Influence of the Jahn-Teller distortion on magnetic ordering in TbMn_(1-x)Fe_xO_3

The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites.In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3（x = 0,0.02,0.05,0.10,and 0.20） single crystals in the basal MnO2 plane.The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn-Teller distortion,which makes the nearest neighboring（NN） FM interaction dominant over the next nearest neighbor（NNN） AFM interaction.This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering,which collapses when x ≥ 0.05.The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.

The Magnetic Order in Ion Irradiated Graphite

The magnetism of highly oriented pyrolytic graphite （HOPG） induced by ion implantation is investigated with electron spin resonance （ESR） spectroscopy and magnetization measurements. The results indicate that the ESR spectra of the HOPG sample correlate with ion species, incident energy and dose of implantation. The correlation of the ESR spectra and magnetism of the HOPG sample with ：2C＋ ion implantation and H＋ ion implantation are studied in detail. The ferromagnetism of the HOPG sample is likely related to the asymmetric L1 line, which may be attributed to the interaction between localized defects and itinerant electrons occupied in the ＇impurity＇ band induced by ion implantation.

Magnetic ordering induced magnetodielectric effect in Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5)

Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications.In this paper,we have investigated the structure,magnetic property,and magnetodielectric(MD) effect in Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) poly crystalline samples,which possess a non-centrosymmetric polar structure with space group Pna2_(1).In Ho_(2)Cu_(2)O_(5),Ho^(3+) and Cu^(2+) sublattices order simultaneously,exhibiting a typical paramagnetic to antiferromagnetic transition at 13.1 K.While for Yb_(2)Cu_(2)O_(5),two magnetic transitions which originate from the orderings of Yb^(3+)(7.8 K) and Cu^(2+)(13.5 K) sublattices are observed.A magnetic field induced metamagnetic transition is obtained in these two cuprates below Neel temperature(T_(N)).By means of dielectric measurement,distinct MD effect is demonstrated by the dielectric anomaly at T_(N.)Meanwhile,the MD effect is found to be directly related to the metamagnetic transition.Due to the specific spin configuration and different spin evolution in the magnetic field,a positive MD effect is formed in Ho_(2)Cu_(2)O_(5),and a negative one is observed in Yb_(2)Cu_(2)O_(5).The spontaneous dielectric anomaly at T_(N) is regarded as arising from the shifts in optical phonon frequencies,and the magnetoelectric coupling is used to interpret the magnetic field induced MD effect.Moreover,an H-T phase diagram is constructed for Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) based on the results of isothermal magnetic and dielectric hysteresis loops.

Magnetic Ordering and Exchange Interaction of Laves Compounds Sm0.9Pr0.1(Fe1-xCox)2

Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mossbauer spec-troscopy and standard strain gauge techniques. The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration, deviating from the Vegard's law. Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0. The saturation magnetization Ms at temperatures 1.5 K, 77 K and 300 K have the same variation tendency as the composition dependence of Curie temperature, in consistence with rigid-band model. The easy magnetization direction (EMD) of Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x<0.6, and changes to [110] for x=0.8, while Sm0.9Pr0.1Co2 stays in the paramagnetic state at room temperature. The composition dependence of the average hyperfine field,Hhf , demonstrates a similar variation tendency as that of the saturation magnetization Ms and Curie temperature Tc. The spontaneous magnetostricton Am increases with increasing Co content. The saturation magnetostriction λs decreases monotonically with increasing x, which is caused by the increase of magnetostriction constant λ100 with opposite sign to that of Am. A two-sublattice model has been proposed to understand the intermediate region between the [111] and [110] spin configurations, which can also be used to explain the temperature dependence of magnetization.

Existence of long-range magnetic order in Heisenberg spin nanoribbons with edge modification

Long-range magnetic order appears on a side decorated Heisenberg spin nanoribbon at nonzero temperature,although no spontaneous magnetization exists in a one-or two-dimensional isotropic Heisenberg model at any nonzero temperature according to the Mermin-Wagner theorem.By use of the spin Green's function method,we calculated the magnetizations of Heisenberg nanoribbons decorated by side spins with single-ion anisotropy and found that the system exhibits a nonzero transition temperature,whether the decorated edge spins of the system link together or separate from each other.When the width of the nanoribbon achieves infinite limit,the transition temperatures of the system tend to the same finite constant eventually whether one edge or both edges are decorated by side spins in the nanoribbon.The results reveal that the magnetism of a low-dimensional spin system is different from that of a threedimensional spin system.When the single-ion anisotropy of edge spins in a Heisenberg spin nanoribbon can be modulated by an electric field experimentally,various useful long-range magnetic orders of the system can be obtained.This work can provide a detailed theoretical basis for designing and fabricating next-generation low-dimensional magnetic random-access memory.

