Crystal structures, phase relationships, and magnetic phase transitions of R_5M_4 compounds (R = rare earths, M = Si, Ge)

Our recent studies of the crystal structures, phase transitions, and magnetic properties of intermetallic compounds RsM4 （R = rare earths; M = Si, Ge） are reviewed briefly. First, crystal structures, phase relationships, and magnetic prop- erties of several 5：4 compounds, including Nd5 Si4-xGex, Pr5 Si4_xGex, Gds-xLaxGe4, La5 Si4, and Gd5 Sn4, are presented. In particular, the canted spin structures as well as the magnetic phase transitions in PrsSi2Ge2 and PrsGe4 investigated by neutron powder diffractions and small-angle neutron scattering are reviewed. Second, the crystal structures and magnetic properties of the most studied compounds Gds（Si,Ge）4 are summarized. The focus is on the parent compound GdsGe4, which is an amazing material exhibiting magnetic anisotropy, angular dependent spin-flop transition, metastable magnetic response, Griffiths-like phase, thermal effect under pulsed fields, antiferromagnetic and ferromagnetic resonances, pro- nounced effects of impurities, and high-field induced magnetic transitions.

Magnetic and electronic properties of La-doped hexagonal 4H-SrMnO_(3)

As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites rely on the cubic/orthorhombic structures, while the hexagonal structure is much less studied. Here first-principles calculations are employed to investigate the magnetic and electronic structures of La-doped 4H-SrMnO_(3). By systematically analyzing the two kinds of La-doped positions, our calculations predict that the doped electron with lattice distortion would prefer to form polarons, which contribute to the local magnetic phase transition, nonzero net magnetization, and semiconducting behavior. In addition, the energy gap decreases gradually with increasing doping concentration, indicating a tendency of insulator–metal transition.

Chemical ordering and magnetic phase transitions in multiferroic BiFeO_(3)-AFe_(1/2)Sb_(1/2)O_(3)(A-Pb,Sr)solid solutions fabricated by a high-pressure

synthesisCeramic samples of BiFeO_(3)-based perovskite solid solutions with the highly ordered complex perovskites PbFe_(1/2)Sb_(1/2)O_(3)(PFS)and SrFe_(1/2)Sb_(1/2)O_(3)(SFS)were obtained using high-pressure synthesis at 4-6 GPa.Mössbauer studies revealed that BiFeO_(3)-SFS compositions are characterized by a larger compositional inhomogeneity as compared to BiFeO_(3)-PFS ones.In line with this result,concentration dependence of the magnetic phase transition temperature TN for BiFeO_(3)-SFS compositions is close to the TN(x)dependence for BiFeO_(3)solid solution with disordered perovskite PbFe_(1/2)Nb_(1/2)O_(3)(PFN).In contrast to this TN(x)dependence for BiFeO_(3)-PFS compositions nicely follows the theoretical TN(x)dependence calculated for the case of the ordered distribution of Fe3+and non-magnetic Sb^(5)+ions in the lattice(chemical ordering).

Pressure induced magnetic and semiconductor–metal phase transitions in Cr_2MoO_6

We investigate magnetic ordering and electronic structures of Cr2MoO6under hydrostatic pressure. To overcome the band gap problem, the modified Becke and Johnson exchange potential is used to investigate the electronic structures of Cr2MoO6. The insulating nature at the experimental crystal structure is produced, with a band gap of 1.04 eV, and the magnetic moment of the Cr atom is 2.50 μB, compared to an experimental value of about 2.47 μB. The calculated results show that an antiferromagnetic inter-bilayer coupling–ferromagnetic intra-bilayer coupling to a ferromagnetic inter-bilayer coupling–antiferromagnetic intra-bilayer coupling phase transition is produced with the pressure increasing. The magnetic phase transition is simultaneously accompanied by a semiconductor–metal phase transition. The magnetic phase transition can be explained by the Mo–O hybridization strength, and ferromagnetic coupling between two Cr atoms can be understood by empty Mo-d bands perturbing the nearest O-p orbital.

