共查询到19条相似文献,搜索用时 125 毫秒
1.
用量子理论计算了Dy3Al5O12的晶场能谱、Zeeman劈裂能级和波函数. 在外磁场He为0<He<9 T, 温度为3<T<42 K 范围内, 计算了该晶体的磁矩、磁熵变, 计算结果与相关实验数据吻合较好. 该计算结果表明, Dy3Al5O12内磁性离子间的交换作用非常微弱, 可以忽略. 从理论上给出了绝热退磁过程中温度变化ΔT与T的关系, 并与Gd3Ga5O12晶体进行了比较, 发现不同外磁场下, Dy3Al5O12和Gd3Ga5O12的低温制冷性能在不同温区有差别. 在进行低温(T<10 K)制冷时, 若外磁场较低, 选择Dy3Al5O12作为磁制冷材料较好; 若外磁场较高, 选择Gd3Ga5O12作为磁制冷材料较好. 相似文献
2.
Tb$lt;sub$gt;0.3$lt;/sub$gt;Dy$lt;sub$gt;0.6$lt;/sub$gt;Pr$lt;sub$gt;0.1$lt;/sub$gt;(Fe$lt;sub$gt;1-$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;Al$lt;sub$gt;$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;)$lt;sub$gt;1.95$lt;/sub$gt;合金的磁性、磁致伸缩和穆斯堡尔谱研究 下载免费PDF全文
系统研究了室温下Tb0.3Dy0.6Pr0.1(Fe1-xAlx)1.95 (x=0.05,0.1,0.15,0.2,0.25,0.3)合金中元素Al替代Fe对结构、磁性、磁致伸缩性能和自旋重取向的影响.测量结果发现,x<0.2时Tb0.3Dy0.6Pr0.1(Fe1-xAlx)1.95合金基本上是纯的单相,x=0.2时出现其他杂相,杂相随Al替代量的增加不断增多.随Al替代量x的增加,点阵常数a接近于线性增大,Curie温度TC逐渐下降,而矫顽力Hc急剧下降.振动样品磁强计(VSM)测量发现,磁化强度M随Al替代量x的变化较为复杂.VSM计和磁致伸缩效应测量共同表明,少量Al的替代有利于降低磁晶各向异性,而且随着Al替代量x的增多磁致伸缩系数快速减小,x>0.15时巨磁致伸缩效应消失.穆斯堡尔效应研究发现,随Al含量的增加Tb0.3Dy0.6Pr0.1(Fe1-xAlx)1.95合金中易磁化轴可能在{110}面逐渐偏离了立方晶体的主对称轴,发生自旋重取向,从而引起合金宏观磁性、磁致伸缩性能的变化.
关键词:
磁致伸缩
立方Laves相
自旋重取向
穆斯堡尔谱 相似文献
3.
用全势线性缀加平面波方法,考虑局域自旋密度近似研究虚晶掺杂MgCNi3的超导电性和磁性.计算了自旋极化能带结构、体弹性模量和它对压力的导数、原子磁矩m及其变化率.计算结果表明,对于电子掺杂的Mg1-xAlxCNi3(0≤x≤0.5),超导电性和磁涨落随掺杂量的增加逐渐减小.空穴掺杂的Mg1-xNaxCNi3,在x=0.12处出现铁磁相变,超导电性消失.在MgCNi3少量空穴掺杂区域(0≤x<0.12),表现为超导与磁涨落共存的不稳定状态.
关键词:
超导电性
能带结构
态密度
磁性 相似文献
4.
运用一维和三维微磁学模拟探究了易轴与外场存在偏角β情况下Nd2Fe14B/α-Fe 双层膜的磁矩反转过程, 计算了磁矩反转过程中磁滞回线和磁能积, 并与实验结果进行了对比. 计算结果表明, 在膜面内的易轴偏角β严重影响磁矩反转过程. 当β≠0°时, 磁矩反转过程中无明显成核现象, 随着易轴偏角β的增大, 剩磁显著减小, 磁滞回线方形度变差, 导致磁能积急剧减小. 对于Nd2Fe14B(10 nm)/α-Fe(8 nm)双层膜, β=10°时, 最大磁能积下降30.3%. 在磁矩反转过程中, 总能量最大时对应的外磁场能随易轴偏角的增大而减小, 交换作用能先增大后减小, 磁晶各向异性能则随着易轴偏角的增大而增大. 软磁相厚度越大, 双层膜的磁能积受易轴偏角影响越大. 在膜面外的易轴偏角对磁矩反转过程也有类似的影响.