Accurate characterization of room-temperature long range magnetic order in GaN: Mn by magnetic force microscope

Room-temperature ferromagnetism with a Curie temperature higher than 380 K was studied in GaN: Mn thin films grown by metal-organic chemical vapor deposition. By etching artificial microstructures on the GaN: Mn layer,strong magnetic responses were observed in the magnetic force microscopy (MFM) measurement,which revealed that the films were independent of dopant particles and clusters. Numerical simulation on the data of atomic force microscope (AFM) and MFM measurements covering the whole microstructure validated the formation of long range magnetic order. This result excluded a variety of controversial origins of room-temperature ferromagnetism in the GaN: Mn and gave a strong evidence of our GaN: Mn as the intrinsic diluted magnetic semiconductor (DMS). The forwarded method for accurate characterization of long range magnetic order could be applied to a wide range of DMS and diluted magnetic oxide (DMO) systems.

Alloying and magnetic disordering effects on phase stability of Co_(2)YGa(Y=Cr,V,and Ni)alloys:A first-principles study

The alloying and magnetic disordering effects on site occupation,elastic property,and phase stability of Co_(2)Y Ga(Y=Cr,V,and Ni)shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method.It is shown that with the increasing magnetic disordering degree y,their tetragonal shear elastic constant C′(i.e.,(C_(11)-C_(12))/2)of the L2_(1) phase decreases whereas the elastic anisotropy A increases,and upon tetragonal distortions the cubic phase gets more and more unstable.Co_(2)Cr Ga and Co_(2)VGa alloys with y≥0.2 thus can show the martensitic transformation(MT)from L2_(1)to D0_(22)as well as Co_(2)Ni Ga.In off-stoichiometric alloys,the site preference is controlled by both the alloying and magnetic effects.At the ferromagnetism state,the excessive Ga atoms always tend to take the Y sublattices,whereas the excessive Co atom favor the Y sites when Y=Cr,and the excessive Y atoms prefer the Co sites when Y=Ni.The Ga-deficient Y=V alloys can also occur the MT at the ferromagnetism state by means of Co or V doping,and the MT temperature TMshould increase with their addition.In the corresponding ferromagnetism Y=Cr alloys,nevertheless,with Co or Cr substituting for Ga,the reentrant MT(RMT)from D0_(22)to L2_(1)is promoted and then TMfor the RMT should decrease.The alloying effect on the MT of these alloys is finally well explained by means of the Jahn-Teller effect at the paramagnetic state.At the ferromagnetism state,it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as Y and Ga.

Zigzag magnetic order in a novel tellurate compound Na_(4-δ)NiTeO_6 with S=1 chains

Na_(4-δ)Ni Te O_(6) is a rare example in the transition-metal tellurate family of realizing an S=1 spin-chain structure.By performing neutron powder diffraction measurements,the ground-state magnetic structure of Na_(4-δ)Ni Te O_(6) is determined.These measurements reveal that below T_N~6.8(2)K,the Ni^(2+) moments form a screwed ferromagnetic(FM)spin-chain structure running along the crystallographic a axis but these FM spin chains are coupled antiferromagnetically along the b and c directions,giving rise to a magnetic propagation vector of k=(0,1/2,1/2).This zigzag magnetic order is well supported by first-principles calculations.The moment size of Ni^(2+) spins is determined to be 2.1(1) μ_(B) at 3 K,suggesting a significant quenching of the orbital moment due to the crystalline electric field(CEF)effect.The previously reported metamagnetic transition near H_(c)~0.1 T can be understood as a field-induced spin-flip transition.The relatively easy tunability of the dimensionality of its magnetism by external parameters makes Na_(4-δ)Ni Te O_(6)a promising candidate for further exploring various types of novel spin-chain physics.

Successive magnetic ordering in two Co^(Ⅱ)-ladder metal-organic frameworks

Metal-organic frameworks showing successive magnetic ordering are far less common than inorganic compounds.Here,we report two metal-organic frameworks[Co^Ⅱ(ox)(bphy)·0.1(DMF)·0.1(Me OH)]n(1)and[Co3^Ⅱ(ox)3(bphy)2(DMF)2]n(2)comprised of zigzag and necklace Co^Ⅱ-ladders,respectively.Together with a previously reported compound[Co^Ⅱ(ox)(bphy)·0.2(DMF)]n(3)consisting of spiraling zigzag Co^Ⅱ-ladders,these three compounds provide a good system for comparative structural and magnetic studies.Comprehensive magnetic analysis reveals that the three compounds undergo long-range magnetic ordering at^2.6 K but exhibit vastly different short-range magnetic correlations:compound 1 shows short-range spin-canted antiferromagnetism ordering at^14.0 K;compound 2 demonstrates successive short-range antiferromagnetism ordering at^15.5and^12.6 K;compound 3 shows slow magnetic relaxation with Tb≈4.6 K.These results demonstrate long-range magnetic ordering is readily accessible in the frameworks of ox^2-bridging Co^Ⅱ-ladders linked by bphy,where short-range magnetic correlations can be systematicly tuned by the Co^Ⅱ-ladder structures.