Mossbauer and magnetization studies of magnetic phase transitions in 0.5BiFeO_(3)-0.5NaNbO_(3)and 0.5LaFeO_(3)-0.5NaNbO_(3)solid solutions

0.5AFeO_(3)-0.5NaNbO_(3)(A=Bi,La)solid solution compositions were prepared using a solid phase reaction route from high-purity starting oxides.Mossbauer studies have shown that while for 0.5BiFeO_(3)-0.5NaNbO_(3)the magnetic phase transition temperature T_(M) value is about 150 K,for 0.5LaFeO_(3)-0.5NaNbO_(3),it is only≈25 K.This dramatic difference in T_(M) values seems to be due to additional contribution of the magnetic superexchange between Fe^(3+)ions via the empty 6p-states of Bi^(3+)ions to the overall superexchange.

Magnetic entropy change and magnetic phase transition of LaFe11.4Al1.6Cx （x=0-0.8） compounds

The unit cell volume and phase transition temperature of LaFe11.4Al1.6Cx compounds have been studied. The magnetic entropy change, refrigerant capacity and the type of magnetic phase transition are investigated in detail for LaFe11.4Al1.6Cx with x=0.1, All the LaFe11.4Al1.6Cx （x=0-0.8） compounds have the cubic NaZn13-type structure. The addition of carbon atoms brings about a considerable increase in the lattice parameter. The bulk expansion results in the change of phase transition temperature （Tc）, Tc increases from 187K to 269 K with x varying from 0.1 to 0.8, Meanwhile an increase in the lattice parameter can also cause a change of the magnetic ground state from antiferromagnetic to ferromagnetic. Large magnetic entropy change IASI is found over a large temperature range around Tc and the refrigerant capacity is about 322J/kg for LaFe11.4Al1.6C0.1. The magnetic phase transition belongs in weakly first-order one for x=0.1.

Tunable Electronic and Magnetic Properties from Structure Phase Transition of Layered Vanadium Diselenide

The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory（DFT）. Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.

Deconfinement Phase Transition with External Magnetic Field in the Friedberg-Lee Model

The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. We expand the potentiM around the two locM minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group. By solving the flow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement.

Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metals

The magnetocaloric effect （MCE） in many rare earth （RE） based intermetallic compounds has been extensively in- vestigated during the last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress on studying the magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal（s） （Zn, Mg, and Cd）. Some of them exhibit promising MCE properties, which make them attractive for low temperature magnetic refrigeration. Characteristics of the magnetic transition, origin of large MCE, as well as the potential application of these compounds are thoroughly discussed. Additionally, a brief review of the magnetic and magnetocaloric properties in the quaternary rare earth nickel boroncarbides RENi2B2C superconductors is also presented.

Magnetic properties and magnetocaloric effects in NaZn_(13)-type La(Fe,Al)(13)-based compounds

In this article, our recent progress concerning the effects of atomic substitution, magnetic field, and temperature on the magnetic and magnetocaloric properties of the LaFe13-xAlx compounds are reviewed. With an increase of the aluminum content, the compounds exhibit successively an antiferromagnetic （AFM） state, a ferromagnetic （FM） state, and a mictomagnetic state. Furthermore, the AFM coupling of LaFe13 -xAlx can be converted to an FM one by substituting Si for A1, Co for Fe, and magnetic rare-earth R for La, or introducing interstitial C or H atoms. However, low doping levels lead to FM clusters embedded in an AFM matrix, and the resultant compounds can undergo, under appropriate applied fields, first an AFM-FM and then an FM-AFM phase transition while heated, with significant magnetic relaxation in the vicinity of the transition temperature. The Curie temperature of LaFe13-xAlx can be shifted to room temperature by choosing appropriate contents of Co, C, or H, and a strong magnetocaloric effect can be obtained around the transition temperature. For example, for the LaFel 1.5All.5Co.2Hl.o compound, the maximal entropy change reaches 13.8 J.kg-1.K-1 for a field change of 0-5 T, occurring around room temperature. It is 42% higher than that of Gd, and therefore, this compound is a promising room-temperature magnetic refrigerant.

Phase structure and magnetocaloric effect of (Tb_(1–x)Dy_x)Co_2 alloys

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu2- type structure; with the increase of Dy content, Tc decreased from 240 K （TbCo2） to 130 K （DyCo2）, and the maximum magnetic entropy change ｜ △SM,max｜ increased from 3.133 to 8.176 J/kg-K under low magnetic field of 0-2 T. The Arrott plot and the change of ｜△SM,max｜ showed that magnetic phase transition from second order to first order occured with the increase of Dy content between x=-0.6 and 0.8.

