Perpendicular exchange bias and its control by magnetic,stress and electric fields

Perpendicular exchange bias (PEB) involving perpendicular magnetic anisotropy (PMA) in both the antiferromagnetic (AF) pinning and the ferromagnetic (FM) sensor layer is expected to become important in future perpendicular recording and sensing devices. Further, because of the reduced spin dimensionality, PEB promises to be easier understandable than the conventional planar exchange bias (EB). In addition to its first realization using the Ising-type AF compounds FeF2 and FeCl2 we have tested control strategies of EB being alternative to the conventional magnetic and thermal ones. Indeed, specific symmetry properties of the pinning layer have been shown to enable mechanical (viz. piezomagnetic via FeF2) and electric control (viz. magneto-electric via Cr2O3) of EB, respectively. Electric control promises to become relevant for TMR devices in MRAM technology.     

水热法祖母绿激光晶体的光谱性质研究

报道了温差水热法生长的祖母绿激光晶体(Cr3+:Be3Al2Si6O18)的光学参量特点.通过对祖母绿晶体的吸收光谱和荧光光谱的测量,计算了晶体场强度Dq、Racah参量B和C, Dq/B≈2.3,说明了祖母绿晶体中的Cr3+离子处于中等晶场.室温下的荧光光谱特点显示4T2→4A2的跃迁为700～840nm的宽带辐射跃迁.此外该晶体的有效声子能量h－ω=409.6cm－1,Huang-Rhys因子S=3.5较小,说明祖母绿的电-声子耦合作用较弱.     

火焰原子光谱法分析有机功能试剂改性纳米SiO2对水中Cr2072-的吸附行为

以纳米二氧化硅(Nano-SiO2)为原料,硅烷偶联剂(KH-550)作为交联剂首先合成了氨丙基纳米二氧化硅(Nano-APSG),然后加入有机功能试剂季磷盐(COOH-Ph-CH2-P(C6H5)3Br)通过有机合成反应合成有机功能试剂改性纳米二氧化硅材料(Si|(CH2)3-NH-CO-Ph-CH2-P(C6H5)3Br),利用红外、粒径、热重分析等对结构进行了表征.通过火焰原子吸收光谱法研究此有机功能试剂改性纳米二氧化硅材料对水中Cr2O12-离子的吸附行为,考察了吸附的最佳pH、震荡时间、吸附剂用量等因素的影响,实验结果表明,在pH1,吸附剂用量为0.1 g,震荡时问为30 min时吸附剂对Cr2O72-离子的吸附效率可达95%以上,实验结果表明这种新型的功能材料可实现对废水中Cr2O72离子的分离与处理.     

利用原位红外光谱研究若干过渡金属氧化物-丙酸体系，Fe2Cr（μ3-O）（μ-O2CC2H5）6（H2O）3Cl*xH2O及Cr3（μ3-O）（μ-O2CC2H5）6（H2O）3NO3*xH2O的反应行为

利用原位红外光谱法研究标题化合作在N2 中的反应行为。发现它们在不同温度下能使丙酸分别转化为乙醛和戊酮。金属氧化物对丙酸的戊酮化反应活性顺序是 :Fe3O4 >MnO2 >Cr2 O3>Co2 O3>Ni2 O3,这顺序与下列簇合物对该反应的活性顺序类似 :[Fe2 MnOPH]>[Fe3OPH]>[Fe2 CrOPH]>[Fe2 CoOPH]>[Fe2 NiOPH]>[Cr3OPH][OPH =(μ3 O) (μ O2 CC2 H5) 6(H2 O) 3]。对于戊酮化反应 ,过渡金属氧化物的反应温度明显高于相应的 [Fe2 MOPH]的反应温度 ,这旁证了 [Fe2 MOPH]的活性组分不是其金属氧化物。还讨论了Fe3O4 ,Fe2 O3 对丙酸分别转化为乙醛和戊酮反应活性的明显差异。     

