Mechanically alloyed Cu–Fe studied by Mössbauer spectroscopy

doi:10.1016/S0925-8388(01)01301-9

Journal of Alloys and Compounds

Volume 326, Issues 1–2, 9 August 2001, Pages 188-192

https://doi.org/10.1016/S0925-8388(01)01301-9 Get rights and content

Abstract

Recent studies of mechanically alloyed Fe–Cu powder mixtures have suggested differences in the local magnetic environment of iron atoms. For a more accurate definition of this point, ball-milled Cu₇₀Fe₃₀ and Cu₅₀Fe₅₀ alloys were investigated by Mössbauer spectroscopy in the temperature range 4.2–300 K. The low temperature Mössbauer spectra exhibit a broad magnetic pattern typical of a defect structural configuration. The magnetic splitting strongly decreases with increasing temperature, especially in the case of Cu₇₀Fe₃₀ alloy. But even for this composition there is, at room temperature, an unresolved magnetic pattern. Applying a magnetic field of 3 T, parallel to γ rays, at 4.2 K a rotation of all magnetic moments along the external field is observed. The samples behave as an alloy with continuously distributed local fields.

Introduction

In recent years the Fe–Cu supersaturated solutions have attracted the attention of a remarkable number of researchers. The interest comes either from the physical properties or the possible applications, in particular due to GMR behaviour observed in nanogranular specimens. The most relevant properties are related to a volume expansion (increase of lattice parameter) observed both in f.c.c. and b.c.c. parts of the Fe–Cu solid solutions, when compared with pure elements b.c.c.-Fe and, respectively, f.c.c.-Cu [1], [2] and a net magnetic moment of Fe, at low temperatures, for a Cu content higher than 98% in the case of bulk samples [3] and higher than 90% in the case of ball-milling [4].

In this work a Mössbauer spectroscopy study at various temperatures on several Fe–Cu ball-milled samples is presented, completing previously reported data [1], [2], [5], [6], [7]. Mössbauer spectroscopy is a sensitive tool for iron containing samples and provides useful information about the local co-ordination, as well as about the frozen spin–state and related relaxation mechanisms as a function of temperature.

Section snippets

Experimental

Fe–Cu samples having the atomic proportions Fe₃₀Cu₇₀ and Fe₅₀Cu₅₀ were obtained by mechanical attrition of a mixture of iron and copper powders (99.99 wt.% purity). The milling was performed in hardened steel vials under argon atmosphere to prevent oxidation [1], [2]. The Mössbauer spectra were measured in the temperature range 4.2–300 K in a conventional cryostat (TBT) with a symmetrical linear waveform spectrometer and a source of ⁵⁷Co in a rhodium matrix. A variable temperature cryomagnet

Results and discussion

The Mössbauer data were obtained on Fe₃₀Cu₇₀ milled for 16 and 32 h (samples A and B, respectively) as well as on Fe₅₀Cu₅₀ milled for 16 h (sample C). The experimental data are shown in Fig. 1, Fig. 2, Fig. 3 together with their related B_hf distributions. As previously found [1], [2] for 16 h ball milling, an homogenous solid solution was obtained for both compositions, showing no further increase of lattice parameter. Indeed, the Mössbauer spectra taken at various temperatures, and in

Conclusions

The Mössbauer spectra of ball milled f.c.c. Fe₃₀Cu₇₀ and Fe₅₀Cu₅₀ powders all display a magnetic character in the temperature range 4.2–300 K and a freezing of spin orientations at low temperatures. The broad profile of the spectra suggests that the obtained structure is a solid solution with continuously distributed hyperfine fields at the Fe nuclei. The experimental data compared to theoretical calculations of hyperfine fields lead us to conclude that ball milling of Fe–Cu powders having the

Acknowledgments

Planning and development of the studies presented here form a part of an Italian National Research Project entitled ‘Leghe e composti intermetallici: stabilità termodinamica, proprietà fisiche e reattività’. The authors would like to thank the Italian Ministero della Ricerca Scientifica e Tecnologica (Programmi di Ricerca di Rilevante Interesse Nazionale) for financial support. The authors are grateful to MAE-Italy and ANSTI-Romania for joint financial support in the frame of ‘13th Scientific

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¹: Permanent address: Institute of Instrumentation, D.A. University, Khandwa Road, Indore, India.

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Mechanically alloyed Cu–Fe studied by Mössbauer spectroscopy

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgments

J. Mag. Mag. Mater.

J. Mag. Mag. Mater.

Phil. Mag.

Mater. Sci. Forum

J. Phys. F. (Metal Physics)

J. Appl. Phys.

Mater. Sci. Forum

Phil. Mag.