Search

Deposition of alloy films with a well-controlled concentration gradient obtained by co-sputtering from two magnetron sources is studied experimentally and compared with numerical calculations. This method was used together with a linearly moving shutter to fabricate sperimagnetic Co-Tb alloy films with mutually orthogonal concentration and thickness gradients. Using magnetooptical measurements it was demonstrated that, for thicknesses below 10 nm, the compensation concentration (ccomp) shifts towards higher Tb content as the thickness of the Co-Tb film is reduced. Results for Co-Tb alloy films are compared with those for (Tb/Co)RN multilayers with various repetition numbers (RN). For both sample types, the ccomp decreases in a similar way with increasing total film thickness. Thus, the decrease of ccomp with increasing total thickness (either of alloy films or of multilayers) can be considered a universal behavior.

A magnetic multilayer of substrate/Pt-15 nm/Co-0.8 nm/Pt-wedge 0–7 nm/Co-0.6 nm/Pt-2 nm structure is characterized by a perpendicular anisotropy of the Co layers and by graded interlayer coupling between them. Using magnetooptical Kerr microscopy we observed a distinct influence of magnetic domains in one Co layer on the nucleation field and positions of nucleation sites of reversed domains in the second Co layer. For sufficiently strong interlayer coupling a replication of magnetic domains from the magnetically harder layer to the magnetically softer layer is observed.

Magnetophoresis of micrometer sized superparamagnetic beads on sputtered Ir/Co(1.2 nm)/Ir multilayers with perpendicular magnetic anisotropy has been investigated. We show that domain walls motion in these layer systems is controlling the motion of the beads in an aqueous environment, where the domain wall motion is induced by varying perpendicular external magnetic fields of several kA/m. The magnetic fields of the Neel type walls, and forces calculated based on micromagnetic simulations of their structure, are consistent with viscous forces observed in the experiment. We show that the cylindrical domains can be used to efficiently gather originally scattered beads in a small area.

Detailed knowledge of various couplings present in magnetic thin film systems could contribute to a better predictability of devices. In ferromagnetic multilayers with a perpendicular magnetic anisotropy, a correlated waviness can lead to antiferromagetic coupling between adja-cent layers (Neel's coupling). We show, using micromagnetic simulations, that the coupling energy depends strongly on layers separation and on details of interface profiles. We show, too, that the coupling is slightly field dependent.

We measure magnetization reversal and giant magnetoresistance of CoFe/Au/Co/Au multilayers and use micromagnetic simulations to model them. We characterize the system by perpendicular and easy-plane effective anisotropy of Co and CoFe layers, respectively. We show that minor hystereses of magnetoresistance can be reasonably well described by the model. The simulations show that the variation of resistance with the field depends on the field strength at which the sweep reverses, and is correlated with the number of stripe domains present in the Co layers.

[Co83Fe17/Au/Co/Au]N sputter deposited multilayers displaying a giant magnetoresistance have been investigated. Complementary magnetic measurements were conducted in order to characterize a spin reorientation transition in Co83Fe17 layers sandwiched between Au spacers. The transition from a perpendicular magnetic anisotropy to easy-plane one takes place at the thickness of about 1 nm.

Magnetic hysteresis of [ CoFe / Au / Co / Au ] N multilayers displaying giant magnetoresistance was investigated. It is shown that an effective coupling between the neighboring magnetic layers can be modified by the changes of the structure of the multilayers. It is shown, too, that this coupling is influenced by temperature. Some of the observed dependencies are explained on the basis of micromagnetic simulations.

Results of domain structures observation of individual Ni80Fe20 and Co sublayers in sputter deposited (NiFe/Au/Co/Au)10 multilayers, using an element-sensitive method: the photoemission electron microscopy combined with soft X-ray magnetic circular dichroism, are presented. Also, overall domain structures were studied with magnetic force microscopy. The studies allowed us to reveal submicron stripe domains in the investigated samples and the replication of the stripe domains from the Co layers with perpendicular anisotropy to the NiFe layers with easy-plane anisotropy.

Material selective sensitivity of a magneto-optical polar Kerr effect to magnetizations of films from different materials in a multilayer system is presented. The method is supported by rigorous modeling of magneto-optic response from the multilayer system and by experimental demonstration on the periodic cobalt-permalloy multilayers [Ni80Fe20(2 nm)/Au(2 nm)/Co(0.4, 0.8, and 1.2 nm)/Au(2 nm)]10 .

