1. 
 Abdeldaim, Aly, 1993, et al.
(författare)

Large easyaxis anisotropy in the onedimensional magnet BaMo(PO4)(2)
 2019

Ingår i: Physical Review B.  : AMER PHYSICAL SOC.  24699969 . 24699950. ; 100:21

Tidskriftsartikel (refereegranskat)abstract
 We present an extensive experimental and theoretical study on the lowtemperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO4)(2). The magnetic susceptibility reveals strong antiferromagnetic interactions theta(CW) = 167 K and longrange magnetic order at TN = 22 K, in agreement with a recent report. Powder neutron diffraction furthermore shows that the order is collinear, with the moments near the ac plane. Neutron spectroscopy reveals a large excitation gap Delta = 15 meV in the lowtemperature ordered phase, suggesting a much larger easyaxis spin anisotropy than anticipated. However, the large anisotropy justifies the relatively high ordered moment, Neel temperature, and collinear order observed experimentally and is furthermore reproduced in a firstprinciples calculations by using a new computational scheme. We therefore propose BaMo(PO4)(2) to host S = 1 antiferromagnetic chains with large easyaxis anisotropy, which has been theoretically predicted to realize novel excitation continua.


2. 
 Albaalbaky, Ahmed, et al.
(författare)

Analytical and numerical investigations of noncollinear magnetic ordering in the frustrated delafossite CuCrO2
 2019

Ingår i: Physical Review B.  24699950 . 24699969. ; 99:10

Tidskriftsartikel (refereegranskat)abstract
 The magnetic propagation vector in delafossite CuCrO2 with classical Heisenberg spins is calculated analytically as a function of exchange interactions up to fourthnearest neighbors. Exchange interactions are estimated by a series of density functional theory calculations for several values of lattice distortion. Our calculations show that the magnetic propagation vector is directly affected by the considered distortions providing different stable commensurate or incommensurate magnetic configurations. A realistic set of exchange interactions corresponding to a 0.1% lattice distortion yields the experimental ground state with an incommensurate propagation vector q similar to (0.329, 0.329, 0). We find that a very weak antiferromagnetic interlayer interaction favors an incommensurate ordering even in the absence of lattice distortion. Moreover, the exchange energy of a magnetic configuration of a finite crystal of CuCrO2 with periodic boundary conditions is derived analytically. Based on that, highly accurate Monte Carlo simulations performed on CuCrO2 confirm both the proposed analytical calculations and the density functional theory estimations, where we obtain excellent convergence toward the experimental ground state with a magnetic propagation vector q = (0.3288, 0.3288, 0).


3. 
 Albaalbaky, Ahmed, et al.
(författare)

Effects of Ga doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 : Ab initio and Monte Carlo approaches
 2018

Ingår i: Physical Review B.  : AMER PHYSICAL SOC.  24699950 . 24699969. ; 98:17

Tidskriftsartikel (refereegranskat)abstract
 The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to 30% of Cr3+ ions by Ga3+ ones does not significantly affect the remaining CrCr superexchange interactions. Monte Carlo simulations show that CuCr1xGaxO2 preserves its magnetoelectric properties up to x similar or equal to 0.15 with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing x and eventually disappears at x >= 0.2. Our simulations show that Ga3+ doping increases the CurieWeiss temperature of CuCr1xGaxO2, which agrees well with experimental observations. Moreover, our results show that the incommensurate groundstate configuration is destabilized by Ga3+ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for x <= 0.15 through simulating PE hysteresis loops, which leads to ferroelectricity in the extended inverse DzyaloshinskiiMoriya model.


