Education & Training

  • Ph. D. 1995

    Physics

    University of Uppsala , Sweden & Bangladesh University of Engineering and Technology, Bangladesh

  • M. Phil 1990

    Physics

    University of Dhaka, Bangladesh

  • M.Sc. 1981

    Physics

    University of Dhaka, Bangladesh

  • B. Sc. Honors 1979

    Physics

    University of Dhaka, Bangladesh

Honors, Awards and Grants

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Effects of Structural Modification on Vibrational Modes, Electronic Transitions, and Bandgap of Bi1−xBaxFeO3 (0 ≤ x ≤ 0.30) System

SHAHZAD HUSSAIN, F.A. KHAN, M. AFTAB,3 M. WASEEM, and SAIF ULLAH AWAN

Abstract

BiFeO3 is a very promising material for future technical applications. The effects of the different size and valance state of Bi3+ and Ba2+ as A-site cations in BiFeO3 (BFO) has been studied. The introduction of large-size Ba ions at Bi site resulted in significant lattice strain and a partial structural phase transformation from rhombohedral R3c to cubic Pm3¯mPm3¯m phase. Significant changes in the Raman spectrum, including variation in intensities and full-width at half-maxima, shifts in peak positions, and overlapping of Raman modes, were observed on incorporation of Ba into the lattice. The overlapping of various Raman modes for Ba-doped compositions confirmed the structural transformation. The decrease in intensity of A modes can be ascribed to replacement of Bi by Ba atoms, while the softening of E modes indicates presence of oxygen vacancies and suggests substantial changes in and destabilization of FeO6octahedra. Destabilization of FeO6 octahedra was confirmed by Fourier-transform infrared spectroscopy. Optical spectra showed the presence of charge transfer and doubly degenerate dd transitions. A slight red-shift in the dd transition was observed, attributed to variation in the crystal field strength. The bandgap increased with increasing Ba incorporation, which is related to weakening of dipolar moments due to the structural transformation from a noncentrosymmetric to centrosymmetric structure. Such better understanding of the mechanisms governing the optical response of BFO could enable researchers to engineer the bandgap and conductivity for enhanced photoferroelectric properties.

Influence of manganese substitution on magnetoresistance and magnetic properties of (Fe1-x Mnx)75 P15 C10 alloy ribbons

M.A. Islam, F.A. Khan, M.Z. Ahsan, A.A. Bally

Abstract

This paper reports the effect of Mn substitution in (Fe1−xMnx)75P15C10(0≤x≤0.3) amorphous alloys, which is synthesized by rapidly cooled melt spun technique. The magnetic properties of the fabricated ribbons have shown significant changes upon Mn substitution. M-H measurement at room temperature has shown a gradual transition from soft-to-hard magnetic phase with the increase of Mn concentration. The magnetoresistance is found to increase with Mn concentration at room temperature. The ribbons exhibit high effective ac permeability with low magnetic losses in the high frequency regime. The observed magnetic properties suggest that the antiferromagnetic interactions introduced by Mn atoms cause deviations from a pure ferromagnetic structure at low Mn concentrations.

In-situ synthesis of gold nanocrystals anchored graphene oxide and its application in biosensor and chemical sensor

Mohammad K.Alam, Md. Mahbubur Rahman, Mohammed M.Rahman, DojinKim, Abdullah M.Asiri, Feroz A.Khan

Abstract

  This research demonstrated the development of graphene oxide (GO)-gold nanocrystals (AuNCs) composite-modified glassy carbon electrode (GCE) for the sensitive detection of dopamine (DA), uric acid (UA), and 4-aminophenol (4-AP). The GO was synthesized by modified Hummer's method, which was utilized to prepare GO-AuNCs composites by in situ synthesis method using sodium l(-) malate as a reducing agent. Morphological, X-ray diffraction, and spectral analysis revealed the homogeneous formation of AuNCs with high crystallinity and purity on the GO surface and the sizes of the NCs were decreased with increasing the concentrations of sodium l(-) malate. The optimal GCE/GO-AuNCs sensor exhibited excellent electrocatalytic activity towards the oxidation of DA, UA, and 4-AP. The sensor showed interference-free and selective detection of DA and UA with sensitivities of ca. 30.3 and 17.28 μA/cm2/μM, respectively, and detection limits of ca. 28 and 50 nM, respectively, with wider dynamic ranges, measured by differential pulse voltammetry (DPV) technique. Whereas, it displayed a sensitivity and detection limit of ca. 5.70 μA/cm2/mM and 0.017 nM, respectively, for the detection of 4-AP, using current density (J)-voltage (Vmeasurement method. The sensor also revealed excellent stability, reproducibility, and recoveries of DA, UA, and 4-AP in real samples.

