Third, thermal fluctuations tend to randomize the orientation of the molecular magnetic moment down to temperatures T ≪ TN, which hinders the alignment of the pinned spins in the AFM during the field cooling process. Second, biasing is unlikely to extend from individual sites to a continuous molecular layer, since the magnetic moments of molecules adsorbed next to each other are usually uncoupled. As the molecules constitute discrete magnetic elements, there is no mechanism guaranteeing that the sparse pinning centers of an AFM may bias a single molecule, unless this adsorbs on or creates a pinning site. First, exchange bias is triggered locally by the presence of pinned uncompensated spins in the AFM. These effects offset the response of a FM to applied magnetic fields, currents, and temperature, leading to prominent applications of exchange bias in, for example, spin valve and magnetic tunnel junction devices.ĭoes exchange bias with antiferromagnets also work for molecules? There are rather reasons to doubt it. The tell-tale signature of exchange bias is a shift of the hysteresis loop of the FM along the field axis by an amount HE, termed the exchange field, often accompanied by an enhancement of the coercivity HC. Unidirectional exchange anisotropy sets in below TN, as the interfacial spins of the AFM align with the magnetization of the FM and henceforth remain pinned in the direction of the cooling field. Exchange bias typically occurs in either ferromagnetic/antiferromagnetic (FM/AFM) bilayers or FM/AFM core−shell nanoparticles cooled in a magnetic field from below the Curie temperature of the FM through the Néel temperature (TN) of the AFM. However, because this compensation is not perfect at interfaces, ferromagnetic layers can lock their magnetization to the spins in the antiferromagnets, which gives rise to the phenomenon of exchange bias. Antiferromagnets have zero total magnetization because the magnetic moments of neighbor atoms point in opposite directions, that is, they compensate each other. The possibility of inducing exchange bias between a molecule and an antiferromagnet is also very interesting in this context.
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