Search

Controlling ferromagnetic/antiferromagnetic blocking temperatures in exchange biased based devices appears crucial for applications. The blocking temperature is ascribed to the ability of both antiferromagnetic grains and interfacial spin-glass-like phases to withstand ferromagnetic magnetization reversal. To better understand the respective contributions of grains versus spin-glass, blocking temperature distributions were measured after various thermal treatments for cobalt/iridium-manganese bilayers. The high-temperature contribution linked to antiferromagnetic grains shifts towards lower temperatures above a threshold thermal annealing. In contrast, the occurrence and evolution of training effects for the low-temperature contribution only agree with its inferred interfacial spin-glass-like origin. [ABSTRACT FROM AUTHOR]

In exchange biased spintronic devices such as magnetic random access memories, spin-glass-like regions are randomly spread over ferromagnetic/antiferromagnetic interfaces. They contribute to detrimental distributions of exchange bias properties from memory cell to memory cell. The integrated area of the low-temperature (T) contribution of the blocking temperature (TB) distribution provides information about the amount of these spin-glass like regions. In this paper, we report on the influence of various growth conditions on the low-T contribution of the TB distributions for cobalt/iridium-manganese (IrMn) based bilayers. Top, bottom, on- and off- axis depositions were compared. We show that off-axis deposition, i.e., when the target and substrate are off-centred, does not reduce the low-T contribution despite an expected smoother F/AF interface. We observe that bottom deposition, i.e., when IrMn is deposited first, allows reducing AF spin-glass like regions as compared to top deposition. This contributes to improved exchange bias properties. [ABSTRACT FROM AUTHOR]

Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially periodic domain wall pinning potentials. The potentials are generated non-destructively using the stray magnetic field of ordered arrays of magnetically hard [Co/Pt]m nanoplatelets, which are patterned above and are physically separated from the continuous magnetic layer. The effect of the periodic pinning potentials on thermally activated domain wall creep dynamics is shown to be equivalent, at first approximation, to that of a uniform, effective retardation field, Hret, which acts against the applied field, H. We show that Hret depends not only on the array geometry but also on the relative orientation of H and the magnetization of the nanoplatelets. A result of the latter dependence is that wall-mediated hysteresis loops obtained for a set nanoplatelet magnetization exhibit many properties that are normally associated with ferromagnet/antiferromagnet exchange bias systems. These include a switchable bias, coercivity enhancement, and domain wall roughness that is dependent on the applied field polarity. [ABSTRACT FROM AUTHOR]

For ferromagnetic (F)/antiferromagnetic (AF) nanodots contributions of AF spins to exchange bias is discussed. The relative weights of AF entities located at the dot edges, at the F/AF interface and in the AF grains were obtained by comparing the blocking temperature distribution of an array of nanodots with that of corresponding continuous film. Due to grain cutting, the grain size distribution is altered. We show here that the dot edges constitute additional locations for the formation of spin-glasslike AF regions at the F/AF interface. The result of patterning is thus twofold and weakens the dot ability to resist thermally activated magnetization reversal. [ABSTRACT FROM AUTHOR]

Nanostructures consisting of a stack of two magnetic multilayers with out-of-plane anisotropy and distinct coercivities hold great promises in spintronics devices. Yet their miniaturization leads to interlayer dipolar coupling, which results in detrimental asymmetrical behaviors of magnetization reversal or even in the loss of intermediate antiparallel configuration. In this letter, we take advantage of Ruderman–Kittel–Kasuya–Yosida interactions in order to compensate for this coupling and restore symmetry. The study has been performed on an array of square dots of 200 nm lateral size, each dot consisting of two [Co/Pt] multilayers antiferromagnetically coupled through a thin Ru spacer. [ABSTRACT FROM AUTHOR]