4. 
 Albaalbaky, Ahmed, et al.
(författare)

Magnetoelectric properties of multiferroic CuCrO2 studied by means of ab initio calculations and Monte Carlo simulations
 2017

Ingår i: Physical Review B.  24699950 . 24699969. ; 96:6

Tidskriftsartikel (refereegranskat)abstract
 Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO2 below its Neel temperature TN, we investigate its magnetic and ferroelectric properties using ab initio calculations and Monte Carlo simulations. Exchange interactions up to the third nearest neighbors in the ab plane, interlayer interaction, and single ion anisotropy constants in CuCrO2 are estimated by a series of density functional theory calculations. In particular, our results evidence a hard axis along the [110] direction due to the lattice distortion that takes place along this direction below TN. Our Monte Carlo simulations indicate that the system possesses a Neel temperature TN approximate to 27 K very close to the ones reported experimentally (TN = 2426 K). Also we show that the ground state is a properscrew magnetic configuration with an incommensurate propagation vector pointing along the [110] direction. Moreover, our work reports the emergence of spin helicity below TN which leads to ferroelectricity in the extended inverse DzyaloshinskiiMoriya model. We confirm the electric control of spin helicity by simulating PE hysteresis loops at various temperatures.


5. 
 Arneth, J., et al.
(författare)

Uniaxial pressure effects in the twodimensional van der Waals ferromagnet CrI3
 2022

Ingår i: Physical Review B.  : American Physical Society.  24699950 . 24699969. ; 105:6

Tidskriftsartikel (refereegranskat)abstract
 Magnetoelastic coupling and uniaxial pressure dependencies of the ferromagnetic ordering temperature in the quasitwodimensional layered van der Waals material CrI3 are experimentally studied and quantified by highresolution dilatometry. Clear anomalies in the thermal expansion coefficients at TC imply positive (negative) pressure dependencies partial derivative TC/partial derivative p(i) for pressure applied along (perpendicular to) the c axis. The experimental results are backed up by numerical studies showing that the dominant, intralayer magnetic coupling increases upon compression along the c direction and decreases with negative inplane strain. In contrast, interlayer exchange is shown to initially increase and subsequently decrease upon the application of both outofplane and inplane compression.


6. 
 Belotcerkovtceva, Daria, et al.
(författare)

Insights and Implications of Intricate Surface Charge Transfer and sp3Defects in Graphene/Metal Oxide Interfaces
 2022

Ingår i: ACS Applied Materials and Interfaces.  : American Chemical Society (ACS).  19448244 . 19448252. ; 14:31, s. 3620936216

Tidskriftsartikel (refereegranskat)abstract
 Adherence of metal oxides to graphene is of fundamental significance to graphene nanoelectronic and spintronic interfaces. Titanium oxide and aluminum oxide are two widely used tunnel barriers in such devices, which offer optimum interface resistance and distinct interface conditions that govern transport parameters and device performance. Here, we reveal a fundamental difference in how these metal oxides interface with graphene through electrical transport measurements and Raman and photoelectron spectroscopies, combined with ab initio electronic structure calculations of such interfaces. While both oxide layers cause surface charge transfer induced ptype doping in graphene, in sharp contrast to TiOx, the AlOx/graphene interface shows the presence of appreciable sp3 defects. Electronic structure calculations disclose that significant ptype doping occurs due to a combination of sp3 bonds formed between C and O atoms at the interface and possible slightly offstoichiometric defects of the aluminum oxide layer. Furthermore, the sp3 hybridization at the AlOx/graphene interface leads to distinct magnetic moments of unsaturated bonds, which not only explicates the widely observed low spinlifetimes in AlOx barrier graphene spintronic devices but also suggests possibilities for new hybrid resistive switching and spin valves.


7. 
 Beutier, G., et al.
(författare)

Band Filling Control of the DzyaloshinskiiMoriya Interaction in Weakly Ferromagnetic Insulators
 2017

Ingår i: Physical Review Letters.  : AMER PHYSICAL SOC.  00319007 . 10797114. ; 119:16

Tidskriftsartikel (refereegranskat)abstract
 We observe and explain theoretically a dramatic evolution of the DzyaloshinskiiMoriya interaction (DMI) in the series of isostructural weak ferromagnets, MnCO3, FeBO3, CoCO3, and NiCO3. The sign of the interaction is encoded in the phase of the xray magnetic diffraction amplitude, observed through interference with resonant quadrupole scattering. We find very good quantitative agreement with firstprinciples electronic structure calculations, reproducing both sign and magnitude through the series, and propose a simplified "toy model" to explain the change in sign with 3d shell filling. The model gives insight into the evolution of the DMI in Mott and charge transfer insulators.


