Good Perpendicular Anisotropy Research Articles

Achievement of High Perpendicular Anisotropy and Modification of Heat Treatment Peeling in Micron-Thickness Nd-Fe-B Films Used for Magnetic MEMS.

Thick Nd-Fe-B permanent magnetic films with good perpendicular anisotropy have important applications in magnetic microelectromechanical systems (MEMSs). However, when the thickness of the Nd-Fe-B film reaches the micron level, the magnetic anisotropy and texture of NdFeB film will become worse, and it is also prone to peeling during heat treatment, which seriously limits their applications. In this paper, Si(100)/Ta(100 nm)/NdxFe91-xB9(x = 14.5, 16.4, 18.2)/Ta (100 nm) films with thicknesses of 2-10 μm are prepared by magnetron sputtering. It is found that gradient annealing (GN) could help improve the magnetic anisotropy and texture of the micron-thickness film. When the Nd-Fe-B film thickness increases from 2 μm to 9 μm, its magnetic anisotropy and texture do not deteriorate. For the 9 μm Nd-Fe-B film, a high coercivity of 20.26 kOe and high magnetic anisotropy (remanence ratio Mr/Ms = 0.91) are achieved. An in-depth analysis of the elemental composition of the film along the thickness direction is conducted, and the presence of Nd aggregation layers at the interface between the Nd-Fe-B and the Ta layers is confirmed. The influence of thicknesses of the Ta buffer layer on the peeling of Nd-Fe-B micron-thickness films after high-temperature annealing is investigated, and it is found that increasing the thickness of the Ta buffer layer could effectively inhibit the peeling of Nd-Fe-B films. Our finding provides an effective way to modify the heat treatment peeling of Nd-Fe-B films. Our results are important for the development of Nd-Fe-B micron-scale films with high perpendicular anisotropy for applications in magnetic MEMS.

Magnetization Switching by Spin–Orbit Torque in L10-FePt and Ta/FePt Films With Large Perpendicular Magnetic Anisotropy

The current induced perpendicular magnetization switching in L10-FePt single layer and Ta/FePt bilayer thin films was investigated. Here, L10-FePt (6 nm) single-layer film and Ta (1-5 nm)/FePt (6 nm) bilayer films were deposited on MgO substrate at 700°C, showing good perpendicular anisotropy with the out-of-plane coercivity of 7.5 kOe for FePt and around 5 kOe for Ta/FePt bilayers. It is found that current-induced partial magnetization-based switching was realized with the SOT switching ratio of about 3% in all films. For adding the Ta capping layer, the critical current density is reduced and the stability of the switching loop is relatively better as compared with the single FePt layer. Furthermore, harmonic Hall voltage results demonstrate that the SOT efficiency (βDL) of FePt single-layer is approximately 50 Oe/ (107A cm-2), significantly higher than that of Ta/FePt bilayers, which is several times higher than that of the traditional Ta/CoFeB/MgO structure reported before. More importantly, Ta/FePt bilayer structure exhibits very good memristive switching behavior, which is expected to be applied to the spin-synapse of neural networks in the future.

Control of Microstructure and Magnetic Properties of FePt Thin Films with TiN-MgO Intermediate Layer.

The effects of TiN-MgO intermediate layer on the microstructure and magnetic properties of FePt-SiNx-C films were investigated. With doping MgO into TiN, three components were formed, including titanium dioxide, titanium nitride and titanium oxynitride. This caused the decrease of the surface energy and the increase of the interface energy, and further induced the promotion of island growth of FePt, thus the improvement of the isolation and the decrease of FePt grains. On the other hand, the decrease of surface energy and the forming of some titanium dioxide with doping MgO would accompany the deterioration of epitaxial growth and thus the deterioration of the perpendicular magnetic anisotropy of FePt films in a certain degree. By optimizing the concentration of TiN and MgO, the FePt-SiNx-C films with small grain size of 5.86±1.03 nm and good perpendicular anisotropy would be obtained.

Columnar structural FePt films with good perpendicular anisotropy induced by tuning the crystal structure of doping materials

Crystalline ZrO2 doping would degrade the perpendicular texture of FePt films due to the epitaxial growth of FePt (200) textured phase on the tetragonal (002) textured ZrO2. In the present paper, crystalline HfO2 was used to replace crystalline ZrO2 as the crystalline doping material and FePt media with columnar structure and good perpendicular anisotropy were achieved. It is found that HfO2 crystallized on TiON intermediate layer presented the coexistence of both monoclinic and tetragonal phase. The extremely large lattice mismatch strain (around 25–28%) between FePt and HfO2 would prohibit the (200) or (001) epitaxial growth of FePt phase on HfO2. This would cause FePt-HfO2 film to have better (001) texture and perpendicular anisotropy compared to FePt-ZrO2 films. By tuning the crystal structure of doping crystalline phase material, columnar structural FePt films with better perpendicular anisotropy could be obtained, which may offer a method for the application of FePt media in heat assisted magnetic 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.

