Bismuth ferrite bilayered thin films of different constituent layer thicknesses

Bilayered thin films consisting of (Bi_0.90La_0.10)(Fe_0.85Zn_0.15)O₃ and (Bi_0.90La_0.10)(Fe_0.90Zn_0.10)O₃ layers have been fabricated by radio frequency sputtering. Both multiferroic layers are well retained in these bilayers. Their leakage current, multiferroic properties, and fatigue behavior are largely dependent on the thicknesses of (Bi_0.90La_0.10)(Fe_0.85Zn_0.15)O₃. With an increase of the thickness in the (Bi_0.90La_0.10)(Fe_0.85Zn_0.15)O₃ layer, the leakage current density of bilayers is degraded due to different grain growth modes and an increase in oxygen vacancies, the dielectric constant (?_r) becomes larger due to the introduction of (Bi_0.90La_0.10)(Fe_0.85Zn_0.15)O₃ with a high ?_r value, and their magnetic properties are deteriorated with increasing the thickness ratios of (Bi_0.90La_0.10)(Fe_0.85Zn_0.15)O₃ with a weaker magnetization. All bilayers exhibit a good ferroelectric behavior regardless of varying thicknesses of the (Bi_0.90La_0.10)(Fe_0.85Zn_0.15)O₃ layer, while their coercive field decreases with increasing the thickness of the (Bi_0.90La_0.10)(Fe_0.85Zn_0.15)O₃ layer. An anomalous enhancement in switchable polarization is demonstrated by these bilayers, owing to the involvement of space charges accumulated at the interfaces between two constituent layers.     

Co/Pt multilayer-based pseudo spin valves with perpendicular magnetic anisotropy

Pseudo spin valves(SVs) exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt(5.0 nm)/[Co(0.4 nm)/Pt(0.6 nm)]3/Co(0.4 nm)/Cu(3.0 nm)and Cu(3.0 nm)/[Co(0.4 nm)/Pt(1.5 nm)]4, respectively.The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity(HC) of both layers. The perpendicular giant magnetoresistance(GMR) of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.     

Domain structure and magnetization curves of films with perpendicular anisotropy

Based on a two-dimensional micromagnetic simulation, the dependence of the period of a stripe domain structure on the thickness of Co(0001) and Ni(111) films has been obtained, which agrees well with the experimental data. A comparison has been carried out of the calculated and experimental hysteresis loops for a 50-nm Co film and 200-nm Ni film.     

Enhancement of post-annealing stability in Co/Ni multilayers with perpendicular magnetic anisotropy by Au insertion layers

Enhancement of post-annealing stability in Co/Ni multilayers with perpendicular magnetic anisotropy(PMA) was obtained by inserting Au layers into Ni/Co interfaces.After annealing at 350℃,the effective magnetic anisotropy density(K_(eff)) for Ta(3)/Pt(2)/[Co(0.3)/Ni(0.6)/Au(0.3)]×_3/Co(0.3)/Pt(l)/Ta(3)(in nm) keeps at0.48 ×10~5 J·m~(-3).Scanning transmission electron microscopy-high-angle annular dark field(STEM-HAADF)analysis shows that the diffusion between Ni and Co layers is obstructed by the Au insertion layers among them,which is responsible for the post-annealing stability enhancement of the multilayers.Multilayers with Pt insertion layers were also investigated as reference samples in this work.Compared with Pt-layer-inserted Co/Ni multilayers,the Au insertion layers are found to bring seldom interfacial PMA to the multilayers,making it competitive in being employed to enhance the post-annealing stability of PMA Co/Ni multilayers which are used for magnetic random access memory devices(MRAM).     

