Magnetization Process of a Helical Spin Configuration

Enz, U.

doi:10.1063/1.2000413

Cited by 86 publications

(40 citation statements)

References 4 publications

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“…Yet, it has been shown that spiral magnetic structures can result from isotropic-exchange interactions if the exchange integrals, between ions in the nn planes and the nnn planes, have certain ratios 23,24 ; these structures can require high applied fields (comparable to or larger than the exchange) to reach magnetic saturation, as is actually observed in the present case. It has been shown for Eu 9 that exchange interactions extend over large distances, so that coupling to nnn planes (and beyond) should be important.…”

Section: A First-order Transitionsupporting

confidence: 57%

First-Order Phase Transition in Europium Metal

Cohen¹,

Hüfner²,

West³

1969

Phys. Rev.

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On the basis of our experiments, we cannot interpret the results with the model of the random flipping of the hyperfine field. 1 (The sidebands observed at 4 Mc/sec could not possibly be detected in supermalloy samples, as in Perlow's experiment, because of the large width of the Mossbauer lines at £T rf = 0.) Furthermore, the calculation of x 2 given above for the case of iron has been carried out also for supermalloy samples. The relatively smaller values of k 2 for the latter can be compensated by the relatively larger magnetic energy density. Consequently, the model of the magnetostriction might be valid for supermalloy, if it is for iron.In conclusion, the present experiments yield the following information:(a) The sidebands observed in iron slabs of various thicknesses in the presence of a rf magnetic field cannot be described by a single "modulation index"; a quantum-mechanical derivation of their spectrum accounts satisfactorily for the obtained results.(b) The dependence of the intensity of the sidebands on the static magnetic field HQ, perpendicular to H T i, suggests that the domain-wall contribution, if any, to the observed effect is much smaller than the contribution of the rotation of domain magnetization.(c) The magnetostriction model accounts for the intensity of the sidebands, if the magneto-elastic coupling coefficient k 2 is assumed to be much larger in the dynamic condition than in the static condition.We have used Mossbauer-effect measurements of the hyperfine (hf) interaction in Eu metal to study the behavior of its sublattice magnetization in the vicinity of the magnetic ordering temperature. At 88.6°K, the hf field falls from 0.4 of the saturation value to zero. This results from the existence of a first-order transition coincident with the magnetic ordering. The possible causes of the transition are discussed. The temperature dependence of the hyperfine field just below the transition is analyzed in terms of criticalpoint theory. The results of thermal-expansion measurements are also presented and discussed.

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Section: A First-order Transitionsupporting

confidence: 57%

First-Order Phase Transition in Europium Metal

Cohen¹,

Hüfner²,

West³

1969

Phys. Rev.

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“…In this model, the spiral state is stable when J 1 = 0, J 2 > 0, and |J 1 | < 4|J 2 | [16]. The validity of applying this model to MnAu 2 was confirmed using density functional theory (DFT) calculations [18,19].…”

Section: Introductionmentioning

confidence: 73%

Collapse and control of theMnAu2spin-spiral state through pressure and doping

Glasbrenner

2016

Phys. Rev. B

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MnAu2 is a spin-spiral material with in-plane ferromagnetic Mn layers that form a screw-type pattern around a tetragonal c axis. The spiral angle θ was shown using neutron diffraction experiments to decrease with pressure, and in later studies it was found to suffer a collapse to a ferromagnetic state above a critical pressure, although the two separate experiments did not agree on whether this phase transition is first or second order. To resolve this contradiction, we use density functional theory calculations to investigate the spiral state as a function of pressure, charge doping, and also electronic correlations via a Hubbard-like U . We fit the results to the one-dimensional J1−J2−J3−J4 Heisenberg model, which predicts either a first-or second-order spiral-to-ferromagnetic phase transition for different regions of parameter space. At ambient pressure, MnAu2 sits close in parameter space to a dividing line separating first-and second-order transitions, and a combination of pressure and electron doping shifts the system from the first-order region into the second-order region. Our findings demonstrate that the contradiction in pressure experiments regarding the kind of phase transition are likely due to variations in sample quality. Our results also suggest that MnAu2 is amenable to engineering via chemical doping and to controlling θ using pressure and gate voltages, which holds potential for integration in spintronic devices.

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“…For example, for the helix and fan structures in the continuum limit kd → 0 discussed above that was studied in 1961 [12], the µ xave (H x ) was not presented. However, this can be obtained by averaging cos[φ(z/λ)] for that structure over one wavelength λ for each value of H x /H c .…”

Section: Introductionmentioning

confidence: 99%

Magnetic structure and magnetization of helical antiferromagnets in high magnetic fields perpendicular to the helix axis at zero temperature

Johnston

2017

Phys. Rev. B

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The zero-temperature angles of magnetic moments in a helix or sinusoidal fan confined to the xy plane, with respect to an in-plane magnetic field Hx applied perpendicular to the z axis of a helix or fan, are calculated for commensurate helices and fans with field-independent turn angles kd between moments in adjacent layers of the helix or fan using the classical J0-J1-J2 Heisenberg model. For 0 < kd < 4π/9, first-order transitions from helix to a fan structure occur at fields Ht as previously inferred, where the fan is found to be approximately sinusoidal. However, for 4π/9 ≤ kd ≤ π, different behaviors are found depending on the value of kd and these properties vary nonmonotonically with kd. In this kd range, the change from helix to fanlike structure is usually a crossover with no phase transition between them, although first-order transitions are found for kd = 3π/5 and 8π/11 and a second-order transition for kd = 3π/4. At a critical field Hc, the fan or fanlike structures exhibit a second-order transition to the paramagnetic state. The Hc for a helix undergoing a field-induced change to a fan or fanlike structure is found to be the same as for a sinusoidal fan with the same kd and interlayer interactions. Analytical expressions for Hc versus kd are presented. We also calculated the average x-axis moment per spin µxave versus Hx for helices and fans with crossovers and phase transitions between them. When smooth helix to fanlike crossovers occur in the range 4π/9 ≤ kd ≤ π, µxave exhibits an S-shape behavior with increasing Hx. This predicted behavior is consistent with µxave(Hx) data previously reported by Sangeetha, et al. [Phys. Rev. B 94, 014422 (2016)] for single-crystal EuCo2P2 possessing a helix ground state with kd ≈ 0.85π. The low-field magnetic susceptibility and the ratio Ht/Hc are calculated analytically or numerically versus kd for helices, and are shown to approach the respective known limits for kd → 0.

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Magnetization Process of a Helical Spin Configuration

Cited by 86 publications

References 4 publications

First-Order Phase Transition in Europium Metal

First-Order Phase Transition in Europium Metal

Collapse and control of theMnAu2spin-spiral state through pressure and doping

Magnetic structure and magnetization of helical antiferromagnets in high magnetic fields perpendicular to the helix axis at zero temperature

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