T. H. Noh

Magnetic properties and the crystallization of amorphous Fe83B9Nb7Cu1

The amorphous state of ferromagnetic Fe83B9Nb7Cu1 and its nanocrystallization have been studied by x‐ray, Mossbauer spectroscopy, and magnetic moment measurements. In the amorphous state at 13 K, the Mossbauer spectrum exhibits an essentially symmetric hyperfine field distribution with a half‐width of 72 kOe. The average hyperfine field Hhf(T) of the amorphous state shows a temperature dependence of [Hhf(T)−Hhf(O)]/Hhf(O)=−0.48(T/TC)3/2 u −0.22(T/TC)5/2 for T/TC<0.7, indicative of spin‐wave excitation. The quadrupole splitting just above the Curie temperature TC is 0.43 mm/s, whereas the average quadrupole shift below TC is zero. The Curie and crystallization temperatures are determined to be TC=393 K and Tx=775 K, respectively, for a heating rate of 5 K/min. The occupied area of the nanocrystalline phase at the optimum annealing temperature is about 33%–71%. It is notable that the magnetization of the amorphous phase decreases more rapidly with reduced temperature than those of nanocrystalline ferromagne...

Soft magnetic properties of Fe-B-M-Cu (M=Hf,Zr,Nb) alloys with nanocrystalline and amorphous hybrid structure

The change in magnetic properties with B content and annealing temperature was investigated for Fe-B-M-Cu (M=Hf,Zr,Nb) alloys. In the high B alloys over 8 at% B, the optimum annealing temperatures revealing the excellent soft magnetic properties were below the crystallization temperatures The annealed microstructure had ultrafine BCC-Fe phase grains with a diameter of 5-7 nm and a considerably high fraction (30-50 vol.%) of interfacial amorphous phase. For these alloys, very low core loss and high effective permeability were obtained in the frequency range up to 1 MHz. These behaviors were interpreted to be due their hybrid microstructure and high electrical resistivity. >

The magnetic properties of ultrathin Fe-Al-Nb-B-Cu nanocrystalline alloys

The magnetic properties of ultrathin Fe/sub 75/Al/sub 4/Nb/sub 5/B/sub 12/Cu/sub 1/ nanocrystalline alloy ribbons with 9 /spl mu/m thickness and the effect of Al additions to Fe-B-Nb-Cu alloy for improving the high-frequency magnetic properties were investigated. It was found that the effective permeability at frequencies over 100 kHz was higher and the core loss was lower for the composition Fe/sub 75/Al/sub 4/Nb/sub 5/B/sub 12/Cu/sub 1/ alloy. Moreover, the reduction of the ribbon thickness to 9 /spl mu/m was very effective in improving their permeability and the core loss characteristics up to the MHz frequency range.

Mossbauer studies of nanocrystalline Fe/sub 83/B/sub 9/Nb/sub 7/Cu/sub 1/ alloy by flash annealing

Melt-spun Fe/sub 83/B/sub 9/Nb/sub 7/Cu/sub 1/ alloy with ultrathin ribbon has been studied with Mossbauer spectroscopy and X-ray diffraction. The enhanced magnetic property of the flash-annealed alloy was attributed to the reduced /spl alpha/-Fe phase grain size to 6 nm and the higher effective permeability and smaller magnetic core loss at 1 MHz than conventional annealed alloys. The occupied area of the nanocrystalline phase at the optimum 773 K is about 73% whereas that for conventional annealing temperature at 893 K is about 71%. The flash annealing technique was effective in improving the high-frequency soft magnetic property of nanocrystalline Fe/sub 83/B/sub 9/Nb/sub 7/Cu/sub 1/ alloy.

The Effect Of Magnetic Field Annealing On Magnetic Properties In Ultrathin Fe-based Nanocrystalline Alloys

Ultrathin Fe/sub 78/Al/sub 4/B/sub 12/Nb/sub 5/Cu/sub 1/ and Fe/sub 83/B/sub 9/Nb/sub 7/Cu/sub 1/ nanocrystalline ribbon alloys below 10 /spl mu/m in thickness were annealed in transverse magnetic field, and then the high-frequency soft magnetic properties and their compositional effect were investigated. Very high effective permeability and excellent magnetic core loss characteristics in MHz range were obtained for both alloys after optimum annealing. However, the Al-added alloy was more sensitive to the magnetic field annealing and much improved soft magnetic properties in the high frequency range were revealed.

An effect of nitrogen on magnetic properties and microstructure of Fe–Nb–B–N nanocrystalline thin films

Fe–Nb–B–N films with good soft magnetic properties were fabricated by Ar+N2 reactive sputtering. The quaternary films have better soft magnetic properties than that of Fe–Nb–B films. The best magnetic properties are saturation magnetization of 16.5 kG, coercivity of 0.13 Oe and effective permeability of about 5000 up to 10 MHz. It was observed by transmission electron microscopy that the Fe–Nb–B–N thin film annealed at 590 °C consisted of three phases: a fine α-Fe phase whose grain size is around 7 nm, a Nb–B rich amorphous phase and NbN precipitates with the size of less than 3 nm. The fine grained α-Fe structure, together with finely dispersed NbN precipitates and the amorphous boundary phase are considered to be a main factor for the good magnetic properties.

Crystallization and magnetic properties of Fe/sub 84/B/sub 9/Nb/sub 7/ amorphous ribbons

The amorphous Fe/sub 84/B/sub 9/Nb/sub 7/ and its nanocrystallization have been studied by X-ray, Mossbauer spectroscopy and magnetic moment measurements. The average hyperfine field H/sub hf/(T) of the amorphous state shows a temperature dependence of [H/sub hf/(T)-H/sub hf/(0)]/H/sub hf/(0)=-0.52 (T/T/sub C/)/sup 3/2/-0.34 (T/T/sub C/)/sup 5/2/ for T/T/sub C/<0.7 indicative of spin-wave excitation. The quadrupole splitting just above the Curie temperature T/sub C/ is 0.41 mm/s, whereas the average quadrupole shift below T/sub C/ is zero. The Curie and crystallization temperatures are determined to be T/sub C/=330 K and T/sub x/=750 K respectively, for a heating rate of 5 K/min. The occupied area of the nanocrystalline phase at the optimum annealing temperature is about 73%.