草酸根桥联的钆-铬六核双金属配合物的红外光谱研究

通过２,２′－联吡啶取代的草酸铬化合物和氯化钆在水溶液中反应合成了草酸根桥联的钆－铬六核双金属配合物的晶体。本文着重讨论该配合物的红外光谱。．     

超声场对钛基PbO2电极电化学氧化Cr3+过程电流效率的影响

本文研究了超声场对Ti／SnO2 Sb2O3／PbO2电极电化学氧化Cr3 过程的影响,探讨了在不同的操作电流密度、反应温度、硫酸浓度及Cr3 浓度下,超声场对硫酸介质中Cr3 电化学氧化生成Cr2O72-过程中的电流效率的影响,并用扫描电镜对有无超声场时不同反应时间下的电极形貌进行了分析。实验结果表明:在相同的反应条件下,有超声场作用时Cr3 电化学氧化过程的电流效率明显高于无超声场时的电流效率。扫描电镜测定发现,有超声场作用时不同反应时间下电极的形貌有明显的变化。     

The electronic and chemical structure of the a-B(3)CO(0.5):H(y)-to-metal interface from photoemission spectroscopy: implications for Schottky barrier heights

The electronic and chemical structure of the metal-to-semiconductor interface was studied by photoemission spectroscopy for evaporated Cr, Ti, Al and Cu overlayers on sputter-cleaned as-deposited and thermally treated thin films of amorphous hydrogenated boron carbide (a-B(x)C:H(y)) grown by plasma-enhanced chemical vapor deposition. The films were found to contain ～10% oxygen in the bulk and to have approximate bulk stoichiometries of a-B(3)CO(0.5):H(y). Measured work functions of 4.7/4.5?eV and valence band maxima to Fermi level energy gaps of 0.80/0.66?eV for the films (as-deposited/thermally treated) led to predicted Schottky barrier heights of 1.0/0.7?eV for Cr, 1.2/0.9?eV for Ti, 1.2/0.9?eV for Al, and 0.9/0.6?eV for Cu. The Cr interface was found to contain a thick partial metal oxide layer, dominated by the wide-bandgap semiconductor Cr(2)O(3), expected to lead to an increased Schottky barrier at the junction and the formation of a space-charge region in the a-B(3)CO(0.5):H (y) layer. Analysis of the Ti interface revealed a thick layer of metal oxide, comprising metallic TiO and Ti (2)O (3), expected to decrease the barrier height. A thinner, insulating Al(2)O(3) layer was observed at the Al-to-a-B(3)CO(0.5):H(y) interface, expected to lead to tunnel junction behavior. Finally, no metal oxides or other new chemical species were evident at the Cu-to-a-B(3)CO(0.5):H(y) interface in either the core level or valence band photoemission spectra, wherein characteristic metallic Cu features were observed at very thin overlayer coverages. These results highlight the importance of thin-film bulk oxygen content on the metal-to-semiconductor junction character as well as the use of Cu as a potential Ohmic contact material for amorphous hydrogenated boron carbide semiconductor devices such as high-efficiency direct-conversion solid-state neutron detectors.     

H2O对N复合氧化膜Cr2O3作用机制的理论研究

本文基于第一性原理方法,研究水对N复合氧化膜Cr2O3的作用机制。结果表明N的复合影响H2O在表面的吸附位点及吸附高度,N的溶入与Cr形成稳定作用,减缓H2O对表面Cr-O间的破坏作用,改善氧化膜表层结构,提高表面电化学稳定性。因此,N的复合可增强氧化膜对H2O的作用,同时改善氧化膜的结构稳定性,从而提高不锈钢的抗氧化性。     

Antiferromagnetic interlayer coupling of (111)-oriented La_(0.67)Sr_(0.33)MnO_3/SrRuO_3 superlattices