The electric and magnetic properties of epitaxially grown A0.5-xLaxSr0.5MnO3 （A=Pr, Nd） thin film

The epitaxial （single crystal-like） Pr0.4La0.1Sr0.5MnO3 （PLSMO） and Nd0.35La0.15Sr0.5MnO3 （NLSMO） thin films are prepared and characterized, and the electric and magnetic properties are examined. We find that both PLSMO and NLSMO have their own optimum deposition temperature （To） in their growing into epitaxial thin films. When the deposition temperature is higher than To, a c-axis oriented but polycrystalline thin film grows; when the deposition temperature is lower than To, the thin film tends to be a-axis oriented and also polycrystalline. The most important point is that for the epitaxial PLSMO and NLSMO thin films the electronic phase transitions are closely consistent with the magnetic phase transitions, i.e. an antiferromagnetic phase corresponds to an insulating state, a ferromagnetic phase corresponds to a metallic state and a paramagnetic phase corresponds to a semiconducting state, while for the polycrystalline thin films the electronic phase transitions are always not consistent with the magnetic transitions.

CeAu_(2)In_(4):A candidate of quasi-one-dimensional antiferromagnetic Kondo lattice

Needle-like single crystals of CeAu_(2)In_(4)have been grown from In flux and characterized as a new candidate of quasi-one-dimensional Kondo lattice compound by crystallographic,magnetic,transport,and specific-heat measurements down to very low temperatures.We observe an antiferromagnetic transition at T_(N)≈0.9 K,a highly non-mean-field profile of the corresponding peak in specific heat,and a large Sommerfeld coefficientγ=369 mJ·mol^(-1)·K^(-2).The Kondo temperature T_(K)is estimated to be 1.1 K,being low and comparable to TN.While Fermi liquid behavior is observed deep into the magnetically ordered phase,the Kadowaki-Woods ratio is much reduced relative to the expected value for Ce compounds with Kramers doublet ground state.Markedly,this feature shares striking similarities to that of the prototypical quasi-one-dimensional compounds YbNi_(4)P_(2) and CeRh_(6)Ge_(4) with tunable ferromagnetic quantum critical point.Given the shortest Ce-Ce distance along the needle direction,CeAu_(2)In_(4)appears to be an interesting model system for exploring antiferromagnetic quantum critical behaviors in a quasi-one-dimensional Kondo lattice with enhanced quantum fluctuations.

Magnetic Field Induced Entropy Change for La-Fe Based NaZn_(13)-Typed Compounds

Magnetic field induced entropy change was investigated for La-Fe based NaZn13-type compounds with magnetic first-order phase transition. In view of magnetic refrigeration at room temperature, the developing of the materials and the understanding of the entropy change were., reviewed. For La-Fe-Si compounds, the entropy change about 29 J·kg^- 1·K^-1 was obtained at 190 K under the magnetic field of 5 T.While a large entropy change of about 15 J·kg^-1·K^-1 near room temperature under 5 T can be obtained by the substitution of Co for Fe in the compounds. It is found that the entropy change is mainly composed of that contributed from magnetic ordering and crystal lattice. The large entropy change consumed by lattice contribution is mainly due to the magnetic ordering one.

Light-induced magnetic phase transition in van der Waals antiferromagnets

Control over magnetic properties by optical stimulation is not only interesting from the physics point of view,but also important for practical applications such as magneto-optical devices.Here,based on a simple tight-binding(TB)model,we propose a general theory of light-induced magnetic phase transition(MPT)in antiferromagnets.Considering the fact that the bandgap of the antiferromagnetic(AFM)phase is usually larger than that of the ferromagnetic(FM)one for a given system,we suggest that light-induced electronic excitation prefers to stabilize the FM state over the AFM one,and will induce an MPT from AFM phase to FM phase once a critical photocarrier concentration(αc)is reached.This theory has been confirmed by performing firstprinciples calculations on a series of 2D van der Waals(vd W)antiferromagnets.Interestingly,a linear relationship betweenαc and the intrinsic material parameters is obtained,in agreement with our TB model analysis.Our general theory paves a new way to manipulate 2D magnetism with high speed and superior resolution.

