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Islam, Fhokrul
Publications (10 of 22) Show all publications
Johnson, A. I., Islam, F., Canali, C. M. & Pederson, M. R. (2019). A multiferroic molecular magnetic qubit. Journal of Chemical Physics, 151(17), 1-7, Article ID 174105.
Open this publication in new window or tab >>A multiferroic molecular magnetic qubit
2019 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 17, p. 1-7, article id 174105Article in journal (Refereed) Published
Abstract [en]

The chiral Fe3O(NC5H5)3(O2CC6H5)6 molecular cation, with C-3 symmetry, is composed of three six-fold coordinated spin-carrying Fe3+ cations that form a perfect equilateral triangle. Experimental reports demonstrating the spin-electric effect in this system also identify the presence of a magnetic uniaxis and suggest that this molecule may be a good candidate for an externally controllable molecular qubit. Here, we demonstrate, using standard density-functional methods, that the spin-electric behavior of this molecule could be even more interesting as there are energetically competitive reference states associated with both high and low local spins (S = 5/2 vs S = 1/2) on the Fe3+ ions. Each of these structures allow for spin-electric ground states. We find that qualitative differences in the broadening of the Fe(2s) and O(1s) core levels, shifts in the core-level energies, and the magnetic signatures of the single-spin anisotropy Hamiltonian may be used to confirm whether a transition between a high-spin manifold and a low spin manifold occurs.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-93006 (URN)10.1063/1.5127956 (DOI)000496485600008 ()31703507 (PubMedID)
Available from: 2020-03-19 Created: 2020-03-19 Last updated: 2020-03-19Bibliographically approved
Islam, F., Pertsova, A. & Canali, C. M. (2019). Impurity potential induced gap at the Dirac point of topological insulators with in-plane magnetization. Physical Review B, 99(15), 1-6, Article ID 155401.
Open this publication in new window or tab >>Impurity potential induced gap at the Dirac point of topological insulators with in-plane magnetization
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 15, p. 1-6, article id 155401Article in journal (Refereed) Published
Abstract [en]

The quantum anomalous Hall effect (QAHE), characterized by dissipationless quantized edge transport, relies crucially on a nontrivial topology of the electronic bulk band structure and a robust ferromagnetic order that breaks time-reversal symmetry. Magnetically doped topological insulators (TIs) satisfy both these criteria, and are the most promising quantum materials for realizing the QAHE. Because the spin of the surface electrons aligns along the direction of the magnetic-impurity exchange field, only magnetic TIs with an out-of-plane magnetization are thought to open a gap at the Dirac point (DP) of the surface states, resulting in the QAHE. Using a continuum model supported by atomistic tight-binding and first-principles calculations of transition-metal doped Bi2Se3, we show that a surface-impurity potential generates an additional effective magnetic field which spin polarizes the surface electrons along the direction perpendicular to the surface. The predicted gap-opening mechanism results from the interplay of this additional field and the in-plane magnetization that shifts the position of the DP away from the Γ point. This effect is similar to the one originating from the hexagonal warping correction of the band structure but is one order of magnitude stronger. Our calculations show that in a doped TI with in-plane magnetization the impurity-potential-induced gap at the DP is comparable to the one opened by an out-of-plane magnetization.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Other Physics Topics
Research subject
Physics, Electrotechnology
Identifiers
urn:nbn:se:lnu:diva-81988 (URN)10.1103/PhysRevB.99.155401 (DOI)000463883800004 ()2-s2.0-85064136667 (Scopus ID)
Funder
Swedish Research Council, 621-2014-4785Carl Tryggers foundation , CTS 14:178
Available from: 2019-04-16 Created: 2019-04-16 Last updated: 2019-08-29Bibliographically approved
Islam, F., Canali, C. M., Pertsova, A., Balatsky, A., Mahatha, S. K., Carbone, C., . . . Sessi, P. (2018). Systematics of electronic and magnetic properties in the transition metal doped Sb2Te3 quantum anomalous Hall platform. Physical Review B, 97(15), Article ID 155429.
Open this publication in new window or tab >>Systematics of electronic and magnetic properties in the transition metal doped Sb2Te3 quantum anomalous Hall platform
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 15, article id 155429Article in journal (Refereed) Published
Abstract [en]

