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International audience; It has been predicted that transverse spin current can propagate coherently (without dephasing) over a long distance in antiferromagnetically ordered metals. Here, we estimate the dephasing length of transverse spin current in ferrimagnetic CoGd alloys by spin pumping measurements across the compensation point. A modified drift-diffusion model, which accounts for spin-current transmission through the ferrimagnet, reveals that the dephasing length is about 4-5 times longer in nearly compensated CoGd than in ferromagnetic metals. This finding suggests that antiferromagnetic order can mitigate spin dephasingin a manner analogous to spin echo rephasing for nuclear and qubit spin systemseven in structurally disordered alloys at room temperature. We also find evidence that transverse spin current interacts more strongly with the Co sublattice than the Gd sublattice. Our results provide fundamental insights into the interplay between spin current and antiferromagnetic order, which are crucial for engineering spin torque effects in ferrimagnetic and antiferromagnetic metals.

Spin currents can exert spin-transfer torques on magnetic systems even in the limit of vanishingly small net magnetization, as recently shown for antiferromagnets. Here, we experimentally show that a spin-transfer torque is operative in a macroscopic ensemble of weakly interacting, randomly magnetized Co nanomagnets. We employ element- and time-resolved X-ray ferromagnetic resonance (XFMR) spectroscopy to directly detect subnanosecond dynamics of the Co nanomagnets, excited into precession with cone angle ≳0.003° by an oscillating spin current. XFMR measurements reveal that as the net moment of the ensemble decreases, the strength of the spin-transfer torque increases relative to those of magnetic field torques. Our findings point to spin-transfer torque as an effective way to manipulate the state of nanomagnet ensembles at subnanosecond time scales.

Efficient spin injection from epitaxial ferrimagnetic ${\mathrm{Ni}\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ thin films into a $\mathrm{Pd}$ layer is demonstrated via spin Seebeck effect measurements in the longitudinal geometry. The ${\mathrm{Ni}\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ films (60 nm to 1 $\ensuremath{\mu}$) are grown by pulsed-laser deposition on isostructural spinel ${\mathrm{Mg}\mathrm{Al}}_{2}{\mathrm{O}}_{4}$, ${\mathrm{Mg}\mathrm{Ga}}_{2}{\mathrm{O}}_{4}$, and ${\mathrm{Co}\mathrm{Ga}}_{2}{\mathrm{O}}_{4}$ substrates with lattice mismatch varying between 3.2 and 0.2%. For the thinner films ($\ensuremath{\le}330$ nm), an increase in the spin Seebeck voltage is observed with decreasing lattice mismatch, which correlates well with a decrease in the Gilbert damping parameter as determined from ferromagnetic resonance measurements. High-resolution transmission electron microscopy studies indicate substantial decrease of antiphase boundary and interface defects that cause strain relaxation, i.e., misfit dislocations, in the films with decreasing lattice mismatch. This highlights the importance of reducing structural defects in spinel ferrites for efficient spin injection. It is further shown that angle-dependent spin Seebeck effect measurements provide a qualitative method to probe for in-plane magnetic anisotropies present in the films.

Magnetic damping impacts essential dynamics for spintronic device applications, but its fundamental mechanisms in various materials – including simple ferromagnetic metals – have yet to be understood. Here, we experimentally correlate damping with structural and transport properties of epitaxial thin films of Fe. At room temperature, the effective Gilbert damping parameter is independent of whether these films are coherently strained or partially relaxed. However, at low temperature, we find that coherently strained Fe films with higher crystalline quality and conductivity exhibit higher damping. The enhancement of low-temperature damping is greater than that from classical eddy current loss. Our observation of such conductivity-like damping, possibly governed by the intraband scattering mechanism [1], provides fundamental insight into the role of crystallinity in damping in ferromagnetic metals. [1] K. Gilmore, Y. U. Idzerda, M. D. Stiles, Phys. Rev. Lett. 99, 027204 (2007); M. A. W. Schoen et al. Nat. Phys. 12, 839 (2016).

We report a detailed study of the structural and ferromagnetic resonance properties of spinel nickel ferrite (NFO) films, grown on (100)-oriented cubic MgAl 2 O 4 substrates by direct liquid injection chemical vapor deposition (DLI-CVD) technique. Three different compositions of NFO films (Ni x Fe 3− x O 4 where x =1, 0.8, 0.6) deposited at optimized growth temperature of 600 °C are characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometry (VSM), and broadband ferromagnetic resonance (FMR) techniques. XRD confirms the growth of epitaxial, single crystalline Ni x Fe 3− x O 4 films. The out-of-plane lattice constant ( c ) obtained for Ni 0.8 Fe 2.2 O 4 film is slightly higher than the bulk value (0.833 nm), indicating only partial strain relaxation whereas for the other two compositions ( x =1 and x =0.6) films exhibit complete relaxation. The in-plane and out-of-plane FMR linewidths measurements at 10 GHz give the lowest values of 458 Oe and 98 Oe, respectively, for Ni 0.8 Fe 2.2 O 4 film as compared to the other two compositions. A comprehensive frequency (5–40 GHz) and temperature (10–300 K) dependent FMR study of the Ni 0.8 Fe 2.2 O 4 sample for both in-lane and out-of-plane configurations reveals two magnon scattering (TMS) as the dominant in-plane relaxation mechanism. It is observed that the TMS contribution to the FMR linewidth scales with the saturation magnetization M s . In-plane angle-dependent FMR measurements performed on the same sample show that the ferromagnetic resonance field ( H res ) and the FMR linewidth (Δ H ) have a four-fold symmetry that is consistent with the crystal symmetry of the spinel. SEM measurements show formation of pyramid-like microstructures at the surface of the Ni 0.8 Fe 2.2 O 4 sample, which can explain the observed four-fold symmetry of the FMR linewidth.