RKKY interaction in helical higher-order topological insulators

We theoretically investigate the Ruderman–Kittel–Kasuya–Yosida(RKKY) interaction in helical higher-order topological insulators(HOTIs), revealing distinct behaviors mediated by hinge and Dirac-type bulk carriers. Our findings show that hinge-mediated interactions consist of Heisenberg, Ising, and Dzyaloshinskii–Moriya(DM) terms, exhibiting a decay with impurity spacing z and oscillations with Fermi energy εF. These interactions demonstrate ferromagnetic behaviors for the Heisenberg and Ising terms and alternating behavior for the DM term. In contrast, bulk-mediated interactions include Heisenberg, twisted Ising, and DM terms, with a conventional cubic oscillating decay. This study highlights the nuanced interplay between hinge and bulk RKKY interactions in HOTIs, offering insights into designs of next-generation quantum devices based on HOTIs.

Effect of Quench Treatment on Fe/Mo Order and Magnetic Properties of Double Perovskite Sr_2FeMoO_6

A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2FeMo06 （SFMO）. X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order η of the sample increases to 98.9（2）% from 94.2（3）%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 #s at 300 K, and the one for the traditional sol-gel method sample is 0.946#9. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatment is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO.

Study on magnetic memory signals of medium carbon steel specimens with surface crack precut during loading process

Static tensile test and tensile-tensile fatigue test of medium carbon steel sheet specimens with surface crack precut were performed on MTS810 hydraulic testing machine to clear the meaning of the point of Hp(y) value zero. Magnetic memory signals were measured during the test process. The results show that only one point of Hp(y) zero value exists in all measured magnetic signal curves during the loading process, which should be a sign of intersection of positive-negative magnetic poles after magnetic ordered state appears and does not indicate the position of surface crack precut. The analysis shows that the surface crack precut can not interrupt the magnetic ordered state occurred during the test completely, hence its Hp(y) value is not zero. However, the crack extending to a penetrated defect at the instant of specimen′s fracture leads to the discontinuance of magnetic ordered state.

A novel diluted magnetic semiconductor(Ca,Na)(Zn,Mn)2Sb2 with decoupled charge and spin dopings

We report the successful synthesis of a new diluted magnetic semiconductor(Ca,Na)(Zn,Mn)2Sb2.Na and Mn are doped into the parent compound CaZn2Sb2,which has the same crystal structure as that of"122"type iron-based superconductor CaFe2As2.Na substitution for Ca and Mn substitution for Zn introduce carriers and spins,respectively.Doping Mn atoms alone up to 5%does not induce any type of magnetic ordering.When both Na and Mn are co-doped,a ferromagnetic ordering with maximum TC^10 K has been observed.Iso-thermal magnetization shows that the coercive field is up to^245 Oe at 2 K.Below TC,a negative magneto-resistance with MR^12%has also been achieved.

Antiferromagnetic-ferromagnetic transition in zigzag graphene nanoribbons induced by substitutional doping

Using first-principles calculations based on density functional theory,we show that the ground state of zigzag-edged graphene nanoribbons(ZGNRs)can be transformed from antiferromagnetic(AFM)order to ferromagnetic(FM)order by changing the substitutional sites of N or B dopants.This AFM–FM transition induced by substitutional sites is found to be a consequence of the competition between the edge and bulk states.The energy sequence of the edge and bulk states near the Fermi level is reversed in the AFM and FM configurations.When the dopant is substituted near the edge of the ribbon,the extra charge from the dopant is energetically favorable to occupy the edge states in AFM configuration.When the dopant is substituted near the center,the extra charge is energetically favorable to occupy the bulk states in FM configuration.Proper substrate with weak interaction is necessary to maintain the magnetic properties of the doped ZGNRs.Our study can serve as a guide to synthesize graphene nanostructures with stable FM order for future applications to spintronic devices.