关键词:
微磁学模拟
磁晶易轴
磁能积
能量 相似文献
5.
采用交换相互作用的分子场理论模型对金属间化合物HoMn6Sn6的自旋重取向相变进行了研究. 从理论上计算了HoMn6Sn6的易磁化方向以及Ho和Mn离子磁矩与c轴夹角随温度的变化. 基于单离子模型计算了Ho离子的一阶和二阶磁晶各向异性常数K1R和K2R随温度的变化. 研究表明,为了很好描述该化合物的自旋重取向相变,必须考虑Ho离子的四阶晶场项及相应的二阶磁晶各向异性常数K2R,K2R与K1R和Mn离子磁晶各向异性常数K1t之间的相互竞争是导致HoMn6Sn6自旋重取向相变的重要因素.
关键词:
稀土-过渡族金属间化合物
自旋重取向
磁晶各向异性 相似文献
6.
研究了晶场二级效应在PrF3晶体中的作用,发现该效应可使Pr3+离子的晶场单态与其他态混合,对PrF3晶体磁化率产生明显影响.进一步研究了晶体内的交换作用有效场,其形式为Hin=(1.9-0.02556T)×10-5M,在100—300 K的温度范围内,以此计算的PrF3晶体的倒数磁化率和Verdet常数的倒数与实验值符合较好.结果表明,在PrF3晶体中,晶场二级效应与离子间的交换作用都不能忽略.
关键词:
晶场二级效应
交换作用有效场
Verdet常数
3晶体')" href="#">PrF3晶体 相似文献
7.
8.
研究了低温下NdMnO3单晶的比热随温度和磁场的变化(2K≤T≤200K,0T≤H≤8T ).对应于 Mn磁矩亚晶格的A型反铁磁(A-AF)相变,零场下的比热曲线在85K附近出现尖锐的λ形峰,随 着磁场的增加,此λ峰降低展宽而且平滑变化,这与此温度附近磁化强度的变化规律一致. 与磁有序相变相关的熵变约为理论值的26%,这可能是由于磁有序涨落延续在较大温区造成 的.在20K以下,比热曲线出现了明显的肩膀形状的Schottky反常,其峰值随着磁场的增加而 逐渐向高温移动.考虑了低温下比热的各种贡献,根据Nd3+位有效分子场(H mf) 引起的Nd3+基态双重态(GSD)劈裂对上述现象进行了解释.通过对2K≤T≤2 0K,0T≤ H≤8T范围内比热数据的拟合,得到了样品的GSD劈裂,德拜温度和A-AF自旋波劲度系数以及 它们对磁场的依赖关系.发现GdFeO3型八面体旋转引起的A-AF结构中Mn磁矩亚晶 格的铁磁成分可能是Hmf的来源.
关键词:
比热
Schottky反常
反铁磁相变 相似文献
9.
通过对La0.8Sr0.2Mn1-yCoyO3(y≤02)饱和磁矩和输运的测量,研究了Co对La0.8Sr0.2MnO3的磁电阻影响机制.结果表明,在La0.8Sr0.2Mn1-yCoyO3(y≤02)中Co3+离子是低自旋态.由于Mn3+—O—Co3+—O—Mn3+类型的磁交换与Mn3+-Mn4+离子间双交换作用相比较弱,Curie温度TC附近的磁电阻随着Co掺杂量的增加而降低.与此相反,由于Co2+离子与eg巡游电子的反铁磁交换耦合作用,低温区间的磁电阻随着Co掺杂量的增加而升高.
关键词:
低自旋
磁电阻
磁交换作用 相似文献
10.
La$lt;sub$gt;0.4$lt;/sub$gt;Ca$lt;sub$gt;0.6$lt;/sub$gt;MnO$lt;sub$gt;3$lt;/sub$gt;中Mn-位Fe和Cr掺杂对磁性质的影响 下载免费PDF全文
研究了Fe和Cr掺杂对La0.4Ca0.6MnO3 中电荷有序反铁磁基态的调控作用. 磁性质的测量结果表明, 两种离子掺杂均能有效抑制原型样品中的长程电荷有序相, 但是Fe离子掺杂样品均具有反铁磁的基态, 而Cr掺杂样品中则出现了显著的铁磁性. 结合电输运测量结果显示, Cr掺杂引起的铁磁态同时具有金属性, 表明其中是电子双交换作用占主导. 对比两种掺杂离子的电子结构发现, Cr离子空的eg电子轨道促进了电子双交换作用, 而Fe掺杂则只是引入了不同的自旋交换作用, 导致自旋无序.
