K. F. Dong

Well-isolated L10 FePt–SiNx–C nanocomposite films with large coercivity and small grain size

FePt–SiNx–C films on TiN/CrRu/glass substrate with large coercivity, (001) texture, and small isolated grains were obtained by co-sputtering FePt, Si3N4, and C targets at 380 °C. It was found that when C was doped into the FePt–SiNx films, the out-of-plane coercivity increased while the small in-plane coercivity remained unchanged. Grain size decreased and grain size distribution became more uniform with increasing the C doping concentration. The x-ray photoelectron spectroscopy (XPS) depth profile showed a uniform depth distribution of Si in the FePt layer. The Si2p XPS spectrum implied the existence of Fe–Si bonds, indicating that SiNx was located at the FePt grain boundaries and was stable against diffusion to the surface, thus favoring grain isolation. Well-isolated FePt (001) granular films with coercivity higher than 21.5 kOe and an average grain size of 5.6 nm were obtained by doping 40 vol. % of SiNx and 20 vol. % of C.

High coercive FePt and FePt-SiNx(001) films with small grain size and narrow opening- up of in-plane hysteresis loop by TiN intermediate layer

The effects of a TiN intermediate layer on the epitaxial growth and magnetic properties of FePt films were investigated. It was found that 5 nm TiN can effectively block the diffusion of a CrRu underlayer into a FePt magnetic layer and the magnetic dead layer on the TiN layer was negligible. Compared with an FePt film grown on a MgO intermediate layer, FePt film grown on a TiN interlayer exhibited very high out-of-plane coercivity and very narrow opening-up of in-plane hysteresis loop. With doping 40 vol. % SiNx in FePt film the grain size was reduced to 5.5 nm and the magnetic properties, such as high out-of-plane coercivity and line-like in-plane hysteresis loop, were retained.

Lattice mismatch-induced evolution of microstructural properties in FePt films

FePt (10, 20, 40, and 60 nm) films were fabricated on four different single crystal substrates [MgO (001), KTaO3 (001), SrTiO3 (001), and LaAlO3 (001)], and the effects of lattice mismatch on the microstructure and magnetic properties of FePt films were systematically investigated. The X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results showed that the different lattice mismatch between the substrates and FePt films resulted in the different crystallographic texture and microstructure of the FePt films. Under the tensile strain between the FePt and substrates (MgO, KTaO3, SrTiO3), the FePt films preferred to form L10 FePt (001) texture. The perpendicular anisotropy of the FePt films grown on MgO was larger than that grown on KTaO3 and SrTiO3. For the FePt films grown on the LaAlO3 substrate, both FePt (110) and (001) orientations were found, which indicated the presence of tensile and compressive strain, respectively. With the reduction of the lattice ...

Control of Microstructure and Magnetic Properties of FePt Films With TiN Intermediate Layer

The effects of a TiN intermediate layer on the microstructure and magnetic properties of the FePt films were investigated. It was found that the TiN layer could effectively block the diffusion of Cr into the FePt film. The good epitaxial relationships among these layers were revealed from the transmission electron microscopy (TEM) results. With introducing TiN intermediate layer the chemical ordering and magnetic properties of FePt films significantly improved. The FePt film with 5 nm TiN exhibited a high perpendicular coercivity of 13.7 kOe and a low in-plane coercivity of 0.24 kOe, resulting from the combined contribution of TiN (200) orientation, TiN layer roughness and the effective block of Cr diffusion. Moreover, with doping C into the FePt-SiNx films, the out-of-plane coercivity increased due to the decrease of the exchange coupling, the grain size of FePt films decreased, and well-separated FePt grains and uniform size were formed. By optimizing the sputtering process, the [FePt (4 nm)-SiNx 40 vol·% ]- 20 vol·% C (001) film with coercivity higher than 21.5 kOe, a single layer structure, and small FePt grain size of 5.6 nm in average diameter was obtained, which are suitable for ultrahigh density perpendicular recording.

