Study Of Magnetic Correlations Research Articles

Selection rules for ultrafast laser excitation and detection of spin correlation dynamics in a cubic antiferromagnet

Exchange interactions determine the correlations between microscopic spins in magnetic materials. Probing the dynamics of these spin correlations on ultrashort length and time scales is, however, rather challenging, since it requires simultaneously high spatial and high temporal resolution. Recent experimental demonstrations of laser-driven two-magnon modes---zone-edge excitations in antiferromagnets governed by exchange coupling---posed questions about the microscopic nature of the observed spin dynamics, the mechanism underlying its excitation, and their macroscopic manifestation enabling detection. Here, on the basis of a simple microscopic model, we derive the selection rules for cubic systems that describe the polarization of pump and probe pulses required to excite and detect dynamics of nearest-neighbor spin correlations and can be employed to isolate such dynamics from other magnetic excitations and magneto-optical effects. We show that laser-driven spin correlations contribute to optical anisotropy of the antiferromagnet even in the absence of spin-orbit coupling. In addition, we highlight the role of subleading anisotropy in the spin system and demonstrate that the dynamics of the antiferromagnetic order parameter occurs only in next-to-leading order, determined by the smallness of the magnetic anisotropy as compared to the isotropic exchange interactions in the system. We expect that our results will stimulate and support further studies of magnetic correlations on the shortest length and time scales.

Magnetic diffuse scattering in artificial kagome spin ice

The study of magnetic correlations in dipolar-coupled nanomagnet systems with synchrotron x-ray scattering provides a means to uncover emergent phenomena and exotic phases, in particular in systems with thermally active magnetic moments. From the diffuse signal of soft x-ray resonant magnetic scattering, we have measured magnetic correlations in a highly dynamic artificial kagome spin ice with sub-70-nm Permalloy nanomagnets. On comparing experimental scattering patterns with Monte Carlo simulations based on a needle-dipole model, we conclude that kagome ice I phase correlations exist in our experimental system even in the presence of moment fluctuations, which is analogous to bulk spin ice and spin liquid behavior. In addition, we describe the emergence of quasi-pinch-points in the magnetic diffuse scattering in the kagome ice I phase. These quasi-pinch-points bear similarities to the fully developed pinch points with singularities of a magnetic Coulomb phase, and continually evolve into the latter on lowering the temperature. The possibility to measure magnetic diffuse scattering with soft x rays opens the way to study magnetic correlations in a variety of nanomagnetic systems.

Magnetic Correlations in Some FeNi/Cu(100) Multilayers

We present a first-principles electronic structure based study of magnetic correlations in the paramagnetic phase of some Fe and Ni multilayers on Cu(100) substrates. We have used the screened Korringa–Kohn–Rostoker method to calculate the electronic structure within the spin-density functional theory and used the disordered local moments model to describe the paramagnetic phase above the Curie temperature. We find that in the Ni/Cu(100) films, there are no local moments formation for any thickness. For the multilayers of Fe and Ni, we find that there is some, although very small, local moment formation in the interior of the Ni film if the Ni layer is more than 6 monolayers thick. However, the Ni layers facilitate the magnetic correlation between the Fe layers. The Curie temperatures of the multilayers also depend upon the Ni layer thickness.

Study of magnetic correlations in nanostructured ferromagnets by correlation magnetometry

We propose a theoretically justified experimental magnetometric technique for determining the size of stochastic domains spontaneously formed in the spin system of nanostructured ferromagnets and for evaluating the effective anisotropy in these magnetically correlated regions. The method is based on monitoring the ΔM∼ H−2 relationship in the low-field part of the integral magnetization curve.

ChemInform Abstract: Neutron Scattering Studies of Magnetic Correlations in the Layered Cuprates

All of the copper oxide superconductors contain CuO{sub 2} layers which, when insulating, exhibit strong, two-dimensional (2D) antiferromagnetic correlations due to the unusually large superexchange interaction between nearest-neighbor Cu{sup 2+} atoms. Magnetic correlations survive, although with a reduced correlation length, even when the layers are doped with holes. A short review of neutron scattering studies of magnetic correlations and excitations in the layered cuprates is presented. 19 refs., 6 figs.

Neutron scattering studies of magnetic correlations in reentrant spin glasses

Abstract We review neutron scattering measurements performed on two disparate reentrant spin glass systems: the magnetic insulator EuxSr1−xS and the metallic alloy Fe1−xAlx. We show that the magnetic behavior in the two is very similar and can be explained in terms of random field effects which arise when ferromagnetic and spin glass order parameters are coupled together.