B. Raquet

Dynamical properties of magnetization reversal in an ultrathin AuCo film

Abstract We present a dynamical study of hysteresis loops of a MoS2/[Au/Co/Au] sandwich performed by surface magneto-optical Kerr effect with a field variation rate up to 1.2 MOe/s. An interpretation of dynamical effects at room temperature is proposed, using a modelization of the magnetization reversal. We discuss simulations which describe two different processes of the magnetization reversal to interpret the evolution of the hysteresis loops for several rates of variation of the magnetic field. For a first range of field variation rates lower than 180 kOe/s, the predominant mechanism seems to be wall motion and beyond 180 kOe/s, an expression for the magnetization is given, which supposes micro-domains reversal as a prevailing process. Finally, the general behaviour of the relaxation time, depending on the magnetic field, is investigated.

AF coupling of copper-cobalt multilayers with small grain size

Abstract We report the observation of oscillatory interlayer coupling for a series of Fe 50A [Co 12A -Cu t A ] 15 Cu 50A samples sputtered on glass substrates. The antiferromagnetic (AF) maxima are observed for t = 9 and 20A. The particularities of our samples are their very small grain size ( ~ 20A) without any preferential orientation and the sharpness of their interfaces ( ~ 1A). These characteristics are favorable to strong magnetoresistive effects which exceed 40% at 300 K and 90% at 4.2 K for our best samples. Our results must be confronted by theoretical models that are only valid in the case of ideal single-crystals.

Magneto-optical measurements of magnetization reversal in nanometer scale sputtered Fe thin films

Abstract We present a magneto-optical study of the magnetic behavior of sputtered iron films of various thickness ranging from 2 to 50 nm grown on a silicon substrate. First we calculate the reflection coefficients in the case of an homogeneous magneto-optical layer with in-plane magnetization. Then we describe a technique in which both in-plane magnetization components are detected. Because of the axial deposition procedure, iron films exhibit in-plane uniaxial anisotropy depending on the thickness of the layer. In particular, we show that, for 4 nm thickness, anisotropy induced by slightly tilted columnar growth can be observed, whereas for larger thicknesses this in-plane anisotropy vanishes. Using an accurate acquisition system based upon a rapid analog-to-digital converter we measured the rapid magnetization reversal. The field sweep rate was varied between 100 Oe/s and l MOe/s. We interpret the observed dynamical effects in terms of wall movement and microdomain reversal.

Spin state transition: the origin of structural, magnetic and metal–insulator transitions in GdBaCo2O5+δ (δ≈0.5)

The metal–insulator transition in GdBaCo2O5:5 at TMIE360 K has been investigated by synchrotron X-ray powder diffraction and magnetic measurements. We have found that,at TMI remarkable structural distortions and magnetic changes take place. These changes evidence a spin state transition of Co ions at this temperature that is the origin of the metal–insulator transition. r 2002 Elsevier Science B.V. All rights reserved.

Magnetic and transport properties of Ni/Ti, NiC/Ti and Co/Cu multilayers at high fields

Abstract We studied the magnetoresistance of Ni/Ti, NiC/Ti and Co/Cu sputtered multilayers. In fields below 2 T, the Co/Cu films exhibit previously described giant magnetoresistance. We observe an unusual negative contribution to the magnetoresistance in high fields whose origin is not well understood at this time.

Structural, spin state, and magnetic transitions in GdBaCo2O5+δ (δ≈0.5)

Abstract Structural, spin state, magnetic and field-induced transitions have been studied in GdBaCo 2 O 5.5 over a wide range of temperatures. We have found that, concomitant with a metal–insulator transition at 370 K , remarkable structural changes take place. These changes evidence the onset of orbital order at this temperature. Magnetization measurements, and the observation of a field-induced transition, below 250 K , by applying high magnetic fields, confirm that, below this temperature, an antiferromagnetic arrangement of the magnetic moments is present.

Magneto-optical studies of magnetization reversal of an Au/Co/Au sandwich

Abstract We present a dynamical magneto-optical study of an Au/Co/Au sandwich with a magnetic field variation rate up to 2 MOe/s. An interpretation of dynamical effects at room temperature is proposed, using a modeling of the magnetization reversal. Finally, the magnetic domain structure is observed by Magnetic Force Microscopy.

Magnetization reversal dynamics in ultrathin magnetic layers

Abstract We propose an analytical expression for the magnetization reversal in ultrathin magnetic layers, modelling the aftereffects and, for the first time, taking into account both domain wall motion and nucleation processes. We apply our model to quantify the dynamic properties of the magnetization of a MoS 2 /[Au(40 nm)/Co(0.8 nm)/Au(3 nm)] sandwich.

Dependence on growth conditions of surface anisotropy and magnetization reversal in Au/Co (0.8 nm)/Au/MoS2

Abstract Magnetic properties of Au/Co (0.8 nm)/Au sandwiches elaborated on MoS 2 with different growth rates are presented. The topography of the top most Au layer is investigated by atomic force microscopy (AFM). The magnetic properties are measured by magneto-optical Kerr effect (MOKE) with parallel and perpendicular magnetic field. The reduction of the deposition rate (from 17 ML/min to 4 ML/min) is found to enhance the perpendicular anisotropy and to favour a domain wall motion process for the magnetization reversal when a perpendicular magnetic field is applied. For a low deposition rate (1 ML/min) the obtained structure is made of nearly isolated crystallites (1 μm average diameter). On the scale of a single crystallite, magnetic force microscopy (MFM) reveals that the magnetic domains have a concentric pattern where up and down domains alternate, separated by in-plane magnetized domains.

Magnetic and transport properties of HoZr multilayers

We have elaborated by MBE, Ho/Zr multilayers in which holmium crystallographic parameters are considerably reduced compared to bulk. We correlate magnetoresistance measurements with the magnetization under very high magnetic field. We point out a sharp magnetic transition due to the closing of the conical or helical configurations as in bulk material. This effect disappears for the lower thickness of Ho layers and the transition field changes with the magnetic coupling through the zirconium layers