Diamagnetic Domains Research Articles

Peculiar Magnetic Properties at Low Temperature of MnAs Thin Films Grown on GaAs(001) Substrate

We carried out investigation on the magnetic properties of MnAs thin film grown on GaAs(001) substrate by using molecular-beam epitaxy. The magnetic Curie temperature was ~340 K which was higher than that of the bulk. Magnetization (M) versus magnetic field (H) showed strong two-fold symmetric anisotropy. At low temperature of 2 K, the M-H curve and temperature dependence of magnetization exhibit peculiar behavior that has not been observed before. It should be noted that these unique results were only observed when a magnetic field was applied. We also observed a weak-localization-like magnetoresistance (MR) at 2 K. As an origin of the observed peculiar magnetic properties and MR, we suggest diamagnetic domains which are phase transited from ferromagnetism at low temperature.

Relaxation dynamics and growth modes of metastable spin-crossover materials with magnetic interactions

A two-dimensional spin-1 Blume-Emery-Griffiths (BEG) model is used to describe the relaxation dynamics of spin-crossover (SC) compounds with magnetic interactions from a metastable high-spin state by means of Monte Carlo simulations with Arrhenius dynamics. The model comprises temperature-dependent effective spin exchange interaction accounting for spin-phonon interactions. The growth modes of the stable low-spin state domains are singled out in the model parameters' space. For weak magnetic interactions, numerical results indicated a kind of 2D-nucleation with the birth, spread and coalescence of low-spin diamagnetic domains following the Becker-Doering law. A schematic growth phase diagram is presented.

ChemInform Abstract: Diamagnetic Domains and Nonlinear Electromagnetic Waves in Normal Metals (Review)

AbstractReview: 63 refs.

Diamagnetic domains and nonlinear electromagnetic waves in normal metals (review)

This is a review of experimental and theoretical research on diamagnetic domains in normal metals. Considerable attention is devoted to a new, effective method for studying domain structures: muon spectroscopy based on measuring the induction using the precession frequency of muons in a magnetic field. A number of phenomena which arise in states with magnetic domains, including unusual magnetostriction and hysteresis in the de Haas-van Alphen effect, are discussed. The mechanism of nonlinearity in the propagation of low-frequency electromagnetic waves in metals with strong magnetism of their conduction electrons is examined.

On diamagnetic domains in layered conductors

The magnetic susceptibility and domain structure of a layered conductor are calculated under conditions of a substantial de Haas–van Alphen effect for arbitrary orientation of the external magnetic field with respect to the layers. It is shown that the amplitude of the magnetic susceptibility is an oscillatory function of the angle between the magnetic field and the normal to the layers, with a sharp maximum along preferred directions of magnetic field. The possibility of propagation of low-frequency weakly damped modes of the electromagnetic field is discussed with allowance for the induced magnetism of the conduction electrons.

Spatial distribution of magnetic field and persistent currents in Condon domain phase

The distributions of magnetic field above the surface of the sample due to existence of the diamagnetic domain structure are found. It is shown, that the constant magnetic induction splitting inside of a sample is caused by the magnetization current density, localised in the boundaries between adjacent domains, close to the sample surface. The properties of this current are studied. The influence of the domain wall thickness on the spatial distribution of magnetic field and magnetization current density is present. A possibility of detection of the changes in the magnetic field distribution in vacuum, close to the surface of the sample, by means of Hall probes, is discussed. The measurement of the spatial distribution of magnetic field can give lacking information about characteristic sizes of magnetic domain formation at the conditions of the strong de Haas van Alphen effect.

Quantized Vortices and Diamagnetic Precursor to the Meissner State in High-Tc Superconductors

We report the magnetic imaging for underdoped and optimally-dopedLa2−xSrxCuO4 (LSCO) thin films on single substrates and nearly optimallydoped YBa2Cu3O7−x (YBCO) thin films on tricrystal substrates in the temperature range both below and above Tc using scanning SQUID microscopy. Below Tc, clear integer- and half-integer quantized vortices were observable. Above Tc, however, the inhomogeneous diamagnetic domains appeared. The local diamagnetic domains that led to the Meissner state were found in the broad temperature range for underdoped samples and in the narrow limited temperature range for optimally-doped samples. The results provide evidence that local diamagnetic domains are closely related to the pseudogap state. The continuous connection of the domain state above Tc with the state of a half-integer vortex at the tricritical point in the YBCO film below Tc also indicates that the diamagnetic domains are also closely related to the occurrence of dx2-y2-wave superconductivity.