Study on AC permeability and permittivity of manganese doped cobalt ferrite nanoparticles

M Z Ahsan, F A Khan, M A Islam, Tanzina Tabassum and M K Alam

Abstract

This paper reports the significances of the negative real part of ac permeability and the transition of real part of ac permittivity. The paper also identifies the μ negative media and double negative media in the frequency range 3–120 MHz. The eddy current loss calculated from the measured complex permeability is found to diminish with increasing frequency which is an important factor to be considered for high frequency applications of these materials.

Exploiting of magnetocaloric effect from manganese doped cobalt ferrite nanoparticles for low temperature applications.

M. Z. Ahsan, F. A. Khan, Pk. A. Ahsan, M. A. Islam

Abstract

This paper reports on the magnetocaloric effect exploited from the manganese doped cobalt ferrite nanoparticles using indirect method. The optimum values of magnetic entropy change, adiabatic temperature change, refrigeration capacity, and maximum specific cooling energy are found to be -0.37J kg -1K -1 , 65.01K, 24.05 J kg -1and 192.95J kg -1 under the magnetic field difference 0.2 T between 0.2 – 0.4 T below 200 K temperature range. As such the investigated materials are expected to be suitable for the applications in low temperature physics and also promising for space born applications.

Structural, magnetic, and electrical properties of sol–gel derived cobalt ferrite nanoparticles

A. Hossain, M. S. I. Sarker,  · M. K. R. Khan,  F. A. Khan , · M. Kamruzzaman, · M. M. Rahman

Abstract

This work reports the synthesis and studies of semi-soft ferrimagnetic CoFe2O4 nanoparticles using sol–gel method. The X-ray diffraction patterns confirm the formation of cubic spinel CoFe2O4
nanoparticles. The average crystallite size was found from XRD data is about 30 nm. The high resolution transmission electron microscopy analysis shows that nanoparticles are highly crystalline. The magnetic properties reveal that the particles are ferrimagnetically ordered soft magnetic materials with coercive field of 620 Oe and saturation magnetization Ms = 60 emug−1. The higher value of saturation magnetization is due to the ordered single-domains magnetic nanoparticles and lower magnitude of coercivity is attributed to the decrease of interparticle interactions and magneto-elastic anisotropy. The value of remanence ratio R < 0.5 is responsible for magnetostatic interactions of the particles. The nanoparticles possess low values of dielectric constant which decreased with increasing frequency. The low dielectric constant makes the nanoparticles as a promising candidate for high frequency magnetic devices.

Investigation of dielectric and complex impedance spectroscopic studies of Bi1−xBaxFeO3 (0 ≤ x ≤ 0.30) system

Shahzad Hussain, F.A.Khan, S.K.Hasanain, Saif Ullah Awan, S.Adnan Raza

Abstract

Polycrystalline Bi1−xBaxFeO3 (0 ≤ x ≤ 0.30) samples have been prepared by two stage solid state reaction method. The surface texture of the prepared material exhibited a uniform grain distribution with minor empty space suggesting that the density of the pelletized samples is high and grain size is found to decrease with Ba substitution. An important observation is the stabilization of a dielectric anomaly near the magnetic transition temperature in temperature dependent dielectric studies which is ascribed to the presence of magnetoelectric (ME) coupling. This ME coupling effect has been demonstrated by measuring the effect of varying magnetic fields on the dielectric constant. The dielectric constant increased with increasing applied magnetic field giving a coupling coefficient (εr(H) − εr(0))/εr(0) of 1% at H = 5 kOe at room temperature which demonstrate the importance of these material from application point of view. The dielectric constant is high at low frequencies and is found to decrease at moderate frequencies indicating the Maxwell–Wagner contribution to the dielectric response. The increase in Ba content and temperature resulted in an increase in bulk resistance and exhibits a typical negative temperature coefficient of resistance behavior. A temperature dependent and non-Debye type of relaxation process is revealed by impedance spectroscopic studies. The conductivity spectra revealed the presence of hopping mechanism in the electrical transport process and the activation energies lying in the range from 0.45 to 0.70 eV indicate that the conduction of oxygen vacancies through hopping mechanism.

