Disappearance Of Magnetization Research Articles

Hardening of 80CrV2 in Bladesmith Forge

Some bladesmiths have started to use 80CrV2 because V alloying helps with grain size. Smiths usually forge blades from unalloyed high carbon steels, but if Al deoxidation is not used, they are prone to grain growth. This work studies the forge hardening of 80CrV2 and C75 in the absence of Al. Specimens were heated in a gas-fired forge and austenitization was detected with a magnet. Both steel grades hardened when quenched after the disappearance of magnetism, but 80CrV2, due to Cr alloying, needed about 60°C higher temperature to attain maximum hardness. Grain growth did not start in 80CrV2 despite some overheating, while in C75 it started immediately after austenitization. The tests show that 80CrV2 attains easily good mechanical properties in forge hardening.

High-pressure study of topological semimetals XCd2Sb2 (X = Eu and Yb)

Topological materials have aroused great interest in recent years, especially when magnetism is involved. Pressure can effectively tune the topological states and possibly induce superconductivity. Here we report the high-pressure study of topological semimetals XCd2Sb2 (X = Eu and Yb), which have the same crystal structure. In antiferromagnetic (AFM) Weyl semimetal EuCd2Sb2, the Néel temperature (T N) increases from 7.4 K at ambient pressure to 50.9 K at 14.9 GPa. When pressure is above 14.9 GPa, the AFM peak of resistance disappears, indicating a non-magnetic state. In paramagnetic Dirac semimetal candidate YbCd2Sb2, pressure-induced superconductivity appears at 1.94 GPa, then T c reaches to a maximum of 1.67 K at 5.22 GPa and drops to zero at about 30 GPa, displaying a dome-shaped temperature–pressure phase diagram. High-pressure x-ray diffraction measurement demonstrates that a crystalline-to-amorphous phase transition occurs at about 16 GPa in YbCd2Sb2, revealing the robustness of pressure-induced superconductivity against structural instability. Similar structural phase transition may also occur in EuCd2Sb2, causing the disappearance of magnetism. Our results show that XCd2Sb2 (X = Eu and Yb) is a novel platform for exploring the interplay among magnetism, topology, and superconductivity.

Pressure-Induced Transition from Spin to Superconducting States in Novel MnN2.

The connection between magnetism and superconductivity has long been discussed since the discovery of Fe-based superconductors. Here, we report the discovery of a pressure-induced transition from a spin to a superconducting state in novel MnN2 based on ab initio calculations. The superconducting state can be obtained in two ways: the first is the pressure-induced transition from an AFM-P21/m to an NM-I4/mmm phase at 30 GPa, while the other is the pressure-induced transition from an FM-I4/mmm phase to magnetic vanishing at 14 GPa, which leads to a structural transition with the distortion of octahedrons to tetragonal pyramids. NM-I4/mmm-MnN2 is superconductive with Tc ≈ 17.6 K at 0 GPa. In the second way, electronic structure calculations indicate that the system transforms from a high-spin state to a low-spin state due to increasing crystal-field splitting, causing disappearance of magnetism; more electron occupancy around the Fermi level drives the emergence of superconductivity. Remarkably, I4/mmm-MnN2 can achieve mutual spin-to-superconducting state transformation by pressure. Moreover, the AFM-P21/m-MnN2 phase is extremely incompressible with the hardness above 20 GPa. Our results provide a reasonable and systematic interpretation for the connection between magnetism and superconductivity and give clues for achieving spin-to-superconducting switching materials with certain crystal features.

Magnetic Properties of Nickel-Titanium Alloy during Martensitic Transformations under Plastic and Elastic Deformation

This paper focuses on the processes of the occurrence of magnetization during structure formation in samples of Ni51Ti49 alloy under deformation conditions. The possibility of the existence of a phase with an FCC (face-centered cubic) lattice in titanium nickelide has been demonstrated by electron microscopy and electron diffraction. It has been discovered that the interplanar distances of BCC110 (body-centered cubic), FCC111, and HCP002 (hexagonal close packed) in the alloy under study have similar values, which indicates the possibility of their mutual polymorphic transformation. Based on the modular self-organization, a scheme of martensitic transformations in titanium nickelide from the B2 structure (BCC lattice) to the B19’ structure (HCP lattice) through an intermediate phase with an FCC lattice is proposed. It is shown that lenticular crystals appear in the Ni51Ti49 alloy under tensile deformation until rupture, which is accompanied by the onset of ferromagnetism. The effect of magnetization in Ni51Ti49 samples when immersed in liquid nitrogen has been also discovered. In this case, the reason for the appearance and disappearance of magnetization can be associated with microdeformation processes caused by direct and reverse martensitic transitions that occur during cooling and heating of the samples.

