Multiple magnetic transitions in single crystals of Ce<Subscript>12</Subscript>Fe<Subscript>57.5</Subscript>As<Subscript>41</Subscript> and La<Subscript>12</Subscript>Fe<Subscript>57.5</Subscript>As<Subscript>41</Subscript>

Measurements of magnetic and transport properties were performed on needle-shaped single crystals of Ce₁₂Fe_57.5As₄₁ and La₁₂Fe_57.5As₄₁. 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 Ce₁₂Fe_57.5As₄₁ and La₁₂Fe_57.5As₄₁, 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 Ce₁₂Fe_57.5As₄₁. The field-induced magnetic phase transition occurred from antiferromagnetic to ferromagnetic structure. A strong magnetocrystalline anisotropy was evident from magnetization measurements of Ce₁₂Fe_57.5As₄₁. 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.     

Magnetism and superconductivity in Eu(Fe_(1-x)Ni_x)As_2(x= 0,0.04)

We report Eu-local-spin magnetism and Ni-doping-induced superconductivity(SC)in a 112-type ferroarsenide system Eu(Fe_(1-x)Ni_x)As_2.The non-doped EuFeAs_2exhibits two primary magnetic transitions at ~100 and ~40 K,probably associated with a spin-density-wave(SDW)transition and an antiferromagnetic ordering in the Fe and Eu sublattices,respectively.Two additional successive transitions possibly related to Eu-spin modulations appear at 15.5 and 6.5 K.For the Ni-doped sample with x=0.04,the SDW transition disappears,and SC emerges at T_c=17.5 K.The Eu-spin ordering remains at around 40 K,followed by the possible reentrant magnetic modulations with enhanced spin canting.Consequently,SC coexists with a weak spontaneous magnetization below 6.2 K in Eu(Fe_(0.96)Ni_(0.04))As_2,which provides a complementary playground for the study of the interplay between SC and magnetism.     

Metamagnetic transitions and anomalous magnetoresistance in EuAg_4As_2 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.     

MnFeP_(0.45)As_(0.55)材料中的相变研究

利用不同的测量方法,研究了MnFeP1-xAsx(0·32相似文献   

R_2Fe_17_C化合物的结构与内禀磁性的研究

本文系统研究了R_2Fe_17_C(R=Y,Sm,Gd,Tb、Dy.Er) 化合物的结构与内享磁性, 井与相应的R_2Fe_17_C 化合物进行了比较.R_2Fe_17_C 的居里温度比相应氏R_2Fe_17 的居里温度增加大约200K. 本文讨论了C 原子对该化合物结构与磁性的影响, 同时, 还对Sm_2(Fe_1-xCo_x)_17C系列化合物进行了研充. 关键词：     

Negative Magnetoresistance in Antiferromagnetic Topological Insulator EuSn_2As_2

The measurements of magnetization,longitudinal and Hall resistivities are carried out on the intrinsic antiferromagnetic(AFM) topological insulator ElSn_2 As_2.It is confirmed that our ElSn_2 As_2 crystal is a heavily hole doping A-type AFM metal with the Neel temperature T_N=24 K,with a metamagnetic transition from an AFM to a ferromagnetic(FIM) phase occurring at a certain critical magnetic Held for the different Held orientations.Meanwhile,we also find that the carrier concentration does not change with the evolution of magnetic order,indicating that the weak interaction between the localized magnetic moments from Eu~(2+)4f~7 orbits and the electronic states near the Fermi level.Although the quantum anomalous Hall effect(AHE) is not observed in our crystals,it is found that a relatively large negative magnetoresistance (-13%) emerges in the AFM phase,and exhibits an exponential dependence upon magnetic Held,whose microscopic origin is waiting to be clarified in future research.     

Nonlinear uniaxial pressure dependence of the resistivity in Sr_(1-x)Ba_xFe_(1.97)Ni_(0.03)As_2

Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr_(1-x)Ba_xFe_(1.97)Ni_(0.03)As_2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Sr_(1-x)Ba_xFe_2As_2 is determined by the strength of the magnetic-elastic coupling.     

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)

Y-type hexaferrites with tunable conical magnetic structures are promising single-phase multiferroics that exhibit large magnetoelectric effects. We have investigated the influence of Co substitution on the magnetoelectric properties in the Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)(x = 0.0, 0.4, 1.0, 1.6). The spin-induced electric polarization can be reversed by applying a low magnetic field for all the samples. The magnetoelectric phase diagrams of BaBa(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22) are obtained based on the measurements of magnetic field dependence of dielectric constant at selected temperatures. It is found that the substitution of Co ions can preserve the ferroelectric phase up to a higher temperature, and thus is beneficial for achieving single-phase multiferroics at room temperature.     

Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures

Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Néel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.     

