DC-SQUID magnetization measurements of single magnetic particles

Wernsdorfer, Wolfgang; Hasselbach, K.; Mailly, D.; Barbara, B.; Benoı̂t, A.; Thomas, Luc; Suran, G.

doi:10.1016/0304-8853(94)01621-6

Cited by 185 publications

(82 citation statements)

References 11 publications

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“…For nickel disks with a diameter greater than 300 nm we always observe that the hysteresis loop in zero applied magnetic field has opened up, in agreement with previous investigations on small particles. 2,4 Figure 2 also presents our main result: the hysteresis loops of the three disks do not show inversion symmetry; i.e., when mirrored in the origin they do not map onto themselves. Even when we start from a very large positive field of ϩ 10 T ͑which is ϳ500 times the anisotropy field of nickel and ϳ20 times the bulk saturation field͒ and sweep to a very large negative field of Ϫ10 T, the magnetization curve is not the same as that from a sweep in the opposite direction when mirrored in the origin.…”

Section: Resultsmentioning

confidence: 74%

“…From a fundamental point of view measurements of the magnetization of an individual small particle are equally interesting, since they can provide on a microscopic level proof of the various theoretical models for magnetization reversal in larger, more complex systems. Newly developed techniques such as magnetic force microscopy, 1 microsquids, 2 and high-resolution near-field optical techniques 3 have provided many interesting results on magnetization reversal in submicrometer ferromagnetic particles, [4][5][6] among which are the experimental demonstration of coherent magnetization reversal in an ellipsoidal ␥-Fe 2 O 3 particle 7 and experimental proof for Néel-Brown thermally activated magnetization reversal in a single-domain particle with an activation volume equal to the particle volume. 8 We have developed the technique of ballistic Hall micromagnetometry, a noninvasive technique that can be used to study the magnetization of submicrometer ferromagnetic or superconducting particles at any temperature below 77 K. 10 Here we present results on the magnetization of a set of submicrometer ferromagnetic nickel disks ͑80 nm high, 0.1-1.0 m diameter͒.…”

Section: Introductionmentioning

confidence: 99%

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Memory effects in individual submicrometer ferromagnets

et al. 1998

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We have used ballistic Hall micromagnetometry to study the magnetization of individual submicrometer nickel disks ͑80 nm high, 0.1-1.0 m diameter͒. At low temperatures, hysteresis loops of the disks no longer show inversion symmetry in a magnetic field, as if the time reversal symmetry were broken. Furthermore, the magnetization of the smallest disks can be ''frozen'' in two possible states that are characterized by hysteresis loops which are each other's inverse. At temperatures below 19.5 K a magnetic field as high as 2 T cannot switch between the states, proving that it is extremely difficult to fully polarize a small ferromagnetic particle. On the other hand, at slightly higher temperatures ͑only TϾ19.8 K), a field as low as 0.1 T appears to be enough to fully polarize the disks. We attribute this extraordinary behavior to the glass-liquid transition experienced by spins at the particle surface. ͓S0163-1829͑98͒06542-4͔

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Section: Resultsmentioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Memory effects in individual submicrometer ferromagnets

et al. 1998

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“…B . 4 The applied field is generated by a solenoid and two pairs of Helmholtz coils. The field can be oriented anywhere in space; its maximal amplitude is 0.5 T. The angle resolution of the applied field is given by the smallest field step of 7ϫ10 Ϫ6 T, i.e., much smaller than 0.1°.…”

Section: Methodsmentioning

confidence: 99%

“…Furthermore, particle-particle interactions are difficult to take into account. With the recent arrival of nearfield microscopy and nanolithography, experimental studies [2][3][4][5] of magnetization reversal in individual particles become possible.…”

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confidence: 99%

Dynamical measurement of domain-wall nucleation and annihilation in individual amorphous Co particles

et al. 1996

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We present magnetization measurements of individual amorphous Co particles ͑300 nmϫ200 nmϫ30 nm͒ patterned by electron-beam lithography. The hysteresis loops show mainly two magnetization jumps corresponding to domain-wall nucleation and annihilation. The angular dependence of these magnetization jumps is measured and the temperature dependence ͑0.1-6 K͒ of the nucleation and the annihilation processes is investigated by two independent methods: switching field and switching time measurements. Finally we compare the results obtained on one particle with those of an array of about 2ϫ10 7 particles. We show experimentally that the dynamical properties measured on individual particles are connected with an unusual 1/T relaxation of the array of particles.

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“…A simple model has been developed to investigate magnetic nanoparticle-based systems [13]. The first magnetization measurement of individual single-domain NPs and nanowires (NWs) at very low temperature were presented [14]. Recently, magnetic structure of a NP has been investigated based on the mean-field approximation and Heisenberg Hamiltonian for a composite NP having inner FM core and outer AFM shell has been used [15].…”

Section: Introductionmentioning

confidence: 99%

Spin-1 Model of Noninteracting Nanoparticles

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2008

Acta Phys. Pol. A

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In this work, we presented a spin-1 model to investigate the magnetic properties of noninteracting monodomain nanoparticles based on the pair approximation. Nearest-neighbor pair interactions are incorporated between the Ising spins in three parts that are core, core-surface, and surface within the nanoparticle. Using the spin-1 Ising model of magnetization in the pair approximation, we calculated the free energy and minimized with respect to pair variables to obtain the field-cooled magnetization. Hysteresis loops of the system were plotted for various values of exchange coupling constants, and axial anisotropy of strength which couples the core, core-surface, and surface regions. The coercive field and its linear fit to the data were plotted as a function of radius of ferromagnetic nanoparticles.

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DC-SQUID magnetization measurements of single magnetic particles

Cited by 185 publications

References 11 publications

Memory effects in individual submicrometer ferromagnets

Memory effects in individual submicrometer ferromagnets

Dynamical measurement of domain-wall nucleation and annihilation in individual amorphous Co particles

Spin-1 Model of Noninteracting Nanoparticles

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