Composition influence on the microstructures and magnetic properties of FePt thin films

The FexPt100−x (10 nm) (x = 31−51) thin films are fabricated on Si (100) substrates by using magnetron sputtering. The highly ordered L10 FePt phase is obtained after post-annealing at 700 °C in Fe47Pt53 thin film. The sample shows good perpendicular anisotropy with a square loop and a linear loop in the out-of-plane and the in-plane direction, respectively. The variations of the magnetic domains are investigated in the films when the content value of Fe changes from 31% to 51%.

Nanocomposite L10 FePt–SiNx and FePt–SiNx–C films with large coercivity and small grain size on a TiN intermediate layer

FePt–SiNx–C films with high coercivity, (001) texture and small grain size were obtained by co-sputtering FePt, Si3N4 and C on TiN/CrRu/glass substrate at 380°C. Without C doping, FePt–SiNx films with good perpendicular anisotropy and a single layer structure were obtained. However, the grain size was still too large and the grain isolation was poor. When C was doped into the FePt–SiNx films, the out-of-plane coercivity increased due to the decrease of the exchange coupling. In addition, the grain size of the FePt films decreased, and well-separated FePt grains with uniform size were formed. The microstructure of [FePt–SiNx40vol%]−20vol%C films changed from a single layer structure to a multiple layer structure when the FePt thickness was increased from 4 to 10nm. By optimizing the sputtering process, the [FePt (4nm)–SiNx 40vol%]−20vol%C (001) film with coercivity higher than 21.5kOe, a single layer structure, and small average FePt grain size of 5.6nm was obtained, which makes it suitable for ultrahigh density perpendicular recording.

Effects of Ta seed layer and annealing on magnetoresistance in CoFe∕Pd-based pseudo-spin-valves with perpendicular anisotropy

We have studied the switching characteristics and magnetoresistance of pseudo-spin-valves with perpendicular anisotropy based on CoFe∕Pd multilayers. In unpatterned thin films without exchange biasing, a maximum current-in-plane giant magnetoresistance of 7% was achieved, the highest reported to date in perpendicular pseudo-spin-valves. A Ta seed layer and the fcc (111) orientation of Pd was shown to be important in order to achieve good perpendicular anisotropy and sharp switching behavior. The improvement in perpendicular anisotropy and decay in magnetoresistance upon postdeposition annealing have been attributed to the formation of CoPd alloys at the CoFe∕Pd interfaces.

Effects of composition and temperature of crystallization on the microstructure and magnetic properties of NdFeB thin films for perpendicular recording media

NdFeB thin films were synthesized by a dc magnetron sputtering system. The influence of composition and temperature of crystallization on the microstructure and magnetic properties of NdFeB thin films was investigated. It was found that excessive Nd and B addition was helpful in promoting granular structure and reducing grain growth as well as in modifying magnetic properties. The excess elements were precipitated and well distributed around the shells of hard magnetic grains. This actively decreased the intergranular interactions between hard grains. Films made on heated substrate were also compared to those fabricated by post annealing. The former method was proved to be very effective to produce hard NdFeB thin films with good perpendicular anisotropy on a W underlayer, whereas films made by the latter process were isotropic. The maximum coercivity was obtained near 10 kOe in films annealed at 600 °C. The intergranular interactions were characterized by δM plots. It was found that annealed samples have a much stronger exchange coupling interaction than do the in situ deposited samples. Therefore, the magnetization reversal process in annealed films is mainly controlled by domain wall motion while it is more likely to be dominated by incoherent magnetization reverse in in situ deposited thin films, defined by the dependence of coercivity Hc(θ) on the measuring angle θ. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A comparison of the uniaxial anisotropy in sputtered Co–Re and Co–Cr perpendicular recording media

The effect of the presence of an intermetallic compound on the microstructure, crystalline anisotropic orientation, and perpendicular magnetic hysteretic properties was investigated based on CoRe and CoCr alloys. The results suggest that a phase segregation causes the formation of an intermetallic compound, Co3Cr, in the Co-rich CoCr alloy film. Consequently, it leads to the growth of isolated columnar particles because of the fact that the alloy composition lies within the two-phase region in the phase diagram. For homogeneous CoRe and CoCr alloys at high temperature, the resultant microstructures in a deposited film show equiaxial particles characterized by a large grain diameter. Magnetic hysteretic measurement on the film having various microstructure shows that high coercivity and good perpendicular anisotropy in the CoCr film is primarily due to the formation of isolated columnar particles in addition to the c-axis preferred orientation. Films having good c-axis preferred orientation but not the isolated columnar structure can not give good hysteretic properties for perpendicular recording media application. Also it was concluded in this work that in an isolated columnar structure film, the extent of c-axis dispersion (i.e., the value of Δθ50) affects the sharpness of the knee, but the Hc of the perpendicular hysteresis loop is not affected significantly.