Oscillatory ferromagnetic interlayer coupling in [Pt(5 Å)/Co(4 Å)]3/Cr(x Å)/[Co(4 Å)/Pt(12 Å)]3 multilayers with perpendicular anisotropy

Investigation has been performed on the interlayer coupling between two Co/Pt multilayers with perpendicular anisotropy separated by Cr spacers. As a function of the Cr spacer thickness, only ferromagnetic interlayer coupling has been observed between the two Co/Pt multilayers in contrast to the oscillatory interlayer coupling between ferromagnetic and antiferromagnetic observed in ferromagnetic layers with in-plane anisotropy separated by Cr spacers. It is the strength of the ferromagnetic interlayer coupling that has been observed to be oscillatory as a function of the Cr spacer thickness with a period of about 7 Å.     

Magnetization reversal and domains structures in (Co/Ni/Co/Pt) multilayers

Multilayers of [Co/Ni(t_Ni)/Co/Pt]_×4 are investigated for different Ni insertion layer thicknesses. The resulting magnetic properties and magnetic domain structures are compared with [Co/Ni]_×8 multilayers. As determined by magneto-optical Kerr effect microscopy and a vibrating sample magnetometer measurements, all multilayers exhibited a perpendicular magnetic anisotropy. It is found that the nucleation field and magnetic coercivity of [Co/Ni(t)/Co/Pt]_×4 multilayers are lower than (Co/Ni)_×8 and decreased with Ni thickness. Magnetization decay measurements reveal that these multilayers did not show an exponential decay behavior as was observed in rare earth transition metal alloys. Very narrow wires will remain stables for several hours even with an applied magnetic field closer to the coercivity. Insertion of very thin Ni in (Co/Pt) multilayers offers a good way to optimize the magnetic properties of the material and adjust the domain size for nanowire-based devices.     

Ultrathin (CoFe/Pt)n multilayers with tuned magnetic properties

Perpendicular magnetic anisotropy (PMA) has been investigated in ultrathin (CoFe [0.2] nm/Pt [0.2] nm)_n multilayers. The Pt layers show an fcc crystal structure with a preferred [111] orientation. The multilayers with n=3, 4 show PMA in the as-grown state, which can be enhanced by thermal annealing. However, no PMA is observed in the as-grown state with higher repetitions (n>&=5), although it is observed after thermal annealing. For 1=&<n=&<8, the anisotropy energy is around 10⁵ J/m³ for all (CoFe [0.2]/Pt [0.2])_n stacks. The perpendicular anisotropy is related to layer thickness and interface roughness.     

Influence of Pt thickness on magnetization reversal processes in (Pt/Co)3 multilayers with perpendicular anisotropy

We present a detailed study of the magnetization reversal in perpendicularly magnetized (Pt/Co)₃ multilayers with different values of the platinum interlayer thickness t_Pt. To study the magnetization reversal in our samples we combined measurements of relaxation curves with the direct visualization of domain structures. Magnetization reversal was dominated by domain wall propagation for t_Pt=1 nm and by domain nucleation for t_Pt=0.2 nm, while a mixed process was observed for t_Pt=0.8 nm. We interpret our results within the framework of a model of thermally activated reversal where a distribution of activation energy barriers is taken into account. The reversal process was correlated with the energy barrier distribution.     

Mössbauer effect investigations of Co83Fe17/Au/Co/Au multilayers

[Co₈₃Fe₁₇/Au/Co/Au]_N sputter deposited multilayers displaying a giant magnetoresistance have been investigated. Complementary magnetic measurements were conducted in order to characterize a spin reorientation transition in Co₈₃Fe₁₇ layers sandwiched between Au spacers. The transition from a perpendicular magnetic anisotropy to easy-plane one takes place at the thickness of about 1 nm.     

