Ahmad Ashfaq - Academia.edu (original) (raw)

Ahmad Ashfaq

Address: Islamabad, Islamabad, Pakistan

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Papers by Ahmad Ashfaq

Research paper thumbnail of Amplitude-squared squeezing of the generalized odd-even coherent states of the anharmonic oscillator in a finite-dimensional Hilbert space

Chinese Physics, 2007

... E-mail: stliu@hit.edu.cn http://www.iop.org/journals/cp http://cp.iphy.ac.cn Page 3. 1352 Muh... more ... E-mail: stliu@hit.edu.cn http://www.iop.org/journals/cp http://cp.iphy.ac.cn Page 3. 1352 Muhammad Ashfaq Ahmad et al Vol. 16 2. Anharmonic oscillator in a fin-... S−2 ∑ n=0 R4n+6 (2n + 1)!(2k)2n+1 ]} . (24) Page 5. 1354 Muhammad Ashfaq Ahmad et al Vol. 16 ...

Research paper thumbnail of Amplitude-squared squeezing of superposition of coherent states

Chinese Physics B, 2008

This paper discusses the amplitude-squared squeezing for the superposition of two coherent states... more This paper discusses the amplitude-squared squeezing for the superposition of two coherent states with their phase differences being separately pi/2, 3pi/2, and pi, as well as for the superposition state of two pseudoclassical states. According to the analysis, it is found that the superposition state of two coherent states with their phase differences pi/2 and 3pi/2, and the superposition state

Research paper thumbnail of Ga site occupancy in HDDR-treated Nd 2Fe 14B-based alloy by XAFS

Journal of Alloys and Compounds, 1999

The changes of local structure for Ga in Nd13.0Fe68.2Co10.8Ga1.0Zr0.1B6.9 during hydrogenation, d... more The changes of local structure for Ga in Nd13.0Fe68.2Co10.8Ga1.0Zr0.1B6.9 during hydrogenation, disproportionation, desorption and recombination (HDDR) process are studied by fluorescence XAFS in order to understand the evolution of magnetic anisotropy by HDDR process. Comparing the observed Ga XAFS data with the calculated ones, using ab initio calculation (FEFF), Ga is proved to occupy preferentially an Fe(c) site in the Nd2Fe14B structure before disproportionation and dissolves in α-Fe after the disproportionation. In the recombined state Ga redistributes into two phases, i.e. Nd2Fe14B and a Nd-rich phase. The behavior of Ga during the HDDR process differs from Zr which occupies Fe(j2) sites before disproportionation and after the disproportionation.

Research paper thumbnail of XAFS study of Zr site preference for Nd 16Fe 75.5Zr 0.5B 8 in disproportionated, partially/fully recombined states of HDDR process

Journal of Magnetism and Magnetic Materials, 2000

X-ray absorption fine structure (XAFS) measurements were done for the Zr K-edge of Nd16Fe75.5Zr0.... more X-ray absorption fine structure (XAFS) measurements were done for the Zr K-edge of Nd16Fe75.5Zr0.5 B8 magnets in the disproportionated, partially and fully recombined states of HDDR process. XAFS results reveal that Zr preferentially occupies Fe(j2) and Fe(j1) sites in the Nd2Fe14B structure for the disproportionated, partially and fully recombined states. The partially recombined sample shows larger magnetic anisotropy but a smaller coercivity than the fully recombined one. Fourier analyses of the XAFS results show the rearrangement of Zr atoms as the HDDR process proceeds; some Zr at Fe(j1) sites move to Fe(j2) sites in the partially recombined state but they turn back to Fe(j1) sites in the fully recombined state. The interchange of preferential site occupancy of Zr between Fe(j1) and Fe(j2) sites with proceeding recombination may be responsible for the degree of magnetic anisotropy.

Research paper thumbnail of Redistribution of Zr and Ga in Nd2Fe14B-based magnets during the hydrogen disproportionation desorption recombination process: An x-ray absorption fine structure study

Journal of Applied Physics, 1999

X-ray absorption fine structure (XAFS) measurements were carried out for the Ga K edge of Nd13.0F... more X-ray absorption fine structure (XAFS) measurements were carried out for the Ga K edge of Nd13.0Fe68.2Co10.8Ga1.0Zr0.1B6.9 and the Zr K edge of Nd16Fe75.5Zr0.5B8 magnets during the hydrogen disproprotionation desorption recombination process. XAFS results show that Zr occupies an Fe(j2) site for the as-cast state while Ga occupies an Fe(c2) site in the Nd2Fe14B structure for the homogenized state. Small changes of the Zr XAFS spectra after disproportionation suggest that locally the Nd2Fe14B phase including Zr at an Fe(j2) site is stabilized against disproportionation. Ga changes its occupancy from an Fe(c2) site in Nd2Fe14B structure for the homogenized state to the α-Fe phase for the disproportionated stage. Ga seems to play a different role in the enhancement of magnetic anisotropy than that of Zr.

