16][17] LaAlO 3 , 18,19) MgO, 20) YSZ 21) and Si. 22) STO is particularly advantageous in preparing high quality epitaxial SRO thin films because the lattice parameter of STO (a ¼ 0:391 nm) is almost the same as that of SRO (a ¼ 0:393 nm).…”

Electron-electron interaction and weak localization effects in badly metallicSrRuO3

“…Increasing irradiation doses resulted in an enlargement of the pseudocubic c-lattice parameter. 11 Scanning electron microscopy observations revealed a granular structure with an average grain size of 0.5 m. Surface topography and grain size were not affected by irradiation. Transmission electron microscopy experiments performed using cross-section geometry before and after irradiation showed that the intergrain structure was not changed due to the irradiation process either.…”

“…11 Interestingly enough, ion damage destroys ferromagnetism, while for virgin films grown on the same substrate with different deposition conditions the Curie temperature remains essentially unchanged (T c ϳ160 K). In this paper we present a study of the low-temperature resistivity of poorly conducting thin-film samples of SrRuO 3 obtained by ion irradiation, and virgin samples displaying a low-temperature upturn of the resistivity.…”

Microstructure and Electrical Conductivity of SrRuO<SUB>3</SUB> Thin Films Prepared by Laser Ablation

“…1) Since SRO has a pseudo-cubic perovskite structure similar to ferroelectric PbZr x Ti 1Àx O 3 (PZT) and BaSr x Ti 1Àx O 3 (BST) materials, SRO thin film would provide good bottom electrodes for ferroelectric devices with a layered structure, where well-coherent or epitaxial film with a flat surface texture is required. [2][3][4] SRO thin films have been prepared by sputtering, 3,[5][6][7] metal-organic chemical vapor deposition (MOCVD) 7,8) and laser ablation (pulsed laser deposition). [9][10][11][12] It is known that sputtering often causes a significant difference of composition between targets and films and that MOCVD requires subtle control of the composition due to the difference of chemical stability between alkaline-earth and noble metal precursors.…”