F. Leccabue

Magnetic and morphological study of BaZn2Fe16O27 hexagonal ferrite prepared by chemical coprecipitation method

Polycrystalline samples of the BaZn2Fe16O27 (BaZn2‐W) ferrite prepared by the chemical coprecipitation method have been examined by measuring the magnetic properties (saturation magnetization, coercive and anisotropy field, Curie temperature), thermomagnetic analysis, Mossbauer spectroscopy, and scanning electron microscopy. The correlations between the magnetic properties, the grain morphology, and the relative amounts of the various phases present in samples subjected to different heat treatments are discussed. The samples prepared by optimal heat treatment show a saturation magnetization value σs =77.7 emu/g and an anisotropy magnetic field Ha =12.5 kOe. The magnetic coercive field value is low (iHc ∼150 Oe); this may be related to the large‐grain dimension (≥12 μm) of the material obtained. The Curie temperatures measured for the BaZn2‐W phase vary from 370 to 410 °C depending on the heat treatment of the samples.

Magnetic characterization and anisotropy field of the new “oxygen stabilized” phase in As-cast Nd100−xFex alloys

Abstract As-cast arc melted samples in the Nd 100− x Fe x binary system (2.5 ≤ x ≤ 35) were magnetically characterized by means of thermomagnetic analysis, vibrating sample magnetometry and singular point detection technique. A high anisotropic material, recently reported as a new “oxygen stabilized” phase, exists as the unique ferromagnetic phase in the composition range of 2.5 ≤ x ≤ 20; increasing the Fe concentration, the Nd 2 Fe 17 intermetallic compound appears and becomes the predominant one for a composition of x = 35. This hard magnetic phase shows a well defined Curie temperature of 245° C and a room temperature anisotropy field of 19.5 kOe. The magnetization processes of high coercivity as-cast alloys resemble to that predicted by the Stoner and Wohlfarth model.

Magnetic analysis of rare earth-rich RE100-xFex (RE = Pr, Nd; 2.5 ≤ x ≤ 40) as-cast binary alloys

Abstract Binary alloys RE 100- x Fe x (RE = Nd, Pr) with nominal compositions 2.5 ≤ x ≤ 40 were analyzed by means of thermomagnetic analysis and magnetization measurements from 2 K to the ordering temperature of the magnetic phases present. Special attention was paid to the compositions around the eutectic point. A hard anisotropic phase exists in the as-cast alloys, with a room-temperature anisotropy field value of 19.5 and 18.3 kOe for Nd- and Pr-systems, respectively. In alloys in which this new hard magnetic phase is the only magnetic phase detected, the temperature dependence of saturation magnetization, intrinsic coercivity and anisotropy field is reported.

Effects of mechanical grinding on magneto-structural properties of BaFe12O19 powders

Abstract The structural and magnetic properties of deformed powders of M-type Baferrite, obtained by mechanical grinding, have been investigated using X-ray diffraction, Mossbauer spectroscopy, thermomagnetic analysis, and magnetic measurements. The rapid decrease in the magnetization after short grinding times in air is attributed to the formation of a phase which is paramagnetic at room temperature but at 150 K the phase behaves like a spin-glass, with antiferromagnetic short-range order. From Mossbauer spectra this phase has at least five non-equivalent sites of iron with hyperfine interaction field values Hrf(77 K): H1=38.69; H2=37.01; H3=36.14; H4= 34.31 and H5=30.96 MA/m, and a magnetic moment μFe = 2.1μB. At longer grinding times the deformed BaFe12O19 samples were found to be thermodynamically unstable and decomposed partially into α-Fe2O3 and Fe3O4.

Magnetic characterization of SrFe2Fe16O27 ferrite prepared by chemical coprecipitation method

Abstract Polycrystalline samples of SrFe 2 Fe 16 O 27 have been prepared by thermal decomposition of hydroxide-carbonate coprecipitated salts. The samples were examined by thermomagnetic analysis, Mossbauer spectroscopy, X-ray diffraction, scanning electron microscopy and static magnetic measurements. It was found that this hexaferrite is only formed in a narrow temperature range under an inert atmosphere. The intrinsic magnetic properties obtained are: σ s = 73.6 emu/g, H a = 18.6 kOe and T c = 525° C .

On the magnetic behaviour of Dy15Fe77C8 pseudeternary alloys

Abstract Polycrystalline samples with nominal composition of Dy15Fe77(B1−xCx)8 with 0 ⪕ x ⪕ 1 and Dy15(Fe1−yCoy)77C8 with 0 ⪕ y ⪕ 0.5 were prepared by arc melting under a high purity Ar atmosphere. The main results are: (1) the coercive field is strongly enhanced with the C content: for x = 1 the iHc value is 17 KOe at room temperature; (2) at 4.2K a very low coercive field is measured in respect that both measured at 300 and 77 K; and (3) the Co substitution increases the Curie temperature (for y = 0.5 the Tc value is equal to 675°C) and for y = 0.2 the saturation magnetization exhibits the maximum value.

The effects of mechanical grinding on the structural and magnetic properties of Dy2Fe14B1-xCx alloys

Abstract The effects of mechanical grinding on the magnetic and structural properties and on the phase formation of Dy-Fe-(B, C) alloys have been studied. X-ray diffraction, Mossbauer spectroscopy and thermomagnetic analysis show that there is a decomposition of the Dy 2 Fe 14 (B, C) phase accompanied by the formation of α-Fe. In addition, for boron rich alloys magnetic phases which are revealed in the TMA curves disappear during the measurement. The magnetic measurements showed a gradual fall in coercivity at longer grinding times. The magnetisation falls initially and then rises, due to the amorphisation and decomposition of the original phases and the formation of the α-Fe.