Enhancement of coercivity with reduced grain size in CoCrPt film grown by pulsed laser deposition

We report a pulsed laser deposition (PLD) growth of VMn/CoCrPt bilayer with a magnetic coercivity (H_c) of 2.2 kOe and a grain size of 12 nm. The effects of VMn underlayer on magnetic properties of CoCrPt layer were studied. The coercivity, H_c, and squareness, S, of VMn/CoCrPt bilayer, is dependent on the thickness of VMn. The grain size of the CoCrPt film can also be modified by laser parameters. High laser fluence used for CoCrPt deposition produces a smaller grain size. Enhanced H_c and reduced grain size in VMn/CoCrPt is explained by more pronounced surface phase segregation during deposition at high laser fluence.     

Superlattice CoCrPt/Ru/CoFe structure fabricated by pulsed laser deposition

The synthetic antiferromagnets (SAF) have been used in spin-valve sensor in data storage industry [1]. We report a new hard/Ru/soft sandwich structure (SHBL) fabricated by pulsed lased deposition to replace current single layer structure for information recording application. SHBL consists of two magnetic layers separated by thin nonmagnetic layers, typically with Ru layers of 0.7-1.2 nm, through which antiferromagnetic coupling is induced. Varying the relative thickness of the magnetic layers, the spacer layers, and the type of magnetic materials can alter magnetic properties of CoCrPt/Ru/CoFe superlattice. The coercivity H_c and grain size of magnetic layer is also dependent on the laser fluence. High laser fluence results in both small grain size and high H_c. The observed phenomena are related to high quenching and deposition rates during PLD at high fluence, resulting in more pronounced phase segregation.     

Cr/Ru/PtCo/Ru/PtCo/Ru介质中底层Ru厚度对磁记录特性影响的研究

讨论了Cr/Ru（1）/PtCo（稳定层）/Ru（2）/PtCo（记录层）/Ru（3） 结构的矫顽力Hc_c与层间反铁磁耦合交换场Hex_ex随Ru（1）与Ru（2）厚度变 化的规律.研究发现 ，样品的矫顽力及交换场随Ru（1）厚度增加而增大， 这可能是由Ru（1）hcp结构引起的. 矫顽力及交换场在Ru（2）厚度为08nm处有峰值. 关键词： 磁记录 反铁磁耦合     

Preparation and recording characteristics of granular-type perpendicular magnetic recording media with thin intermediate layer

Granular-type media with thin Ru intermediate layer were prepared on a highly oriented high-B_s FeCo soft underlayer (SUL). A CoPt–TiO₂ recording layer on a Ru intermediate layer of only 2 nm had high-crystal orientation, high H_c of 6.5 kOe, and a high squareness ratio (SQ) of 0.99. The magnetic property of the SUL was also good. The recording performance was measured for the media with different Ru intermediate thicknesses by using a single-pole-type (SPT) head. The media had large reproduced output even for the Ru intermediate layer thickness of 2 nm.     

Effect of continuous layer in CGC perpendicular recording media

The effect of continuous layer on CoCrPt–SiO₂ granular layer is studied in coupled granular continuous (CGC) perpendicular recording media. In the cross-section transmission electron microscope (TEM) observation, magnetic grain in the granular layer shows columnar structure, while Co/Pd multilayer shows continuous layer. The plane-view TEM image of the granular layer shows well-isolated grain structure with average grain size of around 6 nm, and grain-to-grain separation width of around 2 nm. Therefore, the interactions among the grains are negligible (J∼0). By depositing a continuous layer on a CoCrPt–SiO₂ granular layer, the grains in the granular layer are magnetically coupled through capping layer that leads to the suppression of magnetic anisotropy dispersion. This CGC structure reduces the coercivity dispersion (Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$) from 0.26 to 0.15 and saturation field (H_s) from 10.4 to 6.7 kOe. The reduction of H_s and Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$ improves the OW by 21.3 dB. The small Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$ also maintains SNR of CGC media with strong magnetic exchange coupling. Furthermore, the coupling of grains through continuous layer enlarges the magnetic nucleation field (H_n) from 0.4 to −1.7 kOe. Consequently, CGC media shows better thermal stability compared to non-CGC media.     

Magnetic properties of Pr-Fe-B/Mn films with perpendicular anisotropy

The influence of a Mn layer on the magnetic properties of sputtered Pr-Fe-B/Mn films with Cu spacer layer has been investigated for various Mn layer thicknesses. The Pr-Fe-B/Mn films all possess perpendicular anisotropy. An enhancement of the intrinsic coercivity _iH_c is observed for suitable Mn layer thickness and _iH_c exhibits an oscillatory dependence on the thickness of the Mn layer with a period of about 60 nm. The average size of the columnar Pr₂Fe₁₄B grains is about 100 nm. A highest _iH_c value of 22.1 kOe and an optimal (BH)_max value of 18.2 MGOe are reported for these Pr-Fe-B/Mn films.     

