Evidence for domain wall tunnelling in a quasi-one dimensional ferromagnet

Journal of Physics Condensed Matter

Volumn 8, Issue 19, 1996, Pages

  Hong, Kimin ^a   Giordano, N ^a  

^a PURDUE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ELECTRIC CONDUCTIVITY; ELECTRON TUNNELING; FERROMAGNETIC MATERIALS; HIGH TEMPERATURE EFFECTS; LOW TEMPERATURE EFFECTS; MAGNETIC FIELD EFFECTS; QUANTUM THEORY; WIRE;

FERROMAGNETIC WIRES; MAGNETIC DOMAIN WALLS; QUANTUM TUNNELING; QUASI ONE DIMENSIONAL;

MAGNETIC DOMAINS;

EID: 0030572018     PISSN: 09538984     EISSN: None     Source Type: Journal    
DOI: 10.1088/0953-8984/8/19/001     Document Type: Article

References (30)

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7. Recent work on magnetic MQP is reviewed in L Gunther and B Barabara (eds.) 1995 Quantum Tunneling of the Magnetization-QTM '94 (Dordrecht. Kluwer). The evidence for various types of macroscopic quantum phenomena in magnetic systems is not universally accepted, see Garg A 1995 Phys. Rev. Lett. 74 1458 and references therein.
8. Recent work on magnetic MQP is reviewed in L Gunther and B Barabara (eds.) 1995 Quantum Tunneling of the Magnetization-QTM '94 (Dordrecht. Kluwer). The evidence for various types of macroscopic quantum phenomena in magnetic systems is not universally accepted, see Garg A 1995 Phys. Rev. Lett. 74 1458 and references therein.
9. Notable exceptions are the experiments of Lederman M, Schultz S and Ozaki M 1994 Phys. Rev. Lett, 73 1986 and Wernsdorfer W, Hasselbach K, Mailly D, Barbara B, Benoit A, Thomas L and Suran G 1995 J. Mag. Magn. Mater. 145 33 where the magnetization reversal of individual submicron particles was studied.
10. Notable exceptions are the experiments of Lederman M, Schultz S and Ozaki M 1994 Phys. Rev. Lett, 73 1986 and Wernsdorfer W, Hasselbach K, Mailly D, Barbara B, Benoit A, Thomas L and Suran G 1995 J. Mag. Magn. Mater. 145 33 where the magnetization reversal of individual submicron particles was studied.
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12. Typical sample currents were a few μA. Heating due to the sample current or spurious noise is a major concern in experiments of this kind. We were able to check for this by examining the electron-electron contribution to the resistance. This contribution had the expected form and magnitude down to our lowest temperature (1.3 K), indicating that the electrons were indeed cooled to this temperature.
13. This is the thickness of domain walls in bulk Ni (see, for example, [12]). In our polycrystalline samples, this will probably be a lower bound on the wall thickness [12]. We should hasten to add that the structure of the domain walls in our wires may be more complicated than the usual picture of a Bloch or Néel wall. In addition, while the demagnetizing energy will tend to make M lie along the axis, there may be some deviations ('splay') in direction near the ends or edges of the sample (and near the walls, of course). However, we do not believe that this will make the wall thickness less than the sample diameter. It still seems safe, as a first approximation, to think of domains with M directed along the axis of the wire, separated from each other by some sort of wall or 'transition region'. A detailed theoretical analysis will, of course, have to deal with these complications, but since our sample geometry is well characterized, we feel that such an analysis should be feasible.
14. Jiles D 1991 Magnetism and Magnetic Materials (London: Chapman and Hall)
15. One might also imagine that walls could nucleate in pairs at sites along the wire. However, experiments comparing the behaviour with opposite field polarities [14] allow us to rule out this possibility at the fields (near the minimum in the R(H) curve) considered in detail here. We hope to search specifically for nucleation effects in future experiments.
16. Giordano N and Monnier J D 1994 Physica B 194-196 1009; Hong K and Giordano N 1995 Quantum Tunneling of the Magnetization-QTM '94 ed. L Gunther and B Barabara (Dordrecht: Kluwer)
17. Giordano N and Monnier J D 1994 Physica B 194-196 1009; Hong K and Giordano N 1995 Quantum Tunneling of the Magnetization-QTM '94 ed. L Gunther and B Barabara (Dordrecht: Kluwer)
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21. From measurements of the hysteresis, as in figure 1, it is possible to use the size of an R(H) jump to estimate how far the wall has moved. The jumps in figure 2 correspond to a wall displacement of ∼ 1.2 μm.
22. The results for P(H) were stable with time, and were unaffected by thermal cycling, even to room temperature. The results shown in figure 4 all correspond to the first jump in R(H), but jumps at higher fields exhibited similar behaviour.
23. This estimate of the crossover temperature was obtained using equation 3.67 in [6].
24. It is interesting that studies of wall motion in bulk samples, using a rather different approach, also infer larger values of the crossover temperature than expected theoretically; see Barbara B, Wegrowe J E, Sampaio L C, Nozières J P, Uehara M, Novak M, Paulsen C, and Tholence J L 1993 Physica Scripta T49 268.
25. According to the theory [6], the small oscillation frequency and the crossover temperature are functions of material parameters (such as M), sample shape, and the assumed form of the pinning potential.
26. Kurkijärvi J 1971 Phys. Rev. B 6 832; Fulton T A and Dunkleberger L N 1974 Phys. Rev. B 9, 4760; Garg A 1995 to be published
27. Kurkijärvi J 1971 Phys. Rev. B 6 832; Fulton T A and Dunkleberger L N 1974 Phys. Rev. B 9, 4760; Garg A 1995 to be published
28. Kurkijärvi J 1971 Phys. Rev. B 6 832; Fulton T A and Dunkleberger L N 1974 Phys. Rev. B 9, 4760; Garg A 1995 to be published
29. The relation between the escape rate and the escape distribution is discussed in detail in [23] and [2].
30. These width variations were such as to make the central half of the sample ∼ 50 Å narrower than the end regions. The motivation for modifying the wires in this manner arose from the discussion in Gunther L and Barbara B 1994 Phys. Rev. B 49 3926.