8. 
 Bondarenko, Nina G., et al.
(författare)

Spin polaronics : Static and dynamic properties of spin polarons in Ladoped CaMnO4
 2019

Ingår i: Physical Review B.  : American Physical Society.  24699950 . 24699969. ; 100:13

Tidskriftsartikel (refereegranskat)abstract
 The static and dynamic properties of spin polarons in Ladoped CaMnO3 are explored theoretically, by means of an effective lowenergy Hamiltonian. All parameters of the effective Hamiltonian are evaluated from firstprinciples theory. The Hamiltonian is used to investigate the temperature stability as well as the response to an external applied electric field, for spin polarons in bulk, surface, and as single twodimensional layers. Technically this involves atomistic spindynamics simulations in combination with kinetic Monte Carlo simulations. Where a comparison can be made, our simulations exhibit excellent agreement with available experimental data and previous theory. Remarkably, we find that excellent control of the mobility of spin polarons in this material can be achieved, and that the critical parameters deciding this are the temperature and strength of the applied electrical field. We outline different technological implications of spin polarons, and point to spin polaronics as an emerging subfield of nanotechnology. In particular, we demonstrate that it is feasible to write and erase information on an atomic scale, by use of spin polarons in CaMnO3.


9. 
 Bondarenko, Nina, et al.
(författare)

Static and dynamical properties of spinpolarons in Ladoped CaMnO3

Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
 The static and dynamic properties of spinpolarons in Ladoped CaMnO3 are explored theoretically,by means of an eective low energy Hamiltonian. All parameters from the Hamiltoniainare evaluated from rst principles theory, without adjustable parameters. We compare dierentgeometries, like spinpolarons in bulk, surface and as single twodimensional layers. The low energyHamiltonian is used to investigate the temperature stability of the spinpolaron, as well as theresponse to an external applied electric eld. Technically this involves atomistic spindynamics simulationsin combination with kinetic Monte Carlo simulations. Where a comparison can be made,our simulations exhibit an excellent agreement with available experimental data and previous theory.Remarkably, we nd that excellent control of the mobility of spinpolarons in this material canbe achieved, and that the critical parameters deciding this is the temperature and strength of theapplied electrical eld. We outline dierent technological implications of our ndings.


10. 
 Borisov, Vladislav, et al.
(författare)

Heisenberg and anisotropic exchange interactions in magnetic materials with correlated electronic structure and significant spinorbit coupling
 2021

Ingår i: Physical Review B.  : American Physical Society.  24699950 . 24699969. ; 103:17

Tidskriftsartikel (refereegranskat)abstract
 The DzyaloshinskiiMoriya (DM) interaction, as well as symmetric anisotropic exchange, are important ingredients for stabilizing topologically nontrivial magnetic textures, such as, e.g., skyrmions, merons, and hopfions. These types of textures are currently in focus from a fundamental science perspective and they are also discussed in the context of future spintronics information technology. While the theoretical understanding of the Heisenberg exchange interactions is well developed, it is still a challenge to access, from first principles theory, the DM interaction as well as the symmetric anisotropic exchange, which both require a fullyrelativistic treatment of the electronic structure, in magnetic systems where substantial electronelectron correlations are present. Here, we present results of a theoretical framework which allows to compute these interactions in any given system and demonstrate its performance for several selected cases, for both bulk and lowdimensional systems. We address several representative cases, including the bulk systems CoPt and FePt, the B20 compounds MnSi and FeGe as well as the lowdimensional transition metal bilayers Co/Pt(111) andMn/W(001). The effect of electronelectron correlations is analyzed using dynamical meanfield theory on the level of the spinpolarized T matrix + fluctuating exchange (SPTF) approximation, as regards the strength and character of the isotropic (Heisenberg) and anisotropic (DM) interactions in relation to the underlying electronic structure. Our method can be combined with more advanced techniques for treating correlations, e.g., quantum Monte Carlo and exact diagonalization methods for the impurity solver of dynamical meanfield theory. We find that correlationinduced changes of the DM interaction can be rather significant, with up to fivefold modifications in the most distinctive case.

