Magnetic anisotropy of multilayer [Fe/Pt]n structures

The possibility of controlling the magnetic anisotropy of multilayer [Fe/Pt]n structures grown by magnetron sputtering of Fe and Pt plates by varying number n of layers is studied. Mössbauer spectroscopy data and measured magnetic hysteresis loops demonstrate that the multilayer [Fe/Pt]n structures at n = 16 have a predominantly perpendicular magnetic anisotropy. The results of X-ray photoelectron spectroscopy and micromagnetic simulation point to the presence of intermediate layers enriched in iron ions in the structures. The magnetic anisotropy perpendicular to the surface of the [Fe/Pt]n films at n = 16 is found to be caused by the anisotropy of the intermediate layers.     

Magnetic and magnetooptical properties of Fe/Pt and Fe/Pt/Fe thin-film magnetic structures

Results of a study of magnetic and magnetooptical properties of Fe/Pt double-layer and Fe/Pt/Fe three-layer thin-film magnetic structures are presented. A strong effect of the Pt layer on magnetic properties of the studied samples was revealed. It was established that the saturation field of three-layer magnetic structures has an oscillating magnitude with varying Pt layer thickness, and the oscillation period is a function of the Fe layer thickness. The data obtained are explained by the presence of exchange interaction between the Fe layers via the Pt layer. A strong effect of Pt on spectral dependences of the equatorial Kerr effect in the thin-film structures under study is revealed.     

Ferromagnetic resonance in multilayer [Fe/Cr]n structures with noncollinear magnetic ordering

The excitation spectrum in an [Fe/Cr]n multilayer structure with non-collinear magnetic ordering was studied by the ferromagnetic resonance (FMR) method in the frequency interval 9.5–37 GHz at room temperature. Besides an acoustic branch, several additional modes were observed under parallel excitation of resonance. The FMR spectrum was calculated analytically in a biquadratic exchange model, neglecting in-plane anisotropy, for an infinite number of layers in the structure and numerically for a finite number of layers contained in real samples. It was shown that the observed modes correspond to excitation of standing spin waves with wave vectors perpendicular to the film plane. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 690–695 (10 May 1998)     

Structure and magnetic properties of Fe/Cu multilayered films

Mutually insoluble Fe/Cu multilayered films prepared by a dc-magnetron sputtering system with a rotating substrate-holder have been studied. The periodicity of the multilayers was confirmed by X-ray diffraction. The results of magnetization measurements and Mössbauer spectroscopy at 300 and 77 K show that the samples with the Fe layer thinner than 9 Å exhibit superparamagnetism. The temperature dependence of the spontaneous magnetization follows Bloch's law for all samples, with the spin-wave temperature coefficient B inversely proportional to the thickness of the Fe layer. The results of torque measurements show that the magnetization is normal to the film plane for the samples with the Fe layer thinner than 6 Å.     

Magnetic properties and structures of Fe/MgF2 multilayered films

Multilayers composed of Fe and MgF₂ with layer thicknesses between 9 Å and 100 Å and of 30 Å, respectively, were prepared with an ultrahigh-vacuum deposition technique. Medium-angle X-ray data show that the Fe layers in the BCC phase have considerable (1 1 0) texture. Periodicity due to multilayered structures was confirmed by a small-angle X-ray diffraction study and cross-section transmission electron microscope for films with Fe layer thicknesses >45 Å. In an Fe/MgF₂(9 Å/30 Å) sample, an island structure for the Fe layers was suggested by the existence of superparamagnetism in a film. At 4.2 K, enhancements of both magnetization and hyperfine field were observed in films having Fe layers thinner than 40 Å. The maxima in the magnetization (233 emu/g of Fe) and in the average hyperfine field (390 kOe) at 4.2 K were found in an Fe/MgF₂(9 Å/30 Å) film and were approximately 105% and 115% that of the bulk α-Fe, respectively. The thickness dependence suggests a 12% enhancement in the magnetic moment of interface Fe atoms. No exchange bias was found in the films, implying that antiferromagnetic fluorides are not formed at the interface, which is different from the case of Fe/LiF and Fe/CaF₂ multilayers.     

