Total Magnetic Anisotropy Research Articles

Tailoring magnetic softness of Fe-based amorphous alloys with superior magnetization by magnetic field annealing

The inverse relationship between the saturation magnetic flux density (Bs) and coercivity (Hc) of Fe-based amorphous alloys is a very active research topic that has been extensively debated. In this work, we conducted a detailed investigation on the magnetic softness of Fe83.2-xCoxB10C6Cu0.8 (x = 0 and 6 at.%) amorphous alloys based on analysis of the surface morphology, microstructure, magnetic anisotropy, and magnetic domain structure. Enhanced magnetic softness-magnetization synergy was realized in the present alloys by magnetic field annealing (MFA) during the de-stressing process. A dramatic 84 % reduction of Hc to 2.2 A/m was achieved for the Co-doped alloy under MFA, exhibiting excellent magnetic performance with a superb Bs of 1.86 T. The consistency between the experimental results and theoretical analysis revealed that the MFA process can mitigate the trade-off between stress-induced anisotropy and induced uniaxial anisotropy owing to the homogenized structure formed by field annealing. Thus, the process favored a low Hc due to the significant continuous decline in the total magnetic anisotropy, which coincided well with the results of Magneto-optical Kerr microscopy. The study elucidates a mechanism for tuning Hc in Co-doped alloy systems and affords a possible pathway for softening amorphous alloys with high Bs.

Defect effects on the electronic, valley, and magnetic properties of the two-dimensional ferrovalley material VSi2N4.

Due to their novel spin and valley properties, two-dimensional (2D) ferrovalley materials are expected to be promising candidates for next-generation spintronic and valleytronic devices. However, they are subject to various defects in practical applications. Therefore, the electronic, valley, and magnetic properties may be modified in the presence of the defects. In this work, utilizing first-principles calculations, we systematically studied the effects of defects on the electronic, valley, and magnetic properties of the 2D ferrovalley material VSi2N4. It has been found that C doping, O doping, and N vacancies result in the half-metallic feature, Si vacancies result in the metallic feature, and V vacancies result in a bipolar gapless semiconductor. These defect-induced electronic properties can be effectively tuned by changing defect concentration and layer thickness. Since the impurity bands do not affect the K and K' valleys, valley polarization is well maintained in O-doped and N-defective systems. Importantly, these defects play a crucial role in modifying the magnetic properties of the pristine VSi2N4, especially the magnitude of local magnetic moments and the magnetic anisotropy energy. Detailed analysis of the density of states demonstrates that the variations of the total magnetic moment and magnetic anisotropy energy with biaxial strain are determined by the electronic states near the Fermi level rather than the type of defect, which provides a new understanding of the effects of defects on the magnetic properties of 2D materials. Moreover, the layer thickness can affect the magnetic coupling between defects and surrounding V atoms. Our results offer insight into the electronic, valley, and magnetic properties of VSi2N4 in the presence of various point defects.

Large perpendicular magnetic anisotropy of transition metal dimers driven by polarization switching of a two-dimensional ferroelectric In2Se3 substrate.

Large perpendicular magnetic anisotropy (MA) is highly desirable for realizing atomic-scale magnetic data storage which represents the ultimate limit of the density of magnetic recording. In this work, we study the MA of transition metal dimers Co-Os, Co-Co and Os-Os adsorbed on two-dimensional ferroelectric In2Se3 (In2Se3-CoOs, In2Se3-OsCo, In2Se3-CoCo and In2Se3-OsOs) using first-principles calculations. We find that the Co-Os dimer in In2Se3-CoOs has a total magnetic anisotropy energy (MAE) of ∼40 meV. The MAE arising from the Os atom in In2Se3-CoOs is up to ∼60 meV. Such large MAE is attributed to the high spin-orbit coupling constant and the onefold coordination of the Os atom. In addition, perpendicular MA can be enhanced in In2Se3-CoOs and induced in In2Se3-OsCo, In2Se3-CoCo and In2Se3-OsOs by the ferroelectric polarization reversal of In2Se3. We demonstrate that the enlargement of exchange splitting of dxy/dx2-y2 and dxz/dyz orbitals for Os atoms in In2Se3-OsOs, Co atom in In2Se3-CoOs and Os and Co atoms in In2Se3-OsCo is responsible for the increase of MAE; while, for the upper Co atom in In2Se3-CoCo and the Os atom in In2Se3-CoOs, the energy rise of the dz2 orbital owing to the change of the crystal field effect by the reversal of ferroelectric polarization results in the increase of MAE.

