Search

We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields. [ABSTRACT FROM AUTHOR]

Using spin-polarized neutron reflectivity experiments, we demonstrate an unusual proximity behavior when a superconductor (SC) and a ferromagnet (FM) are coupled through an insulator (I) in YBa2Cu3O7−δ (SC)/SrTiO3 (I)/La0.67Sr0.33MnO3 (FM) heterostructures. We have observed an unexpected magnetic reversal confined to the interface region of the FM below the superconducting transition temperature. The magnetization of the interfacial FM layer at the I/FM interface was found to be aligned opposite to the magnetization of the rest of the FM layer. This result indicates that the Cooper pairs tunnel across the insulator, interact with the local magnetization in the interfacial region (extending ∼30 Å) of the FM, and then modify the magnetization at the interface. This unexpected magnetic behavior cannot be explained on the basis of the existing theoretical models. However, the length scale associated here clearly suggests the long-range proximity effect as a result of tunneling of Cooper pairs. The magnetic exchange field-effect across SC/I/FM interfaces driven by tunneling may serve as the basis for application in superconducting spintronic devices. [ABSTRACT FROM AUTHOR]

We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well as magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices. [ABSTRACT FROM AUTHOR]

Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications. [ABSTRACT FROM AUTHOR]

In this article we present a detailed investigation of the structural and magnetic properties of exchange biased NiFe (ferromagnet)/FeMn (antiferromagnet) thin films. The influence of the shape anisotropy on exchange bias and the magnetization reversal mechanism in a sample with patterned lines is compared with a continuous two-dimensional reference sample. Polarized neutron reflectivity (PNR) is employed to study the magnetization reversal by analyzing the spin-flip and non-spin-flip reflectivities. PNR measurements show that the magnetization reversal in the reference two-dimensional film and patterned lines is by domain wall motion rather than coherent rotation of magnetization. [ABSTRACT FROM AUTHOR]

We demonstrate, using spin polarized neutron reflectivity measurements, that one can form a large stack of magnetically decoupled spin-membranes of Gadolinium ions and reduce the effect of the substrate substantially to study short-range two-dimensional (2D) ferromagnetic ordering. No spontaneous magnetization was observed in these membranes as the magnetic field was applied along an in-plane direction. The results are consistent with theoretical predictions of 2D in-plane spin systems having strong interplay of exchange, magneto-crystalline anisotropy and dipolar interactions. These metal–organic multilayer films will enable us to verify various theoretical predictions regarding spin-fluctuations in 2D systems using conventional magnetic measurements and neutron scattering studies. [ABSTRACT FROM AUTHOR]

We present magnetometry data for a range of Fe thicknesses grown on GaAs and InAs substrates in order to determine the factors governing the evolution of the magnetic moment of epitaxial Fe grown on a zinc-blende semiconductor. Fe films grown at room temperature by molecular beam epitaxy were characterized structurally and magnetically. The estimated roughness amplitudes were 0.3 ± 0.2 nm for the Fe/GaAs interface and 0.6 ± 0.2 nm for Fe/InAs. We observe a greater reduction of the Fe magnetic moment for films grown on InAs as compared to GaAs, as the Fe films reach a bulk-like moment (within 10% deviation) at a thickness of ∼5.2 nm and ∼2.2 mn, respectively. We conclude that the growth conditions, in particular interface and interdiffusion effects, are the dominant mechanisms influencing the value of the magnetic moment for ultrathin Fe films on GaAs and InAs. [ABSTRACT FROM AUTHOR]

Factors which contribute to magnetostructural transition control have been demonstrated by study of the effects of Au incorporation on the magnetic and structural character of CsCl-structured equiatomic FeRh thin films. Sputtered films were capped with 2 nm of Au deposited at 873 K and at 323 K and subsequently characterized with magnetometry and synchrotron-based structural probes. Diffusion of Au into the FeRh film layer at 873 K is confirmed by a reduction in the Au capping layer thickness relative to the film capped at 323 K. The impact of Au diffusion on the FeRh magnetostructural character is noted by a decrease in the onset of the transition temperature, a thermally broadened first-order transition and an increased sensitivity of the transition to applied magnetic field. Additionally, magnetization data indicate that Au diffusion causes retention of the ferromagnetic phase well below the normal magnetostructural transition temperature. These results are attributed to a multiphase FeRh film layer created by thermally driven Au diffusion. [ABSTRACT FROM AUTHOR]

The magnetization vector configurations in an epitaxial Si(001)/Cu/Co/Cu/Fe[sub 20]Ni[sub 80]/Cu/Co/Cu double spin valve structure have been investigated at room temperature using polarized neutron reflectivity measurements. The layer-averaged magnetic moment per FeNi atom was found to be 0.99±0.06 μ[sub B] at saturation, while the top (bottom) Co layer moment was 1.69±0.09 μ[sub B] (1.67±0.08 μ[sub B]), which are identical to the bulk values within experimental error. Furthermore, the Co magnetization vectors are found to lie in-plane but canted with respect to the applied field direction for an applied field strength smaller than the coercive fields (∼80 and 130 Oe) of the Co layers. This result indicates that a complete antiparallel alignment of the layer magnetizations is not reached causing a corresponding reduction in the giant magnetoresistance (GMR). These observations emphasize the importance of the detailed spin configuration in determining the GMR amplitude at low fields. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]