Structural and magnetic properties of HCP-CoCrPt–SiO2 granular media

Granular HCP-(CoCrPt)_100−x(SiO₂)_x thin films with Cr underlayers have been fabricated by sputtering multilayers followed by post-deposition annealing. Magnetic and structural properties of the films for potential applications in magnetic recording media have been investigated in detail. In as-deposited films coercivities exceeding 2.5 kOe have been obtained with SiO₂ varying from 8 to 16 vol%; high coercivity of 5.6 kOe and anisotropy of 4.6×10⁶ erg/cm³ have been achieved at low M_rt value (about 0.4 memu/cm²) in the post-annealed films. VSM measurements showed that the magnetic moment lies well in the film plane under proper preparation conditions. Grain isolation in the magnetic layer was improved by segregating SiO₂ into grain boundaries and further enhanced by post-deposition annealing. The rapid increase of the coercivity upon annealing is most likely due to the significant decrease in intergranular exchange coupling, as shown by the δM measurement in which the peak value of δM curves changed from a positive value to a negative value upon annealing. Magnetic reversal properties of the films have also been systematically studied. These results show that the HCP-CoCrPt–SiO₂ granular film is a promising candidate for ultra-high-density recording media up to 100 Gbit/in² or beyond because of its low Pt content and desirable properties.     

The ferroelectric and ferromagnetic characterization of CoFe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 multilayered thin films

The multiferroic (PMN-PT/CFO)_n (n = 1,2) multilayered thin films have been prepared on SiO₂/Si(1 0 0) substrate with LNO as buffer layer via a rf magnetron sputtering method. The structure and surface morphology of multilayered thin films were determined by X-ray diffraction (XRD) and atom force microscopy (AFM), respectively. The smooth, dense and crack-free surface shows the excellent crystal quality with root-mean-square (RMS) roughness only 2.9 nm, and average grain size of CFO thin films on the surface is about 44 nm. The influence of the thin films thickness size, periodicity n and crystallite orientation on their properties including ferroelectric, ferromagnetic properties in the (PMN-PT/CFO)_n multilayered thin films were investigated. For multilayered thin films with n = 1 and n = 2, the remanent polarization Pr are 17.9 μC/cm² and 9.9 μC/cm²; the coercivity H_c are 1044 Oe and 660 Oe, respectively. In addition, the relative mechanism are also discussed.     

Effect of thickness on the microstructure and soft magnetic properties of CoFeHfO thin films

The thickness effects on the microstructure and soft magnetic properties of CoFeHfO thin films have been investigated in the range of 100–600 nm. There was a significant change in the coercivity (H_c) and the anisotropy (H_k) value with increasing film thickness, but the saturation induction and the resistivity almost remain unchanged. H_c and H_k reached a minimum value of 0.19 Oe and a maximum value of 50 Oe, respectively at 200 nm film thickness. The high saturation magnetic induction is 21 kG and resistivity is 500 μΩ cm. The origin of the changing H_c and H_k values is discussed in detail based on change of microstructure along with film thickness.     

The influence of annealing on the structural and magnetic properties of C/CoCrPt/CrTi trilayer recording media

Post-deposition annealing was performed on trilayer films consisting of a C overcoat layer on top of CoCrPt/CrTi/glass substrate. We observed a coercivity of 3600 Oe in the films with a 4 nm C overcoat, which was about three times larger than the coercivity of similar films without a C overcoat. This is most likely due to the significant decrease in intergranular exchange coupling for the films with C overcoat, as shown by the annealing treatment. It is believed that the diffusion of C into CoCrPt grain boundaries promotes magnetic grain isolation.     

Effect of interfacial diffusion on microstructure and properties of FePt/B4C multifunctional multilayer composite films

FePt/B₄C multilayer composite films were prepared by magnetron sputtering and subsequent annealing in vacuum. By changing Fe layer thickness of [Fe/Pt]₆/B₄C films, optimal magnetic property (8.8 kOe and remanence squareness is about 1.0) is got in [Fe(5.25 nm)/Pt(3.75 nm)]₆/B₄C sample whose composition is Fe rich and near stoichiometric ratio. The characterizations of microstructure demonstrate that the diffusion of B and C atoms into FePt layer depends strongly on B₄C interlayer thickness. When B₄C interlayer thickness of [Fe(2.625 nm)/Pt(3.75 nm)/Fe(2.625 nm)/B₄C]₆ films is bigger than 3 nm, stable value of grain size (6-6.5 nm), coercivity (6-7 kOe) and hardness (16-20 GPa) is observed. Finally, the multifunctional single FePt/B₄C composite film may find its way to substitute traditional three-layer structure commonly used in present data storage technology.     

