Thermal Stability of CoFe/Cu/CoFe/IrMn Top Spin Valve

We present a study of thermal stability of the top spin valve with a structure of seed Ta （Snm）/Co75Fe25 （5 nm ） /Cu （2.5 nm） /Co75Fe25 （5 nm ） /Ir20Mn80（12 nm） /cap Ta （8 nm） deposited at room temperature by magnetron sputtering. A vibrating sample magnetometer fixed with a heater was used to record the magnetic hysteresis loops at variational temperatures and x-ray diffraction was performed to characterize the structure of the multilayer. The exchange field Hex and the coercivity of the pinned CoFe layer Hop decrease monotonically with increasing temperature. The coercivity of the free CoFe layer Hcf in the spin valve shows a maximum at 498K. The temperature dependences of Hex, Hop and Hcf have also been discussed.     

Hot-electron transport properties of CoFe/n-Si and CoFe/Cu/n-Si junctions

The hot-electron transport properties of different thickness of CoFe films deposited on n-Si substrate with and without Cu layer were investigated. Diode characteristics were tested to obtain the heights of Schottky barrier for different samples. The dependences of Schottky heights on CoFe thickness were studied. The research shows that the height of the Schottky barrier can be adjusted and a good Schottky diode can be obtained by controlling the thickness of CoFe film accurately. The results are very important for the application of spintronic devices, such as spin valve transistor (SVT) and magnetic tunnel transistor (MTT).     

Magnetoresistance study and interlayer coupling of CoFe/Os/CoFe thin films

The CoFe/Os/CoFe thin films were deposited on natural oxidized Si(1 0 0) substrates at room temperature by an ultra-high vacuum DC-magnetron sputtering system with a base pressure less than 1×10⁻⁸ Torr. The thickness of the ferromagnetic layers was 100 Å in all cases and a series of trilayers with Os spacer ranging from 3 to 20 Å was made. Effects of the Os layer thickness on the magnetoresistance (MR) and magnetic properties were investigated. The results showed that the magnetism switched from ferromagnetic (Os thickness=3, 5 Å) to antiferromagnetic (Os thickness=7–13 Å) and then ferromagnetic (Os thickness=20 Å) again. From the MR study, we see that the AMR ratio decreased from 4.64% to the minimum value 0.69% at 9 Å and then increased; GMR ratio increased from 0.01% to the maximum value 0.43% at 9 Å and then decreased. From the hysteresis loops, the results exhibited that coercivity increased from 16 Oe to the maximum value 92 Oe at 9 Å and then decreased, and squareness value decreased from 0.97 to the minimum value 0.17 at 9 Å and then increased. Dependence of saturation field on Os spacer-layer thickness for CoFe trilayers showed a maximum value 216 Oe at 9 Å. This suggests that the small GMR effect may be related to the small exchange coupling strength in CoFe/Os/CoFe thin films.     

Table of NMR/ON experiments

A tabulation of NMR/ON experiments is given. Results published or communicated up to August 1980 were considered.     

Tuning exchange coupling by replacing CoFe with amorphous CoFeB in the CoFe/Ru/CoFe synthetic antiferromagnetic structure

We studied exchange coupling in the CoFe/Ru/CoFe synthetic antiferromagnetic structure with systematical replacement of the crystalline CoFe with amorphous CoFeB. Antiferromagnetic exchange coupling intensity decreases with an increase in the replacement in the bottom magnetic layer, which indicates that exchange coupling intensity could be tuned by the replacement. The origin of weakening antiferromagnetic exchange coupling is attributed to the amorphous CoFeB replacement inducing incomplete crystallization and disordered orientation in the Ru layer.     

反铁磁Cr插入层对CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻的影响

利用基于密度泛函理论和非平衡态格林函数的第一性原理计算研究了CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻效应。给出了该隧道结隧穿磁电阻与偏压的依赖关系,并计算了平行结构与反平行结构相应的I-V特性曲线和传输谱。通过在一侧电极与势垒层之间插入反铁磁金属Cr层,观察到了隧穿磁电阻、电导随插入层Cr层数增加发生衰减和2个原子层周期的振荡现象,这主要是由于Cr拥有反铁磁结构,在Cr/MgO界面形成了与Cr磁矩取向相关的界面散射。     

