Study Of Magnetic Phase Transitions Research Articles

Study of magnetic phase transitions by helium-3 in DyF3 nanoparticles

The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.7 %) and DyF3 (0.3 %) powders at temperatures of 1.5–3 K was studied by pulsed nuclear magnetic resonance. DyF3 particles have ellipsoidal shape and average size 225 × 153 nm with the magnetic phase transition at temperature Tc = 2.45 K. The temperature dependence of the longitudinal and transverse magnetization relaxation rates of 3He nuclei with a mixture of LaF3 and DyF3 powders has a broad maximum near Tc, which is related to the magnetic phase transition. It is shown that the adsorbed layer of 3He is extremely sensitive to magnetic phase transitions. Preplating the particles surface with adsorbed nitrogen layers allowed to vary the distance from 3He nuclei to the surface of particles in a controlled way. Calculations of the nuclear magnetic relaxation rates with a change in the distance of helium-3 from the particle surface have been carried out, which is in good agreement with experimental data. It was shown that helium-3 is extremely sensitive to surface magnetism and can be used to study surface effects and surface magnetism.

A Study of Magnetic Phase Transitions in Nickel Zinc Ferrites with Differing Structure

A Study of Magnetic Phase Transitions in Nickel Zinc Ferrites with Differing Structure

Influence of static correlation on the magnon dynamics of an itinerant ferromagnet with competing exchange interactions: First-principles study of MnBi

We present first principles calculations of the dynamic susceptibility in strained and doped ferromagnetic MnBi using time-dependent density functional theory. In spite of being a metal, MnBi exhibits signatures of strong correlation and a proper description in the framework of density functional theory requires Hubbard corrections to the Mn $d$-orbitals. To permit calculations of the dynamic susceptibility with Hubbard corrections applied to the ground state electronic structure, we use a consistent rescaling of the exchange-correlation kernel maintaining the delicate balance between the magnon dispersion and the Stoner continuum. We find excellent agreement with the experimentally observed magnon dispersion for pristine MnBi and show that the material undergoes a phase transition to helical order under application of either doping or strain. The presented methodology paves the way for future LR-TDDFT studies of magnetic phase transitions, also for the wide range of materials with pronounced static correlation effects that are not accounted for at the LDA level.

Kerr Microscopy Study of Magnetic Phase Transition in Fe49Rh51

Kerr Microscopy Study of Magnetic Phase Transition in Fe49Rh51

Neutron diffraction studies of magnetic phase transition in mixed (Mn(1-x) Fe(x) WO(4))

Энэ ажилд Вольфрамитын кристалл болон соронзон бүтцийг рентген туяа, дулааны нейтроны сарнилын тусламжтайгаар судлав. Мөн (Mn1-xFex)W04-ийн бага температурт үүсэх соронзон фазын шилжилтийг ажиглаж, соронзон бүтцийг илэрхийлэх параметрүүдийг х=0; 6 утгуудад фаз бурт тодорхойлон харьцуулав.

Unusual magnetic phenomena in dynamic torsion studies of fullerene Rb3C60

In dynamic experiments using a highly sensitive torsion technique, the magnetic properties of the doped Rb3C60 single crystal are studied over a wide temperature range. The critical temperature of the superconducting transition Tc, the critical magnetic field Hc1, the pinning forces of both the Abrikosov vortices and the magnetic moments of dipoles at T >> Tc, at which relaxation processes are important, are determined and investigated. It was shown that the structural transition Fm3m-Pa3 at T = 260 K is accompanied by a reformation of the magnetic structure. Both the usual peaks at T ∼ 160–250 K and the not quite ordinary peaks of gigantic absorption of the energy of the oscillations, which shift to room temperature over time, were observed. The phenomenon is discussed in the framework of the cooperative Jahn-Teller effect, taking into account possible orbital and spin ordering. The relaxation processes at room temperatures (T ∼ 300 K) were studied. After many days of exposure (annealing) of fullerene at T ≥ 40 °C, in experiments with cooling from room temperatures, phenomena typical for a superconducting transition with giant pinning and damped oscillations were observed at T ∼ 200 K. The results of studies of magnetic phase transitions at T = 180–200 K in pure fullerite C60 (99.98% Term. Sublimed), which are related to the detected unusual magnetic phenomena in fullerene Rb3C60, are presented.

