The hysteresis loops of FM/AFM two-layer Bethe lattice

The distinct hysteresis loops (HLs) of ferromagnetic/antiferromagnetic (FM/AFM) two-layer Bethe lattice with the Ising spins of the top layer having only FM interactions and the bottom ones having only AFM interactions with the interlayer coupling is either FM or AFM type are studied by using a pairwise approach. The sublattice magnetizations are studied by increasing and decreasing the external magnetic field (H) to obtain the HLs. The shapes of the HLs are strongly dependent on the competitions among the system parameters and on the phase configurations. The HLs are formed only when the AFM-type interactions are involved. The small loops of hysteresis are also formed because of the reentrant behavior in the FM region.     

GdFeCo/TbFeCo磁超分辨磁光记录薄膜研究

用磁控溅射法制备了GdFeCo/TbFeCo交换耦合两层薄膜,利用不同温度的克尔磁滞回线和VSM磁滞回线研究了读出层(GdFeCo)变温磁化方向变化过程.结果表明,随温度升高读出层从平面磁化转变为垂直磁化,交换耦合两层薄膜具有中心孔探测磁超分辨的基本性能.转变过程主要受饱和磁化强度（M_s）的影响,在GdFeCo的补偿温度附近,读出层的磁化强度较小,退磁场能也较小,在交换耦合的作用下,使读出层(GdFeCo)的磁化方向发生转变.磁化方向的转变在75℃~125℃的温度范围内变化较快.     

Piezoelectric activity of thin PTZ films

The manifestations of the piezoelectric activity of thin ferroelectric PZT films produced by high-frequency cathode sputtering of targets of a stoichiometric composition are studied. The films are found to have natural unipolarity. Possible causes of this phenomenon are discussed. A family of piezoelectric hysteresis loops is experimentally recorded at various frequencies and strengths of an applied bias field. The dependences obtained are compared to classical dielectric hysteresis loops.     

Magnetization reversal in (0 0 1)Fe thin films studied by combining domain images and MOKE hysteresis loops

The magnetization reversal of epitaxial single-crystal Fe films has been studied by combining domain images and hysteresis loops. The reversal is quantitatively described by combining the coherent rotation model and the domain wall displacement model. The pinning energy exerted on the domain walls and the domain wall angle at the switching fields are obtained by fitting this model to experimental hysteresis loops. The field-dependent pinning energy and the domain wall angle in the reversal process, and the contributions of second-order magneto-optic effect to hysteresis loops, are revealed to be two important features of single-crystal Fe films.     

Tuning the coercive field of Ni and CuNi thin films with the embedding of Co nanoparticles: An element-specific study

Cobalt nanoparticles have been embedded either within magnetic thin films of CuNi or Ni, or at their interface with an Al capping layer. Soft X-ray magnetic circular dichroism (XMCD) was used to measure element-specific hysteresis loops, allowing discrimination between the nanoparticles and the host film. The hysteresis shows coupling between the nanoparticles and the films and a reduction in coercivity is observed when positioning the nanoparticles within the film, as opposed to at its interface with the cap. Sum rule analysis of the XMCD spectra makes it possible to determine the orbital to spin moment ratios for Co and Ni in the samples. The difference in the calculated ratios is consistent with the differences in the coercivities, the films appearing more homogenous due to hybridization of the 3d bands of Co and Ni when the nanoparticles are embedded deeper within the films, creating less pinning sites and hence a lower coercivity.     

Measurement of magnetostatic coupling in two-layer ferromagnetic films on a transverse-field magnetometer

A procedure is described for measuring the magnetic properties of two-layer ferromagnetic films on a magnetometer with a transverse field. Measurements of positive and negative coupling between ferromagnetic layers separated by a nonmagnetic layer are reported.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 93–96, September, 1969.     

Nd28Fe66B6/Fe50Co50双层纳米复合膜的结构和磁性

利用磁控溅射法制备了Nd₂₈Fe₆₆B₆/Fe_{50Co50 双层纳米复合磁性薄膜，研究了其结构和磁性.经873K退火处理15min 后，利用x射线衍射仪测定薄膜晶体结构，采用俄歇电子能谱仪估算薄膜厚度和超导量子干 涉仪测量其磁性.磁性测量表明，1)该系列薄膜具有垂直于膜面的磁各向异性.从起始磁化曲 线和小回线的形状特征可知，矫顽力机制主要是由畴壁钉扎控制.2)对于固定厚度（10nm） 层的硬磁相Nd-Fe-B和不同厚度（dFeCo=1—100nm）层软磁相FeCo双层纳米复合 膜,剩磁随软磁相FeCo 厚度的增加快速增加，而矫顽力则减少.当dFeCo=5nm 时 ，最大磁能积达到160×１０^３A/m.磁滞回线的单一硬磁相特征说明，硬磁相Nd -Fe-B层和软磁相FeCo层之间的相互作用使两相很好地耦合在一起.剩磁和磁能积的提高是由 于两相磁性交换耦合所致. 关键词： Nd-Fe-B/FeCo双层纳米复合膜 交换耦合 磁性增强}     