反铁磁Cr插入层对CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻的影响

利用基于密度泛函理论和非平衡态格林函数的第一性原理计算研究了CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻效应。给出了该隧道结隧穿磁电阻与偏压的依赖关系,并计算了平行结构与反平行结构相应的I-V特性曲线和传输谱。通过在一侧电极与势垒层之间插入反铁磁金属Cr层,观察到了隧穿磁电阻、电导随插入层Cr层数增加发生衰减和2个原子层周期的振荡现象,这主要是由于Cr拥有反铁磁结构,在Cr/MgO界面形成了与Cr磁矩取向相关的界面散射。     

Influence of temperature on thermal relaxation of exchange bias field in CoFe/Cu/CoFe/IrMn spin valve

A multilayered spin valve film with a structure of Ta(5 nm)/Co_(75)Fe_(25)(5 nm)/Cu(2.5 nm)/Co_(75)Fe_(25)(5 nm)/Ir_(20)Mn_(80)(12 nm)/Ta(8 nm) is prepared by the high-vacuum direct current(DC) magnetron sputtering. The effect of temperature on the spin valve structure and the magnetic properties are studied by x-ray diffraction(XRD), atomic force microscopy(AFM), and vibrating sample magnetometry. The effect of temperature on the exchange bias field thermomagnetic properties of multilayered spin valve is studied by the residence time of samples in a reverse saturation field. The results show that as the temperature increases, the Ir Mn(111) texture weakens, surface/interface roughness increases, and the exchange bias field decreases. Below 200℃, the exchange bias field decreases with the residence time increasing, and at the beginning of the negative saturation field, the exchange bias field Hex decreases first quickly and then slowly gradually. When the temperature is greater than 200℃, the exchange bias field is unchanged with the residence time increasing.     

High temperature magnetoresistance in (Co,CoFe and NiFe)/Cu/CoFe/IrMn spin-valves

The MR characteristics of temperature variations ranging from room temperature to 570 K for IrMn spin-valves which consist of free layer Co, CoFe and NiFe were studied. Co-SV had the highest MR value in all temperature ranges among them and even at 510 K the MR ratio held more than half of room temperature value. Whereas CoFe-SV had a slightly higher MR than NiFe-SV below 450 K, above 450 K CoFe-SV showed a lower MR ratio than NiFe-SV. MR loops of large coercivity such as CoFe free magnetic layer collapsed in the lower elevated temperature compared to NiFe and Co. Small coercivity of the free magnetic layer would be preferable to spin-valves.     

NMR detected by Mössbauer-effect,applied to the system57CoFe

The ratio of the Larmor frequencies of¹¹¹Cd and²H has been measured in an aqueous solution of CdSO₄ with high accuracy.¹¹¹Cd chemical shifts have been investigated in aqueous solutions of CdCl₂, Cd(NO₃)₂, CdSO₄, and Cd(ClO₄)₂ as a function of concentration. Using these, the ratio of the Larmor frequencies of the¹¹¹Cd nuclei for infinite dilution relative to²H in pure D₂O is given. From this ag _I -factor for¹¹¹Cd has been derived and has been compared with theg _I -factor of an optical pumping experiment. The resulting shielding constant is σ^*(hydrated¹¹¹Cd versus¹¹¹Cd atom)=?1.106(4) · 10^?3. This yields an atomic reference scale for all measured NMR line shifts in the liquid and solid state and the possibility of comparing experimental and theoretical shielding constants. As a consequence, the amount of the Knight shift of metallic cadmium becomes 20% larger.     

Nuclear orientation and NMR/ON of205,207Po

^205,207Po have keen implanted with an isotope separator on-line into cold host matrices of Fe, Ni, Zn and Be. Nuclear magnetic resonance of oriented²⁰⁷Po has been observed in Fe and Ni, of²⁰⁵Po in Fe. The resonance frequencies for zero external field are $$\begin{gathered} v_L (^{207} Po\underline {Fe} ) = 575.08(20)MHz \hfill \\ v_L (^{207} Po\underline {Ni} ) = 160.1(8)MHz \hfill \\ v_L (^{205} Po\underline {Fe} ) = 551.7(8)MHz. \hfill \\ \end{gathered} $$ From the dependence of the resonance frequency on external magnetic field theg-factor of²⁰⁷Po was derived as $$g(^{207} Po) = + 0.31(22).$$ Using this value the magnetic hyperfine fields of Po in Fe and Ni were obtained as $$\begin{gathered} B_{hf} (Po\underline {Fe} ) = + 238(16)T \hfill \\ B_{hf} (Po\underline {Ni} ) = 66.3(4.6)T. \hfill \\ \end{gathered}$$ Theg-factor of²⁰⁵Po follows as $$g(^{205} Po) = + 0.304(22).$$ From the temperature dependence of the anisotropies ofγ-lines in the decay of^205,207Po the multipole mixing of several transitions was derived. The electric interaction frequenciesv _Q=eQV_zz/h in the hosts Zn and Be were measured as $$\begin{gathered} v_Q (^{207} Po\underline {Zn} ) = + 42(3)MHz \hfill \\ v_Q (^{207} Po\underline {Be} ) = - 70(20)MHz \hfill \\ v_Q (^{205} Po\underline {Be} ) = - 42(17)MHz. \hfill \\ \end{gathered}$$      