The quantum anomalous Hall effect (QAHE) has recently been reported to emerge in magnetically doped topological insulators. Although its general phenomenology is well established, the microscopic origin is far from being properly understood and controlled. Here, we report on a detailed and systematic investigation of transition metal (TM) doped Sb2Te3. By combining density functional theory calculations with complementary experimental techniques, i.e., scanning tunneling microscopy, resonant photoemission, and x-raymagnetic circular dichroism, we provide a complete spectroscopic characterization of both electronic and magnetic properties. Our results reveal that the TM dopants not only affect the magnetic state of the host material, but also significantly alter the electronic structure by generating impurity-derived energy bands. Our findings demonstrate the existence of a delicate interplay between electronic and magnetic properties in TM doped topological insulators. In particular, we find that the fate of the topological surface states critically depends on the specific character of the TM impurity: while V-and Fe-doped Sb2Te3 display resonant impurity states in the vicinity of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The single-ion magnetic anisotropy energy and easy axis, which control the magnetic gap opening and its stability, are also found to be strongly TM impurity dependent and can vary from in plane to out of plane depending on the impurity and its distance from the surface. Overall, our results provide general guidelines for the realization of a robust QAHE in TM doped Sb2Te3 in the ferromagnetic state.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-75724 (URN)10.1103/PhysRevB.97.155429 (DOI)000430545100010 ()2-s2.0-85045930314 (Scopus ID)
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2019-08-29Bibliographically approved
Sadowski, J., Kret, S., Siusys, A., Wojciechowski, T., Gas, K., Islam, F., . . . Sawicki, M. (2017). Wurtzite (Ga,Mn)As nanowire shells with ferromagnetic properties. Nanoscale, 9(6), 2129-2137
Open this publication in new window or tab >>Wurtzite (Ga,Mn)As nanowire shells with ferromagnetic properties
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2017 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 6, p. 2129-2137Article in journal (Refereed) Published
Abstract [en]

(Ga,Mn)As having a wurtzite crystal structure was coherently grown by molecular beam epitaxy on the 1100 side facets of wurtzite (Ga,In)As nanowires and further encapsulated by (Ga,Al)As and low temperature GaAs. For the first time, a truly long-range ferromagnetic magnetic order is observed in non-planar (Ga,Mn)As, which is attributed to a more effective hole confinement in the shell containing Mn by the proper selection/choice of both the core and outer shell materials. © The Royal Society of Chemistry.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
Keywords
Crystal structure; Ferromagnetic materials; Ferromagnetism; Gallium; Molecular beam epitaxy; Nanowires; Temperature; Zinc sulfide, Ferromagnetic properties; Hole confinement; Low-temperature GaAs; Magnetic orders; Outer shells; Wurtzite crystal structure; Wurtzites, Manganese
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-61167 (URN)10.1039/c6nr08070g (DOI)000395626600004 ()2-s2.0-85012111095 (Scopus ID)
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2019-09-06Bibliographically approved
Sahoo, S., Islam, F. & Khanna, S. (2015). Using graphene to control magnetic anisotropy and interaction between supported clusters. New Journal of Physics, 17, Article ID 053052.
Open this publication in new window or tab >>Using graphene to control magnetic anisotropy and interaction between supported clusters
2015 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, article id 053052Article in journal (Refereed) Published
Abstract [en]