Structural and Dielectric Properties of Organic Ferroelectric 2-Methylbenzimidazole

2-methylbenzimidazole single crystals and films are obtained by evaporation from an ethanol solution. The films have a texture with a predominant orientation of the pseudotetragonal axis in the film plane. The blocks are split crystals of the spherulite type, in which the pseudotetragonal axis rotates around the block center. Dielectric hysteresis loops are investigated in the crystals and films in the temperature range of 290–350 K. In the films, loops are observed for both in-plane and out-of-plane electric-field orientation. The maximum value of polarization in the films is close to that observed in single crystals P _s ~ 5 μC/cm². The difference in the temperature behavior of the hysteresis loops in the crystals and films is associated with the specific structure of the blocks.     

Magnetization reversal in amorphous gadolinium-cobalt films with a radial gradient of magnetic properties

The integral characteristics of magnetization switching in amorphous gadolinium-cobalt films with perpendicular anisotropy are studied by visualizing the domain structure and measuring magnetooptic hysteresis loops. The films have a radial gradient of magnetic properties that is due to a spatially nonuniform thermal field. Magnetization switching in those film areas where the domain wall motion depends only on the coercive force is simulated in simple terms. In a first approximation, local events of magnetization switching are shown to take place independently of each other and the net hysteresis loop can be represented as a sum of the local loops.     

The effect of silicon-substrate orientation on the local piezoelectric characteristics of LiNbO<Subscript>3</Subscript> films

The domain structure of lithium-niobate thin films grown on Si(111) and Si(100) substrates coated with a native oxide layer with a thickness of no less than 2 nm is investigated by X-ray diffraction, scanning electron microscopy and piezoresponse force microscopy. The films are synthesized by the rf magnetron sputtering of a single-crystal lithium-niobate target. A high degree of grain orientation in the polycrystalline films is demonstrated. The piezoelectric coefficients d _zz of the lithium-niobate films on Si(111) and Si(100) substrates are calculated from the measured dependences of the amplitude of the piezoresponse signal on the ac voltage applied between the cantilever tip and the substrate. Piezoelectric hysteresis loops are obtained in the remanent piezoelectric response regime     

Effect of dielectric layer on ferroelectric responses of P(VDF-TrFE) thin films

The dielectric layer in the sandwich structural device plays a very important role in determining the electrical properties of the ferroelectric film. In this paper, we investigate the effect of the dielectric layers with different thicknesses on switching performance of ferroelectric P(VDF-TrFE) thin films. The hysteresis loops become slanting with increasing thickness of the dielectric layer. A negative slope of the ‘real’ hysteresis loop is apparently observed which demonstrates negative capacitance effect caused by the dielectric layer. This behavior is simulated qualitatively by the Weiss mean field model considering an interfacial dielectric layer in series with a ferroelectric layer. The agreement between experiments and simulations supports that negative capacitance results from the positive feedback among electric dipoles. Furthermore, the switching time of the ferroelectric film increases with the increase of dielectric layer thickness. This study shows that the ferroelectric sandwich structure provides great potential towards low power negative capacitance devices.     

Magnetization of layered Mn-Ni and Mn-Co thin films

We report magnetization hysteresis loops for compositionally modulated films of Ni-Mn and Co-Mn. The films, prepared by evaporation, have nominal layer thicknesses of 5 to 25 Å and total thickness of 1 μm. Measurements were made on a SQUID magnetometer at 5 and 50 K with a maximum applied field of 10 kOe. The magnetic behavior observed ranges from ferromagnetism to spin-glassiness. Marked field cooling effects were observed for films with nominal layer thicknesses of 6 Å Ni-6 Å Mn, 13 Å Ni-13 Å Mn, 25 Å Ni-25 Å Mn and 5 Å Co-15 Å Mn.     

Effect of the nonmagnetic layer in a Co/Cu/CoO trilayer structure on the exchange coupling in it

The dependence of the exchange bias of epitaxial single-crystal Co/Cu/CoO trilayer films on the copper layer thickness and temperature is studied. The exchange bias of the hysteresis loops of the ferromagnetic cobalt layer as a function of the copper layer thickness is found to have a well-pronounced oscillating character. The oscillations manifest themselves over the entire temperature range in which an exchange bias takes place (77–220 K). The complex variation of the oscillation amplitude with the nonmagnetic layer thickness can be explained by the superposition of two interlayer exchange coupling oscillation periods (λ₁ ≈ 10–11 Å, λ₂ ≈ 20 Å) having differentamplitudes and temperature dependences.     