Structure, magnetism and magnetocaloric effects in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds

We investigate the structure, magnetic properties, magnetic phase transitions and magnetocaloric effects(MCEs) of Er5Si3Bx(x=0.3,0.6) compounds. The Er5Si3Bx(x = 0.3, 0.6) compounds crystalize in a Mn5Si3type hexagonal structure(space group: P63/cm) and exhibit a successive complicated magnetic phase transition. The extensive magnetic phase transitions contribute to the broad temperature range of MCEs exhibiting in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds, with maximum magnetic entropy change(-ΔSM_(max)) and refrigeration capacity of 10.2 J·kg^(-1)·K^(-1), 356.3 J/kg and 11.5 J·kg^(-1)·K^(-1),393.3 J/kg under varying magnetic fields 0–5 T, respectively. Remarkably, the δTFWHMvalues(the temperature range corresponding to 1/2×|-ΔSM_(max)|) of Er5Si3Bx(x=0.3,0.6) compounds were up to 41.8 K and 39.6 K, respectively. Thus, the present work provides a potential magnetic refrigeration material with a broad temperature range MCEs for applications in cryogenic magnetic refrigerators.

The Influence of Deposition Temperature on the Epitaxial Growth of La_(0.7)Ca_(0.3)MnO_3 Thin Film

The growth conditions of La0.7Ca0.3MnO3(LCMO) epitaxial thin film are investigated.The results indicate that the deposition temperature plays a crucial role on the growth mode of LCMO thin film.There is an optimal deposition temperature,To,for the epitaxial growth of LCMO thin film.Just only at the To,the real epitaxial LCMO thin film can be obtained.When the deposition temperature deviates from the To,the thin film tends to be polycrystalline,although it orientes growth along a certain direction(a or c axis).Moreover,the experimental results show that just only for the epitaxial thin film the ferromagnetic-paramagnetic transition temperature(i.e.the Courier temperature Tc) equals to the metal-semiconductor transition temperature(Tp).The ferromagnetic state shows metallicity and the paramagnetic state exhibits semiconducting character.

Binary perovskite solid solutions and trends in their phase transitions temperatures variation

Some of the known binary ABO_(3)perovskites with ferro-(FE)or antiferroelectric(AFE)at T_(C)and different magnetic phase tran-sitions(PT):ferro-and antiferromagnetic at T_(N)and also some of their solid solutions are considered.Some correlations between their FE or AFE and/or magnetic PTs temperatures,on the one hand,and their interatomic bond A-O strains,on the other hand,have been constructed.It is shown that in the plotted diagrams these temperatures change with a change inδAO values as follows:classical FEs are followed by multiferroics,starting with BiFeO_(3)and ending with YVO_(3),followed by classical AFEs.At the same time,the temperatures T_(C)and T_(N)experience maxima at the corresponding points for BiFeO_(3),then quickly decrease,and the difference between them,T_(C)-T_(N),basically also decreases,slightly increasing along the way to the point EuTiO_(3).which made it possible to systematize these T_(C)and T_(N).

The interplay between the lattice and magnetism in La(Fe_(11.4)Al_(1.6))C_(0.02) studied by powder neutron diffraction

The crystallographic structure and magnetic properties of La（Fell.4Alz.6）C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La（Fe11.4Al1.6）C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites： FeI （8b） and FeII （96i）, and that A1 atoms preferentially occupy the FeII site. A ferromagnetic state can he induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La（Fe11.4Al1.6）C0.02 has no net magnetization in the paramagnetic （T 〉 TN = 182 K） or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances.

Improved multiferroic in EuTiO_(3) films by interphase strain engineering

Interphase strain engineering provides a unique methodology to significantly modify the lattice structure across a single film,enabling the emergence and manipulation of novel functionalities that are inaccessible in the context of traditional strain engineering methods.In this work,by using the interphase strain,we achieve a ferromagnetic state with enhanced Curie temperature and a room-temperature polar state in EuO secondary phase-tunned EuTiO_(3) thin films.A combination of atomic-scale electron microscopy and synchrotron X-ray spectroscopy unravels the underlying mechanisms of the ferroelectric and ferromagnetic properties enhancement.Wherein,the EuO secondary phase is found to be able to dramatically distort the TiO_6 octahedra,which favors the non-centrosymmetric polar state,weakens antiferromagnetic Eu-Ti-Eu interactions,and enhances ferromagnetic Eu-O-Eu interactions.Our work demonstrates the feasibility and effectiveness of interphase strain engineering in simultaneously promoting ferroelectric and ferromagnetic performance,which would provide new thinking on the property regulation of numerous strongly correlated functional materials.