Nanogranular TiN-ZrO2 intermediate layer induced improvement of isolation and grain size of FePt thin films

The effects of TiN-ZrO2 intermediate layer on the microstructures and magnetic properties of FePt films were investigated. The TiN-ZrO2 intermediate layer was granular consisting of grains of solid solution of Ti(Zr)ON segregated by amorphous ZrO2. By doping ZrO2 into TiN intermediate layer, the FePt grains became better isolated from each other and the FePt grain size was reduced. For 20 vol. % ZrO2 doping into TiN, the grain size decreased dramatically from 11. 2 nm to 6. 4 nm, and good perpendicular anisotropy was achieved simultaneously. For the FePt 4nm-SiO2 35 vol. % -C 20 vol. % films grown on top of the TiN-ZrO2 20 vol. % intermediate layer, well isolated FePt (001) granular films with coercivity higher than 18. 1 kOe and an average size as small as 6. 4 nm were achieved.

L10 FePt-ZrO2 (001) nanostructured films with high aspect ratio columnar grains

In order to increase the signal-to-noise ratio of heat assisted magnetic recording, it is desirable to fabricate high magnetic anisotropy FePt media with small grain size and high aspect ratio (grain height to size ratio). In the present paper, we report that FePt media with small grain size and high aspect ratio were achieved by doping ZrO2 into FePt film grown on TiON intermediate layer. The grain size was around 5.6 nm, and the aspect ratio was as high as 2.6. It is believed that this originated from the ZrO2 (002) tetragonal crystalline phase epitaxially grown on TiON intermediate layer. With a 5 vol. % carbon doping into FePt-ZrO2 films, the perpendicular anisotropy was improved and the out-of-plane coercivity was around 23.2 kOe. Doping of crystalline phase material with certain required crystal structure may offer a method for fabrication of nanostructured thin films with high aspect ratio grains at high processing temperature.

Crystalline ZrO2 doping induced columnar structural FePt films with larger coercivity and high aspect ratio

Columnar (001) FePt-ZrO2-C films with large coercivity, small grain size, and high aspect ratio were obtained. By doping ZrO2 into FePt film at high sputtering temperature, tetragonal (002) textured ZrO2 was formed and distributed at the grain boundaries of FePt grains, resulting in the formation of columnar structured FePt films. The perpendicular anisotropy of FePt films was degraded since some (200) FePt grains were formed directly on the (002) textured ZrO2. With a small amount of carbon doping into FePt-ZrO2 35 vol. % films, the perpendicular anisotropy was improved. However, FePt grains were still interconnected. Upon further increasing concentration of ZrO2, (001) textured FePt-ZrO2 40 vol. %-C 5 vol. % films with well isolated grains in average diameter of 5.5 nm and very good columnar structure were obtained.

Highly (001)-Textured L10 FePt-SiO2-C Films with Well-Isolated Small Grains Using TiON Intermediate Layer

The magnetic properties and microstructures of the FePt–SiO2–C films deposited on TiON layers were investigated. It was found that the surface energy could be reduced and/or interfacial energy could be increased by doping O into the TiN layers. Improved grain isolation and grain size reduction were achieved with a TiON intermediate layer. The highly (001)-textured FePt–SiO2–C films and in-plane hysteresis loops with small openings were retained with the TiON layers. With a TiON/TiN dual intermediate layer, the in-plane hysteresis loop became the ideal straight line. Well-isolated grains with a size of 5.7±0.9 nm was obtained on the TiON/TiN dual intermediate layer.

Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer.

The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

Microstructures and Magnetic Properties of FePt Thin Films on TiON Intermediate Layer

The microstructures and magnetic properties of FePt(-SiOx-C) thin films grown on TiON and TiON/TiN intermediate layers were studied. TiON possessed smaller surface energy and smaller lattice constant than TiN. With increasing TiOx doping concentration, FePt grain shape changed from semi-spherical to square and grain size was significantly reduced. Meanwhile, good perpendicular magnetic anisotropy was retained, indicating that TiON intermediate layer could achieve a good balance between island growth and epitaxial growth. Furthermore, using TiON/TiN combined intermediate layer, FePt grain size was further reduced and the opening-up of in-plane M-H loop diminished. With 45 vol.% SiOx-25 vol.% C doping, well-isolated FePt grains with an average size as small as 5.7 nm and the grain size distribution of 0.9 nm were achieved. It also exhibited good perpendicular magnetic anisotropy with an out-of-plane coercivity of 18 kOe.