Studies of magnetic phase transitions in orthorhombic DyMnO3 ceramics prepared by acrylamide polymer gel template method

Abstract Single phase polycrystalline DyMnO3 (DMO) was synthesized using acrylamide polymer gel template method. We report the structural, magnetic, specific heat and dielectric properties of DMO over wide experimental conditions. Room temperature XRD pattern shows the formation of singe phase material without any impurity. The magnetic properties such as magnetization versus temperature (M vs. T) and magnetization versus magnetic field (M vs. H) were studied around the transition temperatures region. The temperature dependent magnetization data suggest two phase transitions corresponding to the lock-in temperature below which ferroelectric ordering exist (around 19 K; Tlock) and antiferromagnetic (AFM) ordering of Dy spin (around 8 K; TN (Dy)). The magnetic hysteresis obtained were fitted to extract weak ferromagnetic (FM) and antiferromagnetic/paramagnetic (AFM/PM) contribution to the magnetic data. The order of magnetic transitions were analyzed from Arrott plot. The temperature dependent specific heat measurement shows all three phase transitions corresponding to (i) AFM ordering of Mn spin (around 38 K; TN(Mn)), (ii) Tlock transition and (iii) TN(Dy) transition. The effect of magnetic field to the transitions were studied using specific heat capacity measurement. The peak intensity of TN(Dy) decreases on the application of magnetic field whereas peak intensity of Tlock increases with increase in magnetic field in specific heat measurement. Further the third anomaly, TN (Mn) remains more or less unaffected by the application of magnetic field. The intrinsic dielectric behaviour of the material was observed up to 160 K, above this temperature there is large increase in dielectric value due to the contribution from Maxwell- Wagner polarization.

Scaling study of magnetic phase transition and critical behavior in Nd0.55Sr0.45Mn0.98Ga0.02O3 manganite

Microscopic magnetic interactions and magnetism can be probed by studying the critical paramagnetic–ferromagnetic phase transition of magnetic materials. In this work, the critical behavior of the lightly Ga-doped manganites Nd0.55Sr0.45Mn0.98Ga0.02O3 (NSMGO) has been investigated. Scaling analysis reveals the critical exponents β=0.308, γ=1.197, and δ=4.916, where their self-consistency and reliability are verified by the Widom scaling law and the scaling equation. These exponents indicate that the magnetic phase transition in NSMGO belongs to the anisotropic 3D-Ising universality class. Nevertheless, the asymptotic critical exponents βeff and γeff are found to approach to the values of 3D-Heisenberg model, implying the existence of isotropic short-range magnetic interactions. We suggest that, although the Nd-based manganites possess a strong magnetocrystalline anisotropy, this effect can be partly averaged out in view of the present polycrystalline NSMGO. Therefore, in the asymptotic critical region, the phase transition reveals the crossover from the scaling of 3D-Ising toward 3D-Heisenberg universality class.

Magnetic phase transitions in ZnO doped by transition metals

AbstractIn this work we present the results on experimental study of magnetic phase transitions in ZnO thin films doped by Mn and Co by using the thermal diffusivity and specific heat measurements. The inverted lambda‐shaped peaks observed in the temperature dependencies of the thermal diffusivity demonstrate the existence of the second order phase transitions in these samples. The magnetic entropy derived from the specific heat gives the number of magnetic ions involved in the magnetic ordering. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

31P NMR study of magnetic phase transitions of MnP single crystal under 2 GPa pressure

Superconductivity on the border of the long-range magnetic order has been discovered in MnP under high pressures. In order to investigate the nature of the magnetic properties adjacent to the superconducting state, we performed zero-field 31P NMR for MnP single crystal under ambient and hydrostatic pressure of 2 GPa, respectively. Radio frequency power level was used to determine whether NMR signal originates from a helical state or not. When 2 GPa pressure was applied, the signal from helical state exists even above 160 K, while that from the ferromagnetic phase was not observed. Our NMR results indicate that the magnetic phase which is adjacent to the superconducting state is in a helical magnetic structure.

Bethe Approximation in the Theory of "Average Spin"

The modeling study of magnetic phase transition with account of short-range order has been carried out in the approximation of random interaction between atomic magnetic moments of the nearest neighbours and in the frame of Ising model. Curie temperature has been calculated for different kinds of crystalline lattice.

Theoretical study of magnetic phase transitions of cubic SrMnO3 under physical and chemical pressures

A magnetic configuration phase transition from antiferromagnetic (AFM) to ferromagnetic (FM) ordering is observed in cubic SrMnO3 under negative pressure of −9GPa by density functional calculations, while the ground state of G-type AFM ordering is maintained under the positive pressure. To realize the negative pressure, SrMnO3 with chemical pressure by Sr site doping of Ba and La ions is further investigated, respectively. It is found that the required negative pressure is reduced by ∼1GPa for the cubic SrMnO3 favoring FM configuration when doped with Ba, though it keeps C- or G-AFM under positive pressures. In addition, the stability of G-AFM configuration is destroyed in cubic SrMnO3 when doped with La under various pressures.