Effect of Cooling on the Occurrence of Magnetization in Titanium Nickelide

The occurrence of magnetization in alloys of the nickel-titanium system is still studied insufficiently. Our early work showed the possibility of magnetization arising during multiple cycles of forward and reverse martensitic transitions in the Ni51Ti49 alloy, as well as after deformation of this alloy by tensile stress to rupture. The purpose of this paper is devoted to revealing the effect of magnetization in samples of the Ni51Ti49 alloy as a result of their single cooling in liquid nitrogen, as well as the disappearance of magnetization when the samples are heated to room temperature. Using an induction hysteresigraph it is found out that the sample has a high magnetization immediately after cooling. As the sample is heated, the hysteresis loops change, acquiring a smaller inclination to the horizontal axis. It indicates a decrease in the magnetic induction to almost zero as the temperature rises to room temperature. The reason for the occurrence and disappearance of magnetization can be associated with micro-deformation processes related to forward and reverse martensitic transitions during cooling and heating of the samples.

First-principles study of the stability and edge stress of nitrogen-decorated graphene nanoribbons

Edge functionalization of graphene nanoribbons with nitrogen atoms for various adatom configurations at armchair and zigzag edges are investigated. We provide comprehensive information on the electronic and magnetic properties and investigate the stability of the various systems. Two types of rippling of the nanoribbons, namely edge and bulk rippling depending on the sign of edge stress induced at the edge, are found. They are found to play the decisive role for the stability of the structures. We also propose a type of edge decoration in which every third nitrogen adatom at the zigzag edges is replaced by an oxygen atom. In this way, the electron count is compatible with a full aromatic structure, leading to additional stability and a disappearance of magnetism that is usually associated with zigzag nanoribbons.

Evidence for a dimensionality crossover at the disappearance of magnetism in the Kondo lattice alloyCeCo1−xFexSi

Structural, magnetic, and thermal measurements performed on ${\mathrm{CeCo}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{Si}$ alloys are reported. Three regions can be recognized: (i) Co rich ($x\ensuremath{\le}0.20$) with a decreasing long-range antiferromagnetic order which vanishes at finite temperatures, (ii) an intermediate region ($0.20<x\ensuremath{\le}0.30$) showing a broad magnetic anomaly (${C}_{A}$) in specific heat, and (iii) the nonmagnetic region progressively changing from a non-Fermi-liquid-type behavior towards a Fermi-liquid one as Fe concentration increases. The ${C}_{A}$ anomaly emerges as an incipient contribution above ${T}_{N}$ already at $x=0.10$, which indicates that this contribution is related to short-range correlations likely of quasi-two-dimensional type. Both ${T}_{N}$ transition and ${C}_{A}$ anomaly are practically unaffected by an applied magnetic field up to $B\ensuremath{\approx}10\phantom{\rule{0.28em}{0ex}}\mathrm{T}$.

Substrate effects: Disappearance of adsorbate-induced magnetism in graphene

In this theoretical work, we show that substrates play key roles in the properties of layered systems such as graphene by focusing on magnetic properties associated with adsorbates. Local magnetic moments formed in fluorinated and hydrogenated graphene layers are quenched when they are deposited on a copper substrate due to several interconnected effects: doping by the substrate, increased structural distortion, and broadening of the defect states. We find that these effects contribute in different degrees to the changes in the structural, electronic and magnetic properties of the system and that they vary between adsorbates. The most important factor in the disappearance of magnetism in the functionalized graphene is shown to be the formation of metal-carbide bonds and the subsequent broadening of the impurity states that erases their spin splitting. We show that interactions with the substrate and the formation of local magnetic moments can be modified using multiple layers of graphene.

