Magnetoresistance and structural study of electrodeposited Ni-Cu/Cu multilayers

Electrodeposition was used to produce Ni Cu/Cu multilayers by two-pulse plating (galvanostatic/potentiostatic control) from a single sulfate/sulfamate electrolyte at an optimized Cu deposition potential for the first time. Magnetoresistance measurements were carried out at room temperature for the Ni Cu/Cu multilayers as a function of the Ni Cu and Cu layer thicknesses and the electrolyte Cu2+ ion concentration. Multilayers with Cu layer thicknesses above 2 nm exhibited a giant magnetoresistance (GMR) effect with a dominating ferromagnetic contribution and with low saturation fields (below 1 kOe). A significant contribution from superparamagnetic (SPM) regions with high saturation fields occurred only for very small nominal magnetic layer thicknesses (around 1 nm). The presence of SPM regions was concluded from the GMR data also for thick magnetic layers with high Cu contents. This hints at a significant phase-separation in Ni-Cu alloys at low-temperature processing, in agreement with previous theoretical modeling and experiments. Low-temperature measurements performed on a selected multilayer down to 18 K indicated a strong increase of the GMR as compared to the room-temperature GMR. Structural studies of some multilayer deposits exhibiting GMR were performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns of Ni Cu/Cu multilayers exhibited in most cases clear satellite peaks, indicating a superlattice structure which was confirmed also by cross-sectional TEM. The deterioration of the multilayer structure revealed by XRD for high Cu-contents in the magnetic layer confirmed the phase-separation concluded from the GMR data

Magnetoresistance and surface roughness study of the initial growth of electrodeposited Co/Cu multilayers

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

Giant magnetoresistance (GMR) in electrodeposited multilayer films: the influence of superparamagnetic regions

When preparing an alternating sequence of magnetic (Co or Ni) and non-magnetic (Cu) layers by electrodeposition using the two-pulse plating technique, a dissolution of the lessnoble magnetic Co and Ni atoms can take place during the deposition of the more noble and non-magnetic Cu atoms. This process results in changes of the actual sublayer thicknesses with respect to the nominal values and can also cause some chemical intermixing at the magnetic/non-magnetic interfaces. As a consequence, superparamagnetic (SPM) regions with “loose magnetic moments” can form as has been demonstrated for electrodeposited Ni-Cu/Cu multilayers. We have also shown recently for electrodeposited Co-Cu/Cu multilayers that if some fraction of the magnetic layers exhibits SPM behaviour then the observed giant magnetoresistance (GMR) can be quantitatively decomposed into a ferromagnetic (FM) and a SPM contribution. In this paper, the results of a similar GMR decomposition study are presented for two electrodeposited Co-Cu/Cu multilayers. In the multilayer with strongly non-saturated magnetoresistance curves, the dominant GMR term was due to SPM regions, whereas in the other multilayer for which the magnetoresistance is mostly saturated in magnetic fields around 1 to 2 kOe, the FM contribution to the GMR is much larger. At the same time, magnetic measurements on the first multilayer sample have also revealed the presence of a large SPM contribution to the magnetization

Hazai fitoftórás növénybetegségek felmérése és a kórokozók feno- és genotípusos vizsgálata = Pheno- and genotypic studies on Phytophthora spp. occurring and causing plant diseases in Hungary