Prediction of high spin polarization and perpendicular magnetic anisotropy in two dimensional ferromagnetic Mn2CXX’ (X, X′=F, Cl, Br, I) Janus monolayers

Two dimensional layered transition metal carbides and nitrides, owing to their unique electronic properties, have potential applications in novel low-dimensional spintronic devices. However, only a few materials with half metallic and easy axis in perpendicular direction make possible for practical applications in spintronics. Here, the electronic structure and magnetic anisotropy of Mn2CXX’ (X, X' = F, Cl, Br, I) Janus monolayers are investigated by first-principles calculations. It is found that the Mn2CXX′ Janus monolayers are half metallic, showing a high spin polarization at Fermi level. The magnetic anisotropy of Mn2CXX′ monolayers can be modulated by replacing the adsorbed atoms. Mn2CFCl, Mn2CClI and Mn2CClBr show easy axis in perpendicular direction, while the easy axis of Mn2CFBr is in-plane direction. When biaxial strains are −2%, ±4 % and −6%, the easy axis direction of Mn2CClI changes from out-of-plane to in-plane, where the total magnetic anisotropy of I atom can be regulated. The easy axis in in-plane direction comes from the hybridization between I-pz and I-px orbital. However, the easy axis of Mn2CClI maintains perpendicular direction at biaxial strains of 2 % and 6 %. The Mn2CXX′ monolayers with half metallicity and easy axis in perpendicular direction have the potential applications in spintronic devices.

First principles and atomistic calculation of the magnetic anisotropy of Y2Fe14B

We present a study of the effects of strain on the magnetocrystalline anisotropy energy and magnetic moments of Y2Fe14B bulk alloy. The study has been performed within the framework of density functional theory in its fully relativistic form under the generalized gradient approximation. We have studied seven different in-plane a lattice constant values ranging from 8.48 up to 9.08 Å with an increment of δa=0.1 Å. For each a value, we carried out an out-of-plane c parameter optimization, achieving the corresponding optimized lattice pair (a,c). We find a large variation in the site resolved magnetic moments for inequivalent Fe, Y, and B atoms for different lattice expansions and a negative contribution to the total moment from the Y sites. We find a strong variation in the magnetocrystalline anisotropy with the c/a ratio. However, the calculated variation when coupled with thermodynamic spin fluctuations is unable to explain the experimentally observed increase in the total magnetic anisotropy, suggesting that a different physical mechanism is likely to be responsible in contrast with previous interpretations. We show that opposing single- and two-ion anisotropy terms in the Hamiltonian gives good agreement with the experiment and is the probable origin of the non-monotonic temperature dependence of the net anisotropy of Y2Fe14B bulk alloy.

Spin Canting in Silica-Coated Nickel Ferrite (NiFe2O4@SiO2) Nanoparticles: a Mössbauer Spectroscopy Study

We present a comparative study on superparamagnetic uncoated and silica-coated NiFe2O4@SiO2 nanoparticles with identical NiFe2O4 cores and two different silica coating thicknesses, focusing on the surface spin arrangement on NiFe2O4. For the investigation of surface spin dynamics, in addition to the SQUID magnetometry experiments which probe the macroscopic behaviour of particle magnetization, Mossbauer spectroscopy was utilized as being a local technique with superior characteristic measurement time. It was revealed that two common aspects observed in nanoscaled magnetic particles, namely the surface spin canting and interparticle dipolar interactions, are intertwined with respect to their contributions to the total magnetic anisotropy, where the latter is significantly decreased with silica coating thickness and allowed surface effects to manifest itself in Mossbauer spectra. The reduced saturation magnetization of uncoated NiFe2O4 nanoparticles with respect to their bulk counterparts indicated the existence of a “magnetically dead” layer on NiFe2O4 surface. In opposite to some assumptions in the literature, the Mossbauer spectra confirmed that such reduced magnetization arises from spin disorder, rather than a change in coordination from inverse spinel to the mixed spinel structure. On the other side, emergence of broad sextet peaks at room temperature Mossbauer spectra showed that for NiFe2O4@SiO2 samples, silica coating further enhanced the spin canting on NiFe2O4 surface. Similarly, for NiFe2O4@SiO2 sample, an unusual asymmetric hysteresis loop at spin freezing temperature was observed as a signature of the existence of disordered spins in the SiO2/NiFe2O4 interface. It was shown that the sextet components in Mossbauer spectra can be reproduced with a continuous hyperfine field distribution due to the frustrated local spin arrangement at the surface. The thickness of the “magnetically dead” disordered surface spin layer was estimated for uncoated NiFe2O4, and average spin canting angle was calculated for NiFe2O4@SiO2 nanoparticles.