Electrical and magnetic properties of Co-substituted MnZnFe2O

Ahmad Zubair, Saima A. Siddiqui, F. A. Khan, and Mohammad A. Alim

Abstract

The electrical and magnetic properties of polycrystalline as-sintered and annealed Co0.3Mn0.2Zn0.5Fe2O4prepared by using conventional electroceramic processing steps in the laboratory are presented. The microstructures are examined via scanning electron micrographs and energy dispersive X-ray (EDX)analysis. The ac electrical behavior represented via complex plane plots in the frequency range 160–211 MHz reveals inductive contribution via resonance originated within the material system. The ac permeability is presented in the frequency range 50–300 MHz affirmed resonance behavior. The inductive response in the complex planes (impedance Z and modulus M) reflecting resonance behavior due to magnetic softness is obvious around 140 MHz whereas in the permeability dispersion negative domain is observed at about150 MHz attributing to the spin rotation.

Recrystallization Phenomena in Melt-Spun (Fe100-xVx)75P15C10 Alloys

M. A. S. Karal, K. Barner, M. Kamruzzaman, . K. Saha, and F. A. Khan

Abstract

(Fe100-xVx)75P15C10 (x=0, 5, 10 and 15) semi-amorphous alloys were prepared by the melt spinning technique and their structural, thermal and magnetic properties were investigated. The structure of the alloys was studied by X-ray diffraction (XRD) for annealing temperatures of 400 ºC to 650 ºC within a 30 minute annealing time. The XRD patterns show that the samples contain a BCC structure for temperatures between 400 ºC to 450 ºC and a hexagonal structure for the temperatures between 500 ºC to 650 ºC. The lattice parameter of the BCC structure changes from 2.854 to 2.870 Å with the temperature. The lattice parameters a and c for the hexagonal structure are (5.011- 5.045) Å and (13.676-13.822) Å, respectively. The grain size is found to vary from 10 to 60 nm. The recrystallization temperatures of the amorphous phase volume and weight changes were measured by differential thermal analysis (DTA) and thermogravimetry (TG), respectively. The saturation magnetization gradually decreases with the increase of the substitution of Fe by V at room temperature (RT).

Structural and magnetic properties of LiCu mixed spinel ferrites

S. M. Hoque, M. S. Ullah, F.A. Khan, M. A. Hakim, D. K. Saha

Abstract

Exchange spring magnetic properties of Fe71(NdPr)4Co5Cu0.5Nb1B18.5 alloy,
 

 F. A. Khan, S. M. Hoque, M. A. Hakim,

Abstract

A melt-spun Fe71(NdPr)4Co5Cu0.5Nb1B18.5 amorphous alloy has been studied for their exchange spring behavior in the nanocrystalline state and hence its potential use as an exchange spring magnet. Steep recoil curves of the samples annealed at 870 and 970 K show the typical spring exchange characteristic with smaller loop area. Temperature dependence of (BH)max and the remanence ratio Mr/Ms have been investigated over a wide range of temperature from 5 up to 380 K using a superconducting quantum interference device (SQUID). It is observed that the temperature dependence of these parameters decrease with increasing temperature indicating gradual weakening of exchange coupling energy between the magnetic nanograins with the rise of temperature. A change in the shape of the hysteresis loop is observed below 100 K indicating a possible spin reorientation in the hard magnetic phase.

Giant magnetocaloric effect around room temperature at moderate low field variation in La0.7(Ca1-xSrx)0.3MnO3perovskite

M.S. Islam*, D.T. Hanh, F.A. Khan, M.A. Hakim D.L. Minh, N.N.Hoang, N.H. Hai, N. Chau

