The Spin Wave Gap and Switching Field in Thin Films with In-Plane Anisotropy

In this paper, we have calculated the spin wave gap and the angular dependence of magnetization reversal in a single-layer thin magnetic film that includes the strong perpendicular magnetic anisotropy and in-plane anisotropy. The film is assumed to be under the influence of the out-of-plane direction of the applied magnetic field at zero temperature. Using the quantum model, it is shown that the calculated equations present a nonzero spin wave gap at zero magnetic field which is strongly affected by anisotropies. The effects of the in-plane anisotropy and the role of the applied field were examined. We also discussed a simple theoretical model for the angular variation of switching field by using a quasi-classical argument. We used some constants in connection with experimental data which are reported for chromium telluride thin films grown by molecular beam epitaxy.     

Random Magnetic Anisotropy Studies in SmCo<Subscript>5</Subscript> Thin Films

SmCo₅ thin films with different thicknesses were prepared by electron beam evaporation on Kapton substrates. The out-of-plane hysteresis loops for different thicknesses reveal a maximum coercive field when the thickness is 15 nm. Using random magnetic anisotropy model, the thickness dependence of magnetic properties was studied in SmCo₅ nanocrystalline films and several fundamental magnetic parameters were extracted. We have determined the local magnetic anisotropy constant K ₁ which is found to increase with increasing film thickness except for t =?7 nm which is thought to arise from the structural imperfection of the SmCo₅ films.     

Experimental Determination of the Q-factors of Microcantilevers Coated With Thin Metal Films

Abstract:  Microelectromechanical systems (MEMS) are typically fabricated out of materials that are mechanically sound at the microscale, but can be relatively poor electrical conductors. For this reason, areas of MEMS can be coated with various thin metal films to provide electrical pathways. These films, however, may drastically alter mechanical properties of the device. In this paper we investigate how metallization of microcantilevers affects the quality factors, (Q). Using two sets of silicon microcantilevers that are coated with aluminium films from 5 nm to 30 nm thick, on one side and two sides, respectively, the Q-factors are experimentally determined using the ring-down method. The ring-down method entails mechanically exciting the microcantilevers at their fundamental resonance frequency, abruptly stopping the excitation, and then measuring the decay of oscillation amplitude as a function of time. From this ring-down curve, the Q-factor of each microcantilever can be determined. Results show that the greater the thickness of the aluminium film, the lower the Q-factor will be. We also show a significant temperature dependency of the Q-factor of aluminium coated microcantilevers.     

Studies of the Vortex Related Phase Transition in YBCO Thin Films with Strong In-Plane Anisotropy

We have studied the vortex-related phase transition in a number of YBCO thin films that have in-plane anisotropy due to the c-axis lying at an angle to the substrate normal. The critical parameters T _t , z, and have been extracted from the scaling of dc I-V measurements made along the two principal transport directions in magnetic fields up to 1 tesla. The dependence of T _t upon the direction of the transport current in some classes of film and the very high z values cast doubt upon the established interpretation based simply upon a vortex liquid–vortex glass phase transition.     

Rotation Speed-Induced Uniaxial In-Plane Anisotropy in Thin Films Deposited Onto a Rotating Substrate

The Rotating Cryostat system consists of a rapidly rotating, liquid-nitrogen-cooled drum, around which a substrate can be placed. The possibility of using multiport sources gives the system wide capabilities for producing new materials. The effects of various rotation speeds of 1900, 1500, 1000, 500, and 0 rpm on the magnetic properties of thin iron films deposited on different (glass, silicon, and Kapton) substrates from a resistively heated evaporation source and a dc sputtering source have been investigated. Magnetic measurement showed that the films have an in-plane magnetic anisotropy for all films deposited at high speeds on all types of substrates and the degree of magnetic anisotropy decreased with decreasing rotational speed for flexible Kapton substrate. While the glass and silicon substrates was stationary, in-plane magnetic anisotropy of the films dropped down to zero. The films deposited on Kapton showed the rotational-speed-dependent magnetic properties. Estimation of magnetic anisotropy confirms in-plane anisotropy in the films. Furthermore, as expected for all iron films no magnetic anisotropy perpendicular to film plane was observed irrespective of rotation speed and type of substrate used.     

Analysis of the Anisotropy Field and the Saturation Magnetization for Ultrathin Ferromagnetic Films

We study the magnetic in-plane anisotropic fields for a two-dimensional film by including magnetic field in the basal plane for an easy axis film. We present the balance between the applied field and in-plane anisotropic field at equilibrium. We have also investigated the approach to saturation of magnetization and numerically solving the nonlinear equation for equilibrium, and results are discussed in connection with experimental data reported for Co films.     

