Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins inNi81Fe19∕α‐Fe2O3

Abstract

We report studies of exchange bias and coercivity in ferromagnetic Ni 81 Fe 19 layers coupled to antiferromagnetic (AF) (0001), (1120), and (1102) α-Fe 2 O 3 layers. We show that AF spin configurations which permit spin-flop coupling give rise to a strong uniaxial anisotropy and hence a large coercivity, and that by annealing in magnetic fields parallel to specific directions in the AF we can control either coercivity or exchange bias. In particular, we show for the first time that a reversible temperature-induced spin reorientation in the AF can be used to control the exchange interaction.

Exchange bias in a nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry

“…The best explanation for this is that, at 300 K, our sample lies above the Morin temperature which occurs at <100 K for nanocrystallites, whereas the other group stated that, for their strained epitaxial films, this transition is enhanced to 400 K. 22 Similar suppression of the exchange bias temperature has been reported previously for nanostructured hematite systems. 24 The absence of exchange bias, even in the presence of an interface moment, is not altogether surprising since the Morin transition is concurrent with a sizable increase in the uniaxial anisotropy 6 of hematite towards low temperature, which in turn, stabilizes antiferromagnetic order within the small grains against superparamagnetic activation, 46,47 reversal, 48 and canting. If the magnetocrystalline anisotropy of antiferromagnetic spins is sufficiently low, canted antiferromagnetic spins can be more easily polarized through coupling to ferromagnetic neighbors but concurrently provide less of an energy barrier during reversal.…”

“…21 In particular, the wide range of temperatures where exchange bias occurs for ferromagnetic/hematite bilayer thin films 11,[22][23][24] lacks a convincing explanation. The diversity in blocking temperature for chemically identical bilayers implies that the exchange bias relies on a complex interplay of the finite-size effects described above.…”

Magnetic properties of double exchange biased diluted magnetic alloy/ferromagnet/antiferromagnet trilayers

“…However in this paper the interfacial spin configuration of the hematite layer [23] was not investigated while, due to the reduced Py thickness, an in-plane easy axis for the Py layer was assumed instead [52]. .2) trilayer are reported.…”

“…Here we investigate the problem working on the diluted side of the CuMn phase diagram where, as it will be seen in the following, the magnetic behavior is dominated by frustrated clusters and therefore the system cannot be considered a canonical SG. On the other hand, hematite is considered very attractive for EB applications because of both large giant magnetoresistance ratios and high bulk Néel temperature [22,23]. In particular, being the hematite layer a native oxide film here, the resulting trilayer comes effectively from the fabrication of only two layers.…”

Correlating Uncompensated Antiferromagnetic Moments and Exchange Coupling Interactions in Interface Ion-Beam Bombarded Co90Fe10/CoFe-Oxide Bilayers

“…Exchange bias [1][2][3][4][5][6], i.e., the shift of the hysteresis loop of a ferromagnetic (FM) material in contact with an antiferromagnetic (AFM) material after a field-cooling process, depends on many factors including the particular materials involved [7][8][9][10], film growth conditions [11][12][13][14], the structural, compositional and magnetic details of the interfaces [15][16][17][18], the magnetic stiffness of the AFM moments, and the field-cooling conditions [19][20][21][22].…”