LaBaMnO薄膜的铁磁共振

用电子自旋共振实验研究La_0.65Ba_0.35MnO₃(LBMO)薄膜的磁性,从磁性膜的各向异性铁磁共振谱得到不同角度θ_h时的共振磁场B_r,求出样品的等效磁场B_eff及旅磁比γ,并通过样品的饱和磁化强度M_s,求出各向异性常数K.     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

在制备出Gd3(Fe1-xCox)29-yCry化合物基础上,成功制备出Sm3(Fe1-xCox)29-yCry化合物,通过x射线衍射和热磁分析对R3(Fe1-xCox)29-yCry(R＝Gd,Sm)化合物相稳定性进行了研究,利用原子半径的几何因素解释了高Co含量3:29型化合物必须要有较多稳定元素的原因.对于不同的稳定元素,稳定元素半径越大,所需稳定元素含量越少,可是稳定元素的半径愈大,其增大晶格常数的能力愈强,这反而不利于稳定3:29相.通过对R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性的研究,成功地制备出具有室温单轴磁晶各向异性的Gd3(Fe1-xCox)29-yCry(0.4≤x≤1.0;4.0≤y≤6.5)及新的Sm3(Fe1-xCox)29-yCry(0.4≤x≤1.0;4.5≤y≤7.5)化合物.     

应力各向异性下耦合三层薄膜铁磁共振

研究铁磁/铁磁/反铁磁三层薄膜中应力各向异性场对共振场的影响.得到系统存在声学和光学两种模,并且随着应力场的增强,在某些区域声学模和光学模共振场均向高值方向移动.此外发现声学模共振场对两铁磁层厚度的依赖较大,对光学模而言,随着两铁磁层厚度的改变,应力各向异性场对其共振场的影响甚微.     

垂直磁各向异性自旋阀结构中的铁磁共振

本文在理论上研究了垂直磁各向异性自旋阀结构中磁场激发和调节的铁磁共振. 通过线性展开包含自旋转移矩项的Landau-Lifshitz-Gilbert方程,获得了磁场激发和调节的铁磁共振谱. 给出了共振线宽、共振频率和共振磁场随直流电流密度大小和方向以及直流磁场的变化关系. 通过调节直流电流密度的大小和方向,系统的有效阻尼可以达到最小. 关键词： 自旋阀 自旋转移矩 垂直磁各向异性 铁磁共振     

铁磁共振实验中值得注意的几个问题

与顺磁样品相比铁磁样品的磁共振信号不仅是强得多,铁磁样品的许多特点都会在铁磁共振(FMR)谱中反映出来.诸如,起始磁化过程的FMR谱线与有剩余磁化强度Mr的FMR谱是不同的,起始磁化过程中的巴克豪森跳跃也会在FMR谱中反映出来.样品的磁晶各向异性、形状各向异性,铁磁高温顺磁的磁性相变等等都能用FMR方法加以研究.     

外应力场下双层铁磁薄膜中的铁磁共振性质

用铁磁共振方法得到了双层铁磁薄膜的色散关系解析表达式.发现共振场依赖于层间耦合强度和应力场.假定层间为反铁磁性耦合，且铁磁层Ａ有较强的平面内各向异性.随着外磁场的增强，铁磁层Ｂ中的磁化强度突然由最初的反平行转为平行，从而导致色散曲线的阶跃，并且发现光学模阶跃幅度比声学模大.随着应力场的增强，Ｂ层中磁化强度反转所需的外磁场减弱.此外，在不同的交换耦合强度和应力场下，光学模共振场对外磁场方向的依赖性较强. 关键词： 双层铁磁薄膜 界面相互作用 应力各向异性场 铁磁共振     

