Pressure-induced Magnetic Transition Research Articles

Pressure-induced magnetic and topological transitions in non-centrosymmetric MnIn2Te4

In recent years, the study of magnetic topological materials, with their variety of exotic physics, has significantly flourished. In this work, we predict the interplay of magnetism and topology in the non-centrosymmetric ternary manganese compound MnIn2Te4under external hydrostatic pressure, using first-principles calculations and symmetry analyses. At ambient pressure, the ground state of the system is an antiferromagnetic insulator. With the application of a small hydrostatic pressure (∼0.50 GPa), it undergoes a magnetic transition, and the ferromagnetic state becomes energetically favorable. At ∼2.92 GPa, the ferromagnetic system undergoes a transition into a Weyl semimetallic phase, which hosts multiple Weyl points in the bulk. The presence of non-trivial Weyl points have been verified by Wilson bands computations and the presence of characteristic surface Fermi arcs. Remarkably, we discover that the number of Weyl points in this system can be controlled by pressure and that these manifest in an anomalous Hall conductivity (AHC). In addition to proposing a new candidate magnetic topological material, our work demonstrates that pressure can be an effective way to induce and control topological phases, as well as AHC, in magnetic materials. These properties may allow our proposed material to be used as a novel pressure-controlled Hall switch.

Pressure-Induced Phase Diagram and Electronic Structure Evolves during the Insulator-Metal Transition of Bulk BiFeO3.

BiFeO3 is the most widely known multiferroic at room temperature, possessing both ferroelectricity and antiferromagnetism. It has high Curie temperature and Néel temperature, i.e., 1103 and 643 K, respectively. Despite these unique properties, the pressure-induced phase diagram of bulk BiFeO3 has remained controversial. Based on the ab initio evolutionary algorithm, we systematically searched for the potential stable structures of bulk BiFeO3 at 0-50 GPa. It is identified that there are five pressure-induced phase transition sequences R3c-G-AFM →(5GPa) C2/m-G-AFM →(15GPa) Pnma-G-AFM →(24GPa) Pnma-FM →(35GPa) Imma-FM →(45GPa) Cmcm-FM, which provided a comprehensive pressure-induced phase diagram. As the pressure increases, we discovered an interesting phenomenon: a pressure-induced magnetic sequence transition, i.e., BiFeO3 transitions from an antiferromagnetic to a ferromagnetic sequence. Concurrently, the electronic structure evolves during the insulator-metal transition, influenced not only by the pressure but also by the phase transition. Our research has elucidated the long-standing question of the phase transition sequence of the BiFeO3 system under pressure and provided theoretical support for the insulator-metal transition.

Raman spectroscopy investigation on the pressure-induced structural and magnetic phase transition in two-dimensional antiferromagnet FePS3

The layered van der Waals antiferromagnetic FePS3 has received considerable attention because long range magnetic ordering can remain with single atoms layer, which offers potential applications in future ultrathin devices. Here, we perform Raman spectroscopy to systematically explore the variations of lattice vibration and crystal structure under pressure up to 18.9 GPa. We observe two structural phase transitions at approximately 4 GPa and 13 GPa, respectively. Moreover, by monitoring spin-related Raman modes, we demonstrate a pressure-induced magnetic structure transition above 2 GPa. These modes disappear accompanying the second structural phase transition and insulator-to-metal transition (IMT), indicating the suppression of long-range magnetic ordering, in agreement with earlier neutron powder diffraction experiments.

Valence transition in topological Kondo insulator

We investigate the valence transition in three-dimensional topological Kondo insulator through slave-boson analysis of periodic Anderson model. By including the effect of intra-atomic Coulomb correlation between conduction and local electrons, we find a first-order valence transition from Kondo region to mixed valence state upon ascending of local f- level above a critical , and this valence transition usually occurs very close to or simultaneously with a topological transition. Near the parameter region of zero-temperature valence transition, rise of temperature can generate a thermal valence transition from mixed valence to Kondo region, accompanied by a first-order topological transition. Remarkably, above a critical which is considerably smaller than that generating paramagnetic valence transition, the original continuous antiferromagnetic transition is shifted to first order one, at which a discontinuous valence shift takes place. Upon increasing , the paramagnetic valence transition approaches then converges with the first-order antiferromagnetic transition, leaving a significant valence shift on the magnetic boundary. The continuous antiferromagnetic transition, first-order antiferromagnetic transition, paramagnetic valence transition and topological transitions are all summarized in a global phase diagram. Our proposed exotic transition processes can help to understand the thermal valence variation as well as the valence shift around the pressure-induced magnetic transition in topological Kondo insulator candidates and in other heavy-fermion systems.