Magnetic dipole moment of127Sb by NMR/ON

The technique of NMR on oriented nuclei has been applied to¹²⁷Sb to measure the magnetic dipole moment of the¹²⁷Sb ground state. Resonant destruction of gamma-ray anisotropy from¹²⁷Sb^g (I =7/2⁺) has been observed at 139.6(2) MHz forB _app=0.30(1) T andat 138.7(1) MHz forB _app=0.25(1) T. The deduced magnetic moment is ||=2.697(6) µ_N.     

Influence of Ga+ ion irradiation on the magnetisation reversal process and magnetoresistance in CoFe/Cu/CoFe/IrMn spin valves

Ga+ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance(MR) are investigated.The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose.The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6×10 13 ions/cm 2 and the step disappears afterwards.Two peaks in the R-H curve are found to be asymmetric.     

Sign of excited state nuclearg-factors using gamma detected NMR/ON

Integral nuclear orientation and conventional CW NMR/ON studies using parity conserving gamma radiation can yield the nuclear moment μ, g and hence the nuclear spin, I, of the radioactive parent nuclei, but not the sign of g. In principle, the sign of g is accessible using parity non conserving beta radiation but is technically difficult; also, some nuclei decay without particle emission. We describe a novel spin echo NMR/ON technique that overcomes these previous difficulties and allows determination of the sign of the g-factor using gamma radiation.     

Antiferromagnet IrMn thickness dependence in exchange-biased perpendicular magnetic anisotropy based on CoFe/Pt/CoFe/[IrMn(tIrMn)] multilayers

The effect of the antiferromagnetic IrMn thickness upon the magnetic properties of CoFe/Pt/CoFe/[IrMn(t_IrMn)] multilayers is studied. An oscillatory interlayer coupling (IEC) has been shown in pinned CoFe/Pt(t_Pt)/CoFe/IrMn multilayers with perpendicular anisotropy. The period of oscillation corresponds to about 2 monolayers of Pt. The oscillatory behavior of IEC depends on the nonmagnetic metallic Pt thickness and is thought to be related to the antiferromagnetic ordering induced by the IrMn layer. From the extraordinary Hall voltage amplitude (EHA) curves as function of IrMn thickness, we report that the oscillation dependence of IEC for the [CoFe/Pt/CoFe] multilayer system induced by IrMn with spacer-layer thickness is a important features of perpendicular exchange biased system.     

Double resonance NMR/ON of185IrNi and188IrFe

In order to establish small quadrupole splittings the double resonance NMR/ON method was applied to¹⁸⁵IrNi and¹⁸⁸IrFe at 7 and 8.6 mK, respectively. With r.f. power applied at the strongest resonance frequency, a second frequency was used to simultaneously investigate the second resonance component, where the splitting is caused by an electric quadrupole interaction. Enhanced quadrupole subresonances were observed. In these experiments we have demonstrated the powerful capability of the double resonance NMR/ON method to observe a small quadrupole interaction when the resulting subresonances are well resolved.     

Transient field measurements on56Fe- and80Se-ions using segmented Fe-layers

Measurements of transient magnetic fields (TF) were performed on swift heavy ions of⁵⁶Fe and⁸⁰Se, with Coulomb excitation of their first 2⁺ state as probe, traversing thin Fe layers with segmented and unsegmented structures. The 50 µm×50 µm squares of the segments were accomplished applying the techniques of photolithography and ion etching. The magnitude of the TF deduced clearly shows that by segmentation of the targets the ion beam induced attentuations can be eliminated. This finding has direct applications tog-factor measurements.     

橄榄苦甙的NMR数据解析

对橄榄苦甙进行了¹H和¹³C MNR检测, 通过DEPT和¹H-¹H COSY、HMQC、HMBC、NO ESY等2D NMR对其¹H和¹³C NMR数据进行了全归属和较详细的解析, 并指出其NMR数据特征.