Investigation of Rayleigh region in strip like amorphous FINEMET samples after different heat treatments

In this paper we have investigated the influence of thermal treatment on magnetization processes in the low magnetic field range (Rayleigh region). For this study, rapidly quenched FINEMET ribbons in the as-prepared amorphous state were used. It has been observed that the various annealing temperature lead to the different behavior of a studied material as a consequence of a relaxation of the quenched-in internal stresses in the investigated samples. However, neither of the effects of the atomic diffusion has been observed after low temperature heat-treatments. Moreover, it was detected that the partial elimination of internal stresses has a reduction effect on total magnetic anisotropy.

Surface Functionalization Tailored Electronic Structure and Magnetic Properties of Two-Dimensional CrC2 Monolayers

Spintronics is the promising technology for next-generation information storage due to its low energy consumption, high speed, and high circuit integration density, where the high spin polarization is pursued. The bipolar magnetic semiconductor (BMS) is proposed to easily achieve the reverse spin orientation. Surface chemical modification is a valid method to manipulate the electronic structure of two-dimensional materials. Here, the CrC2 monolayer with single-side and both-side functionalization is investigated by first-principles calculations. The monolayer CrC2 functionalized with O atoms (named 2OX) at both sides shows the bipolar half-metallic characteristics at high symmetry point X, while it is a BMS by being functionalized with H atoms (named 2HX). Under the tensile uniaxial strains along both a (εa) and b (εb) directions, the 2OX model turns into the p-type half-semiconductor, which shows robust characteristics with 100% spin-up polarization against the varied uniaxial strains. Total magnetic anisotropy energy (MAE) of the 2OX model fluctuates with varied uniaxial strain εa and decreases as tensile uniaxial strain εb decreases. The 100% spin-up polarized carriers and 100% spin-down polarized carriers appear in the 2HX model by 0.1 hole doping formula unit (f.u.) and 0.1 electron doping f.u., respectively. The results show that the functionalized CrC2 monolayer has potential applications in two-dimensional spintronics.

Parallel magnetic anisotropy in few layers MoS2 films

Many efforts have been made recently to develop new materials that can be applied in more efficient data storage devices, such as 2D magnetic materials. MoS2 is the most studied 2D material beyond graphene due to its unique optical, electronic, mechanical and magnetic properties. This paper presents a systematic study of magnetic anisotropy in MoS2 sheets prepared by liquid exfoliation method. We have applied an extension method in order to obtain ferromagnetic anisotropy by separating paramagnetic contribution from total magnetic anisotropy. MoS2 thin films exhibit ferromagnetic order on 2D-MoS2 remaining until room temperature and a magnetization easy plane.

On the limits of Reactive-Spark-Plasma Sintering to prepare magnetically enhanced nanostructured ceramics: the case of the CoFe2O4-NiO system

Magnetic materials are crucial for the efficiency of the conversion-storage-transport-reconversion energy chain, and the enhancement of their performance has an important impact on technological development. The present work explores the possibility of preparing hetero-nano-structured ceramics based on magnetic oxides, by coupling a ferrimagnetic phase (F) with an antiferromagnetic one (AF) on the nanometric scale. The field-assisted sintering technique or SPS (Spark-Plasma Sintering), adopted at this purpose, ensures the preservation of nano-sized crystals within the final solid structure. The aim is to establish how exchange bias may affect the resulting nano-consolidates and to investigate the potential of this process to increase the total magnetic anisotropy of the CoFe2O4 grains, and thus their coercive field, while keeping the saturation magnetization the same. The structure, microstructure and magnetic properties of the ceramics obtained were studied by several techniques. The results show that the sintering process, along with its typical reductive atmosphere, modifies the composition of the constituents. A new metallic phase appears as a consequence of the reciprocal diffusion of Co and Ni cations, leading to a change in the amount and structure of the AF phase. We propose a schematic representation of the atomic movements that hinder an exchange bias effect between the F and AF phases.

