Sr_2RuO_4正常态的c方向的磁阻的研究

研究了典型的层状钙钛矿结构超导单晶Sr2RuO4在c方向的磁阻(Δρ/ρ0)(H∥ab,J∥c)的变化.实验发现,磁阻表现出强烈的各向异性,并且随着温度T的降低,磁阻效应越明显;当在平面ab内旋转磁场H的方向时,磁阻成周期性变化;实验表明,磁场沿(110)方向时,出现磁阻的极大值.分别从Sr2RuO4的费米面的各向异性、载流子散射率、c方向能带色散的各向异性等方面来解释这些输运性质.     

GdBa2Cu3O7-δ单晶的各向异性研究

本文报道了对GdBa₂Cu₃O_7-δ单晶正常态电阻率、超导临界温变,以及磁转变的各向异性观测结果,发现ab平面上及c轴方向的电阻率,除T_c附近由于超导涨落引起的明显偏离以外,在正常态都能很好地满足Anderson-Zou关系:ρ=A/T+BT,但两方向的A,B存在显著差异说明其输运电荷是由不同机制产生,它具有显著的二维特征;沿c轴方向的超导电性比沿ab平面的超导电性要弱,T_ce⊥比T_ce∥低2K;H∥ab平面时的交流屏蔽效应仅是H⊥ab平面时的76％。 关键词：     

La2-xSrxCuO4单晶的平面内磁阻研究

测量了三种不同组分La2-xSrxCuO4(x＝0.09,0.18,0.24)单晶的平面内横向(H∥c,J∥ab)和纵向(H∥J∥ab)磁阻,发现平面横向与纵向磁阻都是正的,并且纵向磁阻与横向磁阻相比较很小,表明横向磁阻的主要贡献是电子轨道部分,也反映了ab面内和c方向电子有效质量的各向异性.三种成分单晶样品的平面内横向磁阻在不同温度随Sr含量x的变化显示在最佳掺杂浓度附近平面横向磁阻最大.     

正磷酸盐晶体Ba3(PO4)2和Sr3(PO4)2高温拉曼光谱研究

测量了碱土金属正磷酸盐Ba₃(PO₄)₂和Sr₃(PO₄)₂常温及高温拉曼光谱, 对拉曼振动模式进行指认, 并分析了晶体拉曼振动光谱及晶体结构在高温下的变化. 在温度升高的过程中, 拉曼振动频率向低频移动且振动峰宽度展宽, 晶体中的P-O平均键长随温度升高而变长, 但O-P-O的键角并未发生变化. 晶体在900 ℃以下无结构相变发生. 关键词： 3(PO₄)₂和Sr₃(PO₄)₂')" href="#">Ba₃(PO₄)₂和Sr₃(PO₄)₂ 高温拉曼光谱 振动模式 高温结构     

Correlation between mechano-electronic features and scattering rates using deformation potential theory

This research paper provides valuable insight into the electronic,mechanical and transport properties of the Sr₂RuO₂F₂ compound.The study shows that the Sr₂RuO₄ compound exhibits a metallic ground state and that the energy gap widens with oxygen substitution with fluorine.The concept of absolute deformation potential and its correlation with band energies and strains is explained using deformation potential theory.The paper also examines the...     

蓝色长余辉材料Sr2MgSi2O7：Eu2+,Dy3+及其基质的VUV-UV激发特性

Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺是一种有效的蓝色长余辉材料,采用高温固相法合成了Sr₂MgSi₂O₇,Sr₂MgSi₂O₇:Dy³⁺,Sr₂MgSi₂O₇:Eu²⁺及Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺,利用同步辐射研究了它们的VUV-UV激发特性.在真空紫外光激发下,在基质中发现了稍弱的位于385nm的发射带,在双掺杂的样品中,除了Eu²⁺的4f5d→4f发射带(465nm)外,还观察到了575nm处的发射峰;通过和Dy³⁺单掺杂样品的发射谱比较,发现它是来自于Dy³⁺的4f-4f(⁴F_9/2→6H_13/2)跃迁.在它们的激发谱上可以看出Dy³⁺与基质发射的有效激发均处于真空紫外区,在近紫外及可见区激发下未见到它们发光.另外在Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺中观察到Dy³⁺的发射也说明了Dy³⁺在该类长余辉材料中不仅作为陷阱用来延长余辉,而且也以发光中心形式存在于基质中.     