Abstract

Among the perovskite manganites, a series of La1-xCaxMnO3 has the largest magneto-caloric effect (MCE) (|ΔSm|max=3.2-6.7 J/kg K at ΔH=13.5 kOe), but the Curie temperatures, TC, are quite low (165-270 K). The system of LaSrMnO3 has quite high TC but its MCE is not so large. The manganites La0.7(Ca1-xSrx)0.3MnO3 (x=0, 0.05, 0.10, 0.15, 0.20, 0.25) have been prepared by solid state reaction technique with an expectation of large MCE at room temperature region. The samples are of single phase with orthorhombic structure. The lattice parameters as well as the volume of unit cell are continuously increased with the increase of x due to large Sr2+ ions substituted for smaller Ca2+ ions. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic measurements at low field and low temperatures indicate that there is a spin-glass like (or cluster glass) state occurred. The Curie temperature TC increases continuously from 258 K (for x=0) to 293 K (for x=0.25). A large MCE of 5 J/kg K has been observed around 293 K at the magnetic field change ΔH=13.5 kOe for the sample x=0.25. The studied samples can be considered as giant magneto-caloric materials, which is an excellent candidate for magnetic refrigeration at room temperature region.

Recoil hysteresis and temperature dependence of Coercivity of Nd4Fe73.5Co3Hf0.5Ga0.5B18.5

S. Manjura Hoque, M. A. Hakim, F. A. Khan and N. H. Nghi.

Abstract

Recoil hysteresis and temperature dependence of coercivity have been measured for the sample of composition Nd4Fe73.5Co3Hf0.5Ga0.5B18.5 prepared by rapid quenching method with a wheel speed of 25 m/s and after subsequent annealing in an evacuated quartz tube under a pressure of 10–5 mbar at different temperatures and times. In the optimum and over‐annealed condition, recoil hysteresis loops have been measured by the application of progressively increasing negative field and successive withdrawal to the remanence and found to have steep recoil loop and small recoil area, which is characteristic to exchange‐biased system. Temperature dependence of coercivity in the range of 5 K to 380 K has been measured for the sample of composition Nd4Fe73.5Co3Hf0.5Ga0.5B18.5. Variation in the shape of the hysteresis loop has been observed in this temperature range. In the low temperature region i.e. below 150 K hysteresis loops are constricted due to spin reorientation of Nd2Fe14B at 135 K while above this temperature the hysteresis loops are characterized by convex M (H) curve similar to single‐phase permanent magnet. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and magnetic characterization of Co67Fe4Ni2Si15B12

S. M. Hoque, F. A. Khan, and M. A. Hakim

Abstract

Soft magnetic properties of Co-based amorphous alloy of the composition Co67Fe4Ni2Si15B12 have been investigated by isothermal heat treatment up to the conventional crystallization temperature. In the as-cast condition the Curie temperature of the sample is 272 °C and saturation magnetization is 74 emu/g. Magnetic properties undergo variation depending on the heat treatment temperature. For the heat treatment temperatures of around 420 and 490 °C, superior soft magnetic properties are obtained. For both the temperatures initial permeability, μ′ reaches value up to ten times the value of permeability in the as-received samples. Annealing effect on giant magneto-impedance has been observed for the current-driving frequencies of 4.5 and 6 MHz. Field dependence of magneto-impedance shows hysteresis at low field, which is related to the changes in the magnetization process of the sample.

 Exchange-spring behavior of nanocrystalline (NdPr)4Fe71Co5Cu0.5Nb1B18.5,

S. Manjura Hoque, F. A. Khan and M. A. Hakim,

Abstract

An amorphous alloy of composition (NdPr)4Fe71Co5Cu0.5Nb1B18.5 prepared by a melt spinning technique in an argon atmosphere has been studied to observe exchange‐spring behavior in the nanocrystalline state. Hysteresis loop measurements at room temperature revealed that the highest value of the coercivity, Hc, of 4.08 kOe has been obtained for the sample annealed at 913 K for 10 min. At this annealing temperature (BH)max and Mr/Ms have been found to be 11.06 MGOe and 0.716, respectively. Steep recoil curves of the samples annealed at 873 and 973 K show typical characteristics of the exchange‐spring mechanism having smaller loop area. The temperature dependences of HcMr/Ms and (BH)max in the range of 5 to 380 K generally decrease with the increase of temperature. From the temperature dependence of the hysteresis loop parameters, it has been found that at 5 K the values of Hc and (BH)max are 6.89 kOe and 13.72 MGOe respectively for the sample annealed at 873 K for 10 min and 6.69 kOe and 13.74 MGOe respectively for the sample annealed at 923 K for 10 min. A change in the shape of the hysteresis loops was observed at temperatures below 100 K, related to the spin reorientation in the hard magnetic phase. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Tb substitution on the magnetic properties of exchange-biased Nd2Fe14B/Fe3B,

