Interface Structures and Magnetic Properties of Exchanged-Coupled Co/Cu Multilayers Sputter-Grown on Ta Buffers

Ishiji, Kotaro; Hashizume, H.

doi:10.1143/jjap.45.4187

Cited by 11 publications

(15 citation statements)

References 39 publications

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“…58 Also, the SPM type GMR contribution as discussed above is not unique to electrodeposited multilayers since it was found in several physically deposited multilayers as well. 66,[72][73][74][75][76] V. SUMMARY In order to clarify the controversial results for the spacer layer thickness dependence of GMR in electrodeposited multilayers, a detailed study of the GMR evolution was performed on Co/Cu multilayers prepared under controlled electrochemical conditions with Cu layer thicknesses ranging from 0.5 nm to 4.5 nm. It turned out that for thin Cu layers (up to 1.5 nm) AMR only occurs.…”

Section: Origin Of Gmr In Electrodeposited Co/cu Multilayers and Ementioning

confidence: 99%

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

et al. 2009

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─ A detailed study of the evolution of the magnetoresistance was performed on electrodeposited Co/Cu multilayers with Cu layer thicknesses ranging from 0.5 nm to 4.5 nm. For thin Cu layers (up to 1.5 nm), anisotropic magnetoresistance (AMR) was observed whereas multilayers with thicker Cu layers exhibited clear giant magnetoresistance (GMR) behaviour. The GMR magnitude increased up to about 3.5 to 4 nm Cu layer thickness and slightly decreased afterwards. According to magnetic measurements, all samples exhibited ferromagnetic (FM) behaviour. The relative remanence turned out to be about 0.75 for both AMR and GMR type multilayers. This clearly indicates the absence of an antiferromagnetic (AF) coupling between adjacent magnetic layers for Cu layers even above 1.5 nm where the GMR effect occurs. The AMR behaviour at low spacer thicknesses indicates the presence of strong FM coupling (due to, e.g., pin-holes in the spacer and/or areas of the Cu layer where the layer thickness is very small). With increasing spacer thickness, the pin-hole density reduces and/or the layer thickness uniformity improves which both lead to a weakening of the FM coupling. This improvement in multilayer structure quality results in a better separation of magnetic layers and the weaker coupling (or complete absence of interlayer coupling) enables a more random magnetization orientation of adjacent layers, all this leading to an increase of the GMR. Coercive field and zero-field resistivity measurements as well as the results of a structural study reported earlier on the same multilayers provide independent evidence for the microstructural features established here. A critical analysis of former results on electrodeposited Co/Cu multilayers suggests the absence of an oscillating GMR in these systems. It is pointed out that the large GMR reported previously on such Co/Cu multilayers at Cu layer thicknesses around 1 nm can be attributed to the presence of a fairly large superparamagnetic (SPM) fraction rather than being due to a strong AF coupling. In the absence of SPM regions as in the present study, AMR only occurs at low spacer thicknesses due to the dominating FM coupling.

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Section: Origin Of Gmr In Electrodeposited Co/cu Multilayers and Ementioning

confidence: 99%

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

et al. 2009

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“…With increasing total thickness, the multilayers usually exhibit a surface roughening, 17,19 and this may well be a reason for the large increase of the GMR SPM term. Namely, it was suggested 35 that a possible mechanism of SPM region formation in multilayers is an increase in surface roughness. The peak position values (H p ) of the MR(H) curves were found to increase with total multilayer thickness (Fig.…”

mentioning

confidence: 99%

Giant Magnetoresistance and Structure of Electrodeposited Co/Cu Multilayers: The Influence of Layer Thicknesses and Cu Deposition Potential

