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Register a new userMn12-acetate film pattern generated by photolithography methods
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Authors
K. Kim
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We demonstrate a straightforward way to lithographically fabricate Mn12-acetate (Mn12O12(CH3COO)16(H2O)4 2CH3COOH 4H2O) thin film patterns on Si/SiO2 surfaces, a significant step in light of the chemical volatility of this organic complex. Atomic force microscopy (AFM) images of the film patterns allow the determination of the pattern dimensions. X-ray photoelectron spectroscopy (XPS) data indicate that the patterned material is the intact Mn12-acetate complex. Magnetic measurements of the Mn12-acetate film confirm that the film properties are reminiscent of crystalline Mn12-acetate, suggesting that this approach can be used to fabricate lithographically patterned devices of Mn12-acetate.
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Films of the molecular nanomagnet, Mn12-acetate, have been deposited using pulsed laser deposition and a novel variant, matrix assisted pulsed laser evaporation. The films have been characterized by X-ray photoelectron spectroscopy, mass spectrometry and magnetic hysteresis. The results indicate that an increase in laser energy and/or pulse frequency leads to fragmentation of Mn12, whereas its chemical and magnetic integrity is preserved at low laser energy (200 mJ). This technique allows the fabrication of patterned thin film systems of molecular nanomagnets for fundamental and applied experiments.
Thin films of the molecular magnet Mn12-acetate, [Mn12 O12(CH3COO)16 (H2O)4] 2CH3COOH 4H2O, have been prepared using a laser ablation technique with a nitrogen laser at low laser energies of 0.8 and 2 mJ. Chemical and magnetic characterizations show that the Mn12-acetate cores remain intact and the films show similar magnetic properties to those of the parent molecular starting material. In addition, the magnetic data exhibit a peak in the magnetization at 27 K indicating the creation of an additional magnetic phase not noted in previous studies of crystalline phases.
Using micron-sized thermometers and Hall bars, we report time-resolved studies of the local temperature and local magnetization for two types of magnetic avalanches (abrupt spin reversals) in the molecular magneti Mn12-acetate, corresponding to avalanches of the main slow-relaxing crystalline form and avalanches of the fast-relaxing minor species that exists in all as-grown crystals of this material. An experimental protocol is used that allows the study of each type of avalanche without triggering avalanches in the other, and of both types of avalanches simultaneously. In samples prepared magnetically to enable both types of avalanches, minor species avalanches are found to act as a catalyst for the major species avalanches. magnetically to enable both types of avalanches, minor species avalanches are found to act as a catalyst for the major species avalanches.
Crystals of the molecular magnet Mn12-acetate are known to contain a small fraction of low- symmetry (minor) species with a small anisotropy barrier against spin reversal. The lower barrier leads to faster magnetic relaxation and lower coercive field. We exploit the low coercive fields of the minor species to make a direct determination of the dipole field in Mn12-ac. We find that the dipolar field of a fully magnetized crystal is 51.5 pm 8.5 mT, consistent with theoretical expectations.
For the first time, the morphology and dynamics of spin avalanches in Mn12-Acetate crystals using magneto-optical imaging has been explored. We observe an inhomogeneous relaxation of the magnetization, the spins reversing first at one edge of the crystal and a few milliseconds later at the other end. Our data fit well with the theory of magnetic deflagration, demonstrating that very slow deflagration rates can be obtained, which makes new types of experiments possible.
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