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Le, A.T.,Hoa, N.Q.,Tam, P.D.,Park, D.G.,Phan, M.H.,Srikanth, H.,Yu, S.C. Elsevier 2010 Materials science and engineering B. Advanced Func Vol.166 No.1
The influences of N and Xe ion irradiation on the giant magnetoimpedance (GMI) effect and its magnetic response in Co<SUB>69</SUB>Fe<SUB>4.5</SUB>Al<SUB>1.5</SUB>Si<SUB>10</SUB>B<SUB>15</SUB> amorphous ribbons were systematically investigated. A large enhancement of the GMI effect and its magnetic response were achieved in N and Xe ion-irradiated amorphous ribbons. At a frequency of 3MHz, the GMI ratio and magnetic response for an N-ion-irradiated amorphous ribbon respectively reached the highest values of 130% and 13%/Oe, while for a non-irradiated amorphous ribbon they were only about 53% and 8%/Oe. The enhancement of the GMI effect and magnetic response in the ion-irradiated amorphous ribbons resulted from the enhancement of the permeability due to rotational magnetization. Our studies indicate that low energy ion irradiation is useful for improving the magnetic softness, GMI and magnetic response of amorphous alloys, which is of practical importance for the development of high-performance magnetic sensors.
Hoa, N.Q.,Chau, N.,Yu, S.-C.,Thang, T.M.,The, N.D.,Tho, N.D. Elsevier Sequoia 2007 Materials science & engineering Structural materia Vol.449 No.-
<P><B>Abstract</B></P><P>The structure, crystallization and magnetic properties of ribbons obtained by first making amorphous ribbons and then objecting them to a crystallization annealing have been published elsewhere by us previously. In the present work the soft magnetic ribbons Fe<SUB>73.5−<I>x</I></SUB>Cr<SUB><I>x</I></SUB>Si<SUB>13.5</SUB>B<SUB>9</SUB>Nb<SUB>3</SUB>Au<SUB>1</SUB> (numbers indicate at.%, <I>x</I>=1–5) are prepared by fast quenching on a single copper wheel. X-ray diffraction patterns show that the as-cast samples are amorphous. Differential scanning calorimetry analysis indicates that the crystallization temperature of the α-Fe(Si) phase is a little higher than that of pure Finemet. With the same annealing conditions, the crystallization volume fraction decreases with increasing Cr content substituted for Fe. Hysteresis loops of as-cast samples measured by Permagraph show that domain walls are pinned. After appropriate annealing, the ultrasoft magnetic properties of nanocomposite materials are established. The magnetic entropy change, |Δ<I>S</I><SUB>m</SUB>|, of studied samples has been determined, and a giant magnetocaloric effect is found. Our materials could be considered as promising magnetic refrigerants working at high temperatures (several hundreds °C).</P>
N. Chau,C. X. Huu,N. D. The,N. Q. Hoa 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
This article presents our results for the low-field giant magnetocaloric effect (GMCE) around room temperature in a system of Fe-rich amorphous alloys Fe78-xCrxSi4Nb5B12Cu1 (x = 0 -8). The structural examination indicated that the as-cast alloys were fully amorphous. Thermal transition analysis performed on a dierential scanning calorimetry apparatus showed that both the crystallization temperature and the crystallization activation energy of the mentioned amorphous alloys increased with increasing Cr content. Beside the structural stabilizing enhancement, Cr substitution also improved the anti-corrosion of studied alloys. There is a very sharp ferromagnetic-paramagnetic phase transition at at Curie temperature, which is related to high homogeneity of the alloys. Curie temperature, Tc, linearly decreased from 450 K to 297 K with increasing Cr content from x = 0 to x = 8 due to ferromagnetic dilution. The temperature dependence of the magnetic entropy change, |ΔSm|, was studied in magnetic field variations of 13.5 kOe, 10.0 kOe and 5.0 kOe. The results showed that the maximal values of |ΔSm| occurred near Tc and reduced with increasing Cr content. Namely, for x = 0, |ΔSm|max is 11.2 J/kg.K and this value slightly reduces to 8.16 J/kg.K for x = 8. Especially, a giant magnetocaloric effect of 4.1 J/kg.K for x = 8 at 295 K was obtained in a quite low field change of 5.0 kOe. This material is very promising for magnetic refrigerant applications compared with recent typical magnetocaloric materials.