Rajasekaran

Mani

Tóth

et al. 2015

J. Electrochem. Soc.

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The giant magnetoresistance (GMR) and structure was investigated for electrodeposited Co/Cu multilayers prepared by a conventional galvanostatic/potentiostatic pulse combination from a pure sulfate electrolyte with various layer thicknesses, total multilayer thickness and Cu deposition potential. X-ray diffraction (XRD) measurements revealed superlattice satellite reflections for many of the multilayers having sufficiently large thickness (at least 2 nm) of both constituent layers. The bilayer repeats derived from the positions of the visible superlattice reflections were typically 10 -20% higher than the nominal values. The observed GMR was found to be dominated by the multilayer-like ferromagnetic (FM) contribution even for multilayers without visible superlattice satellites. There was always also a modest superparamagnetic (SPM) contribution to the GMR and this term was the largest for multilayers with very thin (0.5 nm) magnetic layers containing apparently a small amount of magnetically decoupled SPM regions. No oscillatory GMR behavior with spacer thickness was observed at any magnetic layer thickness. The saturation of the coercivity as measured by the peak position of the MR(H) curves indicated a complete decoupling of magnetic layers for large spacer thicknesses. The GMR increased with total multilayer thickness which could be ascribed to an increasing SPM contribution to the GMR due to an increasing surface roughness, also indicated by the increasing coercivity. For multilayers with Cu layers deposited at more and more positive potentials, the GMR FM term increased and the GMR SPM term decreased. At the same time, a corresponding reduction of surface roughness measured with atomic force microscopy indicated an improvement of the multilayer structural quality which was, however, not accompanied by an increase of the superlattice reflection intensities. The present results underline that whereas the structural quality as characterized by the surface roughness generally correlates fairly well with the magnitude of the GMR, the microstructural features determining the amplitude of superlattice reflections apparently do not have a direct influence on the GMR. Due to the large giant magnetoresistance (GMR) effect observed in physically deposited Co/Cu multilayers, 1-3 a lot of efforts have been devoted to the study of GMR also on electrodeposited (ED) Co/Cu multilayers (for detailed references, see a recent review).4 A variety of baths have been used for the preparation of ED Co/Cu multilayers, 4 the simplest one containing merely CoSO 4 and CuSO 4 . Over the last two decades, numerous reports have been published on studying the GMR characteristics of ED Co/Cu multilayers from the pure sulfate bath (containing at most some buffering agents). [5][6][7][8][9][10][11][12][13][14][15] In this list of references, we have included only those works from the much larger number of reports 4 in which the ED Co/Cu multilayers were prepared from the sulfate bath at or close to the electrochemically optimized Cu depositi...

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“…19 It should also be noted that the GMR effect of the stack is by an order of magnitude larger than obtained for the previous stack Si/Cr/Cu//Co/Cu/Co (Fig. 2c).…”

Section: Mr(h) Curves Of the Initialmentioning

confidence: 52%

“…On the other hand, roughness with a small lateral length scale may be detrimental to the GMR due to the onset of an "orange-peel" coupling which is ferromagnetic in nature and leads to a reduction of the GMR as analyzed by Shima et al 18 for ED Co/Cu multilayers. The small-scale interface roughness inherited from a rough substrate was demonstrated 19 to promote the appearance of superparamagnetic (SPM) regions in the magnetic layers which then give rise to a GMR contribution often not saturating even up to 10 kOe (Ref. 5).…”

Section: Introductionmentioning

confidence: 99%

“…It was indeed reported that a rougher substrate leads to a larger SPM contribution to the GMR for Co/Cu multilayers produced by either electrodeposition 15 or sputtering. 19 In most applications of the GMR effect, layered structures consisting of a relatively small number of consecutive FM and NM layers are generally used (so-called spin-valve structures 20 ). It is of great interest, therefore, to investigate the initial stages of GMR multilayer film growth by electrodeposition.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Magnetoresistance and Surface Roughness Study of the Initial Growth of Electrodeposited Co∕Cu Multilayers

Tóth

Péter

Bakonyi

2011

J. Electrochem. Soc.

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─ The giant magnetoresistance (GMR) effect has been widely investigated on electrodeposited ferromagnetic/non-magnetic (FM/NM) multilayers generally containing a large number of bilayers. In most applications of the GMR effect, layered structures consisting of a relatively small number of consecutive FM and NM layers are used. It is of great interest, therefore, to investigate the initial stages of GMR multilayer film growth by electrodeposition.In the present work we have extended our previous studies on ED GMR multilayers to layered structures with a total thickness ranging from a few nanometers up to 70 nm. The evolution of the surface roughness and electrical transport properties of such ultrathin ED Co/Cu layered structures was investigated. Various layer combinations were produced including both Co and Cu either as starting or top layers in order (i) to see differences in the nucleation of the first layer and (ii) to trace out the effect of the so-called exchange reaction. Special attention was paid to measure the field-dependence of the magnetoresistance, MR(H) in order to derive information for the appearance of superparamagnetic regions in the magnetic layers. This proved to be helpful for monitoring the evolution of the layer microstructure at each step of the deposition sequence.

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Interface Structures and Magnetic Properties of Exchanged-Coupled Co/Cu Multilayers Sputter-Grown on Ta Buffers

Cited by 11 publications

References 39 publications

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

Giant Magnetoresistance and Structure of Electrodeposited Co/Cu Multilayers: The Influence of Layer Thicknesses and Cu Deposition Potential

Magnetoresistance and Surface Roughness Study of the Initial Growth of Electrodeposited Co∕Cu Multilayers

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