Structure and magnetic properties of magnetron-sputtered [(Fe/Pt/Fe)/Au]n multilayer films

Using dc magnetron sputtering, Fe/Pt/Au multilayer films were prepared, and the effects of Au layer thickness and annealing temperature on structure and magnetic properties of the Fe/Pt/Au multilayer films were investigated. The as-deposited Fe/Pt/Au multilayer films have good periodic structure with composition modulation along the growth direction. The stress stored in the as-deposited films promoted the ordering of the films annealed at 400 °C. When the films were annealed at 500 °C, the thicker Au layer could restrain the order-disorder transformation region volume and lead to the decrease of the ordered volume fraction with Au layer thickness increasing.     

Thickness-dependent magnetic properties in Pt/[Co/Ni]n multilayers with perpendicular magnetic anisotropy

We systematically investigated the Ni and Co thickness-dependent perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain structures, and magnetization dynamics of Pt(5 nm)/[Co($t_{\rm Co}$)/Ni($t_{\rm Ni}$)]$_{5}$/Pt(1 nm) multilayers by combining the four standard magnetic characterization techniques. The magnetic-related hysteresis loops obtained from the field-dependent magnetization $M$ and anomalous Hall resistivity (AHR) $\rho_{{xy}}$ showed that the two serial multilayers with $t_{\rm Co} = 0.2$ nm and 0.3 nm have the optimum PMA coefficient $K_{\rm U}$ as well as the highest coercivity $H_{\rm C}$ at the Ni thickness $t_{\rm Ni}= 0.6 $ nm. Additionally, the magnetic domain structures obtained by magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the thickness and $K_{\rm U}$ of the films. Furthermore, the thickness-dependent linewidth of ferromagnetic resonance is inversely proportional to $K_{\rm U}$ and $H_{\rm C}$, indicating that inhomogeneous magnetic properties dominate the linewidth. However, the intrinsic Gilbert damping constant determined by a linear fitting of the frequency-dependent linewidth does not depend on the Ni thickness and $K_{\rm U}$. Our results could help promote the PMA [Co/Ni] multilayer applications in various spintronic and spin-orbitronic devices.     

The structures and magnetic properties of Cr/Fe and Mn/Fe thin films

Cr_1-x Fe _x and Mn_1-x Fe _x films were prepared at room temperature by thermal coevaporation at a deposition rate of about 25 Å/min. It was found that an amorphous phase can be obtained for Cr_1-x Fe _x (0.25<x<0.60) films, while a metastable-Mn-type phase was observed for Mn_1-x Fe _x (x<0.70) films. The influence of the structure on the magnetic properties has been studied. The amorphization ability of the two systems was discussed in terms of thermodynamic considerations.     

Bi surfactant effects of Co/Cu multilayered films prepared by sputter deposition

The influence of a Bi surfactant layer on the structural and magnetic properties of Co/Cu multilayers grown onto Cu(1 1 0) buffer layer by RF magnetron sputtering has been studied. The results of X-ray diffraction revealed the initial deposition of a 2.0 Å-thick Bi layer onto the Cu buffer layer prior to the deposition of the Co/Cu multilayer yielded high-quality fcc-(1 1 0) oriented epitaxial films. The X-ray photoelectron spectra revealed that Bi was segregated at around the top of the surface. Therefore, Bi was concluded to be an effective surfactant to enhance the epitaxial growth of Co/Cu(1 1 0) multilayer. The maximum giant magnetoresistance and antiferromagnetic interlayer coupling ratios of the Co/Cu multilayers were increased by using the Bi surfactant layer.     

多层膜［Co85Cr15/Pt］20的磁性、垂直磁记录特性和微结构的关系

采用磁控溅射法制备了性能优良的以Pt为缓冲层的［Co85₈₅Cr15_{15/Pt］2020 多层膜，研究了溅射气压对［Co8585Cr1515/Pt］2020多层膜微结构和磁性的 影响.研究结果表明，Ar溅射气压对［Co8585Cr1515/Pt］2020多层膜的微结构 、垂直磁各向异性和矫顽力有重要的影响 关键词： 溅射气压 多层膜 垂直磁各向异性 有效磁各向异性常数}     

