RESUMEN
The magnetic reversal behavior of a ferromagnet (FM) coupled through an FeMn antiferromagnet (AF) to a pinned ferromagnet has been investigated by polarized neutron reflectivity measurements. With FeMn as the AF layer it is found that there exists 90° interlayer coupling through this layer and that this plays a key role in the transfer of the exchange bias (EB) effect from the FM/AF interface to the AF/pinned-FM interface. Combined with Monte Carlo simulations, we demonstrate that the competition between the interlayer coupling and the anisotropy of the AF layer results in a control of the EB effect which has potential for device applications.
RESUMEN
Yttrium iron garnet has a very high Verdet constant, is transparent in the infrared and is an insulating ferrimagnet leading to its use in optical and magneto-optical applications. Its high Q-factor has been exploited to make resonators and filters in microwave devices, but it also has the lowest magnetic damping of any known material. In this article we describe the structural and magnetic properties of single crystal thin-film YIG where the temperature dependence of the magnetisation reveals a decrease in the low temperature region. In order to understand this complex material we bring a large number of structural and magnetic techniques to bear on the same samples. Through a comprehensive analysis we show that at the substrate -YIG interface, an interdiffusion zone of only 4-6 nm exists. Due to the interdiffusion of Y from the YIG and Gd from the substrate, an addition magnetic layer is formed at the interface whose properties are crucially important in samples with a thickness of YIG less than 200 nm.
RESUMEN
Equi-atomic FeRh is highly unusual in that it undergoes a first order meta-magnetic phase transition from an antiferromagnet to a ferromagnet above room temperature (Tr ≈ 370 K). This behavior opens new possibilities for creating multifunctional magnetic and spintronic devices which can utilise both thermal and applied field energy to change state and functionalise composites. A key requirement in realising multifunctional devices is the need to understand and control the properties of FeRh in the extreme thin film limit (tFeRh < 10 nm) where interfaces are crucial. Here we determine the properties of FeRh films in the thickness range 2.5-10 nm grown directly on MgO substrates. Our magnetometry and structural measurements show that a perpendicular strain field exists in these thin films which results in an increase in the phase transition temperature as thickness is reduced. Modelling using a spin dynamics approach supports the experimental observations demonstrating the critical role of the atomic layers close to the MgO interface.
RESUMEN
We characterise the magnetic state of highly-textured, sputter deposited erbium for a film of thickness 6 nm. Using polarised neutron reflectometry it is found that the film has a high degree of magnetic disorder, and we present some evidence that the film's local magnetic state is consistent with bulk-like spiral magnetism. This, combined with complementary characterisation techniques, show that thin film erbium is a strong candidate material for incorporation into device structures.
RESUMEN
We present a detailed structural and magnetic characterization of sputter deposited thin film erbium, determined by x-ray diffraction, transport measurements, magnetometry and neutron diffraction. This provides information on the onset and change of the magnetic state as a function of temperature and applied magnetic field. Many of the features of bulk material are reproduced. Also of interest is the identification of a conical magnetic state which repeats with a wavevector parallel to the c axis τc = 4/17 in units of the reciprocal lattice parameter c*, which is a state not observed in any other thin film or bulk measurements. The data from the various techniques are combined to construct magnetic field, temperature (H, T)-phase diagrams for the 200 nm-thick Er sample that serves as a foundation for future exploitation of this complex magnetic thin film system.
RESUMEN
We have studied the dependence on the domain wall structure of the spin-transfer torque current density threshold for the onset of wall motion in curved, Gd-doped Ni(80)Fe(20) nanowires with no artificial pinning potentials. For single vortex domain walls, for both 10% and 1% Gd-doping concentrations, the threshold current density is inversely proportional to the wire width and significantly lower compared to the threshold current density measured for transverse domain walls. On the other hand for high Gd concentrations and large wire widths, double vortex domain walls are formed which require an increase in the threshold current density compared to single vortex domain walls at the same wire width. We suggest that this is due to the coupling of the vortex cores, which are of opposite chirality, and hence will be acted on by opposing forces arising through the spin-transfer torque effect.
RESUMEN
We present an unreported magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 (x â¼ 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn(3+)/Mn(4+) to an enriched Mn3+ region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e(g) orbital (d(3)z(2)-r(2). This reconstruction may provide a mechanism for coupling the Mn3+ moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.
RESUMEN
We demonstrate an isolated magnetic interface anisotropy in amorphous CoFeB films on (Al)GaAs(001), similar to that in epitaxial films but without a magnetocrystalline anisotropy term. The direction of the easy axis corresponds to that due to the interfacial interaction proposed for epitaxial films. We show that the anisotropy is determined by the relative orbital component of the atomic magnetic moments. Charge transfer is ruled out as the origin of the interface anisotropy, and it is postulated that the spin-orbit interaction in the semiconductor is crucial in determining the magnetic anisotropy.