Eu3+/Dy3+共掺Sr3Y2(BO3)4荧光粉的发光性质研究

稀土掺杂发光材料一直是科研领域研究的热点,被广泛应用于白光LED、温度传感、显示显像、新能源和激光等领域。基质的结构对于稀土离子光致发光特性有非常重要的影响,在众多发光基质材料中,硼酸盐具有透光范围宽、光学损伤阈值高、较好的热稳定性和化学稳定性等优点。碱土-稀土金属硼酸盐Sr₃Y₂(BO₃)₄具有出色的光学性能,对其发光性能的研究具有重要意义。稀土离子Eu3+具4f6电子层,是一种典型的下转换发光中心离子,常被选作红色发光材料的激活剂。Dy3+具4f9电子层,也是一种典型的下转换发光中心离子,在紫外光激发下,在蓝色光区和橙色光区有较强的荧光发射。采用高温固相法合成了Sr₃Y₂(BO₃)₄∶Eu3+/Dy3+荧光粉,通过XRD和SEM对样品的结构和形貌进行了表征,XRD结果表明,1 000 ℃烧结5 h,H₃BO₃过量20%为最佳制备条件,且少量的Eu3+和Dy3+掺杂并未改变Sr₃Y₂(BO₃)₄的晶格结构。SEM图像表明Sr₃Y₂(BO₃)₄基质的平均晶粒尺寸为2～4 μm,10%Eu3+单掺和5%Eu3+/5%Dy3+双掺样品与基质Sr₃Y₂(BO₃)₄的SEM图像相比,形貌和尺寸并没有发生明显的改变。Sr₃Y₂(BO₃)₄∶Eu3+荧光粉的发光结果表明,分别在395和466 nm激发下,浓度为5%,10%和15%的Eu3+单掺Sr₃Y₂(BO₃)₄荧光粉的主要发光位于593和613 nm的红光发射,峰强度随着Eu3+浓度的增加呈现先增加后降低的变化形式,掺杂浓度为10%时发光强度最大,说明存在浓度猝灭现象。色坐标结果显示,激发波长由395 nm变化到466 nm,Sr₃Y₂(BO₃)₄∶Eu3+荧光粉的发光颜色从橙红色向红色转变。引入Dy3+后,Sr₃Y₂(BO₃)₄∶Eu3+/Dy3+样品的发射光谱出现Dy3+的486 nm的蓝光发射（4F_9/2→6H_15/2）和576 nm的橙光发射（4F_9/2→6H_13/2）,并且随着Dy3+浓度的增加,对Eu3+的5D₀→7F_{1, 2, 3, 4}跃迁有抑制作用。色坐标结果显示通过调整掺杂离子Eu3+和Dy3+的比例可实现Sr₃Y₂(BO₃)₄∶Eu3+/Dy3+荧光粉的颜色从红色区域向橙色区域转变,说明其在显示方面具有良好的应用前景。     

双钙钛矿Sr2CrWO6的磁性与输运性质研究

研究了双钙钛矿Sr₂CrWO₆的磁性和输运性质.Sr₂CrWO₆多晶在Ar气及真空气氛中经固相烧结而形成.X射线衍射分析表明主相为Sr₂CrWO₆,少量杂相为SrWO₄.热磁测量表明样品的居里温度为480K左右.电阻随温度降低而升高,类似于绝缘体,在外场5T,低温下(25K)磁致电阻(MR)可达20%,但MR随温度升高而趋于零.较大的矫顽力(5.97×1 关键词： 双钙钛矿氧化物 磁性质 磁致电阻     

MgO对Sr2SiO4:Eu2+荧光粉发光性质的影响

通过在Sr₂SiO₄:Eu²⁺荧光粉中加入MgO,提高了Sr₂SiO₄:Eu²⁺荧光粉的蓝光和黄光发射带的发射强度,研究了MgO浓度对Sr₂SiO₄:Eu²⁺荧光粉发光强度的影响。当Mg与Si的量比在1.0附近时,荧光粉的亮度较高,且发光颜色为白色。通过调节Sr₂SiO₄:yEu²⁺ ,MgO荧光粉中Eu²⁺的掺杂浓度,可以调节荧光粉的发光颜色。用Sr₂SiO₄:Eu²⁺ ,MgO和400 nm的InGaN管芯制备的白光LED,色坐标优于α'-Sr₂SiO₄:Eu²⁺和β-Sr₂SiO₄:Eu²⁺荧光粉制成的白光LED,显色指数和流明效率高于β-Sr₂SiO₄:Eu²⁺和α'-Sr₂SiO₄:Eu²⁺制成的白光LED。     

