Exchange interactions and the nature of magnetic ordering in Zn0.6Mn2.4O4 particles

This work signifies the next step in our way in the magnetic properties simulation of spin clusters and extended networks containing quantum spins, by original FORTRAN codes based on Heisenberg–Dirac–VanVleck (HDVV) or Ising approaches, using Full Diagonalization Heisenberg Matrix (FDHM) or Monte Carlo–Metropolis (MCM) procedure, respectively. We present the results of magnetic Monte Carlo studies on a magnetite type lattice, Ising model ferrimagnet that provide insight into the exchange interactions involved in Cubic Ferrospinels. We have demonstrated that a comparatively simple model can reproduce ferrimagnetic behavior of ferrospinels, particularly for magnetite.

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DILUTED FERROMAGNETIC SEMICONDUCTORS — ORIGIN OF MAGNETIC ORDERING AND SPIN-TRANSPORT PROPERTIES

International Journal of Modern Physics B ◽

10.1142/s0217979208046116 ◽

2008 ◽

Vol 22 (01n02) ◽

pp. 104-105 ◽

Cited By ~ 1

Author(s):

TOMASZ DIETL

Keyword(s):

Diluted Magnetic Semiconductors ◽

Spin Transport ◽

Correlation Energy ◽

Tight Binding ◽

Spin Current ◽

Magnetic Ordering ◽

Exchange Interactions ◽

Ferromagnetic Phase ◽

Magnetic Characteristics ◽

Ferromagnetic Semiconductors

In the first hour of the lecture the present understanding of the origin of exchange interaction and mechanisms leading to ferromagnetic order in diluted magnetic semiconductors will be presented.1 The lecture will start by discussing energy positions of relevant open magnetic shells, including the correlation energy and excitations within the magnetic ions. The origin and magnitude of sp–d exchange interactions will then be described. This will be followed by presenting the physics of indirect exchange interactions between localized spins contrasting magnetic characteristics in the absence and in the presence of free carriers. The Zener and RKKY models of ferromagnetism will be introduced and the role of confinement, dimensionality, and spin-orbit interaction in determining properties of the ferromagnetic phase will be outlined. The second lecture will be devoted to theory of spin transport in layered structures of diluted ferromagnetic semiconductors, emphasizing the issues important for perspective spintronics devices. A recently developed theory,2 which combines a multi-orbital empirical tight-binding approach with a Landauer–Büttiker formalism will be presented. In contrast to the standard kp method, this theory describes properly the interfaces and inversion symmetry breaking as well as the band dispersion in the entire Brillouin zone, so that the essential for the spin-dependent transport Rashba and Dresselhaus terms as well as the tunneling via k points away from the zone center are taken into account. The applicability of this model for the description of tunneling magnetoresistance (TMR), resonant tunneling spectra, spin-current polarization in Esaki-Zener diodes, and domain-wall resistance will be presented. Note from Publisher: This article contains the abstract only.

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Robust manipulation of magnetism in LaAO3/BaTiO3 (A = Fe, Mn and Cr) superstructures by ferroelectric polarization

IUCrJ ◽

10.1107/s205225251801624x ◽

2019 ◽

Vol 6 (2) ◽

pp. 189-196 ◽

Cited By ~ 5

Author(s):

Dong Chen ◽

Guangbiao Zhang ◽

Zhenxiang Cheng ◽

Shuai Dong ◽

Yuanxu Wang

Keyword(s):

Magnetic Ordering ◽

Exchange Interactions ◽

Perovskite Oxide ◽

Oxygen Octahedra ◽

Ferroelectric Polarization ◽

Structural Basis ◽

Generalized Gradient ◽

Metallic Behavior ◽

Spin Orbital ◽

Ferromagnetic Ordering

Robust control of magnetism is both fundamentally and practically meaningful and highly desirable, although it remains a big challenge. In this work, perovskite oxide superstructures LaFeO3/BaTiO3 (LFO/BTO), LaMnO3/BaTiO3 (LMO/BTO) and LaCrO3/BaTiO3 (LCO/BTO) (001) are designed to facilitate tuning of magnetism by the electric field from ferroelectric polarization, and are systemically investigated via first-principles calculations. The results show that the magnetic ordering, conductivity and exchange interactions can be controlled simultaneously or individually by the reorientation of the ferroelectric polarization of BTO in these designed superstructures. Self-consistent calculations within the generalized gradient approximation plus on-site Coulomb correction did not produce distinct rotations of oxygen octahedra, but there were obvious changes in bond length between oxygen and the cations. These changes cause tilting of the oxygen octahedra and lead to spin, orbital and bond reconstruction at the interface, which is the structural basis responsible for the manipulation. With the G-type antiferromagnetic (G-AFM) ordering unchanged for both ±P cases, a metal–insulator transition can be observed in the LFO/BTO superstructure, which is controlled by the LFO thin film. The LMO/BTO system has A-type antiferromagnetic (A-AFM) ordering with metallic behavior in the +P case, while it shifts to a half-metallic ferromagnetic ordering when the direction of the polarization is switched. LCO/BTO exhibits C-type antiferromagnetic (C-AFM) and G-AFM orders in the +P and −P cases, respectively. The three purpose-designed superstructures with robust intrinsic magnetoelectric coupling are a particularly interesting model system that can provide guidance for the development of this field for future applications.

