Magnetoelectric switching of exchange bias

The perpendicular exchange bias field, H(EB), of the magnetoelectric heterostructure Cr2O3(111)/(Co/Pt)(3) changes sign after field cooling to below the Néel temperature of Cr2O3 in either parallel or antiparallel axial magnetic and electric freezing fields. The switching of H(EB) is explained by magnetoelectrically induced antiferromagnetic single domains which extend to the interface, where the direction of their end spins controls the sign of H(EB). Novel applications in magnetoelectronic devices seem possible.     

Critical behaviour of the linear birefringence in 3d-Heisenberg antiferromagnets : RbMnF3, KNiF3 and KCoF3

The linear birefringence of stress induced single antiferromagnetic T-domains of RbMnF₃, KNiF₃ and KCoF₃ has been measured in the vicinity of T_N. We deduce the critical behaviour in such 3d-Heisenberg systems, showing a symmetry breaking at the transition involving a unique wave vector of the order parameter in the Brillouin zone. The critical exponent $\text{β}$ of the linear birefringence has been found to be larger than 2β, in agreement with the theoretical predictions of G. Gehring.     

Absorption of colloidal silver in KCl

The optical extinction coefficient of colloidal silver formed in KCl in connection with the thermal dissociation of Ag^? centers is investigated. Changes with annealing of the position, half-width, and height of the extinction band are reported. An explanation based on the Mie theory is given in which account is taken of the limitation of electron mean free path by surface scattering in the small colloidal silver particles.     

Magneto-optical studies on ferromagnetic stripe domains in K2CuF4

Ferromagnetic stripe domains are observed in K₂CuF₄ below T_c=6.19 K by use of Faraday rotation (FR). They are about 4 μm wide and lie parallel to the c-planes. They are due to a very small intraplanar anisotropy field as a result of the minute orthorhombic lattice distortion observed by Hidaka and Walker. A stripe domain model, including closure domains for complete demagnetization, is in accordance with the experimental observations if the anisotropy fields H^out_A=1.4kOe and Hⁱⁿ_A=0.1 Oe are introduced. Long-range order, presumably induced by interplanar exchange, is a accompanied by 3d Ising critical behavior as verified by critical exponents obtained from different magneto-optical measurements (α=0.07, β=0.33 and δ=4.6). Changes of the domain structure, of the ac-plane FR, and of the ac-plane linear birefringence due to a transverse magnetic field H 6 a are discussed. A non-vanishing internal field is preceded by a domain instability. The compatibility of the domain structure with neutron scattering results of Hirakawa and Yoshizawa is discussed.     

Magnetoelectricity in multiferroically composed multilayers and multiglasses

Single-crystalline magnetoelectric (ME) antiferromagnetic Cr₂O₃ exchange coupled to a ferromagnetic multilayer (Pt/Co/Pt)_n, n?1, represents a multiphase multiferroic material with sophisticated multifunctional properties. They comprise the possibility of switching the exchange bias (EB) of the ferromagnetic hysteresis loop via the linear ME effect of Cr₂O₃, and to design MERAM and logic cells operating at room temperature. Quadratic and cubic ME effects - promoted by soft-mode quantum fluctuations - are observed at lowest order in ceramic Sr_0.98Mn_0.02TiO₃ at low temperatures. Dipolar and spin glass orders occur simultaneously on the Mn²⁺ subsystem and form a multiglass by analogy with conventional multiferroics.