新型红色荧光粉Sr2ZnMoO6:Sm3+的制备与发光性能

采用高温固相法合成了Sr₂ZnMoO₆:Sm³⁺新型红色荧光材料,并对其发光特性进行了研究。XRD测量结果表明所制备样品为纯相Sr₂ZnMoO₆晶体。样品的发射光谱由一系列锐谱组成,分别位于563 nm(⁴G_5/2→⁶H_5/2)、598 nm(⁴G_5/2→⁶H_7/2)、607 nm(⁴G_5/2→⁶H_7/2)和645 nm(⁴G_5/2→⁶H_9/2),最强发射为645 nm。样品激发光谱由电荷迁移带CT和Sm³⁺离子的特征激发峰组成,主激发峰位于284 nm(CT)和403 nm(⁶H_5/2-⁴L_13/2)。 随着Sm³⁺浓度的增大, Sr_2-xZnMoO₆:xSm³⁺材料的发光强度先增大后减小, 在x≥2%时,发生浓度猝灭现象。根据Dexter理论分析其猝灭机理为电偶极-电偶极相互作用。比较了Li⁺、Na⁺和K⁺作为电荷补偿剂的作用,发现均使Sr₂ZnMoO₆:Sm³⁺材料的发射强度得到增强,但以Li⁺补偿效果最为显著。     

Physical properties and anisotropies of the RNiGe3 series (R = Y, Ce-Nd, Sm, Gd-Lu)

We have studied RNiGe₃ (R=Y, Ce-Nd, Sm, Gd-Lu) single crystals by measuring crystal structure and stoichiometry, magnetic susceptibility, magnetization, electrical resistivity, magnetoresistance, and specific heat. Clear anisotropies as well as antiferromagnetic ordering in the RNiGe₃ series (R=Ce-Nd, Sm, Gd-Tm) have been observed above 1.8 K from the magnetic susceptibility. A metamagnetic transition in this family (except for R=Sm) was detected at 2 K for applied magnetic fields below 70 kOe. The electrical resistivity of this series follows metallic behavior in the high temperature region. Below the antiferromagnetic ordering temperature a significant anisotropy is exhibited in the resistivity and magnetoresistance for different current directions. The anisotropic magnetic, transport, and thermal properties of RNiGe₃ compounds are discussed in terms of Ni site occupancy as well as a combination of the effect of formation of a magnetic superzone gap and the crystalline electric field.     

Glassy-ferromagnetic behavior in Eu0.5Sr0.5CoO3

Polycrystalline perovskite cobalt oxide Eu_0.5Sr_0.5CoO₃ was prepared by the conventional solid-state reaction method. X-ray powder patterns indicated the prepared samples are pure, cubic perovskite structure (Pm3?m), and with no evidence of any secondary phases. The dc magnetization and ac susceptibility measurements were carried out to investigate the magnetic properties of the sample, and which indicated that cluster-glasses properties are suppressed with the increasing of the coercive field. We denied the possibility of spin-glasses and the existence of the Hopkinson effect in Eu_0.5Sr_0.5CoO₃ through the temperature-dependent ac susceptibility measurements, and explained the magnetic behavior of Eu_0.5Sr_0.5CoO₃ with the competition between magnetic anisotropy and the external magnetic field.     

Magnetotransport properties of epitaxial Pr0.5Ca0.5MnO3 films grown by a solution technique

Epitaxial Pr_0.5Ca_0.5MnO₃ films have been synthesized on (0 0 1) SrTiO₃ substrate using a chemical solution deposition technique and two-step post-annealing process. The zero field resistivity of the films shows semiconducting behavior and a characteristic of charge ordering is observed at 230 K. The resistivity of the 10 nm film did not show any effect with the magnetic field. However, melting of charge ordering was observed for the 120 nm film at an applied magnetic field of 4 T. Large decrease in the resistivity of the 120 nm film (<100 K) resulted in magnetoresistance of nearly −100% at 75 K.     

The use of Lorentz microscopy for the determination of magnetic reversal mechanism of exchange-biased Co30Fe70/NiMn bilayer

Lorentz transmission electron microscopy (LTEM) combined with in-situ magnetizing experiments is a powerful tool for the investigation of the magnetization of the reversal process at the micron scale. We have implemented this tool on a conventional transmission electron microscope (TEM) to study the exchange anisotropy of a polycrystalline Co₃₅Fe₆₅/NiMn bilayer. Semi-quantitative maps of the magnetic induction were obtained at different field values by the differential phase contrast (DPC) technique adapted for a TEM (SIDPC). The hysteresis loop of the bilayer has been calculated from the relative intensity of magnetic maps. The curve shows the appearance of an exchange-bias field reveals with two distinct reversal modes of the magnetization: the first path corresponds to a reversal by wall propagation when the applied field is parallel to the anisotropy direction whereas the second is a reversal by coherent rotation of magnetic moments when the field is applied antiparallel to unidirectional anisotropy direction.     