Investigation on interface of NiFeCr/NiFe/Ta films with high magnetic field sensitivity

NiFeCr/NiFe/Ta films with excellent performance were prepared by magnetron sputtering system.The anisotropic magetoresistance (AMR) value (△R/R) and magnetic filed sensitivity (Sv,Sv=[d(△R/R)/dH]max.) for the 12 nm NiFe film deposited on NiFeCr buffer layer were 3.66％ and 1.42 × 10-4 ％T-1,respectively.The higher Sv of the film is close to that of a spin valve (SV).The microstructure analysis shows that the NiFeCr buffer layer has adopted the same structure with the same interplanar distance as the NiFe layer,inducing a strong NiFe (111) texture,and that the NiFeCr/NiFe interface is quite smooth,leading to a high degree of specular reflection of conduction electrons.Both increase the △R and reduce the R in the film,which lead to the high △R/R.Clean substrate surfaces are critical for preparation of high performance NiFeCr/NiFe/Ta films,and sputter cleaning or pre-deposition of 5 nm amorphous A12O3 layer in the deposition chamber can provide the required clean substrate surfaces for the growth of the buffer layer.     

On the theory of a supercritical state of ferromagnetic films with uniaxial perpendicular anisotropy and (001) single-crystal films with positive constants of magnetocrystalline anisotropy

A model of the magnetization distribution in thin ferromagnetic films that are in the so-called supercritical state has been considered. The model makes it possible to take into account the real distribution of the magnetization more precisely in ferromagnetic films than open and closed models. The theoretical results have been compared to the experimental data.     

Magnetic anisotropy of Co/Cu/Co nanocrystalline films upon magnetic annealing

The magnetic anisotropy of Co/Cu/Co films with the thickness of the copper spacer corresponding to the antiferromagnetic and ferromagnetic indirect exchange coupling between Co layers has been studied. The films deposited on naturally oxidized (111) Si single crystals were produced by magnetron sputtering. The films were annealed at 240°C. Such an annealing virtually neither changes the grain size nor leads to the mixing of layers; i.e., no disturbance of the coupling type between the cobalt layers takes place. Changes in the surface and induced magnetic anisotropy and in the effective energy of indirect exchange coupling have been studied upon annealing in the presence and absence of a magnetic field. It has been found that the shape of surface inhomogeneities in the films changes upon annealing in the magnetic field applied along the film plane, which substantially affects, the surface anisotropy. In the films characterized by antiferromagnetic coupling, the easy axis of magnetization is induced only in the magnetic fields exceeding the saturation field. The induced-anisotropy constant estimated theoretically agrees well with those determined experimentally.     

Nuclear resonance reflection of synchrotron radiation from thin dysprosium films with different types of magnetic ordering

Epitaxial thin films of dysprosium have been successfully synthesized by the method of high-vacuum magnetron sputtering and their structure and magnetic properties have been investigated. The opportunity of the nuclear resonance scattering for the investigation of nanostructures containing ¹⁶¹Dy has been considered; the specific features of the spectra of nuclear resonance reflectivity from the films have been analyzed on the energy and time scales at different orientations of the magnetic hyperfine field. The simulation of the angular dependences of nuclear resonance reflectivity for the case of spiral ordering in periodic structures containing ¹⁶¹Dy has been carried out. It has been shown that these dependences make it possible to uniquely determine the period of magnetic ordering.     

One-dimensional dynamics of domain walls in a three-layer ferromagnetic structure with different parameters of magnetic anisotropy and exchange of the layers

The one-dimensional nonlinear dynamics of a domain wall under the effect of an external dc magnetic field in three-layer ferromagnets with different values of the parameters of magnetic anisotropy and exchange in the layers has been studied theoretically. Equations of motion for the coordinate of the center of a domain wall and for the velocity of its motion after passage from one layer into another has been found using perturbation-theory methods. It is shown that, in the case of small defects, the analytical results agree well with the numerical results. The minimum velocity required for a domain wall to pass from one layer into another has been found numerically as a function of the parameters of the material.     

Effective mass of vortexlike domain walls in magnetic films with an in-plane anisotropy

On the basis of the exact allowance for main interactions, including exchange, magnetoanisotropic, and dipole-dipole one, by numerically solving the nonlinear Landau-Lifshitz equation, time dependences of the velocities of motion of vortexlike domain walls which describe the transitions of the walls and their structures into a dynamic state have been found. Using these curves, the effective mass and the viscosity parameter of the domain wall have been found. Dependences of these parameters on the film thickness and field strength perpendicular to the easy axis have been determined. A substantial difference of the effective mass of vortexlike domain walls from the effective mass of one-dimensional Bloch walls has been established.     

