Karin Schmalzl

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Souvik Chatterjee

West Bengal University Of Technology

Santu Baidya

University of Duisburg-Essen

Iowa State University

Nour Said

Thomas Lograsso

Iowa State University

Dr.B.Pradeep Kumar

University of Kerala

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Papers by Karin Schmalzl

Complex magnetic structure and spin waves of the noncollinear antiferromagnet Mn5Si3

Physical Review B, 2022

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Investigating the underlying mechanisms of the magnetocaloric effect with inelastic neutron scattering in Mn5-xFexSi3

Polarization analysis on the new IN12

Magnetische Spinanordnung in Fe50Pt50-xRhx-Filmen

Dimerization in the commensurate antiferromagnetic phase of MnWO4 and NaFe(WO4)2

In multiferoic MnWO4, the relaxation time of the multiferroic domain inversion shows a peculiar t... more In multiferoic MnWO4, the relaxation time of the multiferroic domain inversion shows a peculiar temperature dependence. Upon cooling below the multiferroic transition the relaxation time first increases but becomes faster closer to the commensurate low-temperature phase [1]. We investigated anharmonicities in this material as well as in isostructural NaFe(WO4)2 and propose the enhanced anharmonicities close to the low-temperature magnetic up-up-down-down structure to be responsible for the faster relaxation rates in MnWO4. In both materials there is a similar competition between incommensurate cycloid and commensurate up-up-down-down order, and anharmonic squaring up appears as a precursor in the incommensurate structure [2]. The commensurate magnetic structure is associated with structural dimerization in both materials, that has been quantitatively determined for NaFe(WO4)2 by a four-circle neutron diffraction experiment. [1]: M. Baum, Phys. Rev. B 89, 144406 (2014) [2]: S. Holbein, Phys. Re. B 94, 104423 (2016

Neutron scattering study on the heavy-fermion superconductor CeCu2Si2

Advanced neutron optics on the new IN12

Spin and lattice dynamics of magnetocaloric compound MnFe4Si3

$Research paper thumbnail of Investigation of the magnetic spin configuration in thin Fe50Pt50-x films with polarized neutron diffraction$

Investigation of the magnetic spin configuration in thin Fe50Pt50-x films with polarized neutron diffraction

Topological magnon insulators in two-dimensional van der Waals ferromagnets CrSiTe 3 and CrGeTe 3 : Toward intrinsic gap-tunability

Science Advances, 2021

A new family of topological magnon insulators with intrinsic gap-tunability is realized in 2D van... more

$FIG. Sl. X-ray diffraction and magnetic properties of CrXTe3. (a,b) X-ray diffraction of single-crystal CrSiTe3 and CrGeTe3 at 300 K. The insets are the sample pictures and the corresponding X-ray Laue pattern of the (H,K,0) reciprocal plane. (c,d) ZFC/FC magnetization curves measured under applied magnetic fields along the c and a axes. Insets show the corresponding magnetization as a function of field at 2 K for H || c and H || ab. (e,f) Temperature dependence of the (1,1,0) magnetic Bragg peak intensity of CrSiTe3 and CrGeTe3 measured at DNS, MLZ. The solid lines are the fittings of the experimental data in the vicinity of the ferromagnetic transition.$

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In-plane uniaxial pressure-induced out-of-plane antiferromagnetic moment and critical fluctuations in BaFe2As2

Nature Communications, 2020

A small in-plane external uniaxial pressure has been widely used as an effective method to acquir... more A small in-plane external uniaxial pressure has been widely used as an effective method to acquire single domain iron pnictide BaFe2As2, which exhibits twin-domains without uniaxial strain below the tetragonal-to-orthorhombic structural (nematic) transition temperature Ts. Although it is generally assumed that such a pressure will not affect the intrinsic electronic/magnetic properties of the system, it is known to enhance the antiferromagnetic (AF) ordering temperature TN ( < Ts) and create in-plane resistivity anisotropy above Ts. Here we use neutron polarization analysis to show that such a strain on BaFe2As2 also induces a static or quasi-static out-of-plane (c-axis) AF order and its associated critical spin fluctuations near TN/Ts. Therefore, uniaxial pressure necessary to detwin single crystals of BaFe2As2 actually rotates the easy axis of the collinear AF order near TN/Ts, and such effects due to spin-orbit coupling must be taken into account to unveil the intrinsic electr...