Spin, charge, and orbital orderings in iron-based superconductors

In this article, we briefly review spin, charge, and orbital orderings in iron-based superconductors, as well as the multi-orbital models. The interplay of spin, charge, and orbital orderings is a key to understand the high temperature superconductivity. As an illustration, we use the two-orbital model to show the spin and charge orderings in iron-based superconductors based on the mean-field approximation in real space. The typical spin and charge orderings are shown by choosing appropriate parameters, which are in good agreement with experiments. We also show the effect of Fe vacancies, which can introduce the nematic phase and interesting magnetic ground states. The orbital ordering is also discussed in iron-based superconductors. It is found that disorder may play a role to produce the superconductivity.

Ferrimagnetic Properties of Bond Dilution Mixed Blume-Capel Model with Random Single-Ion Anisotropy

We study the ferrimagnetic properties of spin 1/2 and spin-1 systems by means of the effective field theory. The system is considered in the framework of bond dilution mixed Blume-Capel mode/ （BCM） with random single-ion anisotropy. The investigation of phase diagrams and magnetization curves indicates the existence of induced magnetic ordering and single or multi-compensation points. Special emphasis is placed on the influence of bond dilution and random single-ion anisotropy on normal or induced magnetic ordering states and single or multi-compensation points. Normal magnetic ordering states take on new phase diagrams with increasing randomness （bond and anisotropy）, while anisotropy induced magnetic ordering states are always occurrence no matter whether concentration of anisotropy is large or small. Existence and disappearance of compensation points rely strongly on bond dilution and random singleion anisotropy. Some results have not been revealed in previous papers and predicted by Néel theory of ferrimagnetism.

Exchange coupling and helical spin order in the triangular lattice antiferromagnet CuCrO_2 using first principles

The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradient approxi- mations （GGA）＋U scheme. The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and spin frustration. It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction. Using Monte Carlo simulation, we obtain the Neel temperature to be 29.9 K, which accords well with the experimental value of 24 K. Based on non- collinear magnetic structure calculations, we verify that the incommensurate spiral-spin structure with （110） spiral plane is believable for the magnetic ground state, which is consistent with the experimental observations. Due to intra-layer geometric spin frustration, parallel helical-spin chains arise along the a, b, or a＋ b directions, each with a screw-rotation angle of about I20°. Our calculations of the density of states show that the spin frustration plays an important role in the change of d-p hybridization, while the spin-orbit coupling has a very limited influence on the electronic structure.

Effect of Plastic Deformation on Magnetic Properties of Fe-40%Ni-2%Mn Austenitic Alloy

The effects of plastic deformation on the magnetic properties of austenite structure in an Fe-40% Ni-2 % Mn alloy is investigated by using Mossbauer spectroscopy and Differential Scanning Calorimetry （DSC） techniques The morphology of the alloy has been obtained by using Scanning Electron Microscopy （SEM）. The magnetic behaviour of austenite state is ferromagnetic. After plastic deformation, a mixed magnetic structure including both paramagnet- ic and ferromagnetic states has been obtained at the room temperature. The volume fraction changes, the effective hyperfine fields of the ferromagnetic austenite phase and isomery shift values have also been determined by Mossbauer spectroscopy. The Curie point （Tc） and the Neel temperature （TN） have been investigated by means of DSC system for non-deformed and deformed Fe-Ni-Mn alloy. The plastic deformation of the alloy reduces the TN and enhances the paramagnetic character of austenitic Fe-Ni-Mn alloy.

Renormalization of spin polarised itinerant electron bands in the normal state of a model ferromagnetic superconductor

This paper studies the normal state properties of itinerant electrons in a toy model, which is constructed according to the model for coexisting ferromagnetism and superconductivity proposed by Suhl [Suhl H 2001 Phys. Rev. Lett. 87 167007]. In this theory with ferromagnetic ordering based on localized spins, the exchange interaction J between conduction electrons and localized spin is taken as the pairing glue for s-wave superconductivity. It shows that this J term will first renormalize the normal state single conduction electron structures substantially. It finds dramatically enhanced or suppressed magnetization of itinerant electrons for positive or negative J. Singlet Cooper pairing can be ruled out due to strong spin polarisation in the J 〉 0 case while a narrow window for s-wave superconductivity is opened around some ferromagnetic J.

Structural Dependence of Magnetic and Transport Properties in Doped Manganite Perovskites

In this paper, the magnetic and transport properties in ABO3-type perovskite-like manganites as functions of the structure have been discussed from the viewpoints of A- and B-site doping, respectively. For the A-site doping, two simple parameters, tolerance factor t and variance of the A-cation radius distribution s, can be used to characterize the magnetic/resistive phase diagram. For the B-site doping, the case is complicated due to the direct action to the center of double exchange. However, the dopant-size-induced local strain effect plays an important role in the physical properties besides the size mismatch between A- and B-site ions.