Sputtered Ni 80 Fe 20 /Au/Co/Au multilayers (MLs) exhibit perpendicular anisotropy of Co layers and easy-plane anisotropy of Permalloy layers. In these samples the changes of relative orientation of magnetization between Co and NiFe layers, with magnetic field, can be determined by magnetoresistance measurements. The magnetic structure is discussed for two types of Ni 80 Fe 20 /Au/Co/Au MLs characterized by a weak coupling between ferromagnetic layers: (i) MLs with rectangular hysteresis loops and small coercive field, (ii) MLs with dense stripe domain structure in Co layers.

In this contribution the influence of annealing on magnetization reversal and on the giant magnetoresistance effect of [Ni 80 Fe 20 /Au(t Au )/Co(t Co )/Au(t Au )] 10 multilayers with t Co = 0.6, 0.8 nm and t Au = 1.5, 2.2 nm was studied. Measurements performed for as-deposited samples and after subsequent annealing at T a (423 K < T a < 523 K) show that the GMR effect is stable under annealing below 475 K. It even slightly increases, for T a above 450 K, opening a path for a GMR value control and therefore is important for applications. The most pronounced changes were observed in the saturation field H Co S ∥ which is a measure of perpendicular anisotropy. The significant variations were also noticed in the central part of the M(H) and R(H) curves. They are characterized by the nucleation field H N and the saturation field H S ⊥ which are related to the appearance and disappearance of stripe domains in Co layers, respectively. The influence of T a on values of H Co S ∥, H S ⊥ and H N will be discussed.

Magnetic and magnetotransport properties of (Ni80Fe20/Au/Co/Au)N multilayers with tCo = 0.6 nm and different thicknesses of Au layers (1.5 ≤ tAu ≤ 2.2 nm) have been investigated. The Co layer thickness used ensures its perpendicular anisotropy. We argue that in a hysteretic region of R(H) and M(H) dependencies the reorientation of Py layers is strongly influenced by the magnetic stray fields originating from the domain structure of Co layers. The values of stray fields are determined from R(H) and M(H) measurements and are compared with the calculated ones. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of Ar-ion irradiation on the microstructure, interlayer coupling and giant magnetoresistance (GMR) effect in the model Fe/Cr system was studied by the conversion electron Mossbauer spectrometry (CEMS), vibrating sample magnetometry (VSM), and magnetoresistivity, for the Fe-1.4 nm/Cr- t Cr multilayers with t Cr ranging from 0.73 to 1.85 nm. The loss of antiferromagnetic coupling and the simultaneous degradation of GMR, observed for increasing ion dose, was caused by the formation of pinholes due to the increase of interface roughness and at high ion doses, by the ion-beam mixing leading to the alloying of Fe and Cr at interfaces.

The magnetic properties of sputtered (Ni_(83)Fe_(17)/Au/Co/Au) multilayers with various thicknesses of Au (0.5 ≤ t_(Au) ≤ 3 ㎚), Ni-Fe (1 ≤ t_(Ni-Fe) ≤ 4 ㎚) and Co (0.2 ≤ t_(Co) ≤ 1.5 ㎚) layers were characterized. An alternating inplane and out-of-plane anisotropy of the ferromagnetic layers was achieved for the structures (t_(Au)≥ 1.5 ㎚) showing a weak coupling between the Ni-Fe layers with an in-plane anisotropy and the Co layers (0.3 ≤ t_(Co) ≤ 1.2 ㎚) with a perpendicular anisotropy. For such a structure, a detailed discussion on the GMR effect is presented, relating to the magnetization reversal from a mutually perpendicular magnetic configuration at the remanence to a parallel one at the saturation. An influence of the dense labyrinth domain structure on the magnetoresistance effect is also addressed.

The magnetic properties of the sputter-deposited Cu/NiFe/MnIr/CoFe/Al+Ox/NiFe/Ta system are investigated to create a magnetically optimized TMR system and to tailor the magnetic properties. The unidirectional exchange anisotropy was found to depend strongly on the MnIr layer thickness with no exchange bias for t(MnIr) less than or equal to 5 nm and decreasing bias for t(MnIr) greater than or equal to 10 rim. For t(MnIr) = 15 nm exchange coupling energy was found to be 0.17 mJ/m(2) and the blocking temperature reaches 500 K. The thickness of the CoFe layer was found to strongly influence the shift of the magnetization loop of the upper NiFe layer by magnetostatic coupling. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The magnetoresistive properties of sputtered spin-valve-like Co(t Co1 )/Cu/Co(t Co2 ) multilayers with alternating thicknesses of Co sublayers are investigated. It is shown that annealing at temperatures up to 573 K enhances a magnetoresistance ratio but does not reduce a hysterecity of a R(H) dependence. It is also shown that multilayers with thinner Co sublayers are relatively more stable at higher annealing temperatures.

