Oxygen vacancy control of electrical,optical, and magnetic properties of Fe0.05Ti0.95O2 epitaxial films

High-quality Fe-doped TiO₂ films are epitaxially grown on MgF₂ substrates by pulsed laser deposition. The x-ray diffraction and Raman spectra prove that they are of pure rutile phase. High-resolution transmission electron microscopy (TEM) further demonstrates that the epitaxial relationship between rutile-phased TiO₂ and MgF₂ substrates is 110 TiO₂₂. The room temperature ferromagnetism is detected by alternative gradient magnetometer. By increasing the ambient oxygen pressure, magnetization shows that it decreases monotonically while absorption edge shows a red shift. The transport property measurement demonstrates a strong correlation between magnetization and carrier concentration. The influence of ambient oxygen pressure on magnetization can be well explained by a modified bound magnetization polarization model.     

EuS/Ta异质结的极大磁电阻效应

在铁磁/超导异质结中,铁磁体的交换场通过近邻效应将导致超导体准粒子态密度的塞曼劈裂.基于该效应,在外磁场不强的情况下,通过外加磁场可以有效地调节铁磁/超导界面处的交换作用,从而实现超导体在正常态和超导态之间转换,产生极大磁电阻.本文利用脉冲激光沉积方法制备了EuS/Ta异质结并研究了其电磁特性.Ta在3.6 K以下为超导态,EuS在20 K以下为铁磁态.在2 K时,EuS/Ta异质结中可观测蝴蝶型磁滞回线,证明在低磁场下(<±0.18 T)异质结中EuS铁磁态和Ta超导态共存.磁输运测试表明,通过施加外磁场可以有效调节EuS的交换场,随着交换场的增大,同时也加强了界面处的交换作用,从而抑制Ta的超导态,实现了Ta在超导态和正常态之间的转变,在EuS/Ta异质结中观测到了高达144000%的磁电阻.本文制备的EuS/Ta异质结具有极大磁电阻效应,在自旋电子学器件中有潜在的应用前景.     

Optical manipulation of coupled spins in magnetic semiconductor systems: A path toward spin optoelectronics

Experimental results based on the optical excitations in the III–V-based ferromagnetic semiconductors are reviewed. On the bases of results obtained by both cw- and femto-second-pulse optical excitation, we point out the feasibility of magnetization rotation in the hole-mediated ferromagnetic semiconductor (Ga,Mn)As via the angular momentum and photon energy of light. Here, p–d exchange interaction is the effective channel that transmits a small change in spin axis of the valence band to the ferromagnetically coupled Mn spin sub-system. Within the limit of this picture, we also discuss a hole–Mn spin complex for which hole and Mn spins rotate and relax together upon optical excitation. Partial magnetization reversal observed in the experiments of the electrical current injection in (Ga,Mn)As-based magnetic-tunnel-junction devices is also reviewed in view of the effects caused by the spin-polarized holes. Here, we point out that a spin current of 10⁵ A/cm² may be reduced further if spin injection efficiency can be improved by the optimal designs of the device structure.     

Percolative transport in the vicinity of charge-order ferromagnetic transition in a hole-doped manganite

We report measurements of non-linear charge transport in epitaxial (La_1−x Pr _x )_0.7Ca_0.3MnO₃ thin films fabricated on (100) oriented SrTiO₃ single crystals by pulsed laser deposition. The end members of this series, namely Pr_0.7Ca_0.3MnO₃ and La_0.7Ca_0.3MnO₃ are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr_0.7Ca_0.3MnO₃ is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×10⁵ V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters dispersed in a CO background.     

An investigation of phase separation by magnetic force microscopy in La0.45Sr0.55MnO3-δ(δ≈0.01)

We have found phase separation in La_0.45Sr_0.55MnO_3-δ (LSMO) by means of electron spin resonance, magnetic force microscopy (MFM) and magnetic measurements. Ferromagnetic and antiferromagnetic phases can coexist at low temperatures, and ferromagnetic and paramagnetic phases coexist when the temperature lies between the Néel and Curie temperatures. The size and shape of the ferromagnetic phases (the minority phases) was first observed directly from MFM images. It is suggested that the phase separation in LSMO is not the charge segregation type, but an electroneutral type due perhaps to the nonuniform distribution of oxygen vacancies.     

永磁体等效磁矩的测量

在磁技术应用中，对永磁材料的主要磁性参数的研究及测量已成为人们关注的问题之一．本文提出通过测量磁场从而确定永磁体磁矩的一种简便方法，并就测量所涉及的有关问题作了讨论．     

光频支声子对二维Heisenberg铁磁系统磁激发的影响

在二维复式正方Heisenberg铁磁系统的基础上建立了磁振子-声子相互作用模型. 利用松原格林函数理论研究了系统的磁激发，计算了布里渊区的主要对称点线上的磁振子色散曲线，比较了光频支声子与声频支声子对系统磁激发的影响以及各项参数的变化对磁振子软化的影响. 发现光频支声子-磁振子耦合对磁振子软化起主要作用，尤其是纵向光频支声子对磁振子软化起更大的作用，并且非磁性离子的光频支声子对磁振子软化的作用比磁性离子的光频支声子对磁振子软化的作用更显著.     

横向磁场激励下铁磁梁式板的混沌运动分析

在磁体力分布的磁弹性理论模型和磁场准静态假定模式基础上，对于处在周期时变磁场 中的不可移简支铁磁梁式板非线性磁弹性动力特性进行定性与定量分析．首先利用磁场的摄 动技术和结构变形的模态法，导出了关于模态坐标的非线性动力方程；然后利用Ｍｅｌｎｉｋｏｖ方 法，从理论上给出这一磁弹性动力系统可能出现混沌运动的必要条件及参数范围；最后采用变 步长Ｒｕｎｇｅ－Ｋｕｔｔａ数值积分方法对其磁弹性相互作用的混沌现象进行了定量搜索与模拟，并 利用其轨迹的Ｐｏｉｎｃａｒｅ截面图与Ｌｉａｐｕｎｏｖ指数加以判断．结果表明磁弹性简支梁式板在横 向周期时变磁场中存在混沌吸引子，且在机械阻尼很小时其混沌吸引子表现出稠的特性．     

Mathematical models arising from a survey of ferromagnetic materials under magnetisation

Ab This paper focuses on mathematical models describing the mechanical behavior of ferromagnetic materials under magnetization. Through combination of the electromagnetic field theory with the theory of elastic mechanics, several nonlinear systems of fourth-order partial differential equations were deduced. By making further assumption, the first-order approximation of the above equations was established, of which the solutions are good enough for engineering application.     

ANALYSIS ON THE MAGNETO-ELASTIC-PLASTIC BUCKLING/SNAPPING OF CANTILEVER RECTANGULAR FERROMAGNETIC PLATES

An analysis of buckling/snapping and bending behaviors of magneto-elastic-plastic interaction and coupling for cantilever rectangular soft ferromagnetic plates is presented.Based on the expression of magnetic force from the variational principle of ferromagnetic plates,the buckling and bending theory of thin plates,the Mises yield criterion and the increment theory for plastic deformation,we establish a numerical code to quantitatively simulate the behaviors of the nonlinearly multi-fields coupling problems by the finite element method.Along with the phenom- ena of buckling/snapping and bending,or the characteristic curve of deflection versus magnitude of applied magnetic fields being numerically displayed,the critical loads of buckling/snapping, and the influences of plastic deformation and the width of plate on these critical loads,the plastic regions expanding with the magnitude of applied magnetic field,as well as the evolvement of deflection configuration of the plate are numerically obtained in a case study.