Pressure-induced magnetic transition in Nd2Fe14B based on two-sublattice model

To analyze the magnetic properties of Nd2Fe14B compound under high pressure, an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on magnetization, magnetostriction coefficient, susceptibility and Curie temperature. The calculation results show that the pressure has a stronger effect on the magnetization of Fe sublattice compared to that of Nd sublattice at varied temperatures when the external magnetic field is parallel to the alignment direction. Saturated magnetization, initial susceptibility and magnetic moment of Nd2Fe14B compound are found to decrease gradually with pressure increasing, and the Curie temperature of Nd2Fe14B decreases to about 298 K under an applied pressure of 1.15 GPa. The results suggest that the pressure-induced magnetic phase transition of Nd2Fe14B occurs under 1.15 GPa at room temperature.

Pressure-induced structural, magnetic and transport transitions in Sr2FeO3 from first-principles

The serial system Srn+1FenO2n+1(n=1,2,3…) with the FeO4 square planar motif exhibits abundant phase transitions under pressure. In this work, we investigate the pressure-induced structural, magnetic and transport transitions in Sr2FeO3 from first-principles. Our results show that the system undergoes a structural transition from Immm to Ammm when the volume decreases by 30%, together with a spin-state transition (SST) from high-spin (S = 2) to intermediate-spin (S = 1), an antiferromagnetic-to-ferromagnetic transition and an insulator-to-metal transition (IMT). Besides, the IMT here is a bandwidth controlled transition, but little influenced by the SST.

Pressure-induced magnetic transition exceeding 30 K in the Yb-based heavy-fermion β−YbAlB4

Measurements of the electric resistivity $\rho(T)$ under pressure up to 8 GPa were performed on high-quality single-crystals of the Yb-based heavy fermion system $\beta$-YbAlB$_4$ in the temperature range $2<T<$ 300 K. In the resistivity data, we observed pressure-induced magnetic ordering above the critical pressure $P_{\rm c} \sim$ 2 GPa. Clear difference in the phase diagram under pressure using two types of pressure mediums indicates that the transition temperature may be further enhanced under application of uniaxial pressure. With pressure, this phase transition temperature $T_{\rm M}$ is enhanced reaching 32 K at 8 GPa, which is the highest transition temperature so far recorded for the Yb-based heavy fermion compounds. The power-law exponent $\alpha$ in $\rho=\rho_0+ AT^{\alpha}$ below $T_{\rm M}$ gradually changes from 3/2 to 5/2 with increasing pressure from 2 to 8 GPa. In contrast, the resistivity exhibits a $T$-linear behavior in the temperature range 2 $\le T \le$ 20 K and is insensitive to pressure below $P_{\rm c}$. In this pressure regime, the magnetization is also nearly independent of pressure and shows no anomaly above 2 K. Our results indicate that a quantum critical point for $\beta$-YbAlB$_4$ is also located near $P_{\rm c}$ in addition to the strange metal region near the ambient pressure.

Pressure-induced magnetic transitions with change of the orbital configuration in dimerised systems.

We suggest a possible scenario for magnetic transition under pressure in dimerised systems where electrons are localised on molecular orbitals. The mechanism of transition is not related with competition between kinetic energy and on-site Coulomb repulsion as in Mott-Hubbard systems, or between crystal-field splitting and intra-atomic exchange as in classical atomic spin-state transitions. Instead, it is driven by the change of bonding-antibonding splitting on part of the molecular orbitals. In the magnetic systems with few half-filled molecular orbitals external pressure may result in increase of the bonding-antibonding splitting and localise all electrons on low-lying molecular orbitals suppressing net magnetic moment of the system. We give examples of the systems, where this or inverse transition may occur and by means of ab initio band structure calculations predict that it can be observed in α−MoCl4 at pressure P ~ 11 GPa.

Pressure-induced structural and magnetic transitions in the infinite-chains iron oxide Sr2FeO3: a first-principle investigation

The pressure-induced transition of Sr2FeO3 was studied by first-principle calculation using density functional theory with the generalized gradient approximation plus on-site coulomb repulsion method. It shows that Sr2FeO3 exhibits a structure transition from Immm to Ammm and at about 35 GPa and then a spin transition from high spin S = 2 to intermediate spin S = 1. And it is also revealed that the pressure leads to a change in the Fe three-dimensional electronic configuration from ()1()1()1()1()1 ()1 under ambient conditions to ()1()1()1()1 ()δ()1 ()σ at high pressure, where δ plus σ equals 1.