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Strong spin resonance mode associated with suppression of soft magnetic ordering in hole-doped Ba1-xNaxFe2As2

npj Quantum Materials, 2019

Spin-resonance modes (SRM) are taken as evidence for magnetically driven pairing in Fe-based supe... more Spin-resonance modes (SRM) are taken as evidence for magnetically driven pairing in Fe-based superconductors, but their character remains poorly understood. The broadness, the splitting and the spin-space anisotropies of SRMs contrast with the mostly accepted interpretation as spin excitons. We study hole-doped Ba1−xNaxFe2As2 that displays a spin reorientation transition. This reorientation has little impact on the overall appearance of the resonance excitations with a high-energy isotropic and a low-energy anisotropic mode. However, the strength of the anisotropic low-energy mode sharply peaks at the highest doping that still exhibits magnetic ordering resulting in the strongest SRM observed in any Fe-based superconductor so far. This remarkably strong SRM is accompanied by a loss of about half of the magnetic Bragg intensity upon entering the SC phase. Anisotropic SRMs thus can allow the system to compensate for the loss of exchange energy arising from the reduced antiferromagneti...

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Total interference between nuclear and magnetovibrational one-phonon scattering cross sections

Journal of Physics: Conference Series, 2019

A full phonon intensity cancellation is reported in a longitudinal polarized inelastic neutron sc... more A full phonon intensity cancellation is reported in a longitudinal polarized inelastic neutron scattering experiment performed on the magnetocaloric compound MnFe4Si3, a ferromagnet with TCurie ≈ 305 K. The TA[100] phonon polarized along the c-axis measured from the Brillouin zone center G=(0, 0, 2) is observed only in one ( σ z + + ) of the two non-spin-flip polarization channels and is absent in the other one ( σ z − − ) at low temperatures. This effect disappears at higher temperatures, in the vicinity of TCurie , where the phonon is measured in both channels with nonetheless marked different intensities. The effect is understood as originating from nuclear-magnetic interference between the nuclear one-phonon and the magnetovibrational one-phonon scattering cross-sections. The total cancellation reported is accidental, i.e. does not correspond to a systematic effect, as established by measurements in different Brillouin zones.

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The upgrade of the cold neutron three-axis spectrometer IN12 at the ILL

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016

After nearly 40 years of successful operation the cold three-axis spectrometer IN12 at the Instit... more After nearly 40 years of successful operation the cold three-axis spectrometer IN12 at the Institut Laue-Langevin, Grenoble, France, has been relocated to a new position and the primary spectrometer has been upgraded. Latest modern optical components are employed. A new guide in combination with a virtual source concept and a double focusing monochromator guarantee highest flux. With its high unpolarized and polarized neutron flux IN12 allows for demanding experiments. A velocity selector in the guide ensures a clean beam and a very low background. A gain in flux of about an order of magnitude at the sample position has been achieved compared to the previous instrument and IN12's wavelength range now extends far into the warmish region.

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Strong interplay between stripe spin fluctuations, nematicity and superconductivity in FeSe

Nature materials, Jan 7, 2015

In iron-based superconductors the interactions driving the nematic order (that breaks four-fold r... more In iron-based superconductors the interactions driving the nematic order (that breaks four-fold rotational symmetry in the iron plane) may also mediate the Cooper pairing. The experimental determination of these interactions, which are believed to depend on the orbital or the spin degrees of freedom, is challenging because nematic order occurs at, or slightly above, the ordering temperature of a stripe magnetic phase. Here, we study FeSe (ref. )-which exhibits a nematic (orthorhombic) phase transition at Ts = 90 K without antiferromagnetic ordering-by neutron scattering, finding substantial stripe spin fluctuations coupled with the nematicity that are enhanced abruptly on cooling through Ts. A sharp spin resonance develops in the superconducting state, whose energy (∼4 meV) is consistent with an electron-boson coupling mode revealed by scanning tunnelling spectroscopy. The magnetic spectral weight in FeSe is found to be comparable to that of the iron arsenides. Our results support r...