具有条纹磁畴结构的NiFe薄膜的制备与磁各向异性研究

具有条纹磁畴结构的磁性薄膜表现出面内转动磁各向异性,对于解决高频电子器件的方向性问题起着至关重要的作用.本文采用射频磁控溅射的方法,研究了NiFe薄膜的厚度、溅射功率密度、溅射气压等制备工艺参数对条纹磁畴结构、面内静态磁各向异性、面内转动磁各向异性、垂直磁各向异性的影响规律.研究发现,在功率密度15.6 W/cm~2与溅射气压2 mTorr(1 Torr=1.33322×102Pa)下生长的NiFe薄膜,表现出条纹磁畴的临界厚度在250 nm到300 nm之间.厚度为300 nm的薄膜比250 nm薄膜的垂直磁各向异性场增大近一倍,从而磁矩偏离膜面形成条纹磁畴结构,并表现出面内转动磁各向异性.高溅射功率密度可以降低薄膜出现条纹磁畴的临界厚度.在相同功率密度15.6 W/cm~2下生长300 nm的NiFe薄膜,随着溅射气压由2 mTorr增大到9 mTorr,NiFe薄膜的垂直磁各向异性场逐渐由1247.8 Oe(1 Oe=79.5775 A/m)增大到3248.0 Oe,面内转动磁各向异性场由72.5 Oe增大到141.9 Oe,条纹磁畴周期从0.53μm单调减小到0.24μm.NiFe薄膜的断面结构表明柱状晶的形成是表现出条纹磁畴结构的本质原因,高功率密度下低溅射气压有利于柱状晶结构的形成,表现出规整的条纹磁畴结构,高溅射气压会导致柱状晶纤细化,面内转动磁各向异性与面外垂直磁各向异性增强,条纹磁畴结构变得混乱.     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

在制备出Gd₃(Fe_1-xCo_x)_29-yCr_{y化合物基础上，成功制备出Sm3(Fe1-xCox)29 -yCry化合物，通过x射线衍射和热磁分析对R3(Fe1-x< /sub>Co x)29-yCry 关键词： 3(Fe1-xCox)29-yCry化合物')" href="#">R3(Fe1-xCox)29-yCry化合物 相结构 单轴磁晶各向异性}     

铁磁/反铁磁双层薄膜中应力各向异性研究

采用铁磁共振方法,研究了铁磁/反铁磁双层薄膜中交换各向异性和应力各向异性对其物理性质的影响.结果表明,单向各向异性来源于界面交换作用,应力各向异性对材料的磁化难易程度有较大影响.当外磁场方向与应力场方向平行时,应力场的存在将促进该方向的磁化.反之,应力场将会阻碍该方向的磁化.     

1-3型纳米多铁复合薄膜中电场诱导的磁化研究

运用Landau-Devonshire热力学唯像理论,考虑铁电相和铁磁相的电致伸缩、磁致伸缩效应以及产生于铁电/铁磁和薄膜/基底界面的弹性应力作用,两次重整介电和磁作用系数得到了这种多铁系统在Landau自由能函数下的本征二次方磁电耦合形式,从而研究了外延1-3型纳米多铁复合薄膜中极化、磁化随薄膜厚度、温度的变化以及该薄膜中外加电场诱导的磁化变化.结果表明薄膜平面内的应压力的弛豫使得磁化强度和极化强度随薄膜厚度的增加而减少,外加电场不仅能诱导铁电相极化场翻转,而且由于铁电和铁磁相界面竖直方向的弹性耦合导致 关键词： 多铁 磁电效应 磁致伸缩 薄膜     

Theoretical investigation of ferromagnetic resonance in a ferromagnetic thin film with external stress anisotropy

We use the ferromagnetic resonance(FMR)method to study the properties of ferromagnetic thin film,in which external stress anisotropy,fourfold anisotropy and uniaxial anisotropy are considered.The analytical expressions of FMR frequency,linewidth and the imaginary part of magnetic susceptibility are obtained.Our results reveal that the FMR frequency and the imaginary part of magnetic susceptibility are distinctly enhanced,and the frequency linewidth or field linewidth are broadened due to a strong external stress anisotropy field.The hard-axis and easy-axis components of magnetization can be tuned significantly by controlling the intensity and direction of stress and the in-plane uniaxial anisotropy field.     

Enhancement of ferromagnetic resonance in Al203-doped CozFeAI Heusler alloy film prepared by oblique sputtering

Large and variable in-plane uniaxial magnetic anisotropy in a nanocrystalline （Co2FeA1）97.8（Al2O3）2.2 soft magnetic thin film is obtained by an oblique sputtering method without being induced by magnetic field or post anneaiing. The in-plane uniaxiai magnetic anisotropy varies from 50 Oe to 180 Oe （1 Oe=79.5775 A·m-1） by adjusting the sample＇s position. As a result, the ferromagnetic resonance frequency of the film increases from 1.9 GHz to 3.75 GHz.     