Metal-oxide ${\mathrm{[Fe}}_{K}/(\text{MgO}){}_{L}{\mathrm{]}}_{N}$ multilayers were grown on MgO(001) substrates for various integer numbers $(K,L)$ of the Fe(001) and MgO(001) monolayers, respectively, and the number of repetitions $N$ varied from 6 to 30. Room-temperature conversion electron M\"ossbauer spectroscopy (CEMS) measurements proved that the magnetic properties of these monoatomic multilayers were extremely sensitive to both the Fe and MgO sublayer thicknesses. A stable ferromagnetic state and a strong perpendicular magnetization component at room temperature were obtained by changing the sublayer thickness and the number of multilayer repetitions. The analysis of the CEMS spectra in correlation with the magneto-optic Kerr effect measurements indicated a complicated domain structure in this special type of metal-insulator material. The vortexlike domain structure was confirmed by micromagnetic simulations.

The influence of annealing on giant magnetoresistance (GMR) effect and magnetization reversal processes has been investigated in Py/Cu (Py = Ni 83 Fe 17 ) sputter-deposited multilayers (MLs) with a limited number of magnetic sublayers (N ≤ 6) and equal sublayer thicknesses both for Py and Cu (t Cu = 2 nm, t Py = 2 nm). Based on the magnetization and magnetoresistance measurements it has been shown that the magnetic behavior of such MLs is strongly influenced by annealing driven disruption of magnetic layers (lateral decoupling) and nonmagnetic layers (magnetic bridging between Py layers). A comparison of experimental hysteresis curves with model dependences indicates that annealing causes a change of the magnetization reversal from a local to an absolute energy minimum mode leading to quasi-two-state magnetoresistance characteristics.

The coupling between permalloy and cobalt layers (characterized by in-plane and perpendicular anisotropy, respectively) in NiFe/Au/Co/Au sandwich films and multilayers was investigated. In sandwich samples the main contribution to the effective coupling comes from the structural imperfections (pinholes and interface roughness). For multilayers, due to creation of dense stripe domains in Co layers, the supplementary coupling is observed in the field range defined by the nucleation and annihilation of the domains.

The thickness dependence of magnetoresistance was studied for a series of thin Co 20 Ag 80 films. The room temperature magnetoresistance in perpendicular configuration (CIP) was measured for as-deposited and annealed samples in fields up to 2 T. All samples were annealed for 10 min at temperatures ranging from 423 to 623 K at steps of 100 K. MR values growing with the thickness t were observed. MR varies steeply for small t and saturates at larger thicknesses. Changes of the width of the MR curve with the film thickness were also analyzed.

The magnetisation reversal of polycrystalline permalloy/copper multilayers with antiferromagnetic couplingwas measured as a function of temperature. The magnetisation behavior is discussed in the relation to the exstence of ferromagnetic pinholes bridging neighbouring permalloy layers.

Magnetization reversal of perpendicular anisotropy [Co/Au] multilayers patterned into micrometer wide stripes with a coercivity gradient along the stripes was investigated with polar magnetooptical Kerr effect microscopy. 1 mm-long stripes were bombarded with He+ ions of 10 keV energy to induce the gradient. It was shown that short pulses of a magnetic field applied perpendicularly to the sample plane move domain walls between up- and down-magnetized areas in a direction of regions with higher coercivities.

The magnetoresistive properties of sputtered [NiFe/Cu0.85Ag0.1Au0.05/Co/Cu0.85Ag0.1Au0.05](N) multilayers are reported. It is shown that these structures exhibit large resistance changes within small magnetic field ranges resulting in sensitivities of up to 6.8%/Oe at room temperature, The observed magnetoresistance effect is anisotropic. The largest resistance changes have been observed for magnetic fields applied parallelly to the easy axis of permalloy layers, (C) 2002 Elsevier Science B.V. All rights reserved.