Tailoring magnetism at the nanometer scale in SmCo5 amorphous films.

The thickness dependence of magnetic properties has been studied in SmCo5 amorphous films with imprinted in-plane anisotropy for thicknesses ranging down to the nanometer scale (2.5-100 nm). The field induced in-plane magnetic anisotropy decreases considerably when the film thickness is below 20 nm. Analysis of the magnetic anisotropy energy shows that the decrease of the induced in-plane anisotropy is accompanied by the development of an out-of-plane interface anisotropy. Two different regimes for the coercivity (Hc) change are found: below 3.75 nm, the Hc decreases continuously with decrease of the film thickness, whereas at above 3.75 nm, the Hc decreases with increase of the film thickness. This change in Hc can be understood by considering the decrease of the short range chemical order for the thinnest films (<3.75 nm) and the relative decrease of the interface contribution with increasing film thickness. The changes in anisotropy have a profound influence on the domain structure, in which the angle of the zigzag domain boundaries decreases with the inverse thickness of the layers.

Effect of the nanometric scale thickness on the magnetization steps in Ca3Co2O6 thin films.

We report on the effect of the film thickness on the magnetic properties of Ca3Co2O6films with an emphasis on the magnetization steps usually observed in the M-H curves below 10 K. Films with thicknesses between 35 and 200 nm all present two magnetic transitions at about T(C1) = 22 K and T(C2) = 10 K, corresponding to a 3D long range ferrimagnetic order and the transition to the formation of a frozen spin state, respectively. The magnetization curves at 10 K exhibit the expected stepped variation. However, by decreasing the thickness below a critical value of about 60 nm, no magnetization plateau is observed when the M-H curve is recorded at 2 K. Moreover, an additional transition in the susceptibility curve is observed at 45 K. These changes can be attributed to the reduced coherence length of the propagation vector along and perpendicular to the chains, and are supported by the magnetization relaxation measurements which indicate a reduction of the relaxation time. These results are helpful for understanding the origin of the magnetization steps in the one-dimensional Ca3Co2O6 cobaltite and confront the theoretical models aimed at explaining the magnetic properties in this system.