用表面磁光克尔效应实验系统测量铁磁性薄膜的磁滞回线

用自制的表面磁光克尔效应实验系统开发了研究性近代物理实验,测出铁磁性薄膜的磁滞回线,并求得克尔旋转角和克尔椭偏率.     

L1_0-FePt合金单层磁性薄膜的微磁学模拟

具有四方结构的L10-FePt合金因其具有高磁晶各向异性和良好的化学稳定性而成为超高密度薄膜磁记录介质的最佳选择.对实验制备得到的磁性能良好的垂直取向L10-FePt合金单层膜进行了微磁学分析.在传统微磁学模型的基础上,根据晶体的对称性,引入了四角磁晶各向异性能密度的唯象表达形式;又依据薄膜生长过程中晶格对称性的破坏,考虑了薄膜面内的应力,并引入了磁弹性能.以四角磁晶各向异性能和磁弹性能为重点,对L10-FePt合金单层膜的磁滞回线进行了详细的分析,并且用微磁学方法确定了薄膜面内应力的大小.     

Complex anisotropy and magnetization reversal on stepped surfaces probed by the magneto-optical Kerr effect

So-called split hysteresis loops have been measured for ultrathin ferromagnetic films grown on stepped surfaces. Since the shape of the loops is sensitive to the direction in which the magnetic field is applied with respect to the steps, the sample orientation against the field is particularly important. We performed systematic magneto-optical Kerr effect studies for 15 and 58 ML of Fe grown on Au(1,1,13). In view of the complex magnetic anisotropy of such systems we discuss representative hysteresis loops taken at sample orientations misaligned from the field (and laser beam) direction. In particular, the presence of a so-called low field component to the hysteresis loops is discussed and its reversed polarity is explained.     

Effect of synthesis conditions on the metal-semiconductor phase transition in vanadium dioxide thin films

The effect of the conditions of synthesis and of the substrate material on the metal-semiconductor phase transition in thin vanadium dioxide films prepared using laser ablation has been studied. The broadening of the hysteresis loop is shown to be due to a decrease in the size of the crystal grains making up the film. Conjectures are put forward to explain the formation of asymmetric hysteresis loops.     

Hysteresis of frequency-field dependences and magnetization reversal in barium hexaferrite

The hysteresis of the frequency-field dependences of ferromagnetic resonance is experimentally studied in the range of the transition from a domain into a saturated state and in the reverse direction in normally magnetized epitaxial films and plates of barium hexaferrite. The experimental results are compared with local magnetic hysteresis loops.     

由Pb过量引起的镧钛酸铅铁电薄膜性能异常的研究

采用金属有机物热分解法制备了不同La含量和不同Pb过量的镧钛酸铅铁电薄膜．在研究铁电性时发现：薄膜样品在极化达到饱和之前，电滞回线会出现束腰现象，束腰现象只与薄膜中的Pb过量有关．随Pb过量的增加和La含量的减少，镧钛酸铅薄膜电滞回线的束腰程度加剧．在C-V特性测试中发现：在Pb过量的样品中，C-V曲线会出现异常的四峰现象，随偏压升高或频率增大，异常程度逐渐减弱甚至会转变成正常的双峰．进一步研究表明：这两种实验现象是统一的，可以用铁电薄膜电畴的钉扎效应解释．由于Pb过量使正常的钙钛矿薄膜中出现了多余的Pb 关键词：     

FeCuCrVSiB单层和多层膜的横向巨磁阻抗效应

用射频溅射法制备了Fe_71.5Cu₁Cr_2.5V₄Si₁₂B₉单层膜和结构为(F/S)₃/M/(F/S)₃的多层膜，在制备过程中加72kA/m的纵向磁场.研究表明在制备过程中加磁场明显改善了材料的软磁性能，降低了材料的矫顽力.将样品经不同温度退火热处理后，发现经230℃退火1.5h的单层膜和多层膜具有最佳的软磁性能和最大的磁阻抗效应，单层膜最大横向磁阻抗比为37.5%，多层膜最大横向磁阻抗比高达277%.通过比较单层和多层膜磁阻抗效应随频率和磁场的变化，发现多层膜具有较低的磁阻抗效应的临界频率和峰值特征频率，和较大的磁阻抗变化率，而且有较低的横向磁阻抗效应的饱和场. 关键词： 铁基合金 多层膜 巨磁阻抗效应