The effect of mechanical milling on the structure and magnetic properties of Fe2Sc Laves phase

In the present paper, a high energy milling process has been used to alloy Fe and B in the proportion 2:1. X-ray diffraction and Mössbauer spectroscopy were used to follow the solid state reaction among the alloy components and phase formation during thermal treatments of the final milled alloy, at distinct temperatures and environments. X-ray, DSC and Mössbauer data of the 310 h milled alloy show the presence of three phases: small fractions of α-Fe (n-Fe) and Fe 2 B (n-Fe 2 B) nanocrystalline phases and a large amount of amorphous Fe 2 B (a-Fe 2 B) phase (73%). Heat treatment of the milled alloy was done in a high vacuum furnace, followed by in situ Mössbauer measurements, or by annealing the sample sealed in a quartz tube. It is shown that segregation and crystallization effects thermally induced in the samples have been enhanced by the presence of oxygen in the residual atmosphere, being less effective in the case where the sample was continuously pumped during the annealing. These effects may have occurred due to boron oxidation. Also, the presence of a tet-Fe 3 B phase in the annealed samples has been observed. The high temperature Mössbauer spectra for the sample annealed at 823 K indicate that the n-Fe 2 B, n-Fe 3 B and n-Fe phases exhibit superparamagnetic behaviour, with estimated blocking temperatures of 723 and 823 K, respectively. The amorphous a-Fe 2 B phase has a T C value estimated at about 823 K that fits into the system reported for amorphous Fe/B ribbons.

Section: Resultsmentioning

confidence: 85%

Thermal studies and magnetic properties of mechanical alloyed Fe₂B

Passamani¹,

Tagarro

Larica

et al. 2002

“…materials with metastable phases, or just new materials. In the field of new materials, amorphous phases obtained from the HEM of intermetallic compounds have been extensively studied by Larica et al (1995), Biondo et al (1997), Xia et al (1996) and Zhou and Bakker (1994a, b). It has been found that besides the thermodynamic aspects of the materials under preparation, specific milling conditions are also very important in order to obtain such phases.…”

Section: Introductionmentioning

confidence: 99%

Amorphization of obtained by milling under different atmospheres

Passamani

Larica

Santos

et al. 1999

In the present work, high-energy milling under two different atmospheres was applied to the intermetallic compound and to the chemical elemental powders of Er and Fe with stoichiometric composition. Sample A is the compound milled under Ar, sample B the compound milled under and sample C the elemental powders milled under atmosphere. X-ray diffraction (XRD) and Mössbauer spectroscopy (MS) results of the samples A and B show a segregation process with increase of the milling time. Under atmosphere, the initial compound was nearly dissociated with 50 h of milling, while with Ar atmosphere the segregation process was completed with 100 h of milling. From the analysis of the XRD and MS results, it was possible to observe the appearance of other phases at intermediate milling times, in both samples A and B. One phase was associated with an amorphous alloy with a magnetic ordering temperature, obtained by AC magnetic susceptibility, at about 190 K, a second phase was attributed to nanocrystallites of and a third one associated with an fcc Er high-pressure phase stabilized by N atoms. In the case of sample B, for milling times longer than 400 h, XRD and MS results indicate the presence of an Fe-Er-N disordered alloy, with magnetic ordering temperature above room temperature. The XRD and MS results of sample C show the formation of an amorphous phase, with about 87% of MS relative area in this phase at 68 h of milling.

“…Mechanical milling (MM) is a technique for producing metastable phases. It has been shown that, upon MM, an intermetallic phase can transform to a chemically disordered or an amorphous phase [1][2][3][4] at temperatures near room temperature (RT). Some of these metastable phases prepared by MM have displayed interesting magnetic phenomena [5].…”

Section: Introductionmentioning

confidence: 99%

Chemical order and structure of the mechanically milled Laves phase

Xia

Saitovitch

Silva

et al. 1998

The effects of mechanical milling on the chemical order and structure of the C14 Laves phase have been studied by x-ray diffraction and Mössbauer spectroscopy. The results show that ball milling leads to a segregation of two phases. One, with a lower degree of chemical disorder, maintains the structure of the original intermetallic phase and the other, with a higher degree of chemical disorder, exhibits a disordered structure. At 4.2 K, the two phases exhibit similar hyperfine magnetic fields which are smaller than that of the original intermetallic phase, but much larger than that of the amorphous alloy with the same composition, prepared by sputtering deposition. Differing from the crystalline phase, the structurally disordered phase shows a Curie temperature lower than room temperature.