S. M. Hoque, M. A. Hakim, F. A. Khan and N. H. Dan

Abstract

Tb-substituted (Nd,Tb)2Fe14B/Fe3B nanocomposite ribbons have been synthesized by melt spinning of Nd3Tb1Fe76Cu0.5Nb1B18.5 alloys. Tb substitution has significantly enhanced the value of coercivity and Curie temperature. Highest value of coercivity has been obtained as 4.76 kOe for the sample annealed at 953 K for 10 min. Curie temperature of Tb substituted sample, Nd3Tb1Fe76Cu0.5Nb1B18.5 is 549 K while Curie temperature of the sample without Tb, Nd4Fe76Cu0.5Nb1B18.5 is 535 K. Recoil hysteresis loops measured along the major demagnetization curve are steep having small recoil loop area. Temperature dependence of coercivity, remanent ratio and maximum energy product have been measured for the sample annealed at 893 K and 923 K for 10 min. At 5 K, coercivity and maximum energy product of the sample annealed at 893 K for 10 min are 5.2 kOe and 11.5 MGOe respectively and the sample annealed at 923 K for 10 min are 6 kOe and 13.1 MGOe respectively.

Structural and magnetic characterization of Co67Fe4Ni2Si15B12, , 

S. M. Hoque, F. A. Khan, and M. A. Hakim

Abstract

Soft magnetic properties of Co-based amorphous alloy of the composition Co67Fe4Ni2Si15B12 have been investigated by isothermal heat treatment up to the conventional crystallization temperature. In the as-cast condition the Curie temperature of the sample is 272 °C and saturation magnetization is 74 emu/g. Magnetic properties undergo variation depending on the heat treatment temperature. For the heat treatment temperatures of around 420 and 490 °C, superior soft magnetic properties are obtained. For both the temperatures initial permeability, μ′ reaches value up to ten times the value of permeability in the as-received samples. Annealing effect on giant magneto-impedance has been observed for the current-driving frequencies of 4.5 and 6 MHz. Field dependence of magneto-impedance shows hysteresis at low field, which is related to the changes in the magnetization process of the sample.

 Large magnetocaloric effect around room temperature in La0.7Ca0.3-xPbxMnO3perovskites,

D. T. Hanh, M. S. Islam, F. A. Khan, D. L. Minh, N. Chau,

Abstract

Among perovskite manganites, a series La1−xCaxMnO3 has the largest magnetocaloric effect (MCE) (|ΔSm|max=3.2–6.7 J/kg K in ΔH=1.35 T) but their Curie temperatures, TC, are quite low (165–270 K). A system La1−xPbxMnO3 has quite high TC (235–360 K) but exhibits not so large MCE (0.65–1.53 J/kg K). The manganites La0.7Ca0.3−xPbxMnO3 (x=0.05, 0.10, 0.15, and 0.20) have been fabricated by solid-state reaction technique with the expectation that they could establish large MCE at room temperature region. The prepared samples are of single phase with orthorhombic structure. Lattice parameters as well as volume of unit cell are continuously increased with increasing x due to large Pb2+ ions substituted for smaller Ca2+ ions. There is spin-glass (or cluster glass)-like state occurring in studied samples. TCincreases continuously from 270 K (for x=0.05) to 338 K (for x=0.20). Large MCE has been obtained in all samples and |ΔSm|max reached the highest value of 3.72 J/kg K (with magnetic field variation ΔH=1.35 T) for the sample x=0.05 and the studied samples could be considered as giant magnetocaloric materials working for magnetic refrigeration. The magnetoresistance of samples exhibited colossal value.

