Giant Volume Magnetostriction Caused by Itinerant Electron Metamagnetic Transition and Pronounced Invar Effects in La(Fe_xSi_(1-x))_(13) Compounds

A first-order itinerant electron metamagnetic （IEM） transition above the Curie temperature Tc for ferromagnetic La（FexSi1-x）13 compounds has been confirmed by applying magnetic field. The volume change just above TC for x=0.88 is huge of about 1.5%, which is caused by a large magnetic moment induced by the IEM transition. These compounds have a possibility for practical applications as giant magnetostrictive materials. Pronounced Invar effects bring about a negative thermal expansion below TC, closely correlated with the negative mode-mode coupling among spin fluctuations.

Intrinsic two-way shape memory effect in a Ni-Mn-Sn metamagnetic shape memory microwire

An intrinsic two-way shape memory effect with a fully recoverable strain of 1.0%was achieved in an as-prepared Ni50Mn37.5Sn12.5 metamagnetic shape memory microwire fabricated by Taylor-Ulitovsky method.This two-way shape memory effect is mainly owing to the internal stress caused by the retained martensite in austenite matrix,as revealed by transmission electron microscopy observations and highenergy X-ray diffraction experiments.After superelastic training for 30 loading/unloading cycles at room temperature,the amount of retained martensite increased and the recoverable strain of two-way shape memory effect increased significantly to 2.2%.Furthermore,a giant recoverable strain of 11.2%was attained under a bias stress of 300 MPa in the trained microwire.These properties confer this microwire great potential for micro-actuation applications.

Unconventional metamagnetic phase transition in R_(2)In(R=Nd, Pr)with lambda-like specific heat and nonhysteresis

The phase transition of Nd_(2)In and Pr_(2)In has been studied and found to be between the first-order and second-order nature.Hardly any hysteresis nor obvious cell volume changes are presented.Concurrently the field-triggered metamagnetism is demonstrated with lambda-like peak on specific heat curve.For the field change of 7 T,giant magnetic entropy changes of 13.2 J kg^(-1)K^(-1) and 19.5 J kg^(-1)K^(-1) and adiabatic temperature changes of 6.5 K and 7.4 K have been achieved in Nd_(2)In and Pr_(2) In alloys respectively,which is partially contributed by strong magnetoelastic coupling represented by high saturation magnetostriction of~450 ppm.Such unique feature is proposed to be originated from the delocalized 5d electrons,as evidenced by the negative magnetoresistance caused by the phase transition.

Experimental evidence for field-induced metamagnetic transition of EuCd_(2)As_(2)

Recent studies have shown that layered compound EuCd_(2)As_(2) could exhibit diverse topological states depending on the different magnetic structures,such as Weyl semimetal,Dirac semimetal and topological insulato r.In order to further study the interplay between magnetism and topology of EuCd_(2)As_(2),it is necessary to figure out its magnetic structure.Here,by magnetization(M) measurements and negative magnetostriction(λ) along the [001] direction measured by scanning tunneling microscopy on EuCd_(2)As_(2) single crystals,we observe field-induced metamagnetic phase transition from A-type antiferromagnetic(AFM) ground state to field-polarized state,with canted AFM(CAFM) state in between.Magnetization and magnetostriction are more sensitive to the in-plane field than the out-of-plane field,indicating the magnetic moments lying in the ab plane.The absence of abrupt jump on M-H and λ-H curves demonstrates that the phase transition is a second-order type.In CAFM state,M increases linearly with the field and λ is proportional to M~2.Tunneling conductance spectra show the field-induced evolution of the electronic density of states.Our results provide experimental evidence for understanding the magnetic structure of EuCd_(2)As_(2).

Metamagnetic transitions and anomalous magnetoresistance in EuAg4As2 crystals

In this work,we systematically studied the magnetic and transport properties of EuAg4As2 single crystals.It was found that the two antiferromagnetic transitions(TN1=10 K and TN2=15 K)were driven to lower temperatures by an applied magnetic field.Below TN1,two successive metamagnetic transitions were observed when a magnetic field was applied in the ab plane(H//abplane).For both H//ab and H//c,EuAg4As2 showed a positive,unexpectedly large magnetoresistance(up to 202%)in lower magnetic fields below TN1,and a large negative magnetoresistance(up to-78%)at high fields/intermediate temperatures,thus presenting potential applications in magnetic sensors.Finally,the magnetic phase diagrams of EuAg4As2 were constructed for both H//ab and H//c using the resistivity and magnetisation data.

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.

Corrosion behavior and magnetocaloric effect of FeNi(1J85) coated LaFe_(11.6)Si_(1.4)/Sn composites

The FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were prepared by hot pressing(HP). The microstructure,corrosion behavior and magnetocaloric effect(MCE) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were investigated systematically. The results show that the corrosion resistance of FeNi coated LaFe_(11.6)Si_(1.4)Sn composites is better than that of LaFe_(11.6)Si_(1.4)/Sn composites in deionized water. The maximum magnetic entropy change((-△S_M)^(max)) and relative cooling power(RCP) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites are 13.30 J/(kg-K) and 146.25 J/kg, respectively, which are larger than that((-△S_M)^(max), 10.65 J/(kg·K) and RCP, 106.53 J/kg) of LaFe_(11.6)Si_(1.4)/Sn composites in a low magnetic field change of 2 T. FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites possess a more negative slope. The improvement of magnetic properties is due to high permeability FeNi permalloy(1 J85) which improves the itinerant-electron metamagnetic(IEM) transition. So, the method of coating FeNi can provide a new idea for enhancing the corrosion resistance and magnetocaloric effect of La(Fe_xSi_(1-x))_(13)-based materials.