A gombaszerű, de algákkal rokon növénykórokozó Phytophthora-fajok világszerte súlyos károkat okoznak mezőgazdasági, kertészeti és erdészeti kultúrákban. Magyarországon kevés ismeretünk volt előfordulásuk gyakoriságáról, ezért célunk a hazai fitoftórák és az általuk kiváltott betegségek felmérése és a patogének változékonyságának tanulmányozása volt. Összesen 18 fitoftórát (közülük 7-et hazai viszonylatban első alkalommal) azonosítottunk 19 növényfajról (elsősorban dísznövényekről), erdők és gyümölcsösök talajából, valamint 32 hazánkban eddig le nem írt fitoftóra-gazdanövény kapcsolatot jegyeztünk fel. Leggyakoribb betegségtünet a gyökér- és szártőrothadás volt, minek következtében az egész növény elpusztulhat. Hajtásokon és leveleken ritkábban fordultak elő e patogének. EPPO karantén listás kórokozókat nem azonosítottunk. A beteg növények mintegy felét mindössze néhány különösen elterjedt faj károsította. A már korábban ismert kórokozók mellett azonosítottunk a tudományra nézve új fajokat is, melyek gazdasági szerepének vizsgálata feltétlenül szükséges. Megállapítottuk továbbá, hogy a fitoftórás égerpusztulás okozásáért hazánkban is elsősorban a kórokozó agresszívabb alfaja, a P. alni subsp. alni felelős, melynek ama klónszerű populációja terjedt el Magyarországon, mely Európa más részein is jelen van. Munkánk egy részét nemzetközi együttműködésben végeztük, ill. folytatjuk a továbbiakban. | The genus Phytophthora is a group of ‘fungus-like’ plant pathogens causing severe losses in agriculture, horticulture and forestry. In Hungary, however, these pseudofungi have not been studied in proportion to their importance. Thus our goals were (i) to survey the occurrence of Phytophthoras country-wide, and (ii) to conduct studies on the genetic diversity of populations of the pathogens. Altogether 18 Phythophthoras were identified from 19 plant species representing mainly woody ornamentals, and some were isolated from forestry and soils of orchards. Thirty-two Phytophthora-host combinations new to Hungary were recorded. The most frequent disease symptoms were root rot and stem necrosis, resulting in the death of affected plants in most cases. Shoot and leaf blights were rare. We have not found Phytophthoras listed on the EPPO quarantine or alert lists. Approximately half of the diseased plants were attacked by the same few Phytophthoras. In addition to the old-known pathogens, we also identified new Phytophthora species, of which economic importance needs to be examined. It was also found that the phytophthora disease of alder in Hungary was primarily caused by that clonal population of the aggressive subspecies, P. alni subsp. alni, which is also present in other parts of Europe. Our research work was partly carried out in international co-operations, and will be continued so

A survey in natural forest ecosystems of Vietnam reveals high diversity of both new and described Phytophthora taxa including P. ramorum

In 2016 and 2017, surveys of Phytophthora diversity were performed in 25 natural and semi-natural forest stands and 16 rivers in temperate and subtropical montane and tropical lowland regions of Vietnam. Using baiting assays from soil samples and rivers and direct isolations from naturally fallen leaves, 13 described species, five informally designated taxa and 21 previously unknown taxa of Phytophthora were isolated from 58 of the 91 soil samples (63.7%) taken from the rhizosphere of 52 of the 64 woody plant species sampled (81.3%) in 20 forest stands (83.7%), and from all rivers: P. capensis, P. citricola VII, VIII, IX, X and XI, P. sp. botryosa-like 2, P. sp. meadii-like 1 and 2, P. sp. tropicalis-like 2 and P. sp. multivesiculata-like 1 from Phytophthora major phylogenetic Clade 2; P. castaneae and P. heveae from Clade 5; P. chlamydospora, P. gregata, P. sp. bitahaiensis-like and P. sp. sylvatica-like 1, 2 and 3 from Clade 6; P. cinnamomi (Pc), P. parvispora, P. attenuata, P. sp. attenuata-like 1, 2 and 3 and P. ×heterohybrida from Clade 7; P. drechsleri, P. pseudocryptogea, P. ramorum (Pr) and P. sp. kelmania from Clade 8, P. macrochlamydospora, P. sp. ×insolita-like, P. sp. ×kunnunara-like, P. sp. ×virginiana-like s.l. and three new taxa, P. sp. quininea-like, P. sp. ×Grenada 3-like and P. sp. ×Peru 4-like, from Clade 9; and P. sp. gallica-like 1 and 2 from Clade 10. The A1 and A2 mating types of both Pc and Pr co-occurred. The A2 mating type of Pc was associated with severe dieback of montane forests in northern Vietnam. Most other Phytophthora species, including Pr, were not associated with obvious disease symptoms. It is concluded that (1) Vietnam is within the center of origin of most Phytophthora taxa found including Pc and Pr, and (2) Phytophthora clades 2, 5, 6, 7, 8, 9, and 10 are native to Indochina.info:eu-repo/semantics/publishedVersio

Égerpatogén Phytophthora-fajhibridek mitokondriális genomjainak tanulmányozása = Study of mitochondrial genoms of hybrid alder Phytophtoras