Enhanced initial permeability and magneto-impedance ratio of Co67Fe4Mo2Si15B12,

S. M. Hoque, F. A. Khan, and M. A. Hakim

Abstract

Co-based amorphous alloy exhibits superior soft magnetic properties after appropriate annealing treatment below the crystallization temperature by devitrification of the amorphous phase. The initiation of crystallization temperature has been found as 518 °C from differential thermal analysis for the heating rate of 10 °C/min. Ultra-soft magnetic properties manifested by enhanced initial permeability, μ′ of the order of 5.1 × 104 and reduction of relative loss factor, tan δ/μ′ of the order of 9 × 10− 6 has been achieved for the annealing temperature of 500 °C for 30 min. This has been achieved because at this stage local anisotropy is averaged out by exchange coupling between nanograins embedded in the residual amorphous matrix. Since enhanced magneto-impedance is a typical characteristic of Co-based amorphous alloy, field dependence of magneto-impedance has been measured for as-cast and annealed samples at current driving frequency of 4.5 MHz. Field dependence of magneto-impedance shows hysteresis at low field, which is related to the changes in the magnetization process of the sample.

Thermal behavior and magnetic properties of Co- and Cr-substituted Nd5.5Fe66Cr5Co5B18.5

S. M. Hoque, M. A. Hakim, F. A. Khan, and N. H. Nghi

Abstract

In this study, we have investigated Cr- and Co-substituted Fe3B/Nd2Fe14B-based nanocomposite alloy. Samples have been prepared by using melt-spin technique in an Ar atmosphere. Crystallization temperatures have been identified by differential thermal analysis. Samples have been annealed in an evacuated quartz tube using a pressure of around 10−5 mbar following differential thermal analysis. Structural analysis has been carried out by X-ray diffraction. Coercivity, remanent ratio and maximum energy product have been found to depend strongly on the annealing temperature. Highest value of coercivity of 4.6 kOe has been obtained for the sample annealed at 923 K for 20 min. Temperature dependence of hysteresis loop below 150 K is affected by the spin reorientation temperature of Nd2Fe14B at 135 K. In the temperature range of 250–380 K temperature coefficient of coercivity is −0.21%/°C, which is much lower. Recoil hysteresis loops have been measured by the application of progressively increasing negative field and successive withdrawal to the remanence and found to have small recoil area and high recoil permeability, which is characteristic of exchange-biased system.

Ultra-soft magnetic properties of devitrified Fe75.5Cu0.6Nb2.4Si13B8.5 alloy,

S. Manjura Hoque, M. A. Hakim, F. A. Khan, and N. Chau,

Abstract

Temperature dependence of real part initial permeability (μ′) of Fe75.5Cu0.6Nb2.4Si13B8.5 has been measured with different crystalline state of the material. Enhanced value of initial permeability by two orders of magnitude and very low value of relative loss factor of the order of 10−5 has been observed with the variation of annealing temperature and time, which shows that Fe-based alloys of this composition with lower Cu and Nb content also bears ultra-soft magnetic properties like conventional FINEMET. The results have been correlated with the volume fraction of amorphous and crystalline phases obtained by differential scanning calorimetry. Temperature dependence of initial permeability curve for the annealing temperature, Ta < 475 °C, is characterized by the single amorphous phase. The curve is characterized by the two-phase structure for 475 °C < Ta < 625 °C. The curve is characterized by presence of iron boride phase for Ta > 625 °C.

Large magnetocaloric effect around room temperature in La0.7Ca0.3-xPbxMnO3 perovskite, ,

D.T. Hanh, M.S. Islam, F. A. Khan, D.L.Minh, N.Chau

Abstract

Among perovskite manganites, a series La1-x Ca x MnO3 has the largest magnetocaloric effect (MCE) (|ΔS m|max=3.2-6.7 J/kg K in ΔH=1.35 T) but their Curie temperatures, T C, are quite low (165-270 K). A system La1-x Pb x MnO3 has quite high T C(235-360 K) but exhibits not so large MCE (0.65-1.53 J/kg K). The manganites La0.7Ca0.3-x Pb x MnO3 (x=0.05, 0.10, 0.15, and 0.20) have been fabricated by solid-state reaction technique with the expectation that they could establish large MCE at room temperature region. The prepared samples are of single phase with orthorhombic structure. Lattice parameters as well as volume of unit cell are continuously increased with increasing x due to large Pb2+ ions substituted for smaller Ca2+ ions. There is spin-glass (or cluster glass)-like state occurring in studied samples. T C increases continuously from 270 K (for x=0.05) to 338 K (for x=0.20). Large MCE has been obtained in all samples and vertical bar ΔS m vertical barmax reached the highest value of 3.72 J/kg K (with magnetic field variation ΔH=1.35 T) for the sample x=0.05 and the studied samples could be considered as giant magnetocaloric materials working for magnetic refrigeration. The magnetoresistance of samples exhibited colossal value.