Thickness-dependent magnetic properties in Pt/[Co/Ni]n multilayers with perpendicular magnetic anisotropy

We systematically investigated the Ni and Co thickness-dependent perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain structures, and magnetization dynamics of Pt(5 nm)/[Co($t_{\rm Co}$)/Ni($t_{\rm Ni}$)]$_{5}$/Pt(1 nm) multilayers by combining the four standard magnetic characterization techniques. The magnetic-related hysteresis loops obtained from the field-dependent magnetization $M$ and anomalous Hall resistivity (AHR) $\rho_{{xy}}$ showed that the two serial multilayers with $t_{\rm Co} = 0.2$ nm and 0.3 nm have the optimum PMA coefficient $K_{\rm U}$ as well as the highest coercivity $H_{\rm C}$ at the Ni thickness $t_{\rm Ni}= 0.6 $ nm. Additionally, the magnetic domain structures obtained by magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the thickness and $K_{\rm U}$ of the films. Furthermore, the thickness-dependent linewidth of ferromagnetic resonance is inversely proportional to $K_{\rm U}$ and $H_{\rm C}$, indicating that inhomogeneous magnetic properties dominate the linewidth. However, the intrinsic Gilbert damping constant determined by a linear fitting of the frequency-dependent linewidth does not depend on the Ni thickness and $K_{\rm U}$. Our results could help promote the PMA [Co/Ni] multilayer applications in various spintronic and spin-orbitronic devices.     

Exchange bias in thin-film (Co/Pt)3/Cr2O3 multilayers

We have fabricated exchange-biased Co/Pt layers ((0.3 nm/1.5 nm)×3) on (0 0 1)-oriented Cr₂O₃ thin films. The multilayered films showed extremely smooth surfaces and interfaces with root mean square roughness of ≈0.3 nm for 10 μm×10 μm area. The Cr₂O₃ films display sufficient insulation with a relative low leakage current (1.17×10⁻² A/cm² at 380 MV/m) at room temperature which allowed us to apply electric field as high as 77 MV/m. We find that the sign of the exchange bias and the shape of the hysteresis loops of the out-of-plane magnetized Co/Pt layers can be delicately controlled by adjusting the magnetic field cooling process through the Néel temperature of Cr₂O₃. No clear evidence of the effect of electric field and the electric field cooling was detected on the exchange bias for fields as high as 77 MV/m. We place the upper bound of the shift in exchange bias field due to electric field cooling to be 5 Oe at 250 K.     

Thermoelectric power of TTF[Ni(dmit)2]2

The 1D organic salt TTF[Ni(dmit)₂]₂ becomes superconductor with T_c=1.6 K under an applied hydrostatic pressure of 7 kbar. Structural determinations in this system lead us to suspect that superconductivity (SC) coexists with a charge density wave (CDW) instability at low pressure. In order to better understand how SC emerge from a CDW and to revisit the pressure–temperature phase diagram of the TTF[Ni(dmit)₂]₂ we performed transport and thermoelectric power measurements under pressure.     

具有垂直各向异性(Pt/Co)n/FeMn多层膜的交换偏置

采用磁控溅射方法制备了以Pt为缓冲层和保护层的具有垂直各向异性(Pt/Co)_n/ FeMn多层膜.研究结果表明，多层膜的垂直交换偏置场H_ex和反铁磁层厚度的关 系与其具有平面各向异性的交换偏置场随反铁磁层厚度变化趋势相近.随着铁磁层调制周期 数的增加，垂直交换偏置场H_ex相应减小，并且与铁磁层的调制周期数近似成反 比关系.(Pt/Co)₃/FeMn的垂直交换偏置场H_ex已经达到22.3kA/m.为 关键词： 交换偏置 垂直各向异性 多层膜     

Phase transitions in [Ni(NH3)6](NO3)2

Electric permittivity ^* = ′ − i″ of nickel-hexammino nitrate (NHN) has been measured within the range of temperature from 9 to 300 K at a frequency of 8.8 GHz (X-band). It has been found that the phase transitions at T_k1 = 247 K and T_k2 = 90 K are discontinuous structural transitions between centrosymmetric phases, whereas the transition at T_c = 63 K is a continuous phase transition (glass?).     