Effect of Co layer thickness on the magnetic properties of Tb30Co70/SiNx/Co thin films

The SiN_x (20 nm)/Tb₃₀Co₇₀ (90 nm)/SiN_x (5 nm)/Co (3–37 nm)/SiN_x (10 nm)/Si multilayer films are deposited on naturally oxidized Si wafer by magnetron sputtering. The saturation magnetization (M_s) of the multilayer films is increased with the thickness of high M_s ferromagnetic Co layer. The perpendicular coercivity (_Hc⊥$H_{{\mathrm{c}}^{\perp }}$) value is increased with Co layer thickness as the thickness of the Co layer is lower than 15 nm and then decreases drastically when the thickness of the Co layer further increased. The increase of the _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ value is owing to the interlayer exchange effect [Li Zhang, Physica B 390 (2007) 373] between TbCo and Co layers. Co under-layer with in-plane magnetic anisotropy would pin the magnetic moment of the TbCo layer near by the Co layer and cause the value of _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ to increase. However, as the Co layer is thicker than a critical thickness, the _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ value of the multilayer film would decrease. Therefore, the Co layer with in-plane magnetic anisotropy and soft magnetic properties is expected to dominate the magnetic properties of the multilayer films.     

Ablation of silicon suboxide thin layers

We investigate the ablation of SiO _x thin films on fused silica substrates using single-pulse exposures at 193 nm and 248 nm. Two ablation modes are considered: front side (the surface of a film is irradiated from above) and rear side (a film is irradiated through its supporting substrate). Fluence is varied from below 200 mJ/cm² to above 3 J/cm². SiO _x films of thickness 200 nm, 400 nm, and 600 nm are ablated. In the case of rear-side illumination, at moderate fluences (around 0.5 mJ/cm²) the ablation depth corresponds roughly to the film thickness, above 1 J/cm² part of the substrate is ablated as well. In the case of front-side ablation the single-pulse ablation depth is limited for all film thicknesses to less than 200 nm even at fluences up to 4 J/cm². Experimental results are discussed in relation to film thickness, fluence, and ablation mode. Simple numerical calculations are performed to clarify the influence of heat transport on the ablation process.     

A new method to preserve the c-axis growth of thick YBa2Cu3O7–δ films grown by pulsed laser deposition

YBa₂Cu₃O_7–δ (YBCO) films were prepared on (1 0 0) MgO substrates by pulsed laser deposition (PLD) method. In order to eliminate the a-axis growth, which is commonly observed in the YBCO film thicker than a critical value, we developed a new PLD target that was sintered at a temperature far below YBCO 123 phase formation. The surface analysis made by AFM technique confirmed that very fine particles of around 20 nm size could be ejected from the new target to the substrate. The fine oxide clusters could be easily moved and incorporated into the YBCO phase thus benefited the c-axis growth even in the thick films. For instance, only the c-axis growth in the new film with a thickness of about 650 nm was larger than a critical thickness of the a-axis growth. However, in the standard film of the same thickness, there is 24.5% of the a-axis growth accompanying the main c-axis growth. Therefore, the c-axis growth could be preserved in the very thick YBCO film by a non-superconducting target.     

Reduced dielectric loss and leakage current in CaCu3Ti4O12/SiO2/CaCu3Ti4O12 multilayered films

The CaCu₃Ti₄O₁₂/SiO₂/CaCu₃Ti₄O₁₂ (CCTO/SiO₂/CCTO) multilayered films were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition method. It has been demonstrated that the dielectric loss and the leakage current density were significantly reduced with the increase of the SiO₂ layer thickness, accompanied with a decrease of the dielectric constant. The CCTO film with a 20 nm SiO₂ layer showed a dielectric loss of 0.065 at 100 kHz and the leakage current density of 6×10⁻⁷ A/cm² at 100 kV/cm, which were much lower than those of the single layer CCTO films. The improvement of the electric properties is ascribed to two reasons: one is the improved crystallinity; the other is the reduced free carriers in the multilayered films.     

