6 research outputs found
Influence of bi content on the temperature of the formation of the hard magnetic MnBi phase: simultaneous irreversible drop of resistance
Pulsed laser-deposited (PLD) MnBi films were fabricated by alternating deposition of Mn and Bi layers. In order to obtain the ferromagnetic MnBi phase, heat treatments were performed on the samples. Simultaneously, the resistance of the samples was monitored as a function of the temperature. Thus, on increasing the temperature, a steep decrease in the resistance of the films was observed, simultaneous to the onset of the formation of the MnBi phase. At room-temperature, these annealed samples showed a ferromagnetic behavior, as well as the presence of the characteristic LT-MnBi phase diffraction peaks in the X-ray diffraction patterns. The temperature of the generation of the MnBi phase depended on the relative concentration of Mn and Bi in the different samples: on increasing the Bi atomic concentration, the temperature of the generation of the MnBi phase decreased
Magnetic anisotropy in isotropic and nanopatterned strongly exchange-coupled nanolayers
UPNa. Departamento de FĂsica. Laboratorio de MagnetismoIn this study, the fabrication of magnetic multilayers with a controlled value of the in-plane uniaxial magnetic anisotropy field in the range of 12 to 72 kA/m was achieved. This fabrication was accomplished by the deposition of bilayers consisting of an obliquely deposited (54A degrees) 8-nm-thick anisotropic Co layer and a second isotropic Co layer that was deposited at a normal incidence over the first layer. By changing the thickness value of this second Co layer (X) by modifying the deposition time, the value of the anisotropy field of the sample could be controlled. For each sample, the thickness of each bilayer did not exceed the value of the exchange correlation length calculated for these Co bilayers. To increase the volume of the magnetic films without further modification of their magnetic properties, a Ta spacer layer was deposited between successive Co bilayers at 54A degrees to prevent direct exchange coupling between consecutive Co bilayers. This step was accomplished through the deposition of multilayered films consisting of several (Co8 nm-54A degrees/Co (X nm-0A degrees)/Ta6 nm-54A degrees) trilayers.This work was partially supported by the Spanish government under project MAT2007-66252
Vanadium trapped by oblique nano-sheets to preserve the anisotropy in Co-V thin films at high temperature
In this study, oriented nano-sheets generated during the growth of cobalt-rich CoâV and CoâZn thin films
induced a large anisotropy in the magnetic and transport properties. The regular nano-sheets were tilted
52â54 deg. with respect to the substrate plane, â 3.0â4.0 nm thick, â 30â100 nm wide, and â 200â300 nm
long, with an inter-sheet distance of â 0.9â1.2 nm. In spite of the different microstructures of the two kinds
of samples where the CoâV films were amorphous, whereas the CoâZn films showed a growth of Zn nanocrystals, the oblique nano-sheet morphology conferred noticeable shape anisotropy to both specimens.
This anisotropy resulted in an in-plane uniaxial magnetic anisotropy. The changes in the nano-morphology
caused by thermal treatments, and hence in their anisotropic properties, were studied. While the CoâV
samples retained or increased their magnetic and transport anisotropies, this anisotropic behavior vanished
for the annealed CoâZn films. High resolution transmission electron microscopy, HRTEM, including chemical analysis at the nano-scale, and the dependence of the anisotropic resistance on temperature allowed
to establish the nature and the activation energy spectra of the atomic relaxation processes during heating.
These processes displayed a single peak at 1.63 eV for the CoâV and two peaks at 1.67 and 2.0 eV for the
CoâZn. These spectra and their singularities were associated to the changes induced in the nano-morphology of the films by thermal treatments. The CoâV films retained their nano-sheet morphology almost
up to 500 ÂșC; the CoâZn films lost their nano-sheets at 290 ÂșC. The thermal stability exhibited by the CoâV
films makes them useful for applications in ultra high frequency, optical, magnetostrictive and magnetoelectric devices.C. F., J. V., and V. M. acknowledge the financial support of the
Public University of Navarre. C.M. and M.R.I. acknowledge the financial support from the Spanish Ministerio de EconomĂa y
Competitividad in the project MAT2017â82970-C1 and C2-R and
from the AragĂłn Regional project E26. Open access funding provided
by Universidad PĂșblica de Navarra