Stabilization of magnetic order in clusters/nanoparticles at elevated temperatures is a fundamentallychallenging problem. The magnetic anisotropy energy (MAE) that prevents the thermal fluctuationsof the magnetization direction can be around 1–10Kin free transition metal clusters of around adozen atoms. Here we demonstrate that a graphene support can lead to an order of magnitudeenhancement in the anisotropy of supported species. Our studies show that theMAEof supportedCo5 and Co13 clusters on graphene increase by factors of 2.6 and 25, respectively. The enhancement islinked to the splitting of selected electronic orbitals that leads to the different orbital contributionsalong the easy and hard axis. The conductive support enables a magnetic interaction between thedeposited species and the nature of themagnetic interaction can be controlled by the separation betweensupported clusters or by vacancies offering an unprecedented ability to tune characteristics of assemblies.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-44616 (URN)10.1088/1367-2630/17/5/053052 (DOI)
Available from: 2015-06-16 Created: 2015-06-16 Last updated: 2017-12-04Bibliographically approved
Mahani, M. R., Islam, F., Pertsova, A. & Canali, C. M. (2014). Electronic structure and magnetic properties of Mn and Fe impurities near the GaAs (110) surface. Physical Review B. Condensed Matter and Materials Physics, 89(16), Article ID: 165408
Open this publication in new window or tab >>Electronic structure and magnetic properties of Mn and Fe impurities near the GaAs (110) surface
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 16, p. Article ID: 165408-Article in journal (Refereed) Published
Abstract [en]

Combining density functional theory calculations and microscopic tight-binding models, we investigate theoretically theelectronic and magnetic properties of individual substitutional transition-metal impurities (Mn and Fe) positioned in the vicinity of the (110) surface of GaAs. For the case of the [Mn2+](0) plus acceptor-hole (h) complex, the results of a tight-binding model including explicitly the impurity d electrons are in good agreement with approaches that treat the spin ofthe impurity as an effective classical vector. For the case of Fe, where both the neutral isoelectronic [Fe3+](0) and the ionized [Fe2+](-)states are relevant to address scanning tunneling microscopy (STM) experiments, the inclusion of d orbitals is essential. We find that the in-gap electronic structure of Fe impurities is significantly modified by surface effects. For the neutral acceptor state [Fe2+, h](0), the magnetic-anisotropy dependence on the impurity sublayer resembles the case of [Mn2+, h](0). In contrast, for [Fe3+](0) electronic configuration the magnetic anisotropy behaves differently and it is considerably smaller. For this state we predict that it is possible to manipulate the Fe moment, e. g., by an external magnetic field, with detectable consequences in the local density of states probed by STM.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-27461 (URN)10.1103/PhysRevB.89.165408 (DOI)000334118200003 ()2-s2.0-84899714415 (Scopus ID)
Available from: 2013-07-05 Created: 2013-07-05 Last updated: 2017-04-18Bibliographically approved
Mahani, M. R., Pertsova, A., Islam, F. & Canali, C. M. (2014). Interplay between Mn-acceptor state and Dirac surface states in Mn-doped Bi2Se3 topological insulator. In: MAR14 Meeting of The American Physical Society: . Paper presented at MAR14 Meeting of The American Physical Society, March 3-7, 2014, Denver. Denver, Colorado: American Physical Society
Open this publication in new window or tab >>Interplay between Mn-acceptor state and Dirac surface states in Mn-doped Bi2Se3 topological insulator
2014 (English)In: MAR14 Meeting of The American Physical Society, Denver, Colorado: American Physical Society , 2014Conference paper, Oral presentation with published abstract (Refereed)
Place, publisher, year, edition, pages
Denver, Colorado: American Physical Society, 2014
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-33304 (URN)
Conference
MAR14 Meeting of The American Physical Society, March 3-7, 2014, Denver
Available from: 2014-03-26 Created: 2014-03-26 Last updated: 2017-04-18Bibliographically approved
Mahani, M. R., Pertsova, A., Islam, F. & Canali, C. M. (2014). Interplay between Mn-acceptor state and Dirac surface states in Mn-doped Bi2Se3 topological insulator. Physical Review B. Condensed Matter and Materials Physics, 90, Article ID: 195441
Open this publication in new window or tab >>Interplay between Mn-acceptor state and Dirac surface states in Mn-doped Bi2Se3 topological insulator
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, p. Article ID: 195441-Article in journal (Refereed) Published
Abstract [en]