Voltage control magnetism and ferromagnetic resonance in an Fe19Ni81/PMN-PT heterostructure by strain

Voltage control magnetism has been widely studied due to its potential applications in the next generation of information technology. PMN-PT, as a single crystal ferroelectric substrate, has been widely used in the study of voltage control magnetism because of its excellent piezoelectric properties. However, most of the research based on PMN-PT only studies the influence of a single tensile (or compressive) stress on the magnetic properties due to the asymmetry of strain. In this work, we show the effect of different strains on the magnetic anisotropy of an Fe₁₉Ni₈₁/(011) PMN-PT heterojunction. More importantly, the (011) cut PMN-PT generates non-volatile strain, which provides an advantage when investigating the voltage manipulation of RF/microwave magnetic devices. As a result, a ferromagnetic resonance field tunability of 70 Oe is induced in our sample by the non-volatile strain. Our results provide new possibilities for novel voltage adjustable RF/microwave magnetic devices and spintronic devices.     

Enhancement of ferromagnetic resonance in Al_2O_3-doped Co_2FeAl Heusler alloy film prepared by oblique sputtering

Large and variable in-plane uniaxial magnetic anisotropy in a nanocrystalline(Co2FeAl)97.8(Al2O3)2.2soft magnetic thin film is obtained by an oblique sputtering method without being induced by magnetic field or post annealing. The in-plane uniaxial magnetic anisotropy varies from 50 Oe to 180 Oe(1 Oe = 79.5775 A·m-1) by adjusting the sample’s position. As a result, the ferromagnetic resonance frequency of the film increases from 1.9 GHz to 3.75 GHz.     

A comparison of ferromagnetic resonance and magneto optical Kerr effect on thin Fe films on InAs(001)

A combination of STM, SQUID magnetometry, FMR and MOKE is used to study the structural and magnetic properties of thin iron films grown on InAs(001) (4×2)/c(8×2). The different magnetic characterization methods of this paper allow measurements of the magnetic anisotropies in the saturated and non-saturated state. Here we show results of a SQUID/FMR investigation on a 12 monolayer thick Fe film. As expected, FMR measurements find a four-fold symmetry of the magneto crystalline anisotropy, but with an additional uniaxial contribution. The dependence of the remanence on the magnetization angle computed from the magnetic parameters obtained in the saturated state is compared to experimental remanence data measured using MOKE. Good agreement is found. The InAs-substrate quality prior to growth, the nucleation behavior and the thickness-dependent granular structure of the Fe-layer are studied with STM. The origin of the magnetic anisotropies is discussed in terms of these structural data.     

Crystal field analysis of the magnetic properties of RFe11Ti and RFe11TiH （R=Sm, Tb, Ho）

The crystalline-electric-field parameters Anm for RFe11Ti and RFe11TiH （R=Sm, Tb, Ho） are evaluated by fitting calculations to the magnetization curves measured on the single crystals or on magnetically aligned powder samples at 4.2K and higher temperatures. Interstitial hydrogen atom in RFe11Ti has been found to have a significant effect on crystalline-electric-field parameters Anm. By using the parameters of exchange field 2μBHex estimated from inelastic neutron scattering experiments and the fitted Anm, the calculations can reproduce the experimental curves well.     

Crystal field analysis of the magnetization curves of R2Fe17 and R2Fe17H3 (R=Tb,Ho,Er)

In this paper the values of the crystalline-electric-field parameters A_nm for R₂Fe₁₇ and R₂Fe₁₇H₃ (R=Tb,Ho,Er) are evaluated by fitting calculations to the magnetization curves measured on the single crystal at several temperatures. The fitted A_nm for R₂Fe₁₇ are strikingly different from those for the corresponding R₂Fe₁₇H₃. The energy gaps between the lowest four energy levels for Ho ions in Ho₂Fe₁₇₂ can be reproduced by using the fitted A_nm and exchange field 2μ_BH_ex, which estimated from the fit of the temperature dependence of the spontaneous magnetization combined with inelastic neutron scattering experiment.     

Large tunable FMR frequency shift by magnetoelectric coupling in oblique-sputtered Fe_(52.5)Co_(22.5)B_(25.0)/PZN-PT multiferroic heterostructure

In this study, we observe a strong inverse magnetoelectric coupling in Fe_(52.5)Co_(22.5)B_(25.0)/PZN-PT multiferroic heterostructure, which produces large electric field(E-field) tunability of microwave magnetic properties. With the increase of the E-field from 0 to 8 kV/cm, the magnetic anisotropy field Heffis dramatically enhanced from 169 to 600 Oe, which further leads to a significant enhancement of ferromagnetic resonance frequency from 4.57 to 8.73 GHz under zero bias magnetic field, and a simultaneous decrease of the damping constant α from 0.021 to 0.0186. These features demonstrate that this multiferroic composite is a promising candidate for fabricating E-field tunable microwave components.