We report a strong antiferromagnetic(AFM) interlayer coupling in ferromagnetic La_(0.67)Sr_(0.33)MnO_3/SrRuO_3(LSMO/SRO) superlattices grown on(111)-oriented SrTiO_3 substrate. Unlike the(001) superlattices for which the spin alignment between LSMO and SRO is antiparallel in the in-plane direction and parallel in the out-of-plane direction, the antiparallel alignment is observed along both the in-plane and out-of-plane directions in the present sample. The low temperature hysteresis loop demonstrates two-step magnetic processes, indicating the coexistence of magnetically soft and hard components. Moreover, an inverted hysteresis loop was observed. Exchange bias tuned by the temperature and cooling field was also investigated, and positive as well as negative exchange bias was observed at the same temperature with the variation of the cooling field. A very large exchange field(H_(EB)) was observed and both magnitude and sign of the H_(EB)depend on the cooling field, which can be attributed to an interplay of Zeeman energy and AFM coupling energy at the interfaces. The present work shows the great potential of tuning a spin texture through interfacial engineering for the complex oxides whose spin state is jointly determined by strongly competing mechanisms.     

H13钢激光熔覆Co基涂层组织及热疲劳性能

针对热作模具用H13钢工况下易产生热疲劳失效的问题,采用Nd:YAG激光器在H13钢表面制备Co基合金涂层。利用光学显微镜、扫描电镜、能谱仪和X射线衍射仪,对涂层组织、合金元素分布及物相组成进行检测。利用显微硬度计和热震实验法,测试热疲劳对Co基合金涂层和淬火回火态H13钢硬度影响。结果表明,Co基合金涂层从底部到表层,依次为平面晶、胞状晶、树枝晶和等轴晶。Co基合金涂层物相主要由-Co和M23C6相组成,热疲劳后涂层表面形成M2O3和M3O4(M=Fe,Co,Cr)氧化物。Co基合金涂层硬度最高可达706HV0.2且呈梯度降低;热循环1000次后,Co基合金涂层表面硬度降低24.4%,H13钢表面硬度降低37.7%,Co基合金涂层硬度下降幅度低于H13钢。热循环1000次后,Co基合金涂层表面未发现明显热裂纹,H13钢表面形成大量网状热裂纹。Co基合金涂层中,Cr元素形成致密Cr2O3氧化膜使其热疲劳性能优于H13钢。     

Ferryl (Fe=O) termination of the hematite alpha-Fe2O3(0001) surface

Using scanning tunneling microscopy and infrared reflection absorption spectroscopy we have observed that the alpha-Fe2O3(0001) surface exhibits ferryl (Fe=O) groups, which may coexist with domains of the Fe-terminated surface. We therefore fully support ab initio calculations recently reported in the literature [W. Bergmeyer, H. Schweiger, and E. Wimmer, Phys. Rev. B 69, 195409 (2004)]. The close similarity to the results on the (0001) surfaces of Cr2O3 and V2O3 strongly suggests that the M=O termination under certain oxygen pressure conditions is the most stable for the close-packed surfaces of transition metal oxides with the corundum structure.     

Cooling-field dependence of exchange bias in Mg-diluted Ni1−xMgxO/Ni granular systems

The exchange-bias (EB) properties of Mg-diluted Ni_1−xMg_xO/Ni (0?x?0.3) granular systems have been investigated. Magnetic dilution with Mg greatly affects the EB field and the coercivity. The temperature dependence of the EB field and the coercivity can be explained in terms of formation of domain states. The value of the EB field increases and shows a maximum value with increasing cooling field, which can be explained by the competition between the field-dependent Zeeman energy and the exchange interaction at the interface.     