We investigate the impact of pinned antiferromagnetic order on the decoherence of spin current in polycrystalline IrMn. In NiFe/Cu/IrMn/CoFe multilayers, we coherently pump an electronic spin current from NiFe into IrMn, whose antiferromagnetic order is globally pinned by static exchange-bias coupling with CoFe. We observe no anisotropic spin decoherence with respect to the orientation of the pinned antiferromagnetic order. We also observe no difference in spin decoherence for samples with and without pinned antiferromagnetic order. Moreover, although there is a pronounced resonance linewidth increase in NiFe that coincides with the switching of IrMn/CoFe, we show that this is not indicative of anisotropic spin decoherence in IrMn. Our results demonstrate that the decoherence of electron-mediated spin current is remarkably insensitive to the magnetization state of the antiferromagnetic IrMn spin sink.

Confirming the origin of Gilbert damping by experiment has remained a challenge for many decades, even for simple ferromagnetic metals. In this Letter, we experimentally identify Gilbert damping that increases with decreasing electronic scattering in epitaxial thin films of pure Fe. This observation of conductivity-like damping, which cannot be accounted for by classical eddy current loss, is in excellent quantitative agreement with theoretical predictions of Gilbert damping due to intraband scattering. Our results resolve the longstanding question about a fundamental damping mechanism and offer hints for engineering low-loss magnetic metals for cryogenic spintronics and quantum devices.

Pure spin currents, unaccompanied by dissipative charge flow, are essential for realizing energy-efficient nanomagnetic information and communications devices. Thin-film magnetic insulators have been identified as promising materials for spin-current technology because they are thought to exhibit lower damping compared with their metallic counterparts. However, insulating behavior is not a sufficient requirement for low damping, as evidenced by the very limited options for low-damping insulators. Here, we demonstrate a new class of nanometer-thick ultralow-damping insulating thin films based on design criteria that minimize orbital angular momentum and structural disorder. Specifically, we show ultralow damping in

We study the temperature-dependent static and dynamic magnetic properties of polycrystalline bilayers of permalloy ($\mathrm{N}{\mathrm{i}}_{80}\mathrm{F}{\mathrm{e}}_{20}$, or Py) and gadolinium (Gd) bilayers using DC magnetometry and broadband ferromagnetic resonance. Magnetometry measurements reveal that the 3-nm-thick Gd layers undergo a magnetic ordering transition below 100 K, consistent with finite size suppression of their Curie temperature. Upon cooling below this Gd ordering temperature, ferromagnetic resonance spectroscopy reveals a sharp increase in both the gyromagnetic ratio (\ensuremath{\gamma}) and effective Gilbert damping parameter (${\ensuremath{\alpha}}_{\mathrm{eff}}$) of the neighboring Py layers. The increase of \ensuremath{\gamma} is attributed to the onset of strong antiferromagnetic coupling between the Gd and Py layers as the Gd orders magnetically. We argue that the increase of ${\ensuremath{\alpha}}_{\mathrm{eff}}$, on the other hand, can be explained by spin pumping into the rare-earth layer when taking into account the increase of \ensuremath{\gamma}, the decrease of the Gd spin diffusion length as it orders, and, most significantly, the corresponding increase of the Py/Gd interfacial spin mixing conductance in the vicinity of the magnetic ordering transition. We propose that these observations constitute a qualitative confirmation of a recent theoretical prediction of spin sinking enhancement in this situation.

Interlayer exchange coupling of two ferromagnetic layers through a nonmagnetic spacer is an integral part of many magnetic sensors and devices. The authors use broadband ferromagnetic resonance to investigate the oscillatory interlayer exchange coupling between two Co-Fe layers, as a function of Ru spacer thickness and of temperature. The results show that the temperature dependence of the coupling is governed by the thermal spin-wave model---important insight for engineering magnetic and spintronic components.

The magnetization dynamics of exchange-biased IrMn/CoFe bilayers have been investigated using broadband and in-plane angle-dependent ferromagnetic resonance spectroscopy. The interface energy of the exchange bias effect in these bilayers exceeds values previously reported for metallic antiferromagnets. A strong perpendicular magnetic anisotropy and a small in-plane uniaxial anisotropy are also observed in these films. The magnetization relaxation of the bilayers has a strong unidirectional contribution, which is in part caused by two-magnon scattering. However, a detailed analysis of in-plane angle-- and thickness-dependent linewidth data strongly suggests the presence of a previously undescribed unidirectional relaxation mechanism.