Structural, electric and magnetic properties of (BaFe11.9Al0.1O19)1-x - (BaTiO3)x composites

This paper described to the ceramics (inorganic) two-component composites with controllable magnetic and electrical properties. Ceramic composite samples were produced via solid state reaction method (standard ceramic technique) from initial magnetic (BaFe11.9Al0.1O19 or BF) and ferroelectric (BaTiO3 or BT) phases. BT and BF initial compounds were mixed in stoichiometric ratios (BF)1-x - (BT)x (x = 0, 0.25, 0.5, 0.75 and 1) and sintered. Initial compounds BaFe11.9Al0.1O19 (x = 0) and BaTiO3 (x = 1) were also produced via standard ceramic technique. The constituent materials were chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BF and BT. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and electrical properties versus chemical composition (x) were performed. As structural properties we have defined the features of crystal structure (a and c lattice parameters, volume of unit cell) and peculiarities of microstructure (density, porosity, average grain size). The ferrimagnetic phase transition temperature is almost independent of the content of BT, which is determined by the exchange interactions Fe3+-O2--Fe3+in the magnetic phase. However, the coercivity of composite samples is lower which is due to the contribution of the microstructure dependent shape-anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BT (at about 400 K) and BF (at about 700 K). It was observed that the electrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behavior was discussed in terms of microstructure analysis (grain size, porosity and density).

Magnetic and structural properties of L1-Mn50Ga50-xAlx epitaxially grown thin films

Epitaxially grown L10- MnGa(Al) continuous thin films with the c-axis along the film normal are successfully fabricated on MgO (001) substrates at a substrate deposition temperature Ts of around 400 °C. The order parameter S is found to decrease with Al content, except for that for Al = 0. The films under consideration exhibit the perpendicular magnetic anisotropy constant Ku of about 1 x 107 erg/cm3 at 300 K. In order to clarify the magnetic anisotropy mechanism, the correlation between Ms(T) and Ku(T) is discussed. It is found that the values of n in the power law relation Ku(T) ∼ Ms(T)n are found to be 2.6, 2.3, and 2.0 for the films of 2.5, 5.6, 11.2 Al at%, respectively. The present result suggests that the magnetic anisotropy of L10-MnGaAl thin films may be explained in terms of the two-ion model, where both the contributions of Mn and Ga are significant to the total magnetic anisotropy”. The decrease of the value n with Al addition n is of interest, but the reason for this change is not understood at present.

Preparation and investigation of structure, magnetic and dielectric properties of (BaFe11.9Al0.1O19)1-x - (BaTiO3)x bicomponent ceramics

(BaFe11.9Al0.1O19)1-x - (BaTiO3)x with x = 0, 0.25, 0.5, 0.75 and 1 bicomponent ceramics has been prepared from single-phase compounds of BaFe11.9Al0.1O19 (x = 0) (BFO) and BaTiO3 (x = 1) (BTO) by a standard ceramic technique. The constituent materials have been chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BFO and BTO. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and dielectrical properties versus chemical composition (x) have been performed. The ferrimagnetic phase transition temperature is almost independent of the BTO content, which is determined by intensity of the Fe3+-O2--Fe3+ indirect superexchange interactions in the BFO hexaferrite phase. However, the coercivity of composite samples is lower due to the contribution of the microstructure-dependent shape anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BTO at ~ 400 K and BFO at ~ 700 K. It has been observed that the dielectrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behavior has been discussed in terms of microstructure analysis and such parameters as the grain size, porosity and density.