Research paper thumbnail of Zr site determination and origin of magnetic anisotropy in HDDR processed Nd 2 Fe 14 B-based magnets

Journal of Synchrotron Radiation, 1999

Research paper thumbnail of VCA Booklet text Aug 2012

Research paper thumbnail of Amplitude-squared squeezing of the generalized odd-even coherent states of the anharmonic oscillator in a finite-dimensional Hilbert space

Chinese Physics, 2007

... E-mail: stliu@hit.edu.cn http://www.iop.org/journals/cp http://cp.iphy.ac.cn Page 3. 1352 Muh... more ... E-mail: stliu@hit.edu.cn http://www.iop.org/journals/cp http://cp.iphy.ac.cn Page 3. 1352 Muhammad Ashfaq Ahmad et al Vol. 16 2. Anharmonic oscillator in a fin-... S−2 ∑ n=0 R4n+6 (2n + 1)!(2k)2n+1 ]} . (24) Page 5. 1354 Muhammad Ashfaq Ahmad et al Vol. 16 ...

Research paper thumbnail of Amplitude-squared squeezing of superposition of coherent states

Chinese Physics B, 2008

This paper discusses the amplitude-squared squeezing for the superposition of two coherent states... more This paper discusses the amplitude-squared squeezing for the superposition of two coherent states with their phase differences being separately pi/2, 3pi/2, and pi, as well as for the superposition state of two pseudoclassical states. According to the analysis, it is found that the superposition state of two coherent states with their phase differences pi/2 and 3pi/2, and the superposition state

Research paper thumbnail of Ga site occupancy in HDDR-treated Nd 2Fe 14B-based alloy by XAFS

Journal of Alloys and Compounds, 1999

The changes of local structure for Ga in Nd13.0Fe68.2Co10.8Ga1.0Zr0.1B6.9 during hydrogenation, d... more The changes of local structure for Ga in Nd13.0Fe68.2Co10.8Ga1.0Zr0.1B6.9 during hydrogenation, disproportionation, desorption and recombination (HDDR) process are studied by fluorescence XAFS in order to understand the evolution of magnetic anisotropy by HDDR process. Comparing the observed Ga XAFS data with the calculated ones, using ab initio calculation (FEFF), Ga is proved to occupy preferentially an Fe(c) site in the Nd2Fe14B structure before disproportionation and dissolves in α-Fe after the disproportionation. In the recombined state Ga redistributes into two phases, i.e. Nd2Fe14B and a Nd-rich phase. The behavior of Ga during the HDDR process differs from Zr which occupies Fe(j2) sites before disproportionation and after the disproportionation.

Research paper thumbnail of XAFS study of Zr site preference for Nd 16Fe 75.5Zr 0.5B 8 in disproportionated, partially/fully recombined states of HDDR process

Journal of Magnetism and Magnetic Materials, 2000

X-ray absorption fine structure (XAFS) measurements were done for the Zr K-edge of Nd16Fe75.5Zr0.... more X-ray absorption fine structure (XAFS) measurements were done for the Zr K-edge of Nd16Fe75.5Zr0.5 B8 magnets in the disproportionated, partially and fully recombined states of HDDR process. XAFS results reveal that Zr preferentially occupies Fe(j2) and Fe(j1) sites in the Nd2Fe14B structure for the disproportionated, partially and fully recombined states. The partially recombined sample shows larger magnetic anisotropy but a smaller coercivity than the fully recombined one. Fourier analyses of the XAFS results show the rearrangement of Zr atoms as the HDDR process proceeds; some Zr at Fe(j1) sites move to Fe(j2) sites in the partially recombined state but they turn back to Fe(j1) sites in the fully recombined state. The interchange of preferential site occupancy of Zr between Fe(j1) and Fe(j2) sites with proceeding recombination may be responsible for the degree of magnetic anisotropy.

Research paper thumbnail of Redistribution of Zr and Ga in Nd2Fe14B-based magnets during the hydrogen disproportionation desorption recombination process: An x-ray absorption fine structure study

Journal of Applied Physics, 1999

X-ray absorption fine structure (XAFS) measurements were carried out for the Ga K edge of Nd13.0F... more X-ray absorption fine structure (XAFS) measurements were carried out for the Ga K edge of Nd13.0Fe68.2Co10.8Ga1.0Zr0.1B6.9 and the Zr K edge of Nd16Fe75.5Zr0.5B8 magnets during the hydrogen disproprotionation desorption recombination process. XAFS results show that Zr occupies an Fe(j2) site for the as-cast state while Ga occupies an Fe(c2) site in the Nd2Fe14B structure for the homogenized state. Small changes of the Zr XAFS spectra after disproportionation suggest that locally the Nd2Fe14B phase including Zr at an Fe(j2) site is stabilized against disproportionation. Ga changes its occupancy from an Fe(c2) site in Nd2Fe14B structure for the homogenized state to the α-Fe phase for the disproportionated stage. Ga seems to play a different role in the enhancement of magnetic anisotropy than that of Zr.

Research paper thumbnail of Zr site determination and origin of magnetic anisotropy in HDDR processed Nd 2 Fe 14 B-based magnets

Journal of Synchrotron Radiation, 1999

Research paper thumbnail of VCA Booklet text Aug 2012

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