激光辐照非晶Fe73.5Cu1Nb3Si13.5B 9微量晶化的穆斯堡尔谱研究

在激光功率为40—160W、扫描速度为10mm/s、激光光斑为20mm照射条件下,用CO ₂激 光辐照非晶Fe_73.5Cu₁Nb₃Si_13.5B_{9< /sub>产生微量晶化.利用透射穆斯堡尔谱 （TMS）技术分析了原始态和晶化后样品的超精细结构.确定了穆斯堡尔谱的基本参数——化 学位移(IS)、四极分裂(QS)、内磁场(Hhf)随激光功率变化的规律.分析表明，CO2关键词： 激光辐照 微量晶化 73.5Cu1Nb3 Si13.5B9')" href="#">非晶Fe73.5Cu1Nb3 Si13.5B9 穆斯堡尔谱}     

Magnetoresistance of 2H−NbSe2

The magnetoresistance anisotropy of 2H?NbSe₂ was studied at 9.3 K and 35 K. Data indicate that the Fermi surface above and below the charge-density-wave onset temperature includes one or more sheets that are highly elongated (and possibly open) along the [0001] direction. The magnetoresistance at 9.3 K exhibits an anomalous linear dependence on magnetic field for all field directions studied, similar to that reported previously for $\text{B}$[0001]     

Giant room-temperature magnetoresistance in La0.8Tb0.2MnO3 under the low magnetic fields

Polycrystalline perovskite La_0.8Tb_0.2MnO₃ (LTMO) with an orthorhombic phase was synthesized by conventional solid-state reaction. The magnetic and electric properties of La_0.8Tb_0.2MnO₃ were examined. The striking finding is that the material exhibits giant magnetoresistance at room temperature as high as −31.8% and −35.7% under the low magnetic fields of 100 and 1000 Oe, respectively. This result suggests that La_0.8Tb_0.2MnO₃ has a promising potential in future device developments.     

Si掺杂的铁磁形状记忆合金Co50Ni21Ga29Six的物性研究

成功生长了Co₅₀Ni₂₁Ga₂₉:Si(x=1,2)单晶样品,对其磁性,马氏体相变及其相关性质进行了细致的测量.发现掺Si成分的单晶具有非常迅速的马氏体相变行为、2.5％的大相变应变、大于100 ppm的磁感生应变和4.5％的相变电阻.进一步研究指出,在CoNiGa合金中掺入适量Si元素,能够降低材料的马氏体相变温度,减小相变热滞后,提高材料的居里温度,并使得磁性原子的磁矩有所降低.尤其重要的是Si元素的添加能够增大材料马氏体的磁晶各向异性能,改善马氏体变体的迁移特性,从而获得更大的磁感生应变. 关键词： 铁磁形状记忆合金 Heusler合金 50Ni₂₁Ga₂₉Si_x')" href="#">Co₅₀Ni₂₁Ga₂₉Si_x     

Observation of large magnetic resistance in weak magnetic fields using CuPt/SiO2/Si/SiO2/CuPt structure

The magnetoresistive effect of CuPt(8 nm)/SiO₂(5 nm)/Si(50,000 nm)/SiO₂(5 nm)/CuPt(8 nm) structure made by e-beam evaporation technique is studied in this work. Variation in magnetoresistance obtained by I-V measurements at 77 K and in the presence of less than 5 mT magnetic field applied in parallel to the surface is investigated. We have found that this structure exhibit large magnetoresistance in low magnetic fields (i.e. <5 mT). Our results also indicate that the variation in magnetoresistance in the presence of external magnetic field has oscillatory behavior and has the maximum value of 3295%. This structure due to its high sensitivity to low magnetic fields can also be used as an active element in magnetic field sensor devices.     

Magnetic phase transitions in Nd7Rh3 single crystal

Magnetic phase transitions in rare earth intermetallic compound Nd₇Rh₃ have been investigated using a single crystal. Measurement results of magnetization, magnetic susceptibility, specific heat, and electrical resistivity reveal that Nd₇Rh₃ has two magnetic phase transitions at T_N=34 K, T_t2=9.1 K and a change of the magnetic feature at T_t1=6.8 K in the absence of an external magnetic field. Antiferromagnetic orderings exist in all the three magnetic states; a large magnetic anisotropy between the c-axis and the c-plane is observed. In the magnetic phase below T_t2, an irreversible field-induced magnetic phase transition takes place in the c-plane; after removing external magnetic field, a coexistence state of ferro- and antiferromagnetic ordering or a ferrimagnetic state having a remanent magnetization M_R is stabilized. The M_R decays to a certain value for several hours after the first process; a magnetic field cooling effect was also observed in the c-plane below T_t2. In the antiferromagentic state above T_t2, the irreversibility disappears and an ordinary antiferromagnetic state takes place. As the origin of this phenomenon, a kind of martensitic structural transition that is observed in Gd₅Ge₄ can be considered.