Relative strength of perpendicular magnetic anisotropy at bottom and top interfaces in Pt/Co/MgO trilayers

In Pt/Co/MgO trilayers, the contribution to the total perpendicular magnetic anisotropy from the bottom Pt/Co interface is significantly greater than that from the top Co/MgO interface at intermediate annealing temperatures. However, the relative contribution is reversed at the highest annealing temperature examined in this study, 400 °C. These results indicate that as the annealing temperature increases, the quality of the Pt/Co interface deteriorates owing to the intermixing of Pt and Co, whereas the quality of the Co/MgO interface improves as oxygen atoms, which are interpenetrated into the Co layer during the deposition of MgO, are diffused toward the Co/MgO interface.

Single-particle mechanism of magnetostriction in magnetoactive elastomers.

Magnetoactive elastomers (MAEs) are composite materials comprised of micrometer-sized ferromagnetic particles in a nonmagnetic elastomer matrix. A single-particle mechanism of magnetostriction in MAEs, assuming the rotation of a soft magnetic, mechanically rigid particle with uniaxial magnetic anisotropy in magnetic fields is identified and considered theoretically within the framework of an alternative model. In this mechanism, the total magnetic anisotropy energy of the filling particles in the matrix is the sum over single particles. Matrix displacements in the vicinity of the particle and the resulting direction of the magnetization vector are calculated. The effect of matrix deformation is pronounced well if the magnetic anisotropy coefficient K is much larger than the shear modulus µ of the elastic matrix. The feasibility of the proposed magnetostriction mechanism in soft magnetoactive elastomers and gels is elucidated. The magnetic-field-induced internal stresses in the matrix lead to effects of magnetodeformation and may increase the elastic moduli of these composite materials.

In-plane/out-of-plane disorder influence on the magnetic anisotropy of Fe1−yMnyPt-L1 bulk alloy

The random substitution of a non-magnetic species instead of Fe atoms in FePt-L10 bulk alloy will permit to tune the magnetic anisotropy energy of this material. We have performed by means of first principles calculations a study of Fe1−yMnyPt-L10 (y = 0.0, 0.08, 0.12, 0.17, 0.22, and 0.25) bulk alloy for a fixed Pt concentration when the Mn species have ferro-/antiferromagnetic (FM,AFM) alignment at the same(different) atomic plane(s). This substitution will promote several in-plane lattice values for a fixed amount of Mn. Charge hybridization will change compared to the FePt-L10 bulk due to this lattice variation leading to a site resolved magnetic moment modification. We demonstrate that this translates into a total magnetic anisotropy reduction for the AFM phase and an enhancement for the FM alignment. Several geometric configurations were taken into account for a fixed Mn concentration because of different possible Mn positions in the simulation cell.

Correlation between structure and magnetic properties in CoxFe100−x nanowires: the roles of composition and wire diameter

The structural and magnetic characteristics of CoxFe100−x (0 ≤ x ≤ 100) cylindrical nanowire arrays are investigated for two series of nanowires with diameters of 20 and 40 nm, respectively. The crystalline structure evolves with Co content from bcc Fe through a mixed bcc–fcc phase to a final polycrystalline fcc or hcp phase for 40 and 20 nm diameter Co nanowires, respectively. A monocrystalline structure is found only in a few nanowires with a 40 nm diameter.The magnetic characterization under axial magnetic field reveals an increase in coercivity and remanence for increasing Co content as the crystalline structure evolves from bcc Fe to fcc Co. These parameters decrease when hcp Co with a stronger magnetocrystalline anisotropy and nearly perpendicular ‘c’ axis is formed. Overall higher values are observed in nanowires when the nanowire diameter decreases from 40 to 20 nm.An increase of the total magnetic anisotropy energy density is found with decreasing temperature, especially for Co wires where the strong magnetocrystalline anisotropy plays the most significant role.

The origin of noise and magnetic hysteresis in crystalline permalloy ring-core fluxgate sensors

