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We have used x-ray magnetic circular dichroism, which offers a unique capability to give element specific information at submonolayer sensitivity, to determine the spin and orbital magnetic moments at the Fe/GaAs(100) interface. The wedge samples, grown by molecular beam epitaxy at room temperature, consisted of 0.25-1 monolayer (ML) Fe on GaAs(100)-4x6 capped with 9 ML Co and have shown Fe spin moments of (1.84-1.96)micro(B) and a large orbital enhancement. Our results demonstrate unambiguously that the Fe/GaAs(100)-4x6 interface is ferromagnetic with a bulklike spin moment, which is highly promising for spintronics applications.

Using pulsed-current measurements we investigate the domain-wall depinning via spin-transfer torque from pinning potentials in V-doped Ni 80 Fe 20 wires. The domain-wall depinning boundary, showing the variation of threshold current density with longitudinal magnetic field is measured and reproduced using micromagnetic simulations. This method allows us to determine the spin-current polarization and nonadiabaticity parameter in these materials. By increasing the V concentration we show that the nonadiabaticity parameter is increased while the Gilbert damping is unaffected. On the other hand the spin-current polarization is decreased, resulting in larger threshold current densities. The ability to manipulate domain walls in magnetic materials by applying electrical currents 1 is of great interest for spintronics devices, such as magnetic memory devices. 2 The mechanism responsible for the interaction between spinpolarized currents and domain walls is called the spintransfer torque effect.3 The spin torques acting on a domain wall are composed of two terms, namely, the adiabatic 4 and the nonadiabatic 5,6 spin torques, with the latter being proportional to a material-dependent constant ␤ known as the nonadiabaticity parameter. A number of recent studies have investigated the contribution of the nonadiabatic spin torque in various materials and systems. [7][8][9] The relationship between the two phenomenological constants representing dissipative effects ␤ and the Gilbert damping constant ␣ has also come under debate with theoretical arguments given for both the cases of ␤ ␣ ͑Ref. 10͒ and ␤ = ␣.11 We have recently demonstrated a method to measure the spin-current polarization and nonadiabaticity parameter in Ni 80 Fe 20 .12,13 Since the threshold current required to move or depin a domain wall depends on the value of ␤, methods of controlling the nonadiabatic spin torque are of particular importance. According to theoretical formulations ␤ is inversely proportional to the spin-flip lifetime of conduction electrons. 6 In a recent work on PtCo layers, another method of determining the contribution of the nonadiabatic spin torque has been demonstrated. 14 By introducing an AlO x layer to break the symmetry properties and increase the spin-flip rate, an enhanced spin-torque effect compared to the symmetric PtCoPt structure was shown. In this work we investigate the possibility of modifying ␤ by introducing impurities in Ni 80 Fe 20 . The impurities act as scattering centers for the conduction electrons, reducing the spin-flip lifetimes and thus increasing the value of ␤. Moreover, since the damping in Ni 80 Fe 20 is known to be largely unaffected by V doping up to 10% concentration, 15 this experiment also allows us to investigate the relationship between ␤ and ␣.Notched wires were fabricated on Si/ SiO 2 substrates using e-beam lithography. The material is deposited using sputtering of V-doped Py ͑Py= Ni 80 Fe 20 ͒ targets, Py 99 V 1 , Py 97.5 V 2.5 , and Py 90 V 10 respectively, with 20 nm thickness and a 1.5 nm thi...

Using x-ray photoelectron emission microscopy we have observed the coexistence of ferromagnetic and antiferromagnetic phases in a (3 at%)Pd-doped FeRh epilayer. By quantitatively analyzing the resultant images we observe that as the epilayer transforms there is a change in magnetic domain symmetry from predominantly twofold at lower temperatures through to an equally weighted combination of both four and twofold symmetries at higher temperature. It is postulated that the lowered symmetry Ising-like nematic phase resides at the near-surface of the epilayer. This behavior is different to that of undoped FeRh suggesting that the variation in symmetry is driven by the competing structural and electronic interactions in the nanoscale FeRh film coupled with the effect of the chemical doping disorder. 7 Current address: