Magnetic reorientation transition of Gd(0001)/W(110) films

The Effects of Substrate Temperature on the Growth, Microstructural and Magnetic Properties of Gadolinium-Containing Films on Aluminum Nitride

To facilitate future novel devices incorporating rare earth metal films and III-V semiconductors on Si substrates, this study investigates the mechanisms of growth via molecular beam epitaxy of gadolinium (Gd) on aluminum nitride (AlN) by determining the impact of substrate temperature on microstructure. The Gd films underwent extensive surface analysis via in situ reflective high energy electron diffraction (RHEED) and ex-situ SEM and AFM. Characterization of the surface features of rare earth metal films is important, as surface geometry has been shown to strongly impact magnetic properties. SEM and AFM imaging determined that Gd films grown on AlN (0001) from 80 °C to 400 °C transition from wetting, nodular films to island–trench growth mode to reduce in-plane lattice strain. XRD and Raman spectroscopy of the films revealed that they were primarily comprised of GdN, Gd and Gd2O3. The samples were also analyzed by a vibrating sample magnetometer (VSM) at room temperature. From the room temperature magnetic studies, the thick films showed superparamagnetic behavior, with samples grown between 240 °C and 270 °C showing high magnetic susceptibility. Increasing GdN (111) 2θ peak position and single-crystal growth modes correlated with increasing peak magnetization of the thin films, suggesting that lattice strain in single-crystal films was the primary driver of enhanced magnetic susceptibility.

Magneto-optical Kerr effect susceptometer for the analysis of magnetic domain wall dynamics

Domain wall dynamics in thin magnetic films with perpendicular and in-plane anisotropy is studied using a novel magneto-optical Kerr effect susceptometery method. The method allows for measurements of domain wall motion under ac field excitation and the analysis of dynamic modes as a function of driving frequency and magnetic field amplitude. Domain wall dynamics in the perpendicular anisotropy system, a Co/Pt multilayer, is characterized by thermally activated creep motion. For this dynamic mode, a polydispersivity exponent of β = 0.50 ± 0.03 is derived at small excitation energy, which is in excellent agreement with theoretical models. The dynamics of the other system, a Co wire with transverse uniaxial anisotropy, is dominated by viscous slide motion in a regular magnetic stripe pattern. Analytical expressions are derived for this magnetic configuration and by using these expressions, accurate values for the depinning field and the domain wall mobility are extracted from the susceptibility measurements.

Coupling-induced reorientation phase transitions in ultrathin Fe/Gd films

A phenomenological explanation for the reorientation phase transitions in an Fe/Gd ultrathin film system on the basis of Landau's theory of phase transitions is proposed. We model the film as a strongly coupled bilayer-like system consisting of the surface Fe overlayers and the interfacial Gd layer(s) below them. The total free energy of the system is accordingly obtained and the relevant phases and the order of the phase transitions involved are thus determined. Qualitative accordance between the theory and experiments is obtained. An alternative mechanism is proposed that attributes primarily the observed first-order phase transition in the system to the strong coupling between the Fe and the Gd film and its induced vertical magnetization component of the latter film. Competition between the antiferromagnetic coupling and the anisotropy energy of the Fe-rich ultrathin film is responsible for the other continuous reorientation. The effects of an applied external field including several field-induced first- and second-order phase transitions are predicted for experimental verification of the theory.

Gd(0001): A semi-infinite three-dimensional heisenberg ferromagnet with ordinary surface transition

By comparing the surface and bulk magnetization of smooth, well-ordered Gd samples, we show that the surface has an ordinary transition, i.e., a common Curie temperature for surface and bulk. A quantitative statistical analysis of the temperature dependent magnetization is presented. Critical exponents for both surface, beta(S) = 0.83+/-0.04, and bulk, beta(B) = 0.376+/-0.015, are consistent with the semi-infinite three-dimensional Heisenberg model with homogeneous exchange.