We investigate the properties of a single substitutional Mn impurity and its associated acceptor state on the (111) surface of Bi$_2$Se$_3$ topological insulator. Combining \textit{ab initio} calculations with microscopic tight-binding modeling, we identify the effects of inversion-symmetry and time-reversal-symmetry breaking on the electronic states in the vicinity of the Dirac point. In agreement with experiments, we find evidence that the Mn ion is in ${+2}$ valence state and introduces an acceptor in the bulk band gap. The Mn-acceptor has predominantly $p$--character, and is localized mainly around the Mn impurity and its nearest-neighbor Se atoms. Its electronic structure and spin-polarization are determined by the hybridization between the Mn $d$--levels and the $p$--levels of surrounding Se atoms, which is strongly affected by electronic correlations at the Mn site. The opening of the gap at the Dirac point depends crucially on the quasi-resonant coupling and the strong real-space overlap between the spin-chiral surface states and the mid-gap spin-polarized Mn-acceptor states.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-31785 (URN)10.1103/PhysRevB.90.195441 (DOI)000345538500008 ()2-s2.0-84918831696 (Scopus ID)
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
Islam, F. & Khanna, S. (2014). On the enhancement of magnetic anisotropy in cobalt clusters via non-magnetic doping. Journal of Physics: Condensed Matter, 26(125303)
Open this publication in new window or tab >>On the enhancement of magnetic anisotropy in cobalt clusters via non-magnetic doping
2014 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 125303Article in journal (Refereed) Published
Abstract [en]

We show that the magnetic anisotropy energy (MAE) in cobalt clusters can be significantlyenhanced by doping them with group IV elements. Our firstprincipleselectronic structurecalculations show that Co4C2 and Co12C4 clusters have MAEs of 25 K and 61 K, respectively. The large MAE is due to controlled mixing between Co dandC pstatesand can be furthertuned by replacing C by Si. Larger assemblies of such primitive units are shown to be stablewith MAEs exceeding 100 K in units as small as 1.2 nm, in agreement with the recentobservation of large coercivity. These results may pave the way for the use of nanoclustersinhigh density magnetic memory devices for spintronics applications

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-44561 (URN)10.1088/0953-8984/26/12/125303 (DOI)
Available from: 2015-06-16 Created: 2015-06-16 Last updated: 2017-12-04Bibliographically approved
Islam, F. (2014). Stable magnetic order and charge induced rotation of magnetizationin nano-clusters. Applied Physics Letters, 105(152409)
Open this publication in new window or tab >>Stable magnetic order and charge induced rotation of magnetizationin nano-clusters
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 152409Article in journal (Refereed) Published
Abstract [en]

Efficient control of magnetic anisotropy and the orientation of magnetization are of centralimportance for the application of nanoparticles in spintronics. Conventionally, magnetization iscontrolled directly by an external magnetic field or by an electric field via spin-orbit coupling.Here, we demonstrate a different approach to control magnetization in small clusters. We firstshow that the low magnetic anisotropy of a Co5 cluster can be substantially enhanced by attachingbenzene molecules due to the mixing between p states of C and the d states of Co sites. We thenshow that the direction of magnetization vector of Co5 sandwiched between two benzene moleculesrotates by 90 when an electron is added or removed from the system. An experimental set up torealize such effect is also suggested.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-44555 (URN)10.1063/1.4898670 (DOI)
Available from: 2015-06-16 Created: 2015-06-16 Last updated: 2017-12-04Bibliographically approved
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