Field Effects in Thin Films of Manganites Using a Planar Field Effect Configuration

Modulation of the metal-insulator phase transition of perovskite manganite oxides is achieved by a static electric field. The field is applied using a planar field-effect configuration, which was formed on a monolayer film. In such a field-effect configuration, La_1−x A _x MnO₃ film is used as the channel and substrate acts as the gate. Both divalence-doped (La_0.7Ba_0.3MnO₃, Pr_0.7Sr_0.3MnO₃), and tetravalence-doped (La_0.7Ce_0.3MnO₃) systems demonstrate significant field effects. The field modulations are found being nonlinear and polarity dependent on the applied bias. The results obtained in La_0.7Ce_0.3MnO₃ indicates that electron doped manganites have similar features as those found in hole doped manganites. The observed field effects were discussed with the percolative phase separation picture.     

Asymmetry of the Pinning Force in Thin Nb Films in Parallel Magnetic Field

The pinning force, F _p, is studied in Nb films of different thickness in parallel magnetic field H. The asymmetry in the magnetic field dependence of F _p has been observed for two opposite directions of the transport current. The effect is less pronounced for thin and thick films where, respectively, single vortex pinning and pinning of the internal vortices, is relevant. At intermediate thickness, where the pinning mechanism is mostly caused by surface effects, an asymmetry in the F _p(H) dependence is clearly visible. The different surface barriers that vortices should overcome to enter the sample from opposite sides of the film explain the effect, as confirmed by numerical calculations. These have been obtained by solving the Ginzburg?CLandau equations with asymmetric boundary conditions which take into account the different superconducting properties of the film?Csubstrate and film?Cvacuum interface. Such difference can also explain the reduction of the critical current usually observed in thin films as a function of their thickness.     

Parallel Critical Field in Thin Niobium Films: Comparison to Theory

For the first time, a comparison to the predicted behavior for parallel critical field is carried out for the model of Kogan and the model of Hara and Nagai. In this study, thin niobium films in the moderately dirty regime were considered. Experimental values of the \(-C_{2}\) term are seen to be lower than those from the model of Hara and Nagai. A possible reason for this could be not including the non-spherical Fermi surface of niobium into the model. There is clearly disagreement with the model of Kogan as the films get cleaner and thinner, and two films which should be below his critical thickness still show positive values of \(-C_{2}\), in disagreement with his theory.     

Magnetic Anisotropy Dispersion in FeCo Films

We report on our study of magnetic and nonmagnetic parameters such as coercivity, anisotropy , magnetic dispersion, and stress on FeCo films of various thicknesses from 25 A to 500 A . We used 10 A Ru or NiFe seed layers for two sets of FeCo films. All films showed so-called hard-axis coercivity rocking, i.e., the hard-axis coercivity exhibits two local minima close to the nominal hard axis. Magnetic properties and stress change dramatically with FeCo thickness, but with little difference between the two types of seed materials. We found a correlation between the angular separation of the two local coercivity minima and easy-axis coercivity. The results stress the need to differentiate between two levels of dispersion, one at the microscopic and the other at the macroscopic level.     

碳纳米管薄膜的湿敏特性测试

分别对修饰的和未修饰的多壁碳纳米管(MWCNTs)薄膜的湿敏特性进行了研究,发现修饰的多壁碳纳米管(MWCNTs)薄膜对湿度十分敏感.测量其湿敏特性表明:其电阻值随相对湿度有明显的变化,并呈线性关系,通过拟合计算得到修饰的和未修饰的多壁碳纳米管电阻率相对湿度系数分别为2.354×10-2Ω·m/RH和1.534×10-2Ω·m/RH.研究结果表明,碳纳米管在湿度传感器领域将有巨大的应用前景.     

用组合靶溅射制备Nd2Fe14B薄膜的研究

采用单质Ｆｅ、Ｎｄ、Ｂ组成的靶,用对向靶溅射系统制备出了含有Ｎｄ２Ｆｅ１４Ｂ相的薄膜。发现Ｎｄ２Ｆｅ１４Ｂ相能够较好地形成的基板温度范围是５００℃￣６００℃。并且相对于热氧化硅基板（ＳｉＯ２／Ｓｉ）,Ｎｄ２Ｆｅ１４Ｂ相能够较好地在Ｔａ基板上形成。     

Spontaneous Perpendicular Anisotropy in Ultra-thin Ferromagnetic Films

An atomistic scale study of ultra-thin ferromagnetic films was carried out using Monte Carlo simulations with Metropolis dynamics, and the simulations were performed using a Heisenberg Hamiltonian, surface and crystalline anisotropies, and dipolar interaction. We defined an ?? parameter to bind the dipolar interaction with the anisotropy in order to show how the system would behave at different ratios and scale up the dipolar interaction to observe its effects on small manageable systems. The results show a strong dependency of the shape of the magnetization curves for in-plane and out-of-plane measurements with our ?? parameter. We also included several measures of the magnetization direction at T = 2.5 K after a cooling process, and they show a critical thickness for an ?? below which the magnetization will spontaneously beat the shape anisotropy and become perpendicular to the surface at low temperatures. As a side note, our study also shows results consistent with previous simulations that focused in a in-plane to out-of-plane transition of the magnetization when going from high temperature to low temperature.