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Электронные и магнитные свойства сплавов DyFe-=SUB=-4-=/SUB=-Ge-=SUB=-2-=/SUB=- в области фазового перехода

Физика твердого тела ◽

10.21883/ftt.2020.06.49331.26m ◽

2020 ◽

Vol 62 (6) ◽

pp. 823

Author(s):

М.В. Матюнина ◽

М.А. Загребин ◽

В.В. Соколовский ◽

В.Д. Бучельников

Keyword(s):

Magnetic Properties ◽

Mean Field ◽

Magnetic Ordering ◽

Exchange Interactions ◽

Field Approximation ◽

Mean Field Approximation ◽

Local Spin Density Approximation ◽

Electronic And Magnetic Properties ◽

Strong Localization ◽

The Mean

Abstract The first-principles studies have been performed for the electronic and magnetic properties of DyFe_4Ge_2 alloys near the P 4_2/ mmm – Cmmm phase transition. The calculations are carried out in a local spin density approximation taking into account the Coulomb interaction within the limit of strong localization in a mean field approximation. The electronic and magnetic properties of the tetragonal structure are shown to be weakly changed in the dependence on the Coulomb and exchange interactions and also on the choice of the approximations. In the case of the orthorhombic structure, a change in the parameters of the Coulomb and exchange interactions leads to a change in the magnetic ordering: from the ferromagnetic to ferrimagnetic in the strong localization limit and from the ferromagnetic to paramagnetic in the mean field approximation.

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Putting the Squeeze on Molecule-Based Magnets: Exploiting Pressure to Develop Magneto-Structural Correlations in Paramagnetic Coordination Compounds

10.20944/preprints202007.0489.v1 ◽

2020 ◽

Author(s):

Euan Brechin ◽

Alvaro Etcheverry-Berrios ◽

Simon Parsons ◽

Konstantin Kamenev ◽

Michael Probert ◽

...

Keyword(s):

High Pressure ◽

Structural Changes ◽

Inelastic Neutron Scattering ◽

Magnetic Ordering ◽

Exchange Interactions ◽

Inelastic Neutron ◽

Magnetic Core ◽

Magnetic Behaviour ◽

Paramagnetic Resonance ◽

Bond Angles

The cornerstone of molecular magnetism is a detailed understanding of the relationship between structure and magnetic behaviour, i.e. the development of magneto-structural correlations. Traditionally, the synthetic chemist approaches this challenge by making multiple compounds that share a similar magnetic core but differ in peripheral ligation. Changes in the ligand framework induce changes in the bond angles and distances around the metal ions which are manifested in changes to magnetic susceptibility and magnetisation data. This approach requires the synthesis of series of different ligands and assumes that the chemical/electronic nature of the ligands and their coordination to the metal, the nature and number of counter ions and how they are positioned in the crystal lattice, and the molecular and crystallographic symmetry have no effect on the measured magnetic properties. In short, the assumption is that everything outwith the magnetic core is innocent, which is a huge oversimplification. The ideal scenario would be to have the same complex available in multiple structural conformations, and this is something that can be achieved through the application of external hydrostatic pressure, correlating structural changes observed through high pressure single crystal X-ray crystallography with changes observed in high pressure magnetometry, in tandem with high pressure inelastic neutron scattering (INS), high pressure electron paramagnetic resonance (EPR) spectroscopy and high pressure absorption/emission/Raman spectroscopy. In this review, which summarises our work in this area over the last 15 years, we show that the application of pressure to molecule-based magnets can (reversibly): (1) lead to changes in bond angles, distances and Jahn-Teller orientations; (2) break and form bonds; (3) induce polymerisation/depolymerisation; (4) enforce multiple phase transitions; (5) instigate piezochromism; (6) change the magnitude and sign of pairwise exchange interactions and magnetic anisotropy and (7) lead to significant increases in magnetic ordering temperatures.

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Magnetic properties and site occupancy of iron in nontronite

Clay Minerals ◽

10.1180/claymin.1990.025.1.02 ◽

1990 ◽

Vol 25 (1) ◽

pp. 3-13 ◽

Cited By ~ 9

Author(s):

P. R. Lear ◽

J. W. Stucki

Keyword(s):

Site Occupancy ◽

Magnetic Ordering ◽

Exchange Interactions ◽

Oxidation States ◽

Isomorphous Substitution ◽

Computer Simulation Model ◽

Antiferromagnetic Exchange ◽

Magnetic Exchange Interaction ◽

Magnetic Exchange ◽

Magnetic Dilution

AbstractThe magnetic susceptibilities of seven different nontronites in their natural oxidation states were measured between 5 and 100 K. Results revealed that the magnetic exchange interaction in all samples was antiferromagnetic, except no clear minimum occurred at the Néel temperature. Possible explanations for this phenomenon which are discussed include magnetic dilution due to isomorphous substitution, and antiferromagnetic frustration due to either non-centrosymmetric distribution of octahedral Fe3+ or tetrahedral Fe3+ substitution. A computer simulation model was developed to demonstrate the effects of these variables on long-range magnetic ordering. Magnetic dilution and tetrahedral Fe3+ content could explain the anomalous antiferromagnetic behaviour in some, but not all, samples. The non-centrosymmetric model is the only one which explains the behaviour of all samples. In this model, at least 13% of the octahedral Fe3+ would occupy trans-dihydroxide sites, with the balance in cis sites. Magnetic frustration occurs because two Fe3+ neighbours of a third Fe3+ ion are also neighbours to each other, making the simultaneous satisfaction of all antiferromagnetic exchange interactions impossible.