Optical and magneto-optical properties of Co/Pt multilayered films

Both experimental and computer-simulated magneto-optical (MO) and optical spectroscopies of Co/Pt multilayered films (MLF) with a nearly constant Pt sublayer thickness and variable Co sublayer thickness, as well as pure Co and Pt, and Co_0.51Pt_0.49 alloy films, have been performed in the energy range 1.1–4.7 eV. The simulations were achieved by solving the multireflection task for various models of the MLF. The comparison between experimental and computer-simulated optical properties of the Co/Pt MLF allowed us to evaluate the thickness of the interfacial regions with the alloyed components. The diagonal and off-diagonal components of the optical conductivity tensor were calculated not only for the pure Co and Co_0.51Pt_0.49 alloy films, and the whole Co/Pt MLF, but also for the spin-polarized Pt layers in the Co/Pt MLF.     

Microstructure and optical properties of Ge films prepared by ion beam assisted deposition

Germanium （Ge） films are prepared on BK7 glass and multispectral zinc sulfide （m-ZnS） substrates by ion beam assisted deposition （IBAD）. The effects of substrate temperature, deposition rate, and ion energy on the microstructure and optical properties of the films are investigated. It can be concluded that Ge film deposited with higher rate or ion energy has more optical absorption, while ion energy below 150 eV helps to reduce film absorption. Film refractive index increases with film deposition rate and bombardment ion energy while it is below 300 eV. And higher growth rate or bombardment ion energy can weaken film diffraction intensity.     

Microstructures and magnetic properties of FePt permanent magnets

We have investigated the magnetic properties of Fe38.5Pt, Fe39.5Pt and Fe50.0Pt (at%) alloys after various heat treatment conditions using a vibrating sample magnetometer, and correlated these properties with the microstructures of the alloys by transmission electron microscopy. The Fe50Pt alloy shows poor magnetic hardness regardless of the heat treatment conditions. The magnetic hardness of the Fe39.5Pt alloy shows a maximum value after annealing for 10 h at 873 K, while it monotonically decreases after annealing at 1073 K. The alloy with the highest coercivity was composed of a single phase γ₁ with an average domain size of approximately 10 nm. The electron diffraction results indicate that the alloy is frustrated with accumulated stress, induced by a cubic → tetragonal transformation which occurs without twinning. On the other hand, when stress is relieved by twin formation after prolonged aging, the coercivity decreases. By annealing at 1073 K, the well known polytwin structure evolves. However, only poor hard magnetic properties are observed when this polytwin structure appears. Hence, the highest coercivity is attributed to the formation of nanoscale L1₀ ordered antiphase domains which is expected to be a highly anisotropic single domain magnetic particle.     

[(Fe/Pt/Fe)/Ag]n多层膜低温合成分离的L10相FePt纳米颗粒

制备了[(Fe/Pt/Fe)/Ag]n多层膜,研究了不同温度退火后的微结构和磁特性.实验结果表明温度高于400℃退火后,样品开始形成L10相的FePt纳米颗粒与Ag基体的复合结构.△M曲线的测量表明FePt颗粒之间不存在交换作用,非常清楚地说明非磁基体Ag有效地隔离了FePt磁性颗粒.有序相的低温合成可能和多层膜结构所造成的界面扩散以及Ag层引入的界面缺陷有关,同时,Ag原子较强的迁移性以及FePt与Ag之间表面自由能的显著差异,使FePt纳米颗粒被Ag隔离.     

Structure and magnetic anisotropy of Fe/Pt multilayers

A series of Fe/Pt multilayers prepared by magnetron sputtering have been studied by XRD, conversion electron Mössbauer spectroscopy (CEMS) and SQUID magnetometry. The samples with individual Fe thickness of 3 Å show orientation of the magnetic moment close to perpendicular to the film plane and Curie temperatures near 350 K. Interdiffusion at the interface is manifested in a distribution of hyperfine fields.     

Microstructure and magnetic properties of Co-Cu nanowire arrays fabricated by galvanic displacement deposition

CoCu nanowires were fabricated in anodic alumina templates by a simple metal displacement deposition method and the as-deposited samples were subsequently annealed at 400 °C in vacuum. The CoCu nanowires are 80 nm in diameter and 50 μm in length. The aspect ratio (ratio of length to diameter) is larger than 600, which results in distinctive magnetic anisotropy. Enhanced coercivity (about 2245 Oe) and large squareness of 92% have been observed in the annealed samples.