Magnetic softening and giant magneto-impedance effect of Co68Fe4Ni1Si15B12,

S. Manjura Hoque, M. A. Hakim, and F. A. Khan,

Abstract

Magnetic softening and its correlation with the giant magneto‐impedance effect have been investigated for Co68Fe4Ni1Si15B12 subjected to different annealing temperatures. In the as‐cast condition the Curie temperature is 230 °C and the saturation magnetization is 72.3 emu/g. A very high value of initial permeability of around 59 × 103 and a low value of relative loss factor of the order of 10–6 have been obtained for samples annealed at 420 °C for 1 h. The sensitivity of the field dependence of the giant magneto‐impedance ratio (GMIR) for this annealing temperature is higher than that for as‐cast and other annealed samples. From X‐ray diffraction and differential scanning calorimetry results it has been found that for samples annealed at 420 °C for 1 h the ribbon is in a fully amorphous state. The extraordinary soft magnetic properties at this annealing temperature are mainly due to the structural relaxation, which determines the profile of the field dependence of the GMIR. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermoelectric Power of some (Fe1-xMnx)75P15C10 Amorphous Alloys,

E. Kraus, K. Heinemann, K. Baerner, F. A. Khan, I. V. Medvedeva, H. Schicketanz and P. Terzieff

Abstract

The thermoelectric power S of (Fe1—xMnx)75P15C10 ferromagnetic metallic amorphous alloys with x = 0, 0.05, 0.20, 0.30 has been measured in the temperature range 30 K < T < 350 K. For all compounds, the sign of S is negative, suggesting that the transport properties are dominated by electrons. A humplike structure at low temperatures which is superimposed to a linear rise and seemingly correlated to magnetic order suggests in particular magnon drag added on diffusion thermopower as the main contributions to S(T).

Magnetization and magnetocrystalline anisotropy of Ni-Mo single crystal alloys,

F. A. Khan, M. A. Asgar and P. Nordblad

Abstract

Magnetizations of the binary alloy system Ni1−xMox [x(wt%) = 4, 6, 8, 10] single crystals have been measured at 4.2, 77 and 300 K, respectively, using the Vibrating Sample Magnetometer (VSM) and the Superconducting Quantum Interference Device (SQUID). The determination of magnetocrystalline anisotropy constants have been done by the integral technique using the M versus H curves in the three principal crystallographic directions [1 1 1], [1 1 0] and [1 0 0]. The effect of alloying Nickel with Molybdenum on magnetization is found to be not linear with increasing Mo concentration and the non-linearity increases more rapidly at higher Mo concentration. The ferromagnetic ordering vanishes around 8 at% Mo. The results of magnetocrystalline anisotropy constants agree with the unpublished previous data of J.E. Scott (Ph.D. Thesis, University of Sheffield, UK, 1969) determined by magnetic torque measurements on this alloy system.

Aging in a Magnetic Particle System,

T. Jonsson, J. Mattsson, C. Djurberg, F. A. Khan, P. Nordblad, P. Svedlindh,

Abstract

The influence of dipolar interaction in a frozen ferrofluid has been experimentally studied. The ferrofluid consisted of particles of γ- Fe2O3 with mean diameter 70 Å. Four samples with volume concentration of magnetic particles ranging from 0.03% to 17% have been investigated. The magnetic relaxation of the most concentrated particle system shows typical spin glass dynamics at low temperature, e.g., the relaxation depends on the time spent at constant temperature before applying the magnetic field—the system ages. The most diluted sample shows isolated particle dynamics and no aging.

