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1
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Mössbauer Study of Nanocrystalline Alloys

100%
Kopcewicz M.
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vol. 96
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issue 1
49-68
EN
The current status of the Mössbauer investigations of the soft magnetic nanocrystalline alloys produced by utilizing the first step of crystallization of the amorphous alloys such as FeCuNbSiB and FeZrBCu is reviewed. Conventional Mössbauer measurements allow the identification of phases formed due to annealing of the amorphous precursor and the evaluation of their relative content. The unconventional rf-Mössbauer technique, in which the rf collapse and sideband effects are employed, permits us to distinguish the magnetically soft nanocrystalline bcc-Fe phase from the magnetically harder microcrystalline Fe. Qualitative information concerning the distribution of anisotropy fields in the nanocrystalline grains can be inferred from the dependence of the rf collapsed spectra on the rf field intensity. The rf-sidebands effect reveals strong reduction of magnetostriction due to the formation of the nanocrystalline phase. The rf-Mössbauer technique provides a unique opportunity to study the microstructure and magnetic properties of each phase formed in the amorphous precursor.
2
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Transmission and Conversion Electron Mössbauer Study of Crystallization of Amorphous FeZrB Alloys

64%
Grabias A., Kopcewicz M.
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vol. 96
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issue 1
123-130
EN
The combined conversion electron emission and γ-transmission Mössbauer spectroscopy are used to investigate the differences in the bulk and surface crystallization of the amorphous FeZrB alloy in which the nanocrystalline bcc-Fe phase was formed due to annealing. The measurements were performed for the ribbons in the as-quenched state, after 1 h annealing at 430-600°C and after short time annealing at 600°C. The clear differences in the surface and bulk crystallization behaviours were detected. Not only the surface crystallization starts at lower annealing temperature than the bulk one, but additional phases were detected at the surface which do not form in the bulk. Structural transformations as a function of annealing time (15-120 s) are compared with those induced by 1 h anneals. The enhanced surface crystallization was attributed to the boron depletion of the surface region which leads to the decrease in the crystallization temperature at the surface.
3
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Nanocrystallization of the Amorphous Fe_{14}Ni_{40}Zr_7B_{12} Alloys Studied by the Mössbauer Spectroscopy

51%
Kopcewicz M., Idzikowski B., Kalinowska J.
Acta Physica Polonica A
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2002
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vol. 102
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issue 2
301-307
EN
Formation of the soft magnetic nanostructure in amorphous Fe_{41}Ni_{40}Zr_7B_{12} alloy due to heat treatment is studied by the Mössbauer, differential scanning calorimetry, and X-ray diffraction techniques. Annealing at temperatures 520-580ºC leads to the formation of extremely soft nanocrystalline alloy as revealed by the rf-Mössbauer measurements. The superparamagnetic behaviour was observed for the alloy annealed at 620-640ºC. At higher annealing temperatures good soft magnetic properties deteriorate.
4
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Structural Investigation of Rapidly Quenched FeCoPtB Alloys

51%
Grabias A., Latuch J., Oleszak D., Kopcewicz M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 1
68-71
EN
Two sets of Fe_{52-x}Co_{x}Pt_{28}B_{20} (x=0-26 at.%) and Fe_{60-x}Co_{x}Pt_{25}B_{15} (x=0-40 at.%) alloys were prepared in the form of ribbons by the rapid quenching technique. Structure of the samples was characterized by Mössbauer spectroscopy and X-ray diffraction. In the as-quenched alloys the amorphous phase coexisted with the fcc-(Fe,Co)Pt disordered solid solution. Differential scanning calorimetry measurements performed in the range 50-720 °C revealed one or two exothermal peaks. The magnetically hard ordered L1_{0} (Fe,Co)Pt and magnetically soft (Fe,Co)_{2}B nanocrystalline phases were formed due to thermal treatment of the alloys. The influence of Co content on the structure of the as-quenched and heated alloys was studied.
5
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CEMS and RF-Mössbauer Study of Nanocrystalline Fe_{81}Zr_{7}B_{12} Alloy

51%
Kopcewicz M., Grabias A., Nowicki P.
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EN
The combined conversion electron (CEMS) and γ-transmission Mossbauer spectroscopy is used to investigate the differences in the bulk and surface crystallization of the amorphous Fe_{81}Zr_{7}B_{12} alloy. The radio-frequency induced effects (rf collapse and side bands) are used to study the microstructure and magnetic behaviour of the alloy in the amorphous and nanocrystalline states. Rf-Mossbauer experiment permits us to distinguish soft magnetic nanocrystalline bcc-Fe phase from microcrystalline α-Fe.
6
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Mössbauer Study of Magnetic Properties of Fe_{80-x}Co_{x}Zr_7Si_{13} (x = 0-30~at.%) Boron-Free Amorphous Alloys

39%
Kopcewicz M., Grabias A., Latuch J., Ferenc J., Żuberek R., Nesteruk K.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1257-1260
EN
Amorphous Fe_{80-x}Co_{x}Zr_7Si_{13} (x = 0-30 at.%) alloys in which boron was completely replaced by silicon as a glass forming element have been prepared by melt quenching. Partial substitution of iron by cobalt caused the increase of the hyperfine field and saturation magnetization. The specialized rf-Mössbauer measurements revealed that all amorphous alloys studied are magnetically very soft. The rf-sidebands effect, related to magnetostriction, increases with the increase of Co content. In Fe_{50}Co_{30}Zr_7Si_{13} sample the rf field exposure induced partial crystallization of amorphous phase that was attributed to mechanical deformations related to high frequency magnetostrictive vibrations induced by the rf field. The measurements of the hysteresis loop revealed that coercivity increases for higher Co content.
7
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Influence of Temperature and Annealing on GMR in Sputtered Permalloy/Cu Multilayers