A Superparamagnetic State Induced by a Spin Reorientation Transition in Ultrathin Magnetic Films

We investigate a spin reorientation transition (SRT) in ultrathin magnetic films by Monte-Carlo simulations. We assume that the lateral size of the film is relatively small and it has a single-domain structure. To gain insights into the SRT, we measure a free-energy as a function of perpendicular and in-plane magnetizations. As a result, we find that the system is in a superparamagnetic state at the SRT temperature. The disappearance of magnetization around the SRT temperature, which is observed in experiments, emerges due to dynamical fluctuations in magnetization which are inherent in the superparamagnetic state. This observation is in contrast to that in large ultrathin magnetic films that the disappearance of magnetization is caused by a static magnetic structure with many complex domains.

X-Ray Magnetic Circular Dichroism Measurements in Ni up to 200 GPa: Resistant Ferromagnetism

The structural stability of fcc Ni over a very large pressure range offers a unique opportunity to experimentally investigate how magnetism is modified by simple compression. K-edge x-ray magnetic circular dichroism (XMCD) shows that fcc Ni is ferromagnetic up to 200 GPa, contradicting recent predictions of an abrupt transition to a paramagnetic state at 160 GPa. Density functional theory calculations point out that the pressure evolution of the K-edge XMCD closely follows that of the p projected orbital moment rather than that of the total spin moment. The disappearance of magnetism in Ni is predicted to occur above 400 GPa.

Nonequilibrium phase transitions in ferromagnetic semiconductors (EuO1–δ)

The features of metal-semiconductor kinetic phase transformation in ferromagnetic semiconductors are studied. It is shown that heat release caused by current results in a positive feedback between the current density and the sample temperature, magnetization, and thermal-spin fluctuation amplitude. The Joule heating of the sample leads to disappearance of magnetization and, as a result, to restoration of the forbidden band between the conduction and valence bands. However, the energy gap width continues to change due to an increase in the fluctuations of internal exchange fields splitting the electron states. Within the framework of the developed model, an S-shaped volt-ampere characteristic is obtained for a EuO 1-δ , ferromagnetic semiconductor. The lower branch of the characteristic corresponds to a ferromagnetic metal state (a “cold” phase) and the upper one is due to a semiconductor paramagnetic state (a “hot” phase).

Origin of magnetic moments in i-Al–Pd–Mn quasicrystal

Abstract Using ab-initio density-functional methods in the generalized gradient approximation we have investigated the origin of magnetic moments on Mn atoms in icosahedral (i) Al–Pd–Mn quasicrystals. Two major mechanisms contribute to the formation of magnetic moments on Mn atoms located at special sites – loosely packed environments of the Mn atoms and the interaction of the Mn atoms with nearest-neighbor Pd atoms leading to a shift of the Mn d-band to lower binding energies and an increased partial density of states at the Fermi level. Mn–Pd nearest neighbors exist only at special sites located at intersections of the pseudo-Mackay and the Bergman clusters building the icosahedral structure. A change in the chemical decoration of these sites can lead to a complete disappearance of magnetism in i-Al–Pd–Mn. Total energy calculations show that the models with a chemical ordering disfavoring moment formation on Mn atoms are also lowest in energy.

Quenching of the magnetic moment of Cr inRCr2Si2compounds upon filling with carbon