在N2中[VnCr3—n（μ3—O）（μ—O2CCH3）6（THF）3]X[n=0—3,X=Cl^—1,ClO4^—,（VO5）0.5^—]及[VnFe3—n（μ3—O）（μ—O2CCH3）6（THF）3]X（n=0—3,X=Cl^—1）

The reaction behavior of the title complexes have been investigated by means of in situ IR in nitrogen atmosphere. It has been found that they enabled the acetic acid to convert to acetone and methane in different temperatures. The results indicate that the sequence of the ketonization reaction activity for the clusters was [V3OAT] > [VFe2OAT], [V2CrOAT] > [Fe3OAT], [VCr2OAT] > [Cr3OAT] [OAT = (mu 3-O) (mu-O2CCH3)6 (THF)3], and the sequence of the methanation reaction activity for the clusters was [Cr3OAT] > [VCr2OAT], [V2CrOAT] > [V3OAT] > [VFe2OAT], [Fe2OAH]. The ketonization reaction activity of [Fe3OAT] were obviously lower than that of [Fe3OAH] [OAH = (mu 3-O) (mu-O2CCH3)6 (H2O)3] and the methanation reaction activity of [Cr3OAT] were also much lower than that of [Cr3OAH]. The difference between [Fe3OAH], [Cr3OAT] and [Fe3OAH], [Cr3OAH] mentioned above were discussed.     

格位选择激发下Eu[Cr0.1Al0.9(OH)6Mo6O18]·11H2O的光谱特性

详细研究了Eu[Cr0.1Al0.9(OH)6Mo6O18]·11H2O中Eu3+的发光特性. 通过对实验结果的分析, 确定了体系中Eu3+离子有3种发光中心, 其中一种占主导地位. 样品中存在的Eu3+到Cr3+的能量传递, 也发生在这个中心. 利用低温下的格位选择激发, 成功地分离了3种发光中心的发射光谱. 结果显示, 主要发光中心的格位对称性为C1, 与以前的研究结果一致; 另外两种发光中心则具有较高的对称性. 在共振激发条件下, 测量了不同发光中心在低温下的荧光衰减曲线, 拟合计算给出中心1(主要发光中心)和中心3的5D0能级的寿命分别为107 和599 μs, 相差近6倍. 说明中心3的对称性比中心1高, 和从光谱测量得到的结论一致.     

Brain metabolite concentration ratios in vivo: multisite reproducibility by single-voxel 1H MR spectroscopy

Ten normal subjects were scanned identically at three separate sites (Little Rock, Houston, and New Orleans) to evaluate the reproducibility of brain metabolite ratios in single-voxel (1)H point-resolved spectroscopy sequence (PRESS) magnetic resonance (MR) spectroscopy in vivo. All scans were processed by a single individual at a single site. Coefficients of variation of the measured metabolite ratios generally were in the range found for previous single-voxel, single-site reproducibility studies. No differences were found among the sites for ratios of N-acetylaspartate to creatine (NAA/Cr) or choline to Cr (Cho/Cr) in left thalamus by multivariate ANOVA. Metabolite ratios of Cr or Cho relative to local brain H(2)O did not vary among the sites. However, by multivariate ANOVA, NAA/H(2)O differed between Little Rock and New Orleans, but not between those sites and Houston. Intraclass correlation coefficients suggested reasonable reproducibility between Little Rock and New Orleans, but not between those sites and Houston.     

弱碱性阴离子交换树脂富集ICP-AES测定环境水体中Cr(Ⅵ)和有机态Cr(Ⅲ)的研究

选用331弱碱性阴离子交换树脂,对微污染水体中的Cr(Ⅵ)和有机态Cr(Ⅲ)进行了分离富集作用研究,考察了酸度、富集时间、洗脱液类型、洗脱液浓度及溶液中共存离子对分离富集过程的影响。研究表明,分别用1.0 mol·L-1 HCl和2.0 mol·L-1 NH₄NO₃＋0.5 mol·L-1 NH₃·H₂O可以很好分步洗脱有机态Cr(Ⅲ)和Cr(Ⅵ),利用ICP-AES测定, 该方法对Cr(Ⅲ)和Cr(Ⅵ)的检出限分别为1.1和 1.4 μg·L-1,相应的相对标准偏差RSD(n＝6)平均值分别为3.8％和5.6％。该方法适用于自来水、地下水、地表水及生活污水中痕量Cr(Ⅵ)和有机态Cr(Ⅲ)的分离富集及测定。     