39%
Urbaniak M., Stobiecki F., Luciński T., Kopcewicz M., Grabias A., Aleksiejew J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
539-542
EN
The influence of temperature and annealing on giant magnetoresistance of Si(100)/Cu(20 nm)/Py(2 nm)/(Cu(2 nm)/Py(2 nm))_{100} multilayer (Py = Ni_{83}Fe_{17}) sputtered at room temperature in double face-to-face configuration is reported. It was found that giant magnetoresistance value, ΔR_{GMR}/R_{sat} (where R_{sat} is the resistance in saturation), monotonically decreases with increasing temperature (4.5% at 173 K to about 1% at 373 K). This results from the decrease in magnetic change of resistance, ΔR_{GMR}, and to the lesser extent from an increase in R_{sat}, though both of them are caused by the shortening of electrons mean free path. The observed almost linear decrease in giant magnetoresistance saturation field with increasing temperature is explained by temperature changes of magnetization profile. Vibrating sample magnetometer measurements revealed that the increase in temperature results in pronounced decrease in remnant to saturation magnetization ratio (M_{r}/M_{s}) suggesting that at low temperatures magnetic bridges between Py layers play an important role in magnetization process. It is shown that proper annealing, by an annihilation of bridges and/or lateral decoupling, leads to an increase in giant magnetoresistance ratio from 3.4% in as deposited state to 4.7%.
8
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Magnetic Properties and Structure of Amorphous Fe_{74}Hf_{4}Ta_{1}Cu_{1}Gd_{1}La_{x}Si_{15-x}B_{4} (x = 0, 7) Ribbons

39%
Bardziński P., Kopcewicz M., Rybaczuk M., Hasiak M., Musiał A., Kinzhybalo V., Idzikowski B.
Acta Physica Polonica A
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2015
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vol. 127
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issue 3
827-830
EN
The multi component Fe_{74}Hf_{4}Ta_{1}Cu_{1}Gd_{1}La_{x}Si_{15-x}B_{4} (x = 0, 7) alloys are promising candidates in the search for materials with unusual mechanical and magnetic properties. Amorphous nature of melt-spun samples was confirmed by X-ray diffractometry and Mössbauer spectroscopy. The X-ray diffraction patterns revealed a distinct amorphous halo. The low-field components of magnetic hyperfine field distributions on iron nuclei are observed in the Mössbauer spectra, with average hyperfine field values of 19.9 and 15.7 T for x = 0 and x = 7, respectively. Coercivity studied by vibrating sample magnetometer was about 12 A/m for x = 0 and 82 A/m for x = 7 at 300 K and about 600 A/m for x = 0 and 1200 A/m for x = 7 at 400 K. Remanence also changed with temperature, amounting to 0.64 T for x = 0 and 0.36 T for x = 7 at 300 K, while at 400 K it was 0.43 and 0.11 T for x = 0 and x = 7, respectively. It is shown that La addition has beneficial effect of shifting the Curie point towards lower temperatures together with the increase of magnitude of magnetization.
9
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Complex Magnetic Structure of Strongly Coupled Fe/Si Multilayers

39%
Dubowik J., Stobiecki F., Szymański B., Kudryavtsev Y., Grabias A., Kopcewicz M.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
451-454
EN
Fe/Si multilayers with strong bilinear and biquadratic couplings were investigated. A complex structure revealed by the Mössbauer spectroscopy corresponds to multimode ferromagnetic resonance spectra in a non-saturated state. Simple dispersion relations for antiferromagnetic coupled bilayer structures are shown to be inapplicable to the Fe/Si multilayers with a strong biquadratic component to the antiferromagnetic bilinear coupling.
10
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Content available

Structure and Magnetic Proporties of Polymer Matrix Nanocomposites

33%
Ławecka M., Leonowicz M., Kopcewicz M., Ślawska-Waniewska A., Kozubowski J., Dzhardimalieva G., Rosenberg A., Pomogailo A.
Acta Physica Polonica A
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2002
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vol. 102
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issue 2
317-321
EN
Structure and magnetic properties of the thermal decomposition products of Fe(III)Co(II) acrylate complex were analysed. The crystalline phases, which were found in the fully processed material, at 643 K, were Fe_3O_4, CoFe_2O_4, and CoO and had a mean particle size of about 30 nm. In the intermediate stages of the thermolysis iron was present in a form of Fe^{III} (trivalent low-spin iron), Fe^{2+} (divalent high-spin iron), and Fe_3O_4. The coercivity and remanence were measured versus temperature in the range of 5-300 K, in 1.1 T applied field. Both, _MH_c and M_r, decreased showing room temperature values of 0.038 T and 7.49 mT, for coercivity and remanence, respectively. At temperatures below 200 K the hysteresis loops were asymmetrical, opened and shifted towards negative field values.
11
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Domains Stimulated Magnetostatic Coupling in NiFe/Au/Co/Au Multilayers Investigated by Complementary Methods

27%
Stobiecki F., Urbaniak M., Szymański B., Kuświk P., Schmidt M., Aleksiejew J., Weis T., Engel D., Lengemann D., Ehresmann A., Kopcewicz M.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
345-347
EN
The magnetic structure of Ni_{80}Fe_{20}/Au/Co/Au multilayers characterized by easy-plane and easy-axis perpendicular to the sample plane anisotropies for NiFe and Co, respectively, is strongly modified by magnetostatic coupling resulting from stray fields of stripe domains in the Co layers. Using complementary methods it will be shown that the magnetostatic coupling increases with decreasing Au spacer thickness, with the weakening of the easy plane anisotropy of the NiFe layers and with increasing thickness of the Co layers.
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