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Phan, T. L.,Thanh, P. Q.,Chau, N.,Huu, C. X.,Ngo, D.-T,Ho, T. A.,Thanh, T. D.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.11
<P>Though many previous works focused on studying Cr-doped Fe-Si-Nb-B-Cu amorphous alloys, magnetic-interaction mechanisms in these materials have not been carefully investigated yet. Dealing with these issues, we have prepared the amorphous alloy ribbons Fe<SUB>78-x</SUB>Cr<SUB>x</SUB>Si<SUB>4</SUB>Nb<SUB>5</SUB>B<SUB>12</SUB>Cu<SUB>1</SUB> with x= 1, 3, and 6, and then studied their magnetic and critical properties. Magnetization versus temperature and magnetic-field measurements, MHT, performed on a vibrating sample magnetometer reveal that the Cr-content increase in Fe<SUB>78-x</SUB>Cr<SUB>x</SUB>Si<SUB>4</SUB>Nb<SUB>5</SUB>B<SUB>12</SUB>Cu<SUB>1</SUB> reduces the T<SUB>C</SUB> from 430 K for x= 1 to about 322 K (for x= 6). This indicates the decline of ferromagnetic (FM) exchange interactions between Fe atoms when there is the presence of Cr atoms. We have also analyzed the M(H) data at the temperatures in the vicinity of the T<SUB>C</SUB> using the modified Arrott plot method and the scaling hypothesis, and determined the values of the critical exponents β = 0.367-0.376 and γ = 1.315-1.338. These values are close to those expected for the 3-D Heisenberg model with β = 0.365 and γ = 1.336, proving the existence of short-range FM order in the amorphous alloy ribbons.</P>
Magneto-transport properties of magnetic tunnelling transistors at low and room temperatures
Quang, H D,Huu, C X,Oh, S K,Dang, V S,Sinh, N H,Yu, S C IOP Pub 2006 Nanotechnology Vol.17 No.14
<P>Si(100)/CoFe/AlO<SUB><I>x</I></SUB><I>/</I>CoFe/FeMn/Cu/Ta magnetic tunnelling transistors (MTTs) with differing base thicknesses (<I>W</I>) were investigated. The magneto-transport properties of the MTTs were measured at 77?K and room temperature (RT). We obtained magneto-current ratios of 48.3% and 55.9% for emitter–base bias voltages of 1.45 and 2.0?V, respectively, at 77?K. The transfer ratios are 2.83 ? 10<SUP>−5</SUP> and 1.52 ? 10<SUP>−4</SUP>, respectively, corresponding to bias voltages of 1.45 and 2.0?V. Moreover, the highest tunnel magneto-resistance (TMR) ratios turned out to be 12% and 20% for a base thickness of 30?Šat RT and 77?K, respectively. These properties raise not only some fundamental questions regarding the phenomenon of spin-independent tunnelling at low and room temperatures, but also show some promising aspect for magneto-electronic applications. In addition, we attempted to elucidate the reason behind the outstanding TMR effect at low and room temperatures. Finally, the origin of the decrease in the mean free path asymmetry (<img SRC='http://ej.iop.org/images/0957-4484/17/14/004/nano218705ieqn1.gif' ALIGN='MIDDLE' ALT='\lambda^{ \uparrow }/\lambda^{\downarrow } '/>) was clarified by using x-ray photoelectron spectroscopy profile analysis of the elements existing in the interface between Si and the CoFe base (Co, Fe, Al, Si, O). </P>
Magnetic Properties and Magnetic Viscosity of Pr4Fe76Co10B6Nb3Cu1 Nanocomposite Magnet
N. D. The,N. H. Hai,C. X. Huu,H. D. Anh,L. V. Vu,N. Chau,V. V. Hiep 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
The nanocomposite magnet Pr4Fe76Co10B6Nb3Cu1 has been obtainedbynanocrystallizationofa rapidly-quenchedamorphous ake. Thein uenceoftheannealingprocessonthestructuralandthe magnetic properties are investigated. High magnetic hardness was reached with of large coercivity of Hc = 3.65 kOe, a remanent induction of Mr = 12.0 kG, Mr=Ms = 0.79 and maximum energy product (BH)max = 17.6 MGOe at optimal annealing conditions. The multiphase structures of Fe3B as soft phases and of Pr2Fe14B as hard phase were conrmed by X-ray diraction data. The magneticviscosityasafunctionofthereverseeldwasevaluatedforallspecimen. Theresultsshow thatthemagneticviscositycoecientpeaksatacriticalnucleationeld,atwhichthemagnetization reversal of the specimens becomes irreversible.
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.
Magnetoresistance Study of Patterned Permalloy Nanostructures
D. C. Chen,J. K. Mei,Y. Wang,Y. D. Yao,J. K. Wu,C. X. Huu,N. Chau 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
We demonstrated the domain wall motion along the direction of the perimeter of a permalloy ring in the onion state. From the magnetoresistance (MR) measurement with a rotating ring at different constant elds, the critical eld to form the onion state is near 200 Gauss and the lowest field that can still drag the domain wall is between 20 and 10 Gauss. The results also revealed a tendency for angle shifting and indicated that the lowest field component in the perimeter direction (the tangential component) was near 10 Gauss at an applied field of 20 Gauss. We demonstrated the domain wall motion along the direction of the perimeter of a permalloy ring in the onion state. From the magnetoresistance (MR) measurement with a rotating ring at different constant elds, the critical eld to form the onion state is near 200 Gauss and the lowest field that can still drag the domain wall is between 20 and 10 Gauss. The results also revealed a tendency for angle shifting and indicated that the lowest field component in the perimeter direction (the tangential component) was near 10 Gauss at an applied field of 20 Gauss.
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>
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.