Ligia E. Zamora

Magnetic properties of the FexMn0.70−xAl0.30 (0.40⩽x⩽0.58) alloy series

The magnetic properties of the FexMn0.7−xAl0.30 (0.40⩽x⩽0.58) alloy series have been investigated by means of 57Fe Mossbauer spectroscopy and ac magnetic susceptibility measurements. From our data, we propose a magnetic phase diagram for the system which is adequately reproduced by a diluted and random-bond Ising model which was analyzed on the basis of the mean-field renormalization-group method.

Mössbauer and magnetization evidence of spin-glass phase in the Fe0.45Mn0.25Al0.30 disordered alloy

Abstract A study by Mossbauer spectroscopy and magnetization of the Fe 0.45 Mn 0.25 Al 0.30 disordered alloy is reported. The curves of magnetization versus temperature for zero-filled cooling (ZFC) and field cooling (FC) are different above 60 K. Also, this alloy showed a remanent magnetization and a temporal decrease when the field turns off. This spin-glass behavior was confirmed as a re-entrant spin-glass in the ferromagnetic phase by Mossbauer spectroscopy.

Magnetic phase diagram of the FexMn0.6−xAl0.40 alloys series

This work shows preliminary results on the study of Fe x Mn0.6−x Al0.40 alloys. It includes measurements of the temperature dependence of the acsusceptibility, zero field cooled magnetization, and Mossbauer spectroscopy. From the results obtained, the occurrence of reentrant spin glass behavior from a spin glass phase to an antiferromagnetic one for 0.2≤x≤0.35 and from a spin glass phase to a ferromagnetic one for the x=0.55 sample is proposed. Also, a normal spin glasstransition was detected in the Fe range corresponding to 0.35≤x≤0.5. These results allow us to construct a magnetic phase diagram for the alloy series.

Magnetic properties of the FexMn0.600 −xAl0.400, 0.200 ≤ x ≤ 0.600, disordered alloy series

The magnetic properties of the FexMn0.600 −xAl0.400(0.200 ≤ x ≤ 0.600) disordered alloys were investigated by means of Mossbauer spectrometry, ac magnetic susceptibility, and ac calorimetry measurements. Our results are summarized in a magnetic phase diagram, which includes an antiferromagnetic phase for x ≤ 0.300 at T ≤ 225 K, a ferromagnetic one for x ≥ 0.425 at T ≤ 340 K, and a paramagnetic phase for high temperatures and all the compositions. This phase diagram also shows for the first time both a re-entrant spin-glass–ferromagnetic transition line for x ≥ 0.425 and T ≤ 60 K and a re-entrant spin-glass–antiferromagnetic one for x ≤ 0.300 and T ≤ 40 K. The occurrence of superparamagnetic-like blocked events (for 0.300 ≤ x ≤ 0.600 and at T ≈ 200 K) is associated with the presence of Fe-rich magnetic clusters which can originate from the disordered atomic character of the alloys.

Magnetic properties of FexMn0.3Al0.7-x (0.275 ⩽ x ⩽ 0.525) disordered alloys

We report on the magnetic properties of Fex Mn0.3 Al0.7-x (0.275 ≤ x ≤ 0.525) disordered alloys, which were investigated by means of Mossbauer spectroscopy, ac magnetic susceptibility and magnetization measurements. Our results are summarized in a magnetic phase diagram which includes both a re-entrant spin glass-ferromagnetic transition line for x > 0.425 and a re-entrant spin glass-antiferromagnetic transition line for x < 0.375.

Influence of the milling conditions on the amorphization of Fe82Nb6B12 alloy

Fe 82 Nb 6 B 12 alloy was synthesized from the elemental powders by a planetary high-energy ball mill, at room temperature, using different milling times and different surfactants. The products were measured by X-ray diffraction, magnetic thermogravimetry, vibrating sample magnetometer, and Mossbauer spectroscopy. Amorphization was observed from the X-ray diffraction on a sample ball milled for about 220 h using 595 rpm and cyclohexane as surfactant. Nevertheless, using the same conditions without surfactant, only the bcc Fe was found. The results are compared with data for rapidly quenched materials.

Site-diluted quantum Heisenberg spin model applied to the magnetic properties of Fe–Al disordered alloys

Abstract In this work we present a theoretical study of the magnetic behavior of disordered Fe–Al alloys on the basis of a simple-diluted quantum Heisenberg spin model with the assumption that the exchange interaction J depends on the Al concentration q. We calculated the critical temperature and exponents through the mean field renormalization group method. An acceptable fit to the experimental phase diagram for Al concentration in the range 0.30⩽q⩽0.45 is obtained.

Spin glass behavior in some Fe-Mn-Al disordered alloys

In this work, we report an ac susceptibility study of Fe0.5Mn0.2Al0.3, Fe0.5Mn0.1Al0.4, and Fe0.225Mn0.375Al0.40 disordered alloys. All the samples exhibit only one well defined peak near 58, 18, and 31 K, respectively. When the frequency of the ac field increases, the measured intensities of the peaks decrease and the maxima shift to higher temperatures, and when the dc field increases the intensity of the peaks decreases. This dependence of the position and intensity of the peaks on the field and frequency is evidence of the spin glass character of the transitions in these alloys. Mossbauer spectra at different temperatures were performed for the sample with 30 at. % Al and the plot of the adjusted mean hyperfine field versus temperature shows a kink at 53 K which is further evidence that this sample shows spin glass behavior.

Low‐temperature Mössbauer study of the mechanically alloyed FexMn0.7−xAl0.3 (0.4≤x≤0.5) series

Results are presented concerning the magnetic properties at low temperatures of mechanically alloyed samples of the Fe x Mn0.7−x Al0.3 (0.4≤x≤0.5) series. According to these results the samples were characterized as having a broad spectrum of relaxation times related to the occurrence of clustering. Also, in the particular case of the x=0.40 sample, we were able to detect a reentrant spin glass freezing transition.

Coercivity relaxation in mechanically alloyed amorphous Fe/sub 50/B/sub 50/ samples

Samples of composition Fe/sub 50/B/sub 50/ have been prepared by high energy ball milling. The phase distribution of the as-milled material included a majority amorphous phase, although that distribution depended on the degree of mechanical hardness of the balls used during the preparation process (crystalline phases were detected in the samples alloyed using regular, non-hardened balls). The hysteretic properties depended also on the type of balls used, the as-milled coercive force being smaller in the case of the samples prepared with harder balls. The measurement of this parameter in samples prepared using non-hardened balls and submitted to thermal treatments evidenced the possibility of reducing significantly the as-milled coercive force. The observation of the same phase distribution (and average grain size of the crystalline phase) present in both the as-milled and the annealed samples led us to conclude that a combination of stress relaxation and of improvement of the interphase coupling could be responsible for the enhancement of the soft properties of the samples resulting from the treatments.