Magnetic properties of cobalt-based oxypnictide SmCoAsO

The magnetic properties of cobalt-based oxypnictides SmCoAsO are investigated by measuring magnetization,magnetoresistance and specific heat.The compound undergoes a ferromagnetic(FM) transition around Tc of 80 K,and a ferromagnetic to antiferromagnetic(AFM) transition below TN1 of about 45 K,and finally an AFM order of Sm ion at TN2 of 5.6 K.The weak FM order should originate from the itinerant 3d electrons of Co ions in the CoAs layers.We propose that the magnetic structure should be A-type AFM,which means that the FM order remains within the CoAs layer and the magnetic coupling between the CoAs layers becomes AFM below TN1 of 45 K.The AFM coupling between the CoAs layers should be very weak.A magnetic field μ0H of about 2 T may cause an AFM-FM metamagnetic transition.A rich magnetic phase diagram is established and the interplay between the 3d electrons of Co ions and 4f electrons of Sm ions is discussed.

Excellent mechanical properties and large magnetocaloric effect of spark plasma sintered Ni-Mn-In-Co alloy

The Ni43.75Mn37.5In12.5Co6.25 alloy was obtained by using the spark plasma sintering(SPS)technique.The martensitic transformation,magnetic and mechanical properties of the SPS alloy were investigated.Key findings demonstrate that the martensitic transformation temperature of this alloy is about 10 K lower than that of the as-cast one.Both SPS and as-cast alloys show a 7 layered modulated martensite(7M)at room temperature.The compressive fracture strength and strain of the SPS alloy increase by 176.92%and 33.33%compared with the as-cast alloy,achieving 1440 MPa and 14%,respectively.The maximum magnetic entropy change Smis 17.1 J kg^(-1)K^(-1)for the SPS alloy at the magnetic field of 5 T.

Experimental isothermal section phase diagram of Ho-Fe-In at 773 K and magnetic properties of Ho_(12)Fe_(2.08)In_(2.92) alloy

The isothermal section of the Ho-Fe-In system at 773 K has been constructed by X-ray powder diffraction.One known structure ternary compound Er_(12)Fe_(2) In_(3)-type Ho_(12)Fe_(2) In_(3) has been confirmed.At the same time,solid solutions are not detected in Ho-Fe-In system at 773 K.The magnetic transition and magnetocaloric effect of Ho_(12)Fe_(2.08)In_(2.92) alloy with Er_(12)Fe_(2) In_(3)-type structure were investigated by magnetic susceptibility and isothermal magnetization measurements.One normal antiferromagnetic-paramagnetic transition and another abnormal one are discovered at 18 and 76 K in ground state,respectively.Owing to a first-order field-induced metamagnetic transition(antiferromagnetic-ferromagnetic) at/below the Neel temperature of 18 K),the negative entropy changes are observed at corresponding temperature.There is only a second-order ferromagnetic-paramagnetic transition near Curie temperature(TC),the maximum entropy change(Δ_(Smax)) values are-6.14 J·kg^(-1)·K^(-1) at 3 K and 7.88 J·kg^(-1)·K^(-1) at 28 K in a field range of 0-7 T.The reversible relative cooling power corresponding to negative entropy change can reach about 600 J·kg^(-1) in an wide operating temperature region Δ_(Tcycl)=74 K from 16 to90 K,which suggests that Ho_(12)Fe_(2.08)In_(2.92) could be a potential material for magnetic refrigeration in the corresponding temperature range.

Multiple magnetic transitions in single crystals of Ce12Fe57.5As41 and La12Fe57.5As41

Measurements of magnetic and transport properties were performed on needle-shaped single crystals of Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41).The availability of a complete set of data enabled a side-by-side comparison between these two rare earth compounds.Both compounds exhibited multiple magnetic orders within 2-300 K and metamagnetic transitions at various fields.Ferromagnetic transitions with Curie temperatures of 100 and 125 K were found for Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41),respectively,followed by antiferromagnetic type spin reorientations near Curie temperatures.The magnetic properties underwent complex evolution in the magnetic field for both compounds.An antiferromagnetic phase transition at about 60 K and 0.2 T was observed merely for Ce_(12)Fe_(57.5)As_(41).The field-induced magnetic phase transition occurred from antiferromagnetic to ferromagnetic structure.A strong magnetocrystalline anisotropy was evident from magnetization measurements of Ce_(12)Fe_(57.5)As_(41).A temperature-field phase diagram was present for these two rare earth systems.In addition,a logarithmic temperature dependence of electrical resistivity was observed in the two compounds within a large temperature range of 150-300 K,which is rarely found in 3D-based compounds.It may be related to Kondo scattering described by independent localized Fe 3d moments interacting with conduction electrons.

One-dimensional metal phosphonates based on 6-phosphononicotinic acid:A structural and magnetic study

The reactions of 6-phosphononicotinic acid (pnaH3) and metal salts result in three new compounds, namely, M(pnaH)-(H2O)3·H2O [M = Co(Ⅱ) (1), Ni(Ⅱ) (2), Zn(Ⅱ) (3)]. These compounds are isostructural and contain 21 helical chains made up of corner-sharing {MO5N} octahedra and {PO3C} tetrahedra. The chains are further connected by extensive hydrogen bonds to form a three-dimensional supramolecular structure. Magnetic studies reveal that dominant antiferromagnetic interactions are mediated in both 1 and 2. Interestingly the dehydrated compound 1 shows metamagnetic behavior at low temperature.