Pt插层对铁磁/反铁磁界面交换耦合的影响

在铁磁层(FM)/反铁磁层(FeMn)耦合体系中插入Pt 插层或对靠近FM/FeMn界面处的FeMn掺杂Pt元素,研究了体系的交换偏置场 H_ex及矫顽力H_c随Pt插层深度 d_Pt与Pt掺杂层厚度t_PtFeMn的变化关系. 实验结果表明,引入Pt插层后NiFe/FeMn(d_Pt)/Pt/FeMn体系的未补偿磁矩(UCS)的数量得到很大的提高,从而对H_ex与H_c 起到增强的作用; 同时, 从实验结果可以推测FeMn层内部UCS的分布深度约为1.3 nm. 另外,对靠近FM/FeMn界面处的FeMn掺杂Pt元素,发现掺入Pt元素后体系的H_ex 得到有效增强, 这是因为掺入Pt元素后体系UCS的数量也得到很大的提高.     

Influence of SiO2 additional layers on the laser induced damage threshold of Ta2O5 films

A series of Ta₂O₅ films with different SiO₂ additional layers including overcoat, undercoat and interlayer was prepared by electron beam evaporation under the same deposition process. Absorption of samples was measured using the surface thermal lensing (STL) technique. The electric field distributions of the samples were theoretical predicted using thin film design software (TFCalc). The laser induced damage threshold (LIDT) was assessed using an Nd:YAG laser operating at 1064 nm with a pulse length of 12 ns. It was found that SiO₂ additional layers resulted in a slight increase of the absorption, whereas they exerted little influence on the microdefects. The electric field distribution among the samples was unchanged by adding an SiO₂ overcoat and undercoat, yet was changed by adding an interlayer. SiO₂ undercoat. The interlayer improved the LIDT greatly, whereas the SiO₂ overcoat had little effect on the LIDT.     

Thickness dependence of superconductivity for In/Mo thin films

We report on the superconducting characteristics of the Indium thin films on molybdenum under-layer as a function of the In film thickness. Our molybdenum under-layer with thickness of 50 Å does not cause the occurrence of superconductivity until 1.5 K and the sheet resistance has logarithmic temperature dependence observed in the present investigation. As thickness of In increased, the oscillation phenomenon of T_C was observed at early stage of deposition and the value of T_C is higher than the that for bulk of In. Furthermore, it is found that with increase of the In thickness, there are large differences of the strengths of the upper critical magnetic field H_C2(T), resistivity and T_C between films with thickness below and above 100 Å. On the other hand, the T_C decreases monotonously as sheet resistance increases, when the T_C is plotted against sheet resistance. To clarify the relation of superconducting characteristics and the surface structure of the films with different thickness, we have performed surface observation by atomic force microscope. As a result, we have found that the surface changes from homogeneous structure to inhomogeneous (or percolative) structure, when the thickness of in films pass through about 100 Å. Superconductivity of In/Mo films with relatively thick-inhomogeneous films cannot be explained in terms of the simple percolation theory. Therefore, we analysis the experimental data of H_C2(T) near T_C, using a extended Landau–Ginzburg model. It is found out that our In/Mo films must consider some factors; such as, grain size, the distance of grain space, and the strength of couplings between grains.     

Structural, defect and optical properties of ZnO films grown under various O2/Ar gas ratios

Thin wurtzite (0 0 2) textured ZnO thin films were deposited on glass substrates by radio frequency magnetron sputtering under O₂/Ar ratios R varying from 0.05 to 1.0 at room temperature. The structure of, and defects in, the films were investigated by XRD, SEM and slow positron beam techniques. The XRD spectra showed that ZnO thin films were polycrystalline with hexagonal structure and a good c-axis orientation perpendicular to the substrate. The thickness, grain size and the crystalline quality of the films strongly depended on R; the larger grain size and thicker ZnO films were grown when R was lower. Positron beam Doppler broadening measurements showed that in low R films additional vacancy-type defects (e.g. Zn-related vacancy complexes or clusters) were formed. Photoluminescence spectra found that the film with R = 0.4 had the highest luminescence efficiency, in good agreement with the best c-axis preferential orientation. The transmittance spectra of the films decreased with decreasing R, due to the thickness effect. Correlations between microstructure, defect and optical properties are discussed.     

Preparation and characterization of Cd2Nb2O7 thin films on Si substrates

Thin Cd₂Nb₂O₇ films were grown on single-crystal p-type SiO₂/Si substrates by the metallo-organic decomposition (MOD) technique. The films were investigated by X-ray diffraction, X-ray energy-dispersive spectroscopy, and field emission scanning electron microscopy, and showed a single phase (cubic pyrochlore), a crack-free spherical grain structure, and nanoparticles with a mean size of about 68 nm. A Cauchy model was also used in order to obtain the thickness and index of refraction of the stack layers (transparent layer/SiO₂/Si) by spectroscopic ellipsometry (SE). The dielectric constant (K) of the films was calculated to be about 25 from the capacitance-voltage (C-V) measurements.