First Principles Study of Electronic Structure, Magnetic, and Mechanical Properties of Transition Metal Monoxides TMO(TM=Co and Ni)

Abstract The ground-state properties, electronic structure, magnetic and mechanical properties of cobalt oxide (CoO) and nickel oxide (NiO) are investigated using generalised gradient approximation parameterised by Perdew–Burke–Ernzerhof (GGA-PBE) and GGA-PBE+U formalisms. These oxides are found to be stable in the antiferromagnetic (AFM) state at normal pressure. The computed lattice parameters are in agreement with the experimental and other theoretical works. Pressure-induced magnetic transition from AFM to ferromagnetic (FM) state is predicted in NiO at a pressure of 84 GPa. Both these compounds are found to be mechanically stable in the AFM state at normal pressure.

&lt;i&gt;Ab&lt;/i&gt; &lt;i&gt;Initio&lt;/i&gt; Study of Pressure-Induced Structural Properties of Uranium Chalcogenides

We report a first principles calculation of pressure-induced structural phase transition properties of uranium chalcogenides (UX; X=S, Se and Te). The total energies as a function of volume are obtained by means of self-consistent tight binding linear muffin orbital method (TB-LMTO) by performing spin and non-spin polarized calculations to determine the magnetic and structural stabilities. From the present study, we predict a magnetic phase transition from ferromagnetic (FM) to non-magnetic (NM) state around 67.7 and 10.2 GPa for US and USe, respectively. The pressure-induced magnetic transitions are found second-order in nature. We have also predicted structural phase transition from FM-NaCl-type (B1phase) structure to NM-CsCl-type (B2phase) structure at around 77.5, 23.5 for US and USe, respectively, while UTe undergoes from FM-B1to FM-B2phase around 12.0 GPa.

Ferromagnetic materials under high pressure in a diamond-anvil cell: A magnetic study

A magnetic-parameter measurement system for study of ferromagnetic materials under high pressure using a diamond-anvil cell is built. The factors affecting the measurement sensitivity are analyzed and the possibility of improving the sensitivity is mentioned. Based on the system, the magnetization curves of iron as a function of pressure are obtained. The start point and end point of pressure-induced magnetic transition of iron are observed at room temperature.

Effect of High Pressure on Magnetic Properties of C Doped Alkaline-Earth Oxides

The first-principles plane wave pseudopotential method within the generalized gradient approximation (GGA) is used to calculate the magnetic moment, volume, total energy of C doped alkaline-earth oxides X4CO3 (X=Ca, Sr, and Ba) and band structure, electronic state density of Ca4CO3 at ambient as well as at high pressure. Results show that the X4CO3 ferromagnetism decreases, and finally the second-order magnetic phase transition occurs from ferromagnetic (FM) to nonmagnetic (NM) state when increasing the pressure. The main reason of the pressure-induced magnetic transition and the magnetic collapse result from band widening in anion p states. At 69 GPa, the spin contribution of C atoms in Ca4CO3 decreases remarkably. This is due to the C–p in which majority spin states are increased while minority spin states are decreased.

Instability of Co Spin Moment in ErCo2 Probed by Magnetic Compton Scattering under High Pressure

Magnetic Compton scattering at high pressure is presented for the first time. To study the pressure-induced magnetic transition in Laves-phase ErCo 2 , Er 4 f and Co 3 d spin magnetic moments, together with the conduction electron component, were separately and quantitatively estimated at pressures up to 1.84 GPa. The Co 3 d spin moments show a remarkable reduction with increasing pressure, which is in contrast to the weak pressure variation of the Er 4 f spin moment. The relationship between the magnetic transition and instability of the Co 3 d moment at high pressure is discussed from the viewpoint of lattice contraction and the molecular field of Er 4 f moments.