Roles of interface roughness and internal stress in magnetic anisotropy of CoPt/AlN multilayer films

Magnetic anisotropy of CoPt/AlN multilayer films has been studied by systematically varying the nominal thickness of CoPt layers, t_CoPt (1–10 nm), and the annealing temperature, T_a (300–500 °C). The as-deposited films show in-plane magnetic anisotropy in the full range of t_CoPt, whereas the annealed films show perpendicular magnetic anisotropy (PMA) within small t_CoPt but change to in-plane magnetic anisotropy when t_CoPt is over a certain thickness. The critical thickness for such anisotropic transformations increases as the T_a increases. The maximum PMA obtained in this work is 1.13 × 10⁷ erg cm^?3. The interface roughness was analyzed by cross-sectional high-resolution electron microscopy and X-ray reflectivity using an abrupt interface model with a Debye exponent shape. The internal stress was analyzed by X-ray diffraction using an equal biaxial stress model. The results show that the CoPt/AlN interface roughness decreases from 0.385 nm to 0.158 nm and the internal stress increases from ?2.36 GPa (compressive) to 1.73 GPa (tensile), as the T_a increases to 500 °C. The roles of the interface roughness and the internal stress in the magnetic anisotropy of CoPt/AlN multilayer films are studied.     

Magnetooptical and magnetic properties of Fe/ZnTe/Fe nanoheterostructures: Manifestation of interlayer exchange coupling

Magnetooptical and magnetic properties of Fe/ZnTe bilayers and Fe/ZnTe/Fe sandwiches with a variable thickness of the semiconductor layer t _ZnTe = 6–24 Å prepared by magnetron sputtering on Si(100) substrates at room temperature have been studied. In the sandwiches, two ranges of thicknesses, t _ZnTe = 8–12 and 20–23 Å, were found at which the magnitude of the magnetorefractive effect (MRE) approximately twofold exceeds the magnitude of the MRE in the bilayers. In the field dependences of the transverse Kerr effect at ZnTe thicknesses corresponding to the greatest values of the MRE, two features have been found in the form of kinks (steps) which are absent in the case of bilayers. At the same thicknesses of the semiconductor layer, the magnetic measurements of trilayers revealed a sharp decrease in the imaginary component of the ac susceptibility with increasing temperature from 10 to 300 K. A conclusion is drawn on the appearance of a weak interlayer exchange coupling of the antiferromagnetic type in the Fe/ZnTe/Fe system with increasing temperature.     

Induced magnetic anisotropy and the structure of nanocrystalline Fe-Co-Cu-Nb-Si-B alloys with different content of Co: II structure of alloys with an induced magnetic anisotropy

A connection has been established between the structural state (phase composition) of the nanocrystalline alloys Fe_{73.5 ? x} Co _x Cu₁Nb₃Si_13.5B₉ (x = 0, 10, 20, 30) and the type of the induced magnetic anisotropy (IMA), which is formed in the process of thermomechanical treatment (TMechT), on the one hand, and its thermal stability, on the other hand. It is shown that the addition of cobalt entails a decrease in the quantity of Fe-Si grains and the formation of phases that contain Fe-Co-B. The induced magnetic anisotropy depends on the volume fractions of structural components, their elastic properties, and coherent bonding of their crystal lattices.     

Microstructures and mechanical properties evaluation of TiAlN/CrSiN multilayered thin films with different bilayer periods

The Ti_0.45Al_0.55N/Cr_0.75Si_0.25N nanoscale multilayered coatings were deposited periodically by a bipolar asymmetric pulsed DC reactive magnetron sputtering technique. The structures and bilayer period of multilayer coatings were characterized by an X-ray diffractometer. The surface and cross-sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The surface roughness of thin films was explored by atomic force microscopy (AFM). A nanoindenter, a micro Vickers hardness tester and pin-on-disk wear tests were used to evaluate the hardness, fracture toughness and tribological properties of the thin films, respectively. Six coatings with bilayer period ranges from 6 nm to 40 nm were produced in this work. It was observed that the hardness increased with increasing bilayer period and reached the maximum at 12 nm and then leveled off at periods larger than 12 nm. An optimal hardness, and plastic deformation resistance, as well as adequate tribological behaviors were found on the coating with a critical bilayer period of 12 nm.     