Anisotropy and FOMP in Tb3 (Fe28−xCox) V1.0 (x=0, 3 and 6) compounds

In this work, the structural and magnetic properties of Tb₃ (Fe_28−xCo_x) V_1.0 (x=0, 3, 6) compounds have been investigated. The structural characterization of compounds by X-ray powder diffraction is an evidence for a monoclinic Nd₃(Fe, Ti)₂₉-type structure (A2/m space group). The refined lattice parameters a and b (but not c) and the unit cell volume V, obtained from the XRD data by the Rietveld method, are found to decrease with increasing Co concentration. The unit cell parameters behavior has been attributed to the smaller Co atoms and a preferential substitution of Fe by Co. The anisotropy field (H_a) as well as critical field (H_cr) was measured using the singular point detection (SPD) technique from 5 to 300 K in a pulsed magnetic field of up to 30 T. At T=5 K, a FOMP of type 2 was observed for all samples and persists at all temperatures up to 300 K. For sample x=0, H_cr=10.6 and 2.0 T at 5 and 300 K, respectively, is equal to that reported earlier. The occurrence of canting angles between the magnetic sublattices during the magnetization process instead of high-order anisotropy contributions (at room temperature are usually negligible) has been considered to explain the survival of the FOMP at room temperature. The anisotropy and critical fields behave differently for samples with x=0, 3 compared with x=6. The observed behavior has been related to the fact that the Co substitution for Fe takes place with a preferential entrance in the inequivalent crystallographic sites of the 3:29 structure. The contribution of the Tb-sublattice in the Tb₃(Fe, V)₂₉ compound with uniaxial anisotropy has been scaled from the anisotropy field measured on a Y₃(Fe, V)₂₉ single crystal with easy plane anisotropy.     

Influence of domain wall density on interlayer coupling in CoFe/Au/Co/Au multilayers

We measure magnetization reversal and giant magnetoresistance of CoFe/Au/Co/Au multilayers and use micromagnetic simulations to model them. We characterize the system by perpendicular and easy-plane effective anisotropy of Co and CoFe layers, respectively. We show that minor hystereses of magnetoresistance can be reasonably well described by the model. The simulations show that the variation of resistance with the field depends on the field strength at which the sweep reverses, and is correlated with the number of stripe domains present in the Co layers.     

MgO/Pt界面对增强Co/Ni多层膜垂直磁各向异性及热稳定性的研究

采用直流磁控溅射法在玻璃基片上制备了Pt底层和MgO/Pt双底层的Co/Ni多层膜样品, 通过反常霍尔效应研究了不同MgO厚度和退火温度对样品垂直磁各向异性(perpendicular magnetic anisotropy, PMA)的影响. 随着底层中MgO厚度的逐渐增加, 样品的矫顽力也随之增强, 霍尔电阻变化不大; 对样品进行退火处理后发现, 单纯Pt底层的Co/Ni多层膜随着退火温度的升高, 霍尔电阻逐渐降低, 矫顽力则迅速降低, 热稳定性较差; 而当MgO/Pt双底层的样品在200 ℃退火后矫顽力大幅增加, 霍尔电阻略微有所减小, 更高的退火温度使得Co和Ni合金化, 导致多层膜的PMA特征减弱.     

Influence of growth and anneal conditions on the surface roughness of L10 Fe50PdxPt50−x thin films

We deposit Fe₅₀Pd_xPt_50−x alloy thin films by magnetron sputtering onto a TiN seed layer. Chemically ordered L1₀ films are obtained which display large perpendicular magnetic anisotropy. We find that the surface roughness of the film depends strongly on the growth and anneal conditions as well as the Pd composition of the film. Smooth films are obtained by deposition above the chemical ordering temperature and by removing Pd from the alloy.     

多层膜［Co85Cr15/Pt］20的磁性、垂直磁记录特性和微结构的关系

采用磁控溅射法制备了性能优良的以Pt为缓冲层的［Co85₈₅Cr15_{15/Pt］2020 多层膜，研究了溅射气压对［Co8585Cr1515/Pt］2020多层膜微结构和磁性的 影响.研究结果表明，Ar溅射气压对［Co8585Cr1515/Pt］2020多层膜的微结构 、垂直磁各向异性和矫顽力有重要的影响 关键词： 溅射气压 多层膜 垂直磁各向异性 有效磁各向异性常数}     

Electrical conduction studies on one-dimensional Cs2[Pt(CN)4](FHF)0.39 and Rb2[Pt(CN)4](FHF)0.40

Variable temperature (300-40 K) 4-probe d.c. conduction studies on Cs₂[Pt(CN)₄](FHF)_0.39 and Rb₂[Pt(CN)₄](FHF)_0.40 are described. In these salts T_3D occurs at a lower temperature than in K₂[Pt(CN)₄]Br_0.3·3H₂O and this is attributed to the absence of an inter-chain network of hydrogen bonded water molecules in the bifluorides.     