Abstract. Developed in the 1960s for use in high-performance ring-core fluxgate sensors, 6–81.3 Mo permalloy remains the state of the art for permalloy-cored fluxgate magnetometers. The magnetic properties of 6–81.3, namely magnetocrystalline and magnetoelastic anisotropies and saturation induction, are all optimum in the Fe–Ni–Mo system. In such polycrystalline permalloy fluxgate sensors, a single phenomenon may cause both fluxgate noise and magnetic hysteresis; explain Barkhausen jumps, remanence and coercivity; and avoid domain denucleation. This phenomenon, domain wall reconnection, is presented as part of a theoretical model. In the unmagnetized state a coarse-grain high-quality permalloy foil ideally forms stripe domains, which present at the free surface as parallel, uniformly spaced domain walls that cross the entire thickness of the foil. Leakage flux "in" and "out" of alternating domains is a requirement of the random orientation, grain by grain, of magnetic easy axes' angles with respect to the foil free surface. Its magnetostatic energy together with domain wall energy determines an energy budget to be minimized. Throughout the magnetization cycle the free-surface domain pattern remains essentially unchanged, due to the magnetostatic energy cost such a change would elicit. Thus domain walls are "pinned" to free surfaces. Driven to saturation, domain walls first bulge then reconnect via Barkhausen jumps to form a new domain configuration that I have called "channel domains", which are attached to free surfaces. The approach to saturation now continues as reversible channel domain compression. Driving the permalloy deeper into saturation compresses the channel domains to arbitrarily small thickness, but will not cause them to denucleate. Returning from saturation the channel domain structure will survive through zero H, thus explaining remanence. The Barkhausen jumps, being irreversible exothermic events, are sources of fluxgate noise powered by the energy available from domain wall reconnection. A simplified domain energy model can then provide a predictive relation between ring-core magnetic properties and fluxgate sensor noise power. Four properties are predicted to affect noise power, two of which are well known: saturation total magnetic flux density and magnetic anisotropy. The two additional properties are easy axes alignment and foil thickness. Flux density and magnetic anisotropy are primary magnetic properties determined by an alloy's chemistry and crystalline lattice properties. Easy axes alignment and foil thickness are secondary, geometrical properties related to an alloy's polycrystalline fabric and manufacture. Improvements to fluxgate noise performance can in principle be achieved by optimizing any of these four properties in such a way as to minimize magnetostatic energy. Fluxgate signal power is proportional to B − H loop curvature [d2B/dH2]. The degree to which Barkhausen jumps coincide with loop curvature is a measure of noise that accompanies the fluxgate signal. B − H loops with significant curvature beyond the open hysteresis loop may be used to advantage to acquire the fluxgate signal with reduced noise.

Variations in Magnetic Properties of Nanostructured Nickel

The magnetic properties of carbon nanotube encapsulated nickel nanowires (C.E. nanowires of diameter to approximately 10 nm), and its comparison to other forms of Ni are carried out in this work. The saturation magnetization (Ms) and coercivity (Hc) for C.E. nanowires are 1.0 emu/g and 230 Oe. The temperature dependence of coercivity follows T0.77 dependence indicating a superparamagnetic behavior. The field-cooled and zero-field-cooled plots indicate that the blocking temperature (T(B)) to approximately 300 K. These altered magnetic properties of C.E. nanowires are mainly due to the nanoscale confinement effect from carbon nanotube encapsulation. The shape and magnetic environment enhance the total magnetic anisotropy of C.E. nanowires by a factor of four.

Magnetic anisotropy through cooperativity in multinuclear transition metal complexes: theoretical investigation of an anisotropic exchange mechanism

To be a candidate for a good single-molecule magnet, a compound should have a reasonably large zero-field splitting, a reasonably large total spin, and preferably axial symmetry. We investigate how this can be achieved in multi-heteronuclear d-Block transition metal complexes with both 3d and 5d centres. While spin-orbit coupling is large at the 5d centre, the 3d centres contribute many unpaired electrons. If the heavy-element building block does not have a single-ion anisotropy it might still transfer its spin-orbit effects to the 3d centre(s) through anisotropic exchange. We present spin-orbit configuration interaction calculations on a bi- and trinuclear compound with one OsIII and one or two MnII centres to demonstrate the mechanism. The interaction between the metal centres brings about zero-field splitting that is entirely due to anisotropic exchange. Because of strong spin-orbit coupling, the Os centre behaves as a pseudospin with that shows antiferromagnetic and anisotropic exchange coupling with the Mn centres. The ground state of the binuclear complex has a pseudo S = 2 ground state with an axial zero-field splitting parameter D = +0.59 cm−1, while the trinuclear complex has a pseudo ground state with a negative D = −0.32 cm−1. Coordination of the second Mn centre thus increases total spin and magnetic anisotropy, and reverses the sign of D.