Interphase exchange coupling in Fe∕Sm–Co bilayers with gradient Fe thickness

Abstract

We have fabricated Fe/ Sm-Co bilayers with gradient Fe thicknesses in order to systematically study the dependence of exchange coupling on the thickness of the Fe layer. The Fe layer was deposited at two different temperatures ͑150 and 300°C͒ to study the effect of deposition temperature on the exchange coupling. Magneto-optical Kerr effect and x-ray magnetic circular dichroism ͑XMCD͒ have been employed as nondestructive rapid characterization tools to map the magnetic properties of the gradient samples. Systematic enhancement in exchange coupling between the soft layer and the hard layer is observed as the soft layer thickness is decreased. Separate exchange couplings of the Fe layer with Co and Sm in the hard layer are revealed through measuring the element-specific hysteresis curves using XMCD. The single-phase-like magnetization reversal critical thickness increases from 12 nm for Fe deposited at 150°C to 24 nm for Fe deposited at 300°C, indicating an important role of the state of the interface in the exchange coupling.

Applications of high throughput (combinatorial) methodologies to electronic, magnetic, optical, and energy-related materials

“…[103][104][105][106][107][108] As is the case for combinatorial measurements in general, a significant challenges lies in extracting accurate quantitative values of magnetic properties from a particular location on a library film, such that the value is in agreement with that obtained from a discrete sample of the same composition, using a standard "bulk" measurement technique such as a SQUID magnetometer. Significant variations in some physical properties between bulk and thin film materials of the same composition are often the cause of the lack of agreement.…”

“…In the absence of an external applied field, remnant magnetization may be measured. The magnetic-optical Kerr effect (MOKE) technique 103,105,106 is based on the fact that the polarization of light is rotated upon reflection from the surface of a magnetic material, and further that the rotation angle is directly proportional to the magnetization. MOKE is particularly useful since one can map the magnetic hysteresis loop from different positions on combinatorial samples by sweeping the applied magnetic field, from which one can obtain the saturation magnetization (through calibration) as well as the coercive field values.…”

“…MOKE is particularly useful since one can map the magnetic hysteresis loop from different positions on combinatorial samples by sweeping the applied magnetic field, from which one can obtain the saturation magnetization (through calibration) as well as the coercive field values. 103 The scanning Hall probe can also be used to map saturation magnetization values. 106 In order to obtain absolute values of magnetization from the measured magnetic field without calibration, an inversion technique has been developed, which can be applied to any spatially resolved field distribution data.…”

“…149,150 The gradient thickness approach has also been used to investigate the thickness of a high magnetization Fe layer coupled to a high coercivity SmCo layer using X-ray magnetic circular dichroism (XMCD) to determine the critical soft layer thickness pinned by SmCo. 103 Such research has further been extended to investigate the relationship between soft phase micromagnetic constants and thickness in an Fe-Co/CoPt bilayer square library deposited by e-beam evaporation. Using automated shadow masks, the thickness of the soft phase was varied from 1 to 10 nm in one direction, and the composition of the soft phase, Fe x Co 1Àx , in the other, 151 Fig.…”

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

“…More systematic experimental and theoretical studies would be desirable to fully understand the differences between conventional and inverse systems. The hard-soft exchange coupling between core and shell has been addressed using more advanced characterization approaches such as M-plots [302], first order reversal curves (FORC) [46,295,303], small angle neutron scattering (SANS) [199,304]or element-specific X-ray magnetic circular dichroism (XMCD) [305,306].…”