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Scaling theory of magnetic ordering in the Kondo lattices with anisotropic exchange interactions

Physical Review B ◽

10.1103/physrevb.59.9348 ◽

1999 ◽

Vol 59 (14) ◽

pp. 9348-9356 ◽

Cited By ~ 23

Author(s):

V. Yu. Irkhin ◽

M. I. Katsnelson

Keyword(s):

Magnetic Ordering ◽

Exchange Interactions ◽

Scaling Theory ◽

Anisotropic Exchange

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Magnetic ordering and fluctuation in Kagome lattice anti-ferromagnets, Fe and Cr jarosites

Canadian Journal of Physics ◽

10.1139/p01-108 ◽

2001 ◽

Vol 79 (11-12) ◽

pp. 1511-1516 ◽

Cited By ~ 10

Author(s):

M Nishiyama ◽

T Morimoto ◽

S Maegawa ◽

T Inami ◽

Y Oka

Keyword(s):

Magnetic Transition ◽

Magnetic Ordering ◽

Exchange Interactions ◽

Lattice Relaxation ◽

Spin Correlation ◽

Spin Lattice Relaxation ◽

Kagome Lattice ◽

Kagomé Lattice ◽

Spin Lattice ◽

High Temperature Expansion

Jarosite family compounds, KFe3(OH)6(SO4)2 (abbreviated to Fe jarosite) and KCr3(OH)6(SO4)2 (Cr jarosite) are typical examples of Heisenberg anti-ferromagnets on the Kagome lattice and have been investigated by means of magnetization and NMR experiments. The susceptibility of Cr jarosite deviates from the CurieWeiss law due to the short-range spin correlation below about 150 K and shows the magnetic transition at 4.2 K, while Fe jarosite has the transition at 65 K. The measured susceptibility fits well with the calculated one on the high-temperature expansion for the Heisenberg anti-ferromagnet on the Kagome lattice. The values of the exchange interactions of Cr jarosite and Fe jarosite are derived to be JCr = 4.9 K and JFe = 23 K, respectively. The 1H-NMR spectra of Fe jarosite suggest that the ordered spin structure is the q = 0 type 120° configuration with +1 chirality. The transition is considered to be caused by a weak single-ion type anisotropy. The spin-lattice relaxation rate, 1/T1, of Fe jarosite in the ordered phase decreases sharply with decreasing temperature and can be well explained by the two-magnon process of spin wave with the anisotropy. PACS No.: 75.25+z

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Electronic, Magnetic and Structural Properties of the RFeO3 Antiferromagnetic-Perovskites at Very High Pressures

MRS Proceedings ◽

10.1557/proc-718-d2.7 ◽

2002 ◽

Vol 718 ◽

Cited By ~ 11

Author(s):

Moshe P. Pasternak ◽

W. M. Xu ◽

G. Kh. Rozenberg ◽

R. D. Taylor

Keyword(s):

High Pressure ◽

High Pressures ◽

Ambient Pressure ◽

Magnetic Ordering ◽

Exchange Interactions ◽

Volume Reduction ◽

Metallic State ◽

First Order Phase Transition ◽

Diamond Anvil ◽

First Order Phase

AbstractAt ambient pressure the orthorhombic perovskites R-orthoferrites (R Ξ Lu, Eu, Y, Pr, and La) exhibit very large optical gaps. These large- gap Mott insulators in which the 3d5 high-spin ferric ions carry large local moments and magnetically order at TN > 600 K, undergo a sluggish structural first-order phase transition in the 30-50 GPa range, with the exception of the LuFeO3 which undergoes an isostructural volume reduction resulting from a high to low-spin crossover. High-pressure methods to 170 GPa using Mossbauer spectroscopy, resistance, and synchrotronbased XRD in diamond anvil cells were applied. Following the quasi-isostructural volume reduction (3-5%) the new phase the magnetic-ordering temperature is drastically reduced, to ∼ 100 K, the direct and super-exchange interactions are drastically weakened, and the charge-transfer gap is substantially reduced. The high-pressure (HP) phases of the La and Pr oxides, at their inception, are composed of high- and low-spin Fe3+ magnetic sublattices, the abundance of the latter increasing with pressure but HP phases of the Eu, Y, and Lu oxides consist solely of low-spin Fe3+. Resistance and Mössbauer studies in La and Pr orthoferrites reveal the onset of a metallic state with moments starting at P > 120 GPa. Based on the magnetic and electrical data of the latter species, a Mott phase diagram was established.

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