Domain size and structure in exchange coupled [Co/Pt]/NiO/[Co/Pt] multilayers

We investigate the competing effects of interlayer exchange coupling and magnetostatic coupling in the magnetic heterostructure ([Co/Pt]/NiO/[Co/Pt]) with perpendicular magnetic anisotropy (PMA). This particular heterostructure is unique among coupled materials with PMA in directly exhibiting both ferromagnetic and antiferromagnetic coupling, oscillating between the two as a function of spacer layer thickness. By systematically tuning the coupling interactions via a wedge-shaped NiO spacer layer, we explore the energetics that dictate magnetic domain formation using high resolution magnetic force microscopy coupled with the magneto-optical Kerr effect. This technique probes the microscopic and macroscopic magnetic behavior as a continuous function of thickness and the interlayer exchange coupling, including the regions where interlayer coupling goes through zero. We see significant changes in domain structure based on the sign of coupling, and also show that magnetic domain size is directly related to the magnitude of the interlayer exchange coupling energy, which generally dominates over the magnetostatic interactions. When magnetostatic interactions become comparable to the interlayer exchange coupling, a delicate interplay between the differing energy contributions is apparent and energy scales are extracted. The results are of intense interest to the magnetic recording industry and also illustrate a relatively new avenue of undiscovered physics, primarily dealing with the delicate balance of energies in the formation of magnetic domains for coupled systems with PMA, defining limits on domain size as well as the interplay between roughness, domains and magnetic coupling.     

Chlorine K X-ray absorption-edge structures of CIS-[Pt(NH3)2Cl2], trans-[Pt(NH3)2Cl2], trans-[Pd(NH3)2Cl2] and (NH4)2PdCl4

The K absorption-edge spectra of the ligand chlorine ion in square-planar complex compounds cis- and trans-[Pt(NH₃)₂Cl₂], trans-[Pd(NH₃)₂Cl₂], and (NH₄)₂PdCl₄ are reported and discussed in connection with the chlorine K absorption spectra of K₂PtCl₄ and K₂PdCl₄, reported previously. The observed chemical shift of a white line at the absorption threshold is interpreted in terms of the difference of the ligand-field splitting of electronic states for metal ions. The white line is attributed to the electronic transition from the Cl^? ls level to the lowest unoccupied antibonding molecular orbital (MO), which is specified by a $\text{MO}\text{b}{}_{\mathrm{1g}}\text{(σ}{}^1\text{)}$ in the square-planar complex with D_4h symmetry. The other absorption structures are regarded as continuum “shape resonances” of the outgoing electron trapped by the cage of the surrounding atoms. The effect of geometrical isomerism is found in the chlorine K absorption spectra of cis- and trans-[Pt(NH₃)₂Cl₂].     

A study on magnetoelastic properties of Tb3 (Fe28−xCox) V1.0 (x=0, 3, 6) compounds

In this work, The magnetoelastic properties of polycrystalline samples of Tb₃ (Fe_28−xCo_x) V_1.0 (x=0, 3, 6) intermetallic compounds are investigated by means of linear thermal expansion and magnetostriction measurements in the temperature range of 77–515 K under applied magnetic fields up to 1.5 T. The linear thermal expansion increases with the Co content. The well-defined anomalies observed in the linear thermal expansion coefficients for Tb₃ (Fe_28−xCo_x) V_1.0 (x=0, 3, 6) compounds are associated with the magnetic ordering temperature for x=0 and spin reorientation temperatures for x=3, 6. Below transition temperatures, the value of the longitudinal magnetostriction (λ_Pa) at 1.6 T increases with Co content.     

Perpendicular magnetization and exchange bias in epitaxial NiO/[Ni/Pt]2 multilayers

The realization of perpendicular magnetization and perpendicular exchange bias(PEB)in magnetic multilayers is important for the spintronic applications.NiO(t)/[Ni(4 nm)/Pt(1 nm)]₂multilayers with varying the NiO layer thickness t have been epitaxially deposited on SrTiO;(001)substrates.Perpendicular magnetization can be achieved when t<25 nm.Perpendicular magnetization originates from strong perpendicular magnetic anisotropy(PMA),mainly resulting from interfacial strain induced by the lattice mismatch between the Ni and Pt layers.The PMA energy constant decreases monotonically with increasing t,due to the weakening of Ni(001)orientation and a little degradation of the Ni–Pt interface.Furthermore,significant PEB can be observed though NiO layer has spin compensated(001)crystalline plane.The PEB field increases monotonically with increasing t,which is considered to result from the thickness dependent anisotropy of the NiO layer.