AC Susceptibility Studies of Phase Transitions and Magnetic Relaxation: Conventional, Molecular and Low-Dimensional Magnets

The paper presents the review of AC susceptibility measurements in study of magnetic phase transitions and spin dynamics. Examples of several types of phase transitions in conventional and molecular magnets are shown. The phenomenon of magnetic relaxation is brie y ascribed and illustrated with results on relaxation in low-dimensional molecular magnets, such as single molecule magnets, single chain magnets and quasi 1-dimensional systems showing magnetic phase transition to the long-range ordered phase. The following experimental possibilities of the AC technique, which allow to get insight into properties of novel magnetic materials are mentioned: (i) change of the AC eld amplitude (in order to distinguish ferro-(ferri) and antiferromagnets); (ii) use of a static eld HDC (to conclude on the type of magnetic order and to study the phase diagram); (iii) measurement of nonlinear susceptibilities (to conclude on the type of phase transition); (iv) probing the dependence of both components of susceptibility on frequency of the AC eld (to study magnetic relaxation); (v) tests of the DC eld e ect on the frequency dependence of χAC (to analyze the possibility of blocking or reentrant spin-glass transition).

Magnetic phase transitions in Gd64Sc36 studied using non-contact ultrasonics

The speed and attenuation of ultrasound propagation can be used to determine material properties and identify phase transitions. Standard ultrasonic contact techniques are not always convenient due to the necessity of using couplant; however, recently reliable non-contact ultrasonic techniques involving electromagnetic generation and detection of ultrasound with electromagnetic acoustic transducers (EMATs) have been developed for use on electrically conducting and/or magnetic materials. We present a detailed study of magnetic phase transitions in a single crystal sample of Gd64Sc36 magnetic alloy using contact and non-contact ultrasonic techniques for two orientations of external magnetic field. Phase diagrams are constructed based on measurements of elastic constant C33, the attenuation and the efficiency of generation when using an EMAT. The EMATs are shown to provide additional information related to the magnetic phase transitions in the studied sample, and results identify a conical helix phase in Gd64Sc36 in the magnetic field orientation .

Study of Magnetic Phase Transition in Diluted Nanostructure Spinel Ferrites

The magnetic properties of CoFe2−2xCr2xO4 spinels are studied by different theoretical methods: the mean field theory, the high-temperature series expansions (MFT, HTSE) and the probability distribution law with the different size L (nm). The exchange interactions and the critical temperature Tc (K) are given for the nano-spinel ferrites. The magnetic phase diagram of CoFe2−2xCr2xO4 is deduced. The saturation magnetization, the coercivity field and magnetic energy are obtained.

Calorimetric Study of Magnetic Phase Transition at High Pressures

Calorimetric Study of Magnetic Phase Transition at High Pressures

Study of Magnetic Phase Transition and Spin Frustration in Cobalt Aluminium Oxide Materials based on High Temperature Series Expansions Model

The magnetic properties of CoAl2−2xCo2xO4 for 0 ≤ x ≤ 1 are studied. The values of the nearest neighbour (J1), next‐nearest neighbour (J2), intra‐plane (Jaa) and inter‐plane (Jab,Jac) exchange interactions are calculated by the mean field theory for ordered region and by the probability law adapted of the nature of dilution problem in A‐spinel lattice in spin glass region. The high‐temperature series expansions have been applied in the CoAl2−2xCo2xO4 systems, combined with the Padé approximants method, to determine the Néel temperature TN (K) or freezing temperature TSG (K) in the range 0 ≤ x ≤ 1. The critical exponents associated with the magnetic susceptibility (y) and the correlation lengths (v) are deduced in the range ordered 0.3 ≤ x ≤ 1. The obtained values of y and v are insensitive to the dilution ratio x and may be compared with other theoretical results based on 3D Heisenberg model.

Study of magnetic phase transitions and magnetic structures in a number of rare-earth ferroborates using an erbium spectroscopic probe

This paper discusses exchange splitting in the spectra of Er3+ introduced as a spectroscopic probe in rare-earth ferroborates RFe3(BO3)4(R=Y,Er,Tb,Gd). The temperatures of magnetic ordering are determined [38±1 K for YFe3(BO3)4, 39±1 K for ErFe3(BO3)4, 41±1 K for TbFe3(BO3)4, 37±1 K for GdFe3(BO3)4] and the spin-reorientation transition in GdFe3(BO3)4: TR=7.5±0.5 K. Based on a comparison of the Er3+ spectra in GdFe3(BO3)4, the magnetic structure of which is known, and in other ferroborates, a conclusion is made concerning the orientation of the magnetic moments of iron MFe in the magnetically ordered state: MFe⊥c for yttrium and erbium ferroborates, and MFe||c for terbium ferroborate.

Magnetic X‐Ray Microdiffraction

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Ab initio Studies of Structure and Magnetic Structure in YCo3H2.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.