New Model for Amorphous Magnetism

Harris, R.; Plischke, Michael; Zuckermann, Martin J.

doi:10.1103/physrevlett.31.160

Cited by 672 publications

(225 citation statements)

References 8 publications

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“…3a) of the condensed phases of FeCI, with those of the non-crystalline ferrous halides [2] again show a significant difference : Due to fluctuations in the local exchange integrals [3,4] resp. in the anisotropy fields [5] a considerably less steep rise of the hf field below the magnetic ordering temperature is characteristic for amorphous magnets. The mean magnetization curve of the low temperature vapour quenched phases of FeCl,, however, still has the same functional dependence as that of crystalline FeCl, (Fig.…”

Section: Low Temperature Phasesmentioning

confidence: 99%

LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl₃

1974

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Rbsum6. -Les spectres Mossbauer de FeC13 dtposB a basse temperature a partir de la vapeur montrent deux doublets quadrupolaires au-dessus de 6,5 K et des eclatements magnetiques hyperfins en dessous de 6,5 K. Par chauffage a 300 K, les Bchantillons peuvent &tre transformes irrkversiblement en l'ttat cristallin normal. En dessous de leurs temperatures de transition magnktique, les spectres des phases trempQs a partir de la vapeur ainsi que ceux de la phase cristalline normale montrent des effets de relaxation qui sont attribues i des fluctuations superparamagnktiques. Par opposition aux halogenures ferreux amorphes, les courbes d'aimantation des phases de FeC13 trempees a partir de la vapeur ont la mEme dkpendance fonctionnelle que la phase cristalline. On suggere que la dkposition de FeCl, a basse temperature conduit a des structures microcristallines plut6t qu'amorphes.Abstract. -Mossbauer spectra of FeC13, vapour deposited at low temperatures, show two quadrupole doublets above 6.5 K and magnetic hyperfine splittings below 6.5 K. Upon heating to 300 K the samples can be transformed irreversibly to the normal crystalline phase. Below their magnetic transition temperatures the spectra of both vapour quenched phases and of the normal crystalline phase exhibit relaxation effects which are interpreted as superparamagnetic fluctuations. In contrast to the amorphous ferrous halides, the magnetization curves of the vapour quenched phases of FeC13 show the same functional dependence as the crystalline phase. It is suggested that the low temperature deposition of FeC13 leads to microcrystalline rather than to amorphous structures.

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Section: Low Temperature Phasesmentioning

confidence: 99%

LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl₃

1974

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“…12, is less than 5%. The thermal variation of the neodymium angular moment is related to the magnetic interaction that takes place at the RE whose magnitude can be estimated using the random anisotropy model, also called HPZ model by the name of their authors [51,63]. According to it, the orientation of the angular moment J of the 4f electrons of neodymium depends on the local crystal field and the effective indirect exchange with cobalt, this latter expressed as a molecular field acting on the angular moment.…”

Section: Variation Of the Neodymium Magnetic Moment With The Temperaturementioning

confidence: 99%

Perpendicular magnetic anisotropy in amorphous NdxCo1−x thin films studied by x-ray magnetic circular dichroism

et al. 2017

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The origin of perpendicular magnetic anisotropy (PMA) in amorphous Nd x Co 1−x thin films is investigated using x-ray magnetic circular dichroism (XMCD) spectroscopy at the Co L 2,3 and Nd M 4,5 edges. The magnetic orbital and spin moments of the 3d cobalt and 4f neodymium electrons were measured as a function of the magnetic field orientation, neodymium concentration, and temperature. In all the studied samples, the magnetic anisotropy of the neodymium subnetwork is always oriented perpendicular to the plane, whereas the anisotropy of the orbital moment of cobalt is in the basal plane. The ratio L z /S z of the neodymium 4f orbitals changes with the sample orientation angle, being higher and closer to the atomic expected value at normal orientation and smaller at grazing angles. This result is well explained by assuming that the 4f orbital is distorted by the effect of an anisotropic crystal field when it is magnetized along its hard axis, clearly indicating that the 4f states are not rotationally invariant. The magnetic anisotropy energy associated to the neodymium subnetwork should be proportional to this distortion, which we demonstrate is accessible by applying the XMCD sum rules for the spin and intensity at the Nd M 4,5 edges. The analysis unveils a significant portion of neodymium atoms magnetically uncoupled to cobalt, i.e., paramagnetic, confirming the inhomogeneity of the films and the presence of a highly disordered neodymium rich phase already detected by extended x-ray-absorption fine structure (EXAFS) spectroscopy. The presence of these inhomogeneities is inherent to the evaporation preparation method when the chosen concentration in the alloy is far from its eutectic concentrations. An interesting consequence of the particular way in which cobalt and neodymium segregates in this system is the enhancement of the cobalt spin moment which reaches 1.95 μ B in the sample with the largest segregation.

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“…, where grains form single magnetic domains, and changes of magnetization can take place only by rotation of the local magnetization vector. The model was studied in the mean-field approximation by Harris et al 14 Further investigations suggested that in 3d, the stable low-temperature phase is a spin glass phase, even in the limit of strong anisotropy. In this limit, the spins are forced to be aligned along the anisotropy axis and therefore, the model reduces to a random anisotropy Ising model ͑RAIM͒.…”

Section: Introductionmentioning

confidence: 99%

Hysteresis and avalanches in the random anisotropy Ising model

Vives

Planes

2001

Phys. Rev. B

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The behavior of the random anisotropy Ising model at Tϭ0 under local relaxation dynamics is studied. The model includes a dominant short-range ferromagnetic interaction and assumes an infinite anisotropy at each site along local anisotropy axes which are randomly aligned. As a consequence, some of the effective interactions become antiferromagneticlike and frustration appears. Two different random distributions of anisotropy axes have been studied. Both are characterized by a parameter that allows control of the degree of disorder in the system. By using numerical simulations we analyze the hysteresis loop properties and characterize the statistical distribution of avalanches occurring during the metastable evolution of the system driven by an external field. A disorder-induced critical point is found in which the hysteresis loop changes from displaying a typical ferromagnetic magnetization jump ͑large avalanche spanning a macroscopic fraction of the system͒ to a rather smooth loop exhibiting only tiny avalanches. The critical point is characterized by a set of critical exponents, which are consistent with the universal values proposed from the study of other simpler models.

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New Model for Amorphous Magnetism

Cited by 672 publications

References 8 publications

LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl₃

LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl₃

Perpendicular magnetic anisotropy in amorphous NdxCo1−x thin films studied by x-ray magnetic circular dichroism

Hysteresis and avalanches in the random anisotropy Ising model

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New Model for Amorphous Magnetism

Cited by 672 publications

References 8 publications

LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl3

LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl3

Perpendicular magnetic anisotropy in amorphous NdxCo1−x thin films studied by x-ray magnetic circular dichroism

Hysteresis and avalanches in the random anisotropy Ising model

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Product

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LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl₃

LOW TEMPERATURE PHASES OF MICROCRYSTALLINE FeCl₃