Navegando por Autor "Camley, R. E."
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Artigo Finite-size effects on spin configurations in antiferromagnetically coupled multilayers(American Physical Society, 1992-11-01) Carriço, Artur da Silva; Camley, R. E.; Nörtemann, F. C.; Stamps, R. L.Nonuniform canting states are found for multilayers of a finite size that are constructed from ferromagnetic films which are antiferromagnetically coupled. Our results are applicable to a wide variety of experimentally realizable systems such as Fe/Cr and Co/Ru. We find that at low fields, a twist in the ground-state configuration of the spins reduces the net Zeeman energy and is energetically favorable to the uniform canted state which has previously been assumed by most authors. At higher fields, the character of this twist changes and eventually leads to a state that is fully aligned along the direction of the applied magnetic field. A numerical self-consistent mean-field model is used to examine the properties of these states and a variational method is developed in order to obtain analytic expressions for the lengths and magnitudes of these twists. The deviations from the uniform spin-flop state at both high and low fields can be quite large and involve the entire sample.Artigo Magnetic hysteresis of interface-biased flat iron dots(Physical review B, 2009-03-04) Rebouças, G. O. G.; Silva, A. S. W. T.; Dantas, Ana L.; Camley, R. E.; Carriço, Artur da SilvaWe report a theoretical study of the coercivity and bias of iron dots exchange coupled with an antiferromagnetic substrate. We show that flat dots, with height close to the iron exchange length, and lateral dimensions of a few exchange lengths, exhibit large enhancement of coercivity and exchange bias. For small interface field strength the magnetization reversal is nearly a coherent rotation with symmetrical loops. Interface pinning leads to large reduction in coercivity and asymmetrical loops, if the interface field strength is comparable to the value of the iron exchange field. We discuss the impact of geometrical confinement and interface pinning on the magnetization reversal mechanisms. We show that small area dots with height larger than the exchange length display stronger interface effects.Artigo Magnetic structure of superlattices with biquadratic interlayer exchange coupling(Elsevier B.V., 1995-04) Carriço, Artur da Silva; Camley, R. E.; Tilley, D. R.We calculate the magnetic structure of an infinitely extended magnetic superlattice in the presence of interlayer biquadratic exchange coupling and a 4-fold in-plane anisotropy. An external magnetic field is also applied in the plane of the layers. We consider ground state configurations with unit cells involving 1, 2, or 4 magnetic layers. At low fields a two-layer unit cell structure is found to be the ground state. At higher fields the ground state has the spins in all layers aligned so the unit cell is one layer. Analytic expressions for the magnetic equilibrium structures are obtained in the small field limit, as are expressions for the critical fields for a transition from one state to another. Numerical results are presented for magnetic fields of arbitrary size.Artigo Magnetic thermal hysteresis in Fem/Dyn /Fem and Gdm/Dyn /Gdm trilayers(Physical review B, 2007) Dantas, Ana L.; Camley, R. E.; Carriço, Artur da SilvaWe have performed a theoretical investigation of thermal hysteresis in the magnetization of Fem/Dyn /Fem and Gdm/Dyn /Gdm trilayers, where the interface coupling is antiferromagnetic and ferromagnetic, respectively. Our results show a large number of stable states can exist in these structures. The thermal hysteresis occurs because the transitions between these states occur at different temperatures for the heating and cooling pro- cesses. The thermal hysteresis can be quite large, spanning about 90 K. Furthermore the temperature span of the thermal hysteresis can be substantially reduced by applying a modest external magnetic field.Artigo Phase diagram of thin antiferromagnetic films in strong magnetic fields.(American Physical Society, 1994-11-01) Carriço, Artur da Silva; Camley, R. E.; Stamps, R. L.A theoretical study of the phase diagram of antiferromagnetic thin films is presented. The theory is based on a numerical self-consistent local-field calculation that allows for size and surface effects. The properties of magnetic structures as functions of the temperature and external field are calculated. Spatially nonuniform canted states are shown to intermediate the transition from the antiferromagnetic to the spin-flop phases. The model is applied to thin films of FeF2 and MnF2 as examples in order to clarify the role of anisotropy.Artigo Size and interface effects in the phase transitions of antiferromagnetic superlattices(Elsevier B.V., 1992-04) Carriço, Artur da Silva; Camley, R. E.A self-consistent mean field theory is used to study composition effects on the phase transitions of FeF2/CoF2 and FeF2/MnF2 superlattices under weak applied fields. The temperature dependence of the magnetization is shown to depend strongly on the superlattice layering pattern and also on the interface coupling. Thin films of low anisotropy compounds display stronger shifts of transition temperature. Comparison with bulk results shows that size effects persist even for very thick layers for weakly coupled systems.Artigo Thermal hysteresis of ferromagnetic/antiferromagnetic compensated bilayers(Physical review B, 2009-10-12) Nascimento, F. I. F.; Dantas, Ana L.; Oliveira, L. L.; Mello, V. D.; Camley, R. E.; Carriço, Artur da SilvaWe report a theoretical investigation of thermal hysteresis of fourfold anisotropy ferromagnetic FM film exchange coupled to a compensated antiferromagnetic substrate. Thermal hysteresis occurs if the temperature interval includes the reorientation transition temperature, below which the frustration of the interface exchange coupling leads to a 90° rotation of the magnetization of the ferromagnetic layer. The temperature width of the thermal hysteresis is tunable by external magnetic fields of modest magnitude, with values of 43 K for an external field of 110 Oe and of 14 K for a field of 210 Oe, for a Fe 12 nm/MnF2 110 bilayer. For a Fe 3 nm/FeF2 110 bilayer the width of the thermal hysteresis is 23 K at 110 Oe and 13 K at 300 Oe. We discuss how the thickness of the iron film affects the field tuning of the thermal hysteresis width, and also how the thermal loops may be used to identify the nature of the interface exchange energy.