A3M2GeO12石榴石体系中Cr^3＋离子的宽带发射光谱

首次报道在Ａ３Ｍ２Ｇｅ３Ｏ１２：Ｃｒ（Ａ＝Ｃｄ＾２＋,Ｍ＝Ａｌ＾３＋,Ｇａ＾３＋,Ｓｃ＾３＋）锗酸盐石榴石体系中,Ｃｒ＾３＋离子室温下的红－近红外宽发射带光谱性质。随位于八面体格位上的Ａｌ＾３＋→Ｇａ＾３＋→Ｓｃ＾３＋和十二面体格位上的Ｃｄ＾２＋→Ｃａ＾２＋组成顺序变化,室温下,Ｃｒ＾３＋离子的＾４Ｔ２→＾４Ａ２能级跃迁的Ｒ－ＮＩＲ宽发射带,发射峰及光谱的长波和短波边逐渐向低能长波边移动。     

Room temperature exchange bias in multiferroic BiFeO<Subscript>3</Subscript> nano- and microcrystals with antiferromagnetic core and two-dimensional diluted antiferromagnetic shell

Exchange bias (EB) of multiferroics presents many potential opportunities for magnetic devices. However, instead of using low-temperature field cooling in the hysteresis loop measurement, which usually shows an effective approach to obtain obvious EB phenomenon, there are few room temperature EB. In this article, extensive studies on room temperature EB without field cooling were observed in BiFeO₃ nano- and microcrystals. Moreover, with increasing size the hysteresis loops shift from horizontal negative exchange bias (NEB) to positive exchange bias (PEB). In order to explain the tunable EB behaviors with size dependence, a phenomenological qualitative model based on the framework of antiferromagnetic (AFM) core-two-dimensional diluted antiferromagnet in a field (2D-DAFF) shell structure was proposed. The training effect (TE) ascertained the validity of model and the presence of unstable magnetic structure using Binek’s model. Experimental results show that the tunable EB effect can be explained by the competition of ferromagnetic (FM) exchange coupling and AFM exchange coupling interaction between AFM core and 2D-DAFF shell. Additionally, the local distortion of lattice fringes was observed in hexagonal-shaped BiFeO₃ nanocrystals with well-dispersed behavior. The electrical conduction properties agreed well with the space charge-limited conduction mechanism.     

Effect of dehydration on the ferrimagnetic resonance in [Cr(CN)<Subscript>6</Subscript>][Mn(<Emphasis Type="Italic">S</Emphasis>)-<Emphasis Type="Italic">pn</Emphasis>H(H<Subscript>2</Subscript>O)](H<Subscript>2</Subscript>O) single crystals

The effect of dehydration-induced structural transitions on the ferrimagnetic resonance spectra of the [Cr(CN)₆][Mn(S)-pnH(H₂O)](H₂O) chiral molecular magnet has been studied for three crystalline modifications. The differences in the anisotropy field and exchange interaction constants due to the change in the dimensionality of the magnetic ordering upon the phase transitions have been established. In the dehydrated amorphous phase, apart from the ferrimagnetic resonance, additional isotropic magnetic resonance lines corresponding to the spin-glass state have been revealed.     

Ordering and excitations in the field-induced magnetic phase of Cs3Cr2Br9

Field-induced magnetic order has been investigated in detail in the interacting spin 3/2 dimer system Cs3Cr2Br9. Elastic and inelastic neutron scattering measurements were performed up to H=6 T, well above the critical field H(c1) approximately 1.5 T. The ordering displays incommensurabilities and a large hysteresis before a commensurate structure is reached. This structure is fully determined. Surprisingly, the lowest excitation branch never closes. Above H(c1), the gap increases slowly with the field. An analysis in terms of projected pseudospins is given.