Low temperature conduction in GdBa2Cu3Oy(y<6.4) films
Y. OchiaiFumihiko NakamuraK. SenohToshiyuki TamuraTakahito TerashimaKenji IijimaK. YamamotoK. HirataYoshio BandoY. Narahara
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Magnetism
It has been proposed that antiferromagnetic Fe adatom spins on semiconductor Cu-N surfaces can be used to store information [S. Loth {\it et al}, Science \textbf{335}, 196 (2012)]. Here, we investigate spin dynamics of such antiferromagnetic systems through Monte Carlo simulations. We find out the temperature and size laws of switching rates of N\'{e}el states and show that the N\'{e}el states can become stable enough for the information storage when the number of spins reaches to one or two dozens of the Fe spins. We also explore promising methods for manipulating the N\'{e}el states. These could help realize information storage with such antiferromagnetic spin systems.
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The shifts and the widths of the proton magnetic resonance lines in two Cu2+ salts have been studied to obtain information about the antiferromagnetic short-range order in these crystals. In Cu(NH3)4SO4·H2O, where the Cui+ spins order in antiferromagnetic linear chains, the resonance lines show a strong broadening at decreasing temperatures. This is explained by the decrease of the fluctuations of the Cu2+ spins due to the forming of antiferromagnetic clusters. The experimental results are in agreement with a simple model, relating the fluctuations and the susceptibility of the Cui+ spins. In Cu(NO3)2·3H2O measurements of the lineshifts show that the Cu2+ spins order antiferromagnetically in pairs. No broadening of the PMR lines is observed, which is explained by the absence of cluster forming.
Proton magnetic resonance
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We report the magnetic structure of TaFe1+yTe3 single crystals by means of neutron diffraction measurements. TaFe1+yTe3 possesses a layered structure with a formation of two-leg zigzag ladders along the b-axis. We find that TaFe1+yTe3 undergoes an antiferromagnetic transition at 178 K with Fe1 spins of the intra-ladders ferromagnetically aligned while spins of the inter-ladders antiferromagneitcally coupled. Furthermore, spins of the neighboring interstitial Fe2 (y) ions order parallel to the Fe1 spins of each ladder. These findings are distinct from the magnetic structure of the recently-discovered spin-ladder compound BaFe2Se3. TaFe1+yTe3 may serve as an interesting quasi-one dimensional ferromagnetic system.
Zigzag
Magnetic structure
Spin structure
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The short-range order parameters are evaluated for the triangular and honeycomb Ising nets in ferro- and antiferromagnetic cases by the method of Kaufman and Onsager. For the antiferromagnetic triangular net we also evaluate the probabilities for the various spin configurations. When the three spins are located at the vertices of the smallest regular triangle, the probability that three neighbouring spins are all parallel is zero at T = 0. However, it is 0.035120 or 0.202998 respectively at T = 0 according as the vertical angle of the three neighbouring spins is 120° or 180°. Making use of these values, the configurational probabilities corresponding to four or five neighbouring spins are also evaluated at zero temperature.
Honeycomb
Zero (linguistics)
Ising spin
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The domain state model for exchange bias has been further investigated by considering vector spins for the antiferromagnet instead of Ising spins used in the earlier studies. The qualitative results are similar to those with infinite anisotropy for the antiferromagnet. However, under certain conditions softer spins can lead to an even stronger bias field. The study shows a nontrivial dependence of the exchange bias on the antiferromagnetic anisotropy.
Exchange bias
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Magnetism
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The exchange interaction determines the ferromagnetic (FM) or antiferromagnetic (AFM) ordering of atomic spins. When ferromagnets and antiferromagnets are coupled together, they often exhibit the exchange bias effect, a unidirectional interface exchange field causing a shift of the magnetic hysteresis loop. The effective magnitude of this interface exchange field is at most a few percent of the bulk exchange, arising from pinned interfacial spins in the antiferromagnet. The pinned spins are known to comprise a small fraction of the total number of interface spins, yet their exact nature and physical origin has so far been elusive. Here we show that in the technologically important $\gamma - IrMn_3/CoFe$ structure the pinned interface spins are in fact delocalised over the whole interface layer. The pinned spins arise from the small imbalance of the number of spins in each magnetic sublattice in the antiferromagnet due to the natural atomic disorder. These pinned spins are strongly coupled to the bulk antiferromagnet explaining their remarkable stability. Moreover, we find that the ferromagnet strongly distorts the interface spin structure of the antiferromagnet, causing a large reversible interface magnetisation that does not contribute to exchange bias. The unexpected delocalised nature of the pinned interface spins explains both their small number and their stability, uncovering the mysterious microscopic origin of the exchange bias effect.
Exchange bias
Exchange interaction
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Muon spin spectroscopy
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Solid-state physics
Interface (matter)
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The molecular field treatment of the magnetic properties of ferrites given by N\'eel is extended to take into account the antiferromagnetic exchange interactions within the two magnetic sublattices. On further subdividing the two lattices, we show that the ground state may, (1) have an antiparallel arrangement of the spins on the two sites; or (2) consist of a triangular arrangement of the spins on the sublattices; or (3) have antiferromagnetism in each of the two sites separately. We also show that transitions between various configurations may occur in the same substance at different temperatures, without the assumption of temperature-dependent interactions. Neutron diffraction experiments and specific heat measurements are suggested for the detection of the predicted arrangements.
Antiparallel (mathematics)
Magnetic structure
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