Zinc tin oxide thin films prepared by MOCVD with different Sn/Zn ratios

Zinc tin oxide(ZTO) thin films, with zinc acetate and tributyltin chloride as raw materials, were deposited on glass substrates by the method of metal organic chemical vapor deposition(MOCVD). The crystallization, microstructure and optical properties were investigated by scanning electronic microscope(SEM),X-ray diffraction(XRD) and ultraviolet-visible(UV-Vis)spectrophotometer. The results show that with the increase in Sn/Zn ratio, the crystal changes from wurtzite to rutile phase. When the ratio reaches 11:18,the intensity of Zn_2SnO_4 peaks appears to be the strongest and the optical band gap is about 3.27 eV. Calculated by the envelope method, the thickness of the ZTO thin films is 713.24 nm.Measured by UV-Vis spectrophotometer, the transmittance of the ZTO thin films reaches up to 80% in the wavelength range of 400-1000 nm when the Sn/Zn ratio is 7:18.     

Induced magnetic anisotropy and structure of nanocrystalline Fe-Co-Cu-Nb-Si-B alloys with different content of Co: I. Stress-annealing-induced magnetic anisotropy and its thermal stability

It is shown that the substitution of Co for Fe in the amorphous Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy leads to the change in the type of magnetic anisotropy induced in the alloy as a result of a thermomechanical treatment at 520°C. The type of the induced magnetic anisotropy determines the functional characteristics of these alloys as soft magnetic materials. With the content of Co in the alloy equal to 10 at % Co, there is induced a magnetic anisotropy with the direction of the easy axis across the ribbon axis (transverse induced magnetic anisotropy), just as in the alloy without Co. Upon the introduction of 20–30 at % Co into the alloy, the induced magnetic anisotropy becomes longitudinal, with the easy-axis direction along the ribbon axis. The thermal stability of the magnetic properties of the alloys with induced magnetic anisotropy has been investigated.     

Crystalline texture and magnetic anisotropy of Co-P films prepared by chemical deposition

Chemically deposited Co-P films with a P concentration of 2.5% have been studied by X-ray diffraction (Bragg geometry), electron microscopy, and magnetometry. The films have been found to represent a fine-grained medium in which the orientation of crystallites depends on the film thickness. At a thickness less than 70 nm, the films have a certain crystalline texture with a preferred orientation of the hexagonal axis c of the crystallites perpendicular to the film plane. With increasing film thickness, the character of the texture changes; the c axes of crystallites lie now predominantly in the film plane. At thicknesses exceeding 500 nm, the texture becomes stronger; the c axes are now distributed in the film plane equiprobably. These results can be used when producing magnetic media for longitudinal and transverse magnetic recording.     

含硼、磷添加剂对电沉积CoNiFe软磁薄膜的影响(英文)

采用循环伏安法制备CoNiFe、CoNiFeB和CoNiFeP软磁薄膜。采用SEM、EDS和XRD进行薄膜形貌、成分及相组成分析,应用振动样品磁强计(VSM)测量其软磁性能,并采用电化学阻抗谱(EIS)及极化曲线研究其腐蚀阻力。结果表明,电沉积CoNiFe、CoNiFeB和CoNiFeP软磁薄膜为晶态和非晶态混合体,含硼、磷添加剂可促进非晶相的形成;CoNiFe和CoNiFeB具有纳米结构;含硼添加剂可提高薄膜的致密度和阻力,并使矫顽力从851.48A/m降低至604.79A/m,而磁饱和强度基本不变。含磷添加剂可增加薄膜粒子的尺寸并降低其耐蚀性,并使CoNiFeP薄膜的矫顽力增加至12485.79A/m,磁饱和强度大幅度降低至1.25T。