Structure, Magnetic And Magnetocaloric Properties of La0.7 (Ca1-xBax0.3MnO3 Perovskite manganites,

M.S.Islam, Matthias Hudl, R. Mathieu, M.A.Hakim, F.A.Khan, D.L.Minh, N.Chau, Per Nordblad

Abstract

Magnetic Properties and Magneto-caloric Effect in La0.7 (Ca1-xBax0.3 MnO3 Perovskites

M S Islam, M Hudl, M A Hakim, F. A. Khan, D L Minh, N Chau, P Nordblad

Abstract

Magnetic and structural properties of melt-spun alnico V ribbons, ,

F. A. Khan, A. M. Gabay, O. Akdogan, M. J. Bonder, and G. C. Hadjipanayis

Abstract

Magnetic Phase Transition and Magnetocaloric Effect around room temperature in La0.7 (Ca1-xSrx0.3MnO3 perovskites, 

M.S.Islam, D.T. Hanh, A.Z.Ahmed, M. A. Hakim, F. A. Khan, D. L. Minh, N. H. Hai, N. Chau,

Abstract

Giant magnetocaloric effect around room temperature at moderate low field variation in La0.7(Ca1-xSrx)0.3MnO3 perovskite , 

M. S. Islam, D. T. Hanh, F. A. Khan, D. L. Minh, N. H. Hai, N. Chau,

Abstract

Magnetic permeability and the magnetoresistance of Fe74.5Nb2Si13.5B9Ag1 alloy,
 

F. A. Khan, S. Chowdhury, M. A. Hakim, M. Haque, and S. Ullah

Abstract

Large magnetocaloric effect around room temperature in La0.7Ca0.3-xPbxMnO3 perovskites, ,

M. S. Islam, F. A. Khan, D. L. Minh, and N. Chao

Abstract

Magnetic Phase Transition in Ni-Mo Alloys. 9th International Conference of Physics, ,

M.S. Islam, F. A. Khan, N. Chau, M.A. Asgar

Abstract

Angstrom's turbidity at Dhaka during pre-monsoon period,

F. A. Khan

Abstract

 Evaluation of stress induced anisotropy in kmagnetice amorphous ribbons with composition Fe90-xSixB10 [x= 6, 8, 10, 12, 14],

S. S. Sikder, M. A. Asgar and F. A. Khan,

Abstract

Temperature dependence of magnetocrystalline anisotropy of Nickel around Curie temperature, , Proc. Int. Conf. on Materials Science and Technology, Dhaka, pp. 160-163 (1999). 

F. A. Khan, and T. Haque

Abstract

Atmospheric Turbidity over Dhaka during Post-Monsoon Period;

 F. A. Khan and M.Hussain

Abstract

Magnetocrystalline anisotropy and the associated magnetic properties of Iron- Phosphide(Fe2P);

F. A. Khan, M. A. Asgar and P. Nordblad

Abstract

Thermomagnetic behavior of some cobalt based glassy ribbons, 

M. Rahman, M. Huq, F. A. Khan, M. A. Hakim, and T. Hossain

Abstract

Determination of Atmospheric Turbidity Coefficients at Dhaka from Pyrheliometer data,

M.Hussain and F. A. Khan,

Abstract

Phase separation versus randomization in Heusler alloys and manganites, 

K .Baerner and F. A. Khan

Abstract

Laboratory Personel

  1. Vibrating Sample Magnetometer (Both Low and high temperature)
  2. Wayne Kerr Impedance Analyzer (120 M.Hz.)
  3. Planetary Ball Mill 
  4. Wise Therm Furnace (11000C Max)
  5. Hydraulic Pressure For Sample pressing ( 5000 psi Max)
  6. Ultrasonic Sonicator
  7. Magnetic stirrer 
  8. Analytical Balance
  9. PAR Lock-in-Amplifier
  10. DSP Lock-in-Amplifier
  11. Hewlett Packard DC Power Supply
  12. Magneto-Resistance Measurement set-up
  13. Magnetostriction Measurement set-up
  14. Temperature Dependent Resistivity Measurement set-up
  15. Hewlett Packard DC Power Supply
  16. Keithley 614 Electrometer
  17. Torque Magnetometer
  18. ARS DISPLEX Closed cycle He Refrigerator down to 14Kelvin
  19. Compact Ultra Low Temperature Chamber
  20. Vacuum Pump
  21. Oscilloscope (20 MHz) –3pcs
  22. Nano-Volt Meter(Precision)
  23. Air Compressure
  24. Reichert Polarizing Microscope 2 pcs
  25. Lakeshore Temperature Controller-330
  26. Lakshore Temperature Controller-331
  27. Centrifuging machine
  28. Precision High current dc-Power Supply
  29. Agilent High current dc-Power Supply
  30. AC Variac
  31. Mortar and Pestle 2pcs
  32. Other Hand Tools

 

Research Projects