A kutatás a fitoftórás égervész kórokozójával, a P. alnival foglalkozik. E kórokozó izolátumait 3 klónszerű alfajba sorolják. A P. alni szülőfajai feltehetően az égerre nem patogén P. cambivora és a P. fragariae. Célunk a hibridek és feltételezett szülőfajaik genetikai változékonyságának tanulmányozása volt. Kifejlesztettünk egy olyan DNS-re alapozott eljárást, mellyel a P. alni alfajai kétséget kizáró módon elkülöníthetők egymástól és a feltételezett szülőfajoktól. A módszer alkalmas a hibridek fertőzött növényi mintákban való kimutatására. A mitokondriális (mt)DNS-t tekintve 41 P. cambivora izolátum tizenhét, 19 P. fragariae izolátum négy, 25 P. alni törzs pedig két haplotípust tartalmazott. Nem találtunk a hibridekben és bármelyik szülőfajban közös haplotípust. Régiók szerinti tagozódást sem figyeltünk meg. A P. fragariae szamócáról és málnáról származó tenyészetei viszont egyértelműen elkülönültek. A P. alni ssp. alni kétféle mintázatot tartalmazott. Egyik az egyöntetű P. alni ssp. multiformisban, a másik pedig a szintén egyöntetű P. alni ssp. uniformisban is előfordult. Ez egy olyan genetikai kölcsönhatásra utal, melynek következtében egyes törzsek ssp. alni típusú sejtmagot és ssp. uniformis, vagy ssp. multiformis típusú mitokondriumot örököltek. Különböző mtDNS-típusok jelenléte a hibridekben azt sejteti, hogy nem csak egy-egy szülőizolátum között zajlott le a hibridizációs esemény. Adataink segítik a hibridek kialakulásának megismerését. | The research focuses on Phytophthora alni, the causal agent of alder decline, of which isolates are classified into three clonal subspecies. The putative parental species of P. alni are P. cambivora and P. fragariae, which are not pathogens of alder. Our aim was to study the genetic variability of P. alni and their parental species. We have developed a DNA-based assay that unambiguously differentiates amongst the three subspecies of P. alni and the putative parents. The assay is suitable for detecting the causal agent in the infested plant. Regarding the mitochondrial (mt)DNA, 41 P. cambivora, 19 P. fragariae and 25 P. alni strains contained seventeen, four and two mtDNA haplotypes, respectively. No common haplotype was found in the hybrids and any of the putative parents. Geographical sub-structuring was neither observed. Isolates of P. fragariae were clearly separated according to their hosts (strawberry vs. raspberry). P. alni ssp. alni possessed two types of mtDNA, one also present in the monomorphic P. alni ssp. multiformis, and another one present in P. alni ssp. uniformis. This suggests that certain hybrid strains received ssp. alni-type nucleus but ssp. uniformis-type or ssp. multiformis-type mitochondria. The presence of different mtDNA-types in the hybrids indicates that not only two parental isolates took part in the formation of P. alni hybrids. The data help to understand the evolution of P. alni

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

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 containg 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 GMRFM term increased and the GMRSPM 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

Microstructure formation in electrodeposited Co-Cu/Cu multilayers with GMR effect: influence of current density during the magnetic layer deposition

The influence of the current density applied during the deposition of the magnetic layers on the microstructure formation in electrodeposited Co-Cu/Cu multilayers and on their giant magnetoresistance (GMR) was investigated using a combination of magnetoresistance measurements, wide-angle and small-angle X-ray scattering, high-resolution transmission electron microscopy, atomic force microscopy and chemical analysis. The magnetoresistance measurements revealed that a reduction of the current density stimulates a transition from the formation of the magnetic layers with predominantly ferromagnetic character to the formation of superparamagnetic regions. As based on electrochemical considerations, it was supposed that such a change in the magnetic properties can be caused by an increased amount of Cu codeposited with Co at low current densities. It turned out from the structural studies that a pronounced segregation of Co and Cu occurs at low current densities. In accordance with their very low mutual solubility at room temperature, no atomic scale intermixing of Co and Cu could be detected. The segregation of Cu and Co was related to the fragmentation of the magnetic layers, to the enhancement of the local lattice strains, to the increase of the interface corrugations, to the partial loss of the multilayer periodicity and finally to the formation of Co precipitates in the Cu matrix