Diamagnetic domains and magnetostriction in beryllium

Magnetostriction was for the first time studied under the conditions of formation of diamagnetic domains (Condon domains). Transverse magnetostriction oscillations on a beryllium single crystalline plate oriented normally to magnetic field were measured in magnetic fields up to 7 T at temperatures down to 1.5 K. The relative amplitude of oscillations increased almost as the square of magnetic field and reached 10−5. The signal had a sawtoothed shape corresponding to alternation of homogeneous and inhomogeneous (domain) states in the region of the existence of magnetic domains. The arising of domains was accompanied by singularities in the observed signals which is explained by an anomalous increase in the compressibility coefficient of the domain state: coefficient oscillations were more than 100 times larger than the value predicted by the standard theory. The observed relation between magnetization current and deformation led us to conclude that the compressibility of the metal was fully determined by conduction electrons. Magnetostriction then exactly compensated Fermi level oscillations. The position of the Fermi level therefore remained constant under magnetic field variations. In addition, the domain wall thickness had to increase as the plate grew thicker.

Observation of diamagnetic precursor to the Meissner state above Tc in high- Tc La 2− xSr xCuO 4 cuprates by scanning SQUID microscopy

We have studied the magnetic imaging of the superconducting and anomalous normal states for underdoped La 2− x Sr x CuO 4 (LSCO) thin films deposited by a PLD method and nearly optimal-doped LSCO single crystals grown by a traveling solvent floating zone method by scanning SQUID microscopy. The La 2− x Sr x CuO 4 (LSCO) films and their T c's are 18–19 K. The SSM used here has a pick-up coil of 10 μm diameter and the magnetic flux sensitivity is less than 5 μΦ 0 Hz −1/2. Below T c, clear quantized vortices are observable. Above T c, however, the magnetic image never becomes uniform, and inhomogeneous diamagnetic domains appear. The nucleation of diamagnetic domains starts above 80 K, then they develop with expanding their area as temperature is reduced and connected with the Meissner state at T c. The diamagnetic amplitude of these domains is significantly large in the first stage and then decreases with reducing temperature.

Nonlinear magnetohydrodynamic waves in metals under strong magnetism of conduction electrons

At low temperature the aplitude of the quantum oscillating part of magnetic susceptibility may reach values of order unity. When susceptibility is close to 1/4π the linear terms in the Maxwell's equations may be of the same order as nonlinear terms. As a result, the wave process becomes essentially nonlinear. In this case nonlinear small-amplitude electromagnetic waves can propagate in a conductor. We find nonlinear solutions of the Maxwell's equations and determine the spectrum of nonlinear waves. The process of the formation of inhomogeneous stationary state with diamagnetic domains is analysed.

Anomalous compressibility and magnetostriction of beryllium under the conditions of diamagnetic domain formation

Magnetostriction oscillations are measured for a single-crystal beryllium sample shaped like a plate perpendicular to the direction of the magnetic field. In the range of 2–5 T at a temperature of 1.5 K, i.e., in the region of diamagnetic domain formation (Condon domains), the striction signal has the saw-tooth shape corresponding to the alternation of homogeneous and nonhomogeneous (domain) states. The formation of the domain structure is accompanied by an anomalous increase in compressibility; the oscillations in this coefficient are more than one hundred times greater than the value given by the standard theory. An analysis of the results indicates that the domain wall width should increase with increasing plate thickness.

Application of μSR 2 method to estimate the size of diamagnetic domains

μSR histograms obtained from different regions of a target have to be slightly different since magnetic fields are inhomogeneous. Calculation of a correlation function of these histograms allows to estimate the correlation radius of inhomogeneities. This method was named μSR 2. Application of the μSR 2 method for estimating the sizes of magnetic domains is analyzed. Results of the computer simulation of a μSR 2 experiment to measure domain sizes are given. It is shown that domain sizes can be estimated within the accelerator operating time allocated for a conventional μSR experiment.

Electromagnetic waves in organic conductors under strong magnetism of conduction electrons

Wave processes in layered organic conductors in strong magnetic fields are investigated theoretically at low temperatures when the de Haas–van Alphen effect is manifested strongly. The spectrum and amplitude of weakly attenuating waves are determined in the vicinity of the electron phase transition where the formation of diamagnetic domains takes place.

Feasibility of measuring the average sizes of diamagnetic domains by the μSR 2 method

One of the simplest examples of possible application of the μSR2 method for estimating the sizes of diamagnetic domains is analyzed in detail. The domains have been observed for the first time by means of the μ SR method in beryllium [G. Solt, C. Baines, V. S. Egorov et al., Hyperfine Interactions 104, 257 (1997)]. Results are given from a computer simulation of a μSR2 experiment to measure domain sizes in Be. An algorithm is described for processing the experimental results. It is graphically demonstrated that domain sizes can be estimated within the accelerator operating time allocated for an ordinary μSR experiment.

