H.O. Gupta

360° and 0° walls in multilayer Permalloy films

Abstract 360° walls have been investigated in Permalloy double films and multilayers with intermediate layers of carbon, prepared by electron beam evaporation and dc triode sputtering. They are nucleated in an easy axis field when a Bloch line in one layer is trapped at an inclusion. To minimise the magnetostatic energy through the layers, the 360° walls are inclined at an angle β

Structural and magnetic properties of Fe/Ni and Fe/Co multilayers

Fe/Ni and Fe/Co multilayers (ML) have been deposited by dc triode sputtering, with a layer thickness (t) in the range 1–10 nm. For t≳4 nm both metals are in crystalline form (bcc Fe, fcc Ni, hcp Co). For t<2 nm one has a single‐phase structure (fcc in Fe/Ni ML, bcc in Fe/Co ML) which can be explained by assuming the presence of a 1‐nm‐thick mixed layer at the interfaces. This interfacial mixing affects the magnetic properties. The basic difference between the two systems is the fact that while Fe‐Ni interfacial alloys are magnetically soft those of Fe‐Co are hard which leads to different magnetic behavior. Furthermore, the Fe layers are better crystallized in our samples than those prepared by rf magnetron or ion‐beam sputtering.

Magnetic properties and domain structure studies in dc triode‐sputtered permalloy/carbon multilayer films

Double‐layer and multiple‐layer thin films of permalloy with carbon as a intermediate nonmagnetic spacer were prepared by low‐energy dc triode sputtering. Coupling between the two layers of the double films is investigated on a series of samples with a fixed thickness of permalloy layers (dp = 300 A) and thickness of the carbon layer dc, varying from 0 to 25 A. Thickness dc = 10 A is found to be the limiting value for the carbon layer to be continuous and 20 A for domain structures in the two magnetic films to decouple. Saturation magnetization Ms, uniaxial anisotropy field, Hk, and coercive force Hc of multilayers with dc = 10 A and dp from 50 to 600 A (number of magnetic layers from 12 down to 1) are measured and found consistent with earlier results by other authors. Multiple domain walls in the multilayers are investigated by Lorentz electron microscopy.

Magnetic and structural studies in sputtered Ni/C, Co/C and Fe/C multilayers

Abstract We have prepared TM/C multilayers with TM = Ni, Co and Fe by triode sputtering and carried out structural and magnetic studies. For TM layers thinner than about 30 A, an amorphous structure is obtained. For TM layers thicker than about 60 A, a pure crystalline structure is obtained. Layering is shown to decrease the coercive force and induce an in-plane uniaxial anisotropy. These results and FMR data are discussed.

Wall transitions in Permalloy double films

The transition from twin walls to superimposed walls and vice-versa, in two-layer laminated Permalloy films has been observed. Pictures of walls and quasiwalls have been taken using the high-resolution Kerr effect. The transition occurs at reproducible values of magnetic field applied in the hard direction of the sample, and experimental results indicate that it takes place due to the motion of Bloch lines along the walls. >

Magnetic and structural studies in sputtered Co/C multilayers

Co/C multilayers have been prepared by triode sputtering under controlled conditions. Their structural, magnetic, and FMR (ferromagnetic resonance) properties have been investigated. For t(Co) 6 nm. The magnetization decreases steeply for t(Co) 8 nm, and an easy plane is present for t(Co) >

Magnetostriction of sputtered Co/C multilayers

Abstract The measurements of magnetostriction constant λs of Co/C multilayers have been performed at room temperature using strain modulated ferromagnetic resonance. The dependence of λs on the inverse Co layer thickness is interpreted as arising due to the volume and interface interactions. It is suggested that magnetostriction in Co/C systems arises mainly from dipole-dipole interaction.

Magnetic properties of double Permalloy films

Abstract Two-layered Permalloy films with a carhon intermediate layer of different thickness were investigated to correlate the coercivity values and magnetization process with the strength of the exchange coupling. The interpretation of strong, medium and weak coupling is proposed.

Micromagnetics of two-layer laminated films with superimposed domains

The micromagnetic structure of the walls in two‐layer laminated films has been investigated using the high‐resolution longitudinal Kerr effect. Superimposed Bloch lines of opposite type (cross or circular) in the two magnetic layers are observed and interpreted. The mixed type of walls with twin and superimposed Neel segments is discussed. The magnetization distribution at crossing points between the twin walls nucleated in a hard axis field is deduced from the Kerr effect contrast of the walls and quasiwalls. The appearance of superimposed 360° walls and segments in 90° walls in samples with biaxial anisotropy is shown.

Magnetic and thoretical studies of NiFe layers coupled through a non-magnetic interlayers

Polycrystalline double-permalloy (Ni/sub 80/Fe/sub 20/) films separated by a copper interfilm were investigated by FMR (ferromagnetic resonance), vibrating sample magnetometry, and Lorentz microscopy. The samples are deposited from e-gun sources onto both glass and NaCl substrates in an ultrahigh vacuum. A long-range exchange coupling between the Permalloy films is indicated by the dependence of the resonant field position of the spin wave modes on the thickness of the copper interfilm. Spin wave resonance experiments have shown the onset of exchange coupling to occur at an interfilm thickness of approximately=30 AA and that the coupling is sufficiently strong for the degeneracy of the in-phase and out-of-phase coupled modes to be lifted when the interfilm thickness is >