Hoa, N. Q.,Gam, D. T. H.,The, N. D.,Chau, N.,Son, D. V.,Yu, S. C. WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12
<P>The influence of Nb substituted for Fe on the microstructure and magnetic properties including the magnetoimpedance effect of a Fe-based have been investigated. The nanocomposite structure composed of ultra-fine Fe(Si) grains embedded in an amorphous matrix was obtained by annealing the Fe-based amorphous alloy prepared by rapidly-quenched method. The measurements of thermomagnetic curves indicated that the Curie temperature of the amorphous phase of the samples decreases with increasing Nb content. The optimal heat treatment was performed at T<SUB>a</SUB> = 480 °C for 30 min and showed that the ultrasoft magnetic properties of nanocomposite materials were obtained. The magnetoimpedance (MI) of these samples has been studied in range frequency from 1MHz to 5 MHz and varying a dc magnetic field within 300 Oe. The correlation between the MI effect and the soft magnetic properties is discussed. The incremental permeability ratio (PR) showed the drastic changes of soft magnetic properties as a function of annealing temperatures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Short-range Ferromagnetism in Alloy Ribbons of Fe-Cr-Si-Nb-(Ag, Cu)
P. Q. Thanh,N. Q. HOA,N. Chau,C. X. HUU,D.-T. NGO,판더롱 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.7
We have studied the magnetic properties of two amorphous alloy ribbons Fe72Cr6Si4Nb5B12Ag1(FCSNB-Ag) and Fe72Cr6Si4Nb5B12Cu1 (FCSNB-Cu), prepared by using a melt-spinning technique. Magnetization (M) measurements for various temperatures (T) and magnetic fields (H)indicate that ferromagnetic-paramagnetic (FM-PM) phase transitions take place in FCSNB-Ag andFCSNB-Cu at Curie temperatures (TC) of about 308.3 K and 322.5 K, respectively. Analyses ofM − H data at different temperatures in the vicinity of the FM-PM phase transition based on themodified Arrott plot method and scaling hypothesis yielded the exponent values of = 0.369 ±0.005,= 1.359 ± 0.005 and = 4.7 ± 0.1 for FCSNB-Ag, and = 0.376 ± 0.002,= 1.315± 0.006 and = 4.5 ± 0.1 for FCSNB-Cu. Compared with the values from theoretical models,these values are close to those expected for the 3D Heisenberg model, demonstrating the existenceof short-range FM order in the amorphous alloy ribbons.
Chau, N.,The, N.D.,Hoa, N.Q.,Huu, C.X.,Tho, N.D.,Yu, S.-C. Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>A large number of amorphous ribbons based on Finemet have been prepared by rapid quenching on a single copper wheel with linear speed of <I>v</I>=25–30m/s. The ribbons are 20–25μm thick and 6–8mm wide. All as-cast samples are amorphous. Two criteria producing the colossal magnetocaloric effect (CMCE) in magnetic materials working as magnetic refrigerants are high saturation magnetization and sharp ferromagnetic–paramagnetic phase transition. The Fe-based amorphous ribbons fit these cretia. Thermomagnetic curves as well as isothermal magnetization curves around the Curie temperature of all the studied samples have been determined. The results show that the magnetic entropy change, |Δ<I>S</I><SUB>m</SUB>|, belongs to a class of materials with CMCE and the |Δ<I>S</I><SUB>m</SUB>|<SUB>max</SUB> values have been obtained at a moderately low magnetic field change of 1.35T, moreover |Δ<I>S</I><SUB>m</SUB>|<SUB>max</SUB> occurred at quite high temperature.</P>