Polarized current changes the exchange bias in a current-in-plane spin valve

A spin-polarized current changes the strength and direction of the exchange bias in spin valves with a current-in-plane geometry. The exchange bias can be manipulated and systematically changed by applying current pulses. The changes are nonmonotonic and asymmetric with respect to the directions of the applied field and current pulses. For different current pulses, different exchange-bias fields can be achieved in the same sample. Furthermore, for samples with different exchange bias, the bias field exhibits a dependence on the applied pulse. Since the strength of exchange bias is highly correlated to the micromagnetic state distribution of the antiferromagnet, we explain our observations by the spin torque exerted on the interfacial antiferromagnetic moments, excluding Joule heating and training effects.     

Spin configurations and interfacial diffusion in exchange bias and spin valve systems with Ir–Mn antiferromagnetic pinning layers

Exchange bias and spin valve structures with Fe as ferromagnetic layers selectively enriched in ⁵⁷Fe and Ir–Mn of different compositions as antiferromagnetic pinning layers have been prepared by r.f. sputtering. Conversion Electron Mössbauer Spectroscopy and Magneto Optic Kerr Effect have shown that the local structure and interactions in the whole ferromagnetic layers, with direct influence on their magnetic reversal processes, depend on growing order of the layers and composition of the AF layer. Interfacial atomic diffusion is the main reason of perturbing the local structure of the ferromagnet. Mössbauer Spectroscopy is a powerfool tool which allows a detailed analysis of local configurations, in order to optimize the magnetic and giant magnetoresistive parameters of such multilayers of important technological applications.     

Exchange bias mechanism in FM/FM/AF spin valve systems in the presence of random unidirectional anisotropy field at the AF interface: The role played by the interface roughness due to randomness

We propose an atomistic model and present Monte Carlo simulation results regarding the influence of FM/AF interface structure on the hysteresis mechanism and exchange bias behavior for a spin valve type FM/FM/AF magnetic junction. We simulate perfectly flat and roughened interface structures both with uncompensated interfacial AF moments. In order to simulate rough interface effect, we introduce the concept of random exchange anisotropy field induced at the interface, and acting on the interface AF spins. Our results yield that different types of the random field distributions of anisotropy field may lead to different behavior of exchange bias.     

The effect of annealing on the MR and exchange bias characteristics in dual spin valve with nano-oxide layer

We investigated magnetoresistance (MR) and exchange bias properties by annealing in the dual spin valve (SV) with nano-oxide layer (NOL). By analyzing effects of NOL in top and bottom pinned simple SVs, MR enhancement effect of NOL inserted in the bottom pinned layer was higher than that of NOL in the top pinned layer with annealing. By the enhanced specular scattering of electrons by NOL, the MR ratio of dual SV with NOL was increased to 15.5–15.9% with an annealing of 200–250°C. Exchange coupling constant J_ex was improved rapidly as 0.13–0.16 erg/cm² by annealing in the bottom pinned layer, whereas the effect of annealing was not large in the top pinned layer with J_ex of about 0.09–0.116 erg/cm².     

Correlation between the exchange bias and the degree of ordering of antiferromagnetic layer in PtMn/Co–Fe bilayers

Correlation between the unidirectional anisotropy constant, J_K, and the degree of ordering of PtMn layer was investigated for Pt₅₅Mn₄₅/Co₉₀Fe₁₀ bilayer, as a function of the annealing time and the PtMn layer thickness, d_AF. As a result, we found the linear relations between J_K and the degree of ordering, f_FCT·S, in the cases of the bilayers with d_AF=5–50 nm. From the extrapolation of the linear relations to f_FCT·S=1, meaning the perfect ordering of PtMn layer, we obtained the attainable value of J_K and the intrinsic critical thickness of the PtMn layer to be 0.26 erg/cm² and 6 nm, respectively.     

A study of the effective magnetic anisotropy and the corresponding spin configurations in two dimensional ferromagnetic/antiferromagnetic system

The spin configurations of two dimensional ferromagnetic/antiferromagnetic system were investigated using model calculations and Monte-Carlo simulation methods. The lowest energy state was obtained under various coupling conditions to investigate the role of interfacial interaction on anisotropy. We found that the total ferromagnetic layer anisotropy is contributed not only from its own crystalline anisotropy but also from the antiferromagnetic layer spin flop effect. The overall ferromagnetic layer effective anisotropy is calculated as a function of the exchange energy of antiferromagnetic layer and the interfacial interaction energy. If the effective anisotropy from the spin flop effect is comparable with the crystalline anisotropy, the asymmetric spin configuration is generated. In this configuration, the magnetization direction of the ferromagnetic layer is neither perpendicular nor parallel to the antiferromagnetic spin direction. Temperature effect on the perpendicular-to-collinear coupling transition was also investigated using Monte-Carlo simulation, and the relationship between the effective anisotropy and the temperature was obtained.     

Density of states and phase diagram of the antiferromagnetic spin chain with Dzyaloshinsky–Moriya interaction and spin-phonon coupling

The effects of DM interaction on the density-of-states, the dimerization and the phase diagram in the antiferromagnetic Heisenberg chain coupled with quantum phonons have been studied by a nonadiabatic analytical approach. The results show that the effect of the DM interaction is to increase the staggered antisymmetric spin exchange interaction order but to decrease the spin dimerization and their competitions result in the lattice dimerization ordering parameter to increase for large staggered DM interaction parameter β and decrease for small β. A crossover of β exists in which the dimerization ordering parameter changes non-monotonously. As the DM interaction parameter D increases, depending on the appropriate values of spin-phonon coupling, phonon frequency and β, the system undergoes phase transition from spin gapless state to gapped state or reversely and can even reenter between the two states. The relation between the phonon-staggered ordering parameter, the spin-dimer order parameter and the staggered DM interaction order parameter gives clearly their contributing weights to the lattice dimerization.     

Exchange bias at low fields exhibited by the interface between epitaxial layers of ferromagnetic and charge‐ordered rare‐earth manganites

Epitaxial thin films of ferromagnetic La_0.7Sr_0.3MnO₃ (LSMO) and charge‐ordered, antiferromagnetic Y_0.5Ca_0.5MnO₃ (YCMO) were deposited on SrTiO₃ (100) substrates by pulsed laser deposition (PLD). The heterostructure undergoes tetragonal distortion due to strong biaxial tensile strain imposed by the substrate. The LSMO–YCMO bilayers exhibit significant exchange bias (EB) across the interface even in a very small remnant magnetic field (～5 Oe) present in the superconductor magnet. The unidirectional exchange anisotropy at the interface can be switched by reversing the polarity of the remnant magnetic field.

     

The excited state dynamics study of di‐2‐pyridylketone in the A‐band and B‐band absorptions by using resonance Raman spectroscopy,IR and UV–visible spectroscopy

Excitation wavelengths of 282.4, 273.9 (A band), 252.7, 239.5 and 228.7 nm (B band) resonance Raman spectra were acquired for di‐2‐pyridylketone, and density functional calculations were carried out to help in the elucidation of the photo relaxation dynamics of A‐band and B‐band electronic transitions. The resonance Raman spectra show that the intensity pattern of the A band presents great difference from that of the B band, which indicate that the short‐time A‐band (S₀→S₄) photo relaxation dynamics have substantial difference from that of B band (S₀→S₁₀) . The overall picture of short‐time dynamics and the vibronic coupling mechanisms are interpreted using Albrecht's theory. Copyright © 2012 John Wiley & Sons, Ltd.