Magnetic phase transitions in layered intermetallic compounds

Magnetic, magnetoelastic, and magnetotransport properties have been studied for the RMn₂Si₂ and RMn₆Sn₆ (R is a rare earth metal) intermetallic compounds with natural layered structure. The compounds exhibit wide variety of magnetic structures and magnetic phase transitions. Substitution of different R atoms allows us to modify the interatomic distances and interlayer exchange interactions thus providing the transition from antiferromagnetic to ferromagnetic state. Near the boundary of this transition the magnetic structures are very sensitive to the external field, temperature and pressure. The field-induced transitions are accompanied by considerable change in the sample size and resistivity. It has been shown that various magnetic structures and magnetic phase transitions observed in the layered compounds arise as a result of competition of the Mn–Mn and Mn–R exchange interactions.     

Large magnetic entropy change and magnetic properties in La （Fel－xMnx）ll.TSil.3Hy compounds

Magnetic properties and magnetic entropy change in La(Fe_{1-x}Mn_x)_{11.7}Si_{1.3}H_y compounds have been investigated. A significant increase of the Curie temperature T_C and a small increase of the saturation magnetizations μ_S have been observed after the introduction of interstitial H, which caused a slight volume expansion. The first-order field-induced itinerant-electron metamagnetic (IEM) transition remains and brings about a large magnetic entropy change around room temperatures for the compounds. The maximal magnetic entropy change is about 23.4, 17.7 and 15.9J/kg·K under a magnetic field change from 0 to 5T for x=0.01, 0.02 and 0.03, respectively. Therefore, the compounds appear to be potential candidates for magnetic refrigerants around room temperatures.     

Combined Study of Structural,Magnetic and Transport Properties of Eu_(0.5)Ln_(0.5)BiS_2F Superconductor

Superconductivity below 0.3 K and a charge-density-wave-like(CDW-like) anomaly at 280 K were observed in EuBiS_2F recently.Here we report a systematic study of structural and transport properties in Eu_(0.5)Ln_(0.5)BiS_2F(Ln=La,Ce,Pr,Nd,Sm) by electrical resistivity,magnetization,and specific heat measurements.The lattice constants have a significant change upon rare earth substitution for Eu,suggesting an effective doping.As Ln is changed from Sm to La,the superconducting transition temperature T_c increases from 1.55 K to 2.8 K.In contrast to the metallic parent compound,the temperature dependence of electrical resistivity displays semiconductinglike behavior for all the Eu_(0.5)Ln_(0.5)BiS_2F samples.Meanwhile,the CDW-like anomaly observed in EuBiS2F is completely suppressed.Unlike the mixed valence state in the undoped compound,Eu ions in these rareearth-doped samples are mainly divalent.A specific anomaly at 1.3 K resembling that in EuBiS2F suggests the coexistence of superconductivity and spin glass state for Eu_(0.5)La_(0.5)BiS_2F.Coexistence of ferromagnetic order and superconductivity is found below 2.2 K in Eu_(0.5)Ce_(0.5)BiS_2F samples.Our results supplies a rich diagram showing that many interesting properties can be induced in BiS_2-based compounds.     

MAGNETIC PROPERTIES OF NEW SERIES R-Mo-Fe NITRIDES WITH THE ThMn12-TYPE STRUCTURE AT A LOWER Mo CONTENT

A systematic study has been made on formation condition, crystallographic structure and magnetic properties of RMo_1.5Fe_10.5N_x, where R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er. The interstitial nitrogen atom effects on Curie temperature, saturation magnetization and magneto-crystalline anisotropy have been investigated. Two important preliminary results have been obtained. (1) A single phase crystallized in the ThMn₁₂-type structure was stabilized with a smaller content of molybdenum, thus, the compounds possess a higher Curie temperature and a larger spontaneous magnetization. (2) A complete system of compounds with 1:12 type structure containing the light rare earth cerium and praseodymium was synthesized, which will be favorable for developing new rare earth hard magnetic materials.     

类钙钛矿化合物Ca（Mn2Cu1）Mn4O12的磁性与磁电阻效应

利用固相反应法制备了名义成分为Ca(Mn2Cu1)Mn4O12的类钙钛矿锰氧化物.x射线衍射表明，为了获得较为致密的样品和减小杂相含量，可以采用高温烧结再在1073K长时间空气中退火的制备方法.样品在低温下同时存在铁磁相和反铁磁相，由于反铁磁相的存在导致样品在4.5K时的磁化强度显著降低，并在8T的高磁场下仍未达到饱和.样品呈半导体导电性质，在85K和6T磁场下磁电阻比的最大值可达-46%. 关键词： ［AC3］(B4)O12类钙钛矿锰氧化物 庞磁电阻效应 铁磁性 反铁磁性     

Long-Time Magnetic Relaxation in Antiferromagnetic Topological Material EuCd_2As_2

Magnetic topological materials have attracted much attention due to the correlation between topology and magnetism. Recent studies suggest that EuCd_2As_2 is an antiferromagnetic topological material. Here by carrying out thorough magnetic, electrical and thermodynamic property measurements, we discover a long-time relaxation of the magnetic susceptibility in EuCd_2As_2. The(001) in-plane magnetic susceptibility at 5 K is found to continuously increase up to ~10% over the time of ~14 hours. The magnetic relaxation is anisotropic and strongly depends on the temperature and the applied magnetic field. These results will stimulate further theoretical and experimental studies to understand the origin of the relaxation process and its effect on the electronic structure and physical properties of the magnetic topological materials.     