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Magnetic order and phase transitions in Fe50Pt50–x Rh x

Journal of Applied Crystallography, 2015

Polarized and unpolarized neutron diffraction techniques have been applied to study the temperatu... more Polarized and unpolarized neutron diffraction techniques have been applied to study the temperature-dependent magnetic and structural properties of four 200 nm-thick Fe50Pt50−x Rh x films with x = 5, x = 10, x = 17.5 and x = 25. Similar to the bulk system, an antiferromagnetic to ferromagnetic transition can be found in the films with decreasing Rh concentration. The application of structure factor calculations enables one to determine the microscopic magnetic configuration of the different films as a function of temperature and Rh concentration. The developed models indicate a magnetic transition from a dominant antiferromagnetic order in the out-of-plane direction to a dominant ferromagnetic order in the in-plane direction with decreasing Rh concentration. The different magnetic configurations can theoretically be described by a phenomenological model which includes a two-ion and a one-ion interaction Hamiltonian term with different temperature dependencies of the anisotropy const...

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Competing Ferri- and Antiferromagnetic Phases in Geometrically FrustratedLuFe2O4

Physical Review Letters, 2012

We present a detailed study of magnetism in LuFe2O4, combining magnetization measurements with ne... more We present a detailed study of magnetism in LuFe2O4, combining magnetization measurements with neutron and soft x-ray diffraction. The magnetic phase diagram in the vicinity of TN involves a metamagnetic transition separating an antiferro-and a ferrimagnetic phase. For both phases the spin structure is refined by neutron diffraction. Observed diffuse magnetic scattering far above TN is explained in terms of near degeneracy of the magnetic phases.

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Magnetic anisotropic energy gap and low-energy spin wave excitation in the antiferromagnetic block phase of K2Fe4Se5

Physical Review B, 2013

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Coexistence of Eu antiferromagnetism and pressure-induced superconductivity in single-crystal EuFe2As2

Physical Review B, 2019

By performing high-pressure single-crystal neutron diffraction measurements, the evolution of str... more By performing high-pressure single-crystal neutron diffraction measurements, the evolution of structure and magnetic ordering in EuFe2As2 under hydrostatic pressure were investigated. Both the tetragonal-toorthorhombic structural transition and the Fe spin-density-wave (SDW) transition are gradually suppressed and become decoupled with increasing pressure. The antiferromagnetic order of the Eu sublattice is, however, robust against the applied pressure up to 24.7 kbar, without showing any change of the ordering temperature. Under the pressure of 24.7 kbar, the lattice parameters of EuFe2As2 display clear anomalies at 27(3) K, well consistent with the superconducting transition observed in previous high-pressure resistivity measurements. Such an anomalous thermal expansion around Tc strongly suggests the appearance of bulk superconductivity and strong electron-lattice coupling in EuFe2As2 induced by the hydrostatic pressure. The coexistence of long-range ordered Eu-antiferromagnetism and pressure-induced superconductivity is quite rare in the EuFe2As2-based iron pnictides.

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Nature of the Magnetic Order in CeCu2Si2 and Interplay with Superconductivity

229 The interplay of superconductivity and antiferromagnetic order continues to be of general int... more 229 The interplay of superconductivity and antiferromagnetic order continues to be of general interest in condensed matter physics. While the coexistence of antiferromagnetism and superconductivity can easily be understood if different electronic subsystems are involved in the two phenomena, the situation might be different if the same electron system is responsible for both. In the case of the heavyfermion compound CeCu2Si2 the Ce-4f electrons do not only order magnetically, but are also involved in the formation of superconducting Cooper pairs [1,2]. The heavy-fermion compound CeCu2Si2 forms only in a very narrow range of the ternary phase diagram Ce:Cu:Si around the 1:2:2 composition. However, the ground state in CeCu2Si2 depends very delicately on the actual composition. Thus, Cu-rich samples exhibit only superconductivity (Stype) and Si-rich only show a magnetically ordered phase, called A-phase, while in stoichiometric samples (A/S-type) a complex interaction between supercond...

Complex magnetic structure and spin waves of the noncollinear antiferromagnet Mn5Si3

Physical Review B, 2022

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Investigating the underlying mechanisms of the magnetocaloric effect with inelastic neutron scattering in Mn5-xFexSi3

Polarization analysis on the new IN12

Magnetische Spinanordnung in Fe50Pt50-xRhx-Filmen

Dimerization in the commensurate antiferromagnetic phase of MnWO4 and NaFe(WO4)2