Diamagnetic domains in beryllium observed by muon-spin-rotation spectroscopy

Dia- and paramagnetic (Condon) domains were observed in single crystal beryllium for applied fields $\mathit{H}||[0001]$ of 1--3 T, at temperatures $T=0.1--3$ K, by muon-spin-rotation $(\ensuremath{\mu}\mathrm{SR})$ spectroscopy at PSI. On varying H, the domains with magnetization parallel and opposite to $\mathit{H}$ reappear in each de Haas--van Alphen period $\ensuremath{\Delta}H,$ detected by the doublet splitting in the precession frequency spectrum. As H varies within the ``domain section'' $\ensuremath{\delta}H$ of a dHvA cycle, the domain inductions ${B}_{1}{,B}_{2}$ stay constant, while the volume fractions of the para- and diamagnetic regions vary linearly. The beat in the susceptibility amplitude $a(B)=4\ensuremath{\pi}{(dM/dB)}_{\mathrm{max}},$ with a period of $\ensuremath{\approx}33\ensuremath{\cdot}\ensuremath{\Delta}H,$ allowed us to determine ${B}_{i}$ and $\ensuremath{\delta}H$ for different regimes. As a increases by a factor of $\ensuremath{\approx}3,$ the sections $\ensuremath{\delta}H$ grow, $|{B}_{2}\ensuremath{-}{B}_{1}\stackrel{\ensuremath{\rightarrow}}{|}\ensuremath{\Delta}H,$ and the uniform state between two domain sections shows an increasingly strong diamagnetism, $\ensuremath{-}4\ensuremath{\pi}\ensuremath{\chi}\ensuremath{\gg}1.$ The domains persist up to $T\ensuremath{\approx}3$ K and at fields down to $H\ensuremath{\approx}1$ T. On varying H, a slight ``field overheating'' was observed. The domain area in the phase diagram is much larger than expected, while other predictions of the theory proved to be qualitatively correct.

Linear optical properties from Ni ultrathin films in the diamagnetic domain

Optical properties of Ni ultrathin films deposited by radio-frequency sputtering on SiO 2 (glass) and Si substrates are obtained. Thickness dependence infrared (IR) reflectance ( R) measurements are used to characterize these metallic films. For our quantum well system the local field calculation of the optical diamagnetic response in a quantum well is made to correlate our experimental findings. Also, an experimental approximation (to the first order of d/ λ) for the imaginary part of the Ni dielectric function is given. Finally, we measure R in the presence of a fixed magnetic field ( B-field) in the direction perpendicular to the plane of the metallic film. From these results, quantum size effects revealed as fine oscillations in R are altered when the B-field is applied. In both cases, with and without the B-field, R from Ni/SiO 2 keeps its diamagnetic behavior unchanged. To insure the two conditions: d≪ λ and near normal incidence, an external field from a tunable CO 2 laser tuned to a p-polarized wavelength of 9.201 μm and angle of incidence of 7° is chosen.

Observation of diamagnetic domains in beryllium

We have observed diamagnetic domains (Condon domains) in a beryllium single crystal in magnetic fields H⩽3 T (H∥[0001]) at liquid-helium temperatures. The formation of the domain structure was determined according to magnetic-breakdown quantum oscillations of the resistance thermoelectric power as well as according to the splitting of the resonance peak of the free spin precession frequency of muons (µSR). The alternation of a uniform state (with one µSR peak) and a state with domain structure (with two peaks) is consistent as regards the periodicity with the de Haas-van Alphen effect, the period is ΔH≅78 Oe, and the range of existence of domains and the difference in their magnetizations are ΔB=4πΔM=B2−B1≅30 Oe.

ChemInform Abstract: Diamagnetic Domains in Beryllium as Seen by Muon Spin Rotation Spectroscopy

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Capabilities of a muon method for studying the diamagnetic domains accompanying the de Haas-van Alphen effect

This paper analyzes the capabilities of a muon (μSR) method for studying the de Haas-van Alphen effect and the diamagnetic domain structure accompanying it. It is shown that, unlike the NMR method, the μSR method makes it possible to observe the formation of a diamagnetic domain structure in all metals. It is not currently known what type of domain structure accompanies the de Haas-van Alphen effect: one-dimensional (laminar) or two-dimensional. It is shown that the line shape of the Fourier spectrum of the signal makes it possible to determine both the character of the domain structure (two-dimensional or laminar) and the magnetic field distribution in the domains.

Observation of diamagnetic domains in beryllium by muon spin rotation spectroscopy.

Spectroscopic evidence is given for the recurrent ``domain phase'' with oppositely magnetized regions in diamagnetic beryllium. A periodic splitting of the precession frequency of implanted muons in a Be single crystal was observed as the strength of the applied field $\mathbf{H}\ensuremath{\parallel}〈0001〉$ varied near ${H}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.74\mathrm{T}$. On sweeping $H$ downwards, the doublet emerges and persists within more than one third of each de Haas\char21{}van Alphen cycle, the positions of the lines fixed, with the lower frequency (diamagnetic) component gaining and the higher (paramagnetic) one losing intensity. The line splitting gives $\ensuremath{\Delta}B\ensuremath{\approx}29\mathrm{G}$ for the induction difference in domains at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.8\mathrm{K}$.