Tip-Pressure-Induced Incoherent Energy Gap in CaFe_2As_2

In CaFe_2As_2,superconductivity can be achieved by applying a modest c-axis pressure of several kbar.Here we use scanning tunneling microscopy/spectroscopy(STM/S) to explore the STM tip pressure effect on single crystals of CaFe_2As_2.When performing STM/S measurements,the tip-sample interaction can be controlled to act repulsive with reduction of the junction resistance,thus to apply a tip pressure on the sample.We End that an incoherent energy gap emerges at the Fermi level in the differential conductance spectrum when the tip pressure is increased.This energy gap is of the similar order of magnitude as the superconducting gap in the chemical doped compound Ca_(0.4)Na_(0.6)Fe_2As_2 and disappears at the temperature well below that of the bulk magnetic ordering.Moreover,we also observe the rhombic distortion of the As lattice,which agrees with the orthorhombic distortion of the underlying Fe lattice.These Endings suggest that the STM tip pressure can induce the local Cooper pairing in the orthorhombic phase of CaFe_2As_2.     

Physical properties and crystal chemistry of Ce2Ga12Pt

Single crystals of the new ternary compound Ce(2)Ga(12)Pt were prepared by the self-flux technique. The crystal structure with the space group P4/nbm was established from single crystal x-ray diffraction data and presents a derivative of the LaGa(6)Ni(0.6) prototype. Magnetic susceptibility measurements show Curie-Weiss behaviour due to local Ce(3+) moments. At high temperatures, the magnetic anisotropy is dominated by the crystal-electric-field (CEF) effect with the easy axis along the crystallographic c direction. Ce(2)Ga(12)Pt undergoes two antiferromagnetic phase transitions at T(N,1) = 7.3 K and T(N,2) = 5.5 K and presents several metamagnetic transitions for the magnetic field along c. Specific-heat measurements prove the bulk nature of these magnetic transitions and reveal a doublet CEF ground state. The 4f contribution to the resistivity shows a broad maximum at T(max) ≈ 85 K due to Kondo scattering off the CEF ground state and excited levels.     

Raman scattering studies on the collapsed phase of CaCo_2As_2

In this work,Raman scattering measurements have been performed on the collapsed phase CaCo_2As_2 crystals.At least 8 Raman modes were observed at room temperature though CaCo_2As_2 is structurally similar to other 122 compounds like BaFe_2As_2.Two Raman modes are assigned to the intrinsic A_(1g)and B_(1g)of this material system respectively.The other ones are considered to originate from the local vibrations relevant to cobalt vacancies.Careful polarized measurements allow us to clearly resolve the four-fold symmetry of the B_(1g)mode,which put strong constraints on possible point group symmetries of the system with Co vacancies.The temperature-dependent measurements demonstrate that the anomalies in both frequency and width of the B_(1g)mode occur around Neel temperature T_N.The anomalies are considered to be related to the gap opening near the magnetic transition.The study may shed light on the structural and magnetic changes and their correlations with superconductivity in 122 systems.     

Effects of chemical pressure on diluted magneticsemiconductor(Ba,K)(Zn,Mn)_2As_2

Chemical pressure induced by iso-valent doping has been widely employed to tune physical properties of materials. In this work, we report effects of chemical pressure by substitution of Sb or P into As on a recently discovered diluted magnetic semiconductor(Ba,K)(Zn,Mn)_2 As_2, which has the record of reliable Curie temperature of 230 K due to independent charge and spin doping. Sb and P are substituted into As-site to produce negative and positive chemical pressures, respectively.X-ray diffraction results demonstrate the successful chemical solution of dopants. Magnetic properties of both K-underdoped and K-optimal-doped samples are effectively tuned by Sb-and P-doping. The Hall effect measurements do not show decrease in carrier concentrations upon Sb-and P-doping. Impressively, magnetoresistance is significantly improved from7% to 27% by only 10% P-doping, successfully extending potential application of(Ba,K)(Zn,Mn)_2 As_2.     

MAGNETIC PROPERTIES OF NEW SERIES R-Mo-Fe NITRIDES WITH THE ThMn12-TYPE STRUCTURE AT A LOWER Mo CONTENT

A systematic study has been made on formation condition, crystallographic structure and magnetic properties of RMo_1.5Fe_10.5N_x, where R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er. The interstitial nitrogen atom effects on Curie temperature, saturation magnetization and magneto-crystalline anisotropy have been investigated. Two important preliminary results have been obtained. (1) A single phase crystallized in the ThMn₁₂-type structure was stabilized with a smaller content of molybdenum, thus, the compounds possess a higher Curie temperature and a larger spontaneous magnetization. (2) A complete system of compounds with 1:12 type structure containing the light rare earth cerium and praseodymium was synthesized, which will be favorable for developing new rare earth hard magnetic materials.