Spinel ferrite NiFe2 O4 thin films have been grown on three isostructural substrates, MgAl2 O4 , MgGa2 O4 , and CoGa2 O4 using pulsed laser deposition. These substrates have lattice mismatches of 3.1%, 0.8%, and 0.2%, respectively, with NiFe2 O4 . As expected, the films grown on MgAl2 O4 substrate show the presence of the antiphase boundary defects. However, no antiphase boundaries (APBs) are observed for films grown on near-lattice-matched substrates MgGa2 O4 and CoGa2 O4 . This demonstrates that by using isostructural and lattice-matched substrates, the formation of APBs can be avoided in NiFe2 O4 thin films. Consequently, static and dynamic magnetic properties comparable with the bulk can be realized. Initial results indicate similar improvements in film quality and magnetic properties due to the elimination of APBs in other members of the spinel ferrite family, such as Fe3 O4 and CoFe2 O4 , which have similar crystallographic structure and lattice constants as NiFe2 O4 .

Risk is the potential for realization of undesirable consequences of an event. In other words, risk can be defined as the threat or probability that an action or event will adversely or beneficially affect an organization's ability to achieve its objectives. Implementation of Enterprise Resource Planning (ERP) projects are always accompanied by various risks and because of high rate of failure in such projects, managing of the risks in order to neutralize or at least decrease their effects on the success of the project is strongly essential. In this paper it is introduced a two stage Fuzzy Neural Network (FNN) which includes expertise to evaluate risk of ERP projects implementation. 18 risk factors are concluded from literature and for each of them two linguistic variables are considered: the probability of failure and the severity of impact. These variables are the inputs of first stage of the proposed FNN. The outputs of first stage, which are also the inputs of second stage, are values of ERP risk factors. Eventually, output of second stage is total risk of implementation of ERP project and it is derived from a feed-forward neural network. The architecture of the proposed framework and the development procedure are discussed, and numerical examples are provided.

Risk management in software projects plays a vital role in the success of the project. Various risk factors in such projects make it difficult to make reliable and quick decisions in order to accept, mitigate, transfer or reject these risks and obtain an overall view of the whole project. In this paper it is introduced a fuzzy expert system which includes expertise to evaluate risk of software projects in all respects. Fuzzy inference has been used because of its capability in dealing with ambiguity and linguistic variables. Risk factors, the probability of failure and the severity of impact, are very close to fuzzy theory concepts. To develop our fuzzy expert system we deal with a rule base with about 17 million rules. Instead of constructing the whole rule base, a heuristic programming was created to infer the inputs without losing any rules. The output of the model is numerical values which present state of risk for each factor as well as the risk of project called the total risk. The results show better performance compared with traditional risk analysis system. The proposed tool can be used as a decision support system for top management to compare different projects or better risk mitigation in these projects.

Epitaxial Co2FeAl films were synthesized using the Biased Target Ion Beam Deposition technique. Post annealing yielded Co2FeAl films with an improved B2 chemical ordering. Both the magnetization and the Gilbert damping parameter were reduced with increased B2 ordering. A low damping parameter, ∼0.002, was attained in B2 ordered Co2FeAl films without the presence of the L21 Heusler phase, which suggests that the B2 structure is sufficient for providing low damping in Co2FeAl. The spin polarization was ∼53% and was insensitive to the chemical ordering.

B2-ordered Co2FeAl films were synthesized using an ion beam deposition tool. A high degree of chemical ordering ∼81.2% with a low damping parameter (α) less than 0.004 was obtained in a 50 nm thick film via rapid thermal annealing at 600 °C. The perpendicular magnetic anisotropy (PMA) was optimized in ultra thin Co2FeAl films annealed at 350 °C without an external magnetic field. The reduced thickness and annealing temperature to achieve PMA introduced extrinsic factors thus increasing α significantly. However, the observed damping of Co2FeAl films was still lower than that of Co60Fe20B20 films prepared at the same thickness and annealing temperature.

This paper is concerned with routing problem with consideration of quality of service (QoS). In the absence of comprehensive analytical methods in this area because of high complexity of such systems, managers need applied approaches to help them in making appropriate routing decisions. We consider a set of n heterogeneous servers which differ in service time and QoS. Customers are also divided into m levels with regard to their service ranks. We present a threshold policy for heterogeneous servers (TPHS) which depends on number of different customers in the queues as a practical and flexible dynamic routing policy. Two performance measures are discussed: the QoS and the average waiting time (AWT). The TPHS is compared with both a static routing policy which maximises the QoS level and the minimum expected delay (MED) policy which minimises the AWT in the queues. The TPHS is optimised using stochastic simulated annealing (SSA). Numerical example validate that the proposed TPHS is more effective than other policies if both measures are regarded.