Structural and magnetic properties of the $R{\text{Cr}}_{2}{\text{Si}}_{2}\text{C}$ compounds ($R=\text{Y}$, La--Sm, Gd--Er) with the carbon-filled ${\text{CeMg}}_{2}{\text{Si}}_{2}$-type structure (space group $P4/mmm$) have been studied by means of powder and single-crystal x-ray diffractions, magnetic measurements, and neutron powder diffraction. The compounds with $R=\text{Pr}$, Nd, Gd--Dy order ferromagnetically at low temperature $({T}_{C}\ensuremath{\le}35\text{ }\text{K})$, whereas those with $R=\text{Y}$, La, Ce, and Sm do not exhibit any magnetic ordering down to 2 K. On the contrary, the ``parent'' ${\text{ThCr}}_{2}{\text{Si}}_{2}$-type (space group $I4/mmm$) $R{\text{Cr}}_{2}{\text{Si}}_{2}$ compounds ($R=\text{Y}$, Sm, Tb--Lu) exhibit strong antiferromagnetic properties $({T}_{N}>600\text{ }\text{K})$ linked to a large magnetic moment $(\ensuremath{\sim}1.9\text{ }{\ensuremath{\mu}}_{B})$ on the Cr sublattice. In order to better understand the role played by carbon on structural and magnetic properties in these systems, ab initio electronic structure calculations of $R{\text{Cr}}_{2}{\text{Si}}_{2}$ and $R{\text{Cr}}_{2}{\text{Si}}_{2}\text{C}$ compounds with $R=\text{Y}$ and La have been performed, using the Korringa-Kohn-Rostoker (KKR) method, in the ${\text{ThCr}}_{2}{\text{Si}}_{2}$- and ${\text{CeMg}}_{2}{\text{Si}}_{2}$-types as well as their corresponding C-``filled'' types, with C atoms located in Cr (001) planes. This study has allowed elucidating the particular role of carbon in the breakdown of the local magnetic moment on the Cr sublattice. KKR calculations clearly evidence that strong hybridization between $d$ states on Cr atoms and $p$ states on C atoms leads to a marked decrease in the density of states in the vicinity of ${E}_{F}$ (well below the Stoner limit). Since similar electronic structure modifications are observed whatever the crystal structure, we tentatively conclude that the Cr-C interactions are more predominant in the disappearance of magnetism in $R{\text{Cr}}_{2}{\text{Si}}_{2}\text{C}$ than the effect of the rearrangement of Si and $R$ atomic planes when passing from the ${\text{ThCr}}_{2}{\text{Si}}_{2}$ type to the ${\text{CeMg}}_{2}{\text{Si}}_{2}$-type structure. Moreover, KKR calculations with the coherent-potential approximation undertaken for the ``model'' $R{\text{Cr}}_{2}{\text{Si}}_{2}{\text{C}}_{x}$ system $(0\ensuremath{\le}x\ensuremath{\le}1)$ well illustrate the evolution of the electronic structure and magnetic properties upon increasing carbon concentration.

POLARIZATION OF DIFFERENT INTERFACES OF Rh AND Ag STUDIED BY RECURSION TECHNIQUES

We investigate the reasons for the discrepancy between experimental and theoretical findings concerning the onset of magnetic moment when Rh , which is nonmagnetic in the bulk form, is coated on Ag (001). To perform the calculation we use a recently developed recursion method in the reciprocal space for the derivation of the density of states of multilayered systems. The local magnetic moments are deduced versus the exchange integral J. We found that a single-monolayer of Rh epitaxially grown on Ag (001) presents a high magnetic moment. This magnetic moment decreases when the Rh monolayer is covered by a Ag overlayer. However, the magnetic moment is not entirely killed as obtained also previously by recent full-potential linearized-augmented-plane-wave calculations. Therefore, there seems to be, discrepancy with recent surface-magneto-optic-Kerr effect experiments which have not detected any long-range order in the case of a monolayer of Rh on Ag (001). We study intermixing effects between Rh and Ag using different model structures containing ordered Ag .50 Rh .50 layers. The disappearance of magnetism in experimentally studied samples can be explained by such intermixing effects.

MAGNETOVOLUME EFFECTS IN Fe3Pt

Equilibrium values of the energy for the magnetic and non-magnetic structures were derived for Fe3Pt using the scalar relativistic ASW method. The stable ground state is found to be ferromagnetic. Calculations were extended to obtain total energy curves as a function of moment and volume via the FSM method. Results were fitted using a polynomial in M and V within a Landau-Ginzburg model of spin fluctuations. Relevant properties to Invar such as the magnetic contribution to the thermal expansion coefficient and the critical pressure for the disappearance of magnetism and its pressure dependence were derived.

Volume collapse in the Kondo lattice

The α-γ transition of Ce and its compounds are explained within a compressible Kondo lattice model where the variation of | J|/ D with volume is taken into account. We show that, contrary to the valence change model, the Kondo contribution is sufficient to induce a first order transition at low temperature from a magnetic to a Kondo phase. The disappearance of magnetism is then related to an extremely high Kondo temperature. Applications to Ce and CeAl 2 cases are given.

On the dissymmetry of mossbauer spectra in iron-nickel alloys

Valuable information about the disappearance of magnetism in the invar region (concentration of 30–45 pct of nickel) may be obtained by the examination of Mössbauer spectra. I–5 However, it appears that some characteristics of these spectra are already present in non invar spectra have not been taken in account up to now: even in a 50 pct alloy, the six lines have anomalous widths and heights, and it is the aim of this note to put a quantitative interpretation of this fact, letting for the future the extension to invar spectra.