Observation of recoil magnetization curves outside the major loop in Co, Fe, and Ni films

We report a peculiar magnetization reversal observed in magnetron-sputtered Co, Fe, and Ni films. We found that some recoil (minor) magnetization curves lie entirely and way outside the major loop, a phenomenon referred to here as a recoil-curve overshoot. The greatly enhanced recoil curve’s remanence and coercivity result in an up to 2.5-fold increase of loop’s area. The model of pairs of exchange-coupled grains with misaligned anisotropy axes reproduces, in a very good agreement with the experiment, all key features of the recoil-curve overshoot as well as the kink that some major loops present before saturation. The disclosed features of the ferromagnetic hysteresis provide further insights into this important classical phenomenon

Influence of the interfaces on the structural and magnetic properties of thin films that present recoil-gurve overshoot

Neste trabalho, utilizamos a técnica de desbastamento iônico para produção de filmes finos ferromagnéticos policristalinos de cobalto, níquel com diferentes espessuras crescidos sobre substrato de Si(100) com óxido natural de silício (SiO2) em sua superfície. Estas amostras foram produzidas com o intuito de estudar a influência das propriedades estruturais e de anisotropias nas curvas de magnetização, ciclos de histereses, laços menores de histereses e curvas de remanência. Como resultados observamos que, para orientações angulares específicas entre o campo magnético aplicado H e o eixo de fácil magnetização das camadas ferromagnéticas, alguns laços menores de histerese (minor loops) tornam-se externos ao ciclo principal de histerese; este fenômeno foi denominado Recoil-Curve Overshoot (RCO) [1]. Para estas curvas, maiores valores de campo coercivo e magnetização remanente podem ser observados, resultando em um produto de energia B x H maior que do ciclo principal de histerese. Também é apresentada uma discussão sobre as causas deste fenômeno, sendo atribuídas ás interações magnéticas e dispersões de anisotropia.In this work we use the magnetron sputtering technique to produce polycrystalline ferromagnetic thin films of cobalt, nickel with different thicknesses, grown on Si(100) substrate with natural silicon oxide (SiO2) on its surface. These samples were produced in order to study the influence of structural and anisotropy properties on magnetization curves, hysteresis cycles, major and minor hysteresis loops and remanence curves. As a result we observe that, for specific angular orientations between the applied magnetic field H and the easy magnetization axis of the ferromagnetic layers, some minor hysteresis loops become external to the major hysteresis loop; this phenomenon was called Recoil-Curve Overshoot (RCO) [1]. For these curves, higher values of coercive field and remanent magnetization can be observe, resulting in an energy product B x H greater than the major hysteresis loop. A discussion about the cause of this phenomenon is also presented, being attributed to the magnetic interactions and anisotropy dispersions