Thermoelastic property and high-pressure stability of Fe7C3: Implication for iron-carbide in the Earth's core

To investigate the physical property of Fe7C3, we carried out in situ X‑ray diffraction experiments using a Kawai-type multi-anvil apparatus and a diamond anvil cell up to 71.5 GPa and 1973 K. The carbide was found to be stable under these experimental conditions. However, we found anomalous behavior in its isothermal compression and thermal expansivity. These anomalies could be due to the magnetic phase transition in Fe7C3 from a ferromagnetic (fm) to a paramagnetic (pm) phase. The Curie temperature of 523 K at 1 bar (Tsuzuki et al. 1984) decreases with pressure, and the pressure-induced magnetic transition is estimated to occur at ~18 GPa and 300 K. The pressure-volume-temperature (P-V-T) data set for the pm-Fe7C3 was fitted by the Mie-Grüneisen-Debye (MGD) equation of state (EOS) and the following parameters were obtained: unit-cell volume V0 = 184.2 ± 0.3 Å3, bulk modulus K0 = 253 ± 7 GPa, the pressure derivative of bulk modulus K'0 = 3.6 ± 0.2, Grüneisen parameter γ0 = 2.57 ± 0.05, Debye temperature θ0 = 920 ± 140 K, and q = 2.2 ± 0.5, respectively, at zero pressure. The calculated density for Fe7C3 provides a good explanation for the density of the Earth’s inner core obtained from seismological observations.

First principles study of pressure-induced magnetic transition in CrN

First principles calculation was performed using tight-binding LMTO method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of chromium nitride. The equilibrium geometries, the magnetic moment, the electronic band structure, the total and partial DOS are obtained under various pressures and are analyzed in comparison with the available experimental data. The most stable structure of CrN is NaCl structure in the FM state. A pressure-induced second order magnetic phase transition from ferromagnetic (FM) to non-magnetic (NM) at very high pressure of 0.5549Mbar is predicted. Our results indicate that CrN can be used as a hydrogen storage material.

Absence of abrupt pressure-induced magnetic transitions in magnetite

The structural properties of magnetite ${\text{Fe}}_{3}{\text{O}}_{4}$ under pressure have been extensively studied and are well established. This is not the case for its electronic and magnetic properties. We report a high-pressure x-ray magnetic circular dichroism study of magnetite up to 41 GPa. We observe a continuous evolution of the magnetic moment in the whole pressure range, in agreement with a band-structure description of the electronic state of magnetite. We highlight distinct regimes of magnetism. The x-ray absorption spectra do not suggest any major modification in the local structure in this pressure range.

Competition between ferromagnetic and antiferromagnetic ground states in multiferroicBiMnO3at high pressures

The crystal and magnetic structures of ${\text{BiMnO}}_{3}$ were studied at high pressures up to 10 GPa by means of neutron diffraction in the temperature range 2--300 K. Three structural modifications, two monoclinic and one orthorhombic were found to exist in the pressure range studied and their structural parameters were determined. A suppression of the initial ferromagnetic state and formation of a new antiferromagnetic state with a propagation vector (1/2 1/2 1/2) was observed at $P\ensuremath{\sim}1\text{ }\text{GPa}$, accompanied with the monoclinic-monoclinic structural transformation. Possible mechanisms of the pressure-induced magnetic transition and origin of magnetoelectric phenomena in ${\text{BiMnO}}_{3}$ are discussed.

High-pressure magnetic transition in hcp-Fe

High-pressure experiments and ab initio calculations on the hexagonal close-packed (hcp) structure of pure iron were performed to investigate a pressure-induced magnetic transition and the equation of state in the pressure range of 0-107 and 0-400 GPa, respectively. The experimental data at room temperature showed a significant change in the cell parameter ratio at 55 GPa without any major structural changes occurring. Ab initio calculations at 0 K indicate that the change in the cell parameter ratio observed in the high-pressure experiments corresponds to a magnetic transition from an antiferromagnetic state to a nonmagnetic state. If the hcp-Fe is stable under inner core conditions, then the density of nonmagnetic hcp-Fe is ~6% denser than that of the inner core, as determined using the PREM model. This supports the view that the composition of the inner core should be composed of iron and a significant amount of lighter elements.

Pressure-induced variation of Kondo behavior on the heavy fermion compounds YbT2Zn20 (T = Co, Rh, Ir)

We have performed the electrical resistivity measurement on single crystal heavy fermion compounds YbT2Zn20 (T = Co, Rh, Ir) under pressure up to 12 GPa. A pronounced resistivity maximum Tmax, which scales with the Kondo temperature, develops with increasing pressure. In the case of YbCo2Zn20, Tmax initially decreases with increasing pressure, reaches a minimum around 1 GPa, above which the pressure-induced magnetic ordering emerges at low temperature. For YbRh2Zn20 and YbIr2Zn20, Tmax also exhibits a minimum at approximately 3 GPa, suggesting the appearance of pressure-induced magnetic transition below 2 K. Our results indicate the proximity to a magnetic instability in YbT2Zn20 systems at ambient pressure.