关键词:
磁性氧化物
反铁磁 相似文献
11.
Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(Ga_xFe_(1-x))_(1.9) compounds 下载免费PDF全文
《中国物理 B》2021,30(6):67504-067504
The magnetostriction, magnetization, and spin reorientation properties in Pr(Ga_xFe_(1-x))_(1.9) alloys have been investigated by high-precision x-ray diffraction(XRD) step scanning, magnetization, and Mo¨ssbauer spectra measurements. Ga substitution reduces the magnetostriction(λ_(||)) with magnetic field H ≥ 8 kOe(1 Oe = 1.33322×10~2 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations(SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mo¨ssbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature(T_(SR)) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(T_x Fe_(1-x))_(1.9)(T = Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction(EMD) or T_(SR) for developing an anisotropic compensation system. 相似文献
12.
Structure and frustrated magnetism of the two-dimensional triangular lattice antiferromagnet Na2BaNi(PO4)2 下载免费PDF全文
A new frustrated triangular lattice antiferromagnet Na2BaNi(PO4)2 was synthesized by high temperature flux method. The two-dimensional triangular lattice is formed by the Ni2+ ions with S =1. Its magnetism is highly anisotropic with the Weiss constants θCW =-6.615 K (H⊥c) and -43.979 K (H||c). However, no magnetic ordering is present down to 0.3 K, reflecting strong geometric spin frustration. Our heat capacity measurements show substantial residual magnetic entropy existing below 0.3 K at zero field, implying the presence of low energy spin excitations. These results indicate that Na2BaNi(PO4)2 is a potential spin liquid candidate with spin-1. 相似文献
13.
Viscosities of pure Ga, Ga_(80)Ni_(20), and Ga_(80)Cr_(20) metallic melts under a horizontal magnetic field were investigated by a torsional oscillation viscometer. A mathematical physical model was established to quantitatively describe the viscosity of single and binary metallic melts under a horizontal magnetic field. The relationship between the viscosity and the electrical resistivity under the horizontal magnetic field was studied, which can be described as η_B = η +(2H/πΩ)B~2(η_B is the viscosity under the horizontal magnetic field, η is the viscosity without the magnetic field, H is the height of the sample,? is the electrical resistivity, and B is the intensity of magnetic field). The viscosity under the horizontal magnetic field is proportional to the square of the intensity of the magnetic field, which is in very good agreement with the experimental results. In addition, the proportionality coefficient of ηB and quadratic B, which is related to the electrical resistivity,conforms to the law established that increasing the temperature of the completely mixed melts is accompanied by an increase of the electrical resistivity. We can predict the viscosity of metallic melts under magnetic field by measuring the electrical resistivity based on our equation, and vice versa. This discovery is important for understanding condensed-matter physics under external magnetic field. 相似文献
14.
We have measured the resistivity of textured Bi1.84Pb0.4Sr2Ca2Cu3Oy silver-clamped thick films as a function of temperature, current density ranging from 10 to 1×103 A/cm2 and magnetic field up to 0.3 T. We find that the effective activation energy Ue follows Ue(T,J,H)=U0(1−T/Tp)mln(Jc0/J)H− with m=1.75 for Hab-plane and 2.5 for Hc-axis and =0.76 for Hab and 0.97 for Hc, for the current density regime above 100 A/cm2, where Tp is a function of applied magnetic field and current density. This result suggests the effective activation energy Ue be correlated with the temperature, current density and magnetic field. The possible dissipative mechanisms responsible for the temperature, current density and magnetic field dependence of the effective activation energy are discussed. 相似文献
15.
研究了具有Dzyaloshinskii-Moriya(DM)相互作用的一维横场XY自旋链的量子相变和量子相干性.采用约旦-维格纳变换严格求解了哈密顿量,并描绘了体系的关联函数和相图,相图包含反铁磁相、顺磁相和螺旋相.利用相对熵和Jensen-Shannon熵讨论了XY模型的量子相干性.研究发现,相对熵与Jensen-Shannon熵所表现的行为都可以很好地表征该模型的量子相变.非螺旋相中量子相干性不依赖DM相互作用,而在螺旋相DM相互作用对量子相干性有显著影响.此外,指出了在带有DM相互作用的这一类反射对称破缺体系中关联函数计算的常见问题. 相似文献
16.
Anomalous magnetotransport phenomena have been observed in θ-(BEDT-TTF)2I3 crystals at temperatures below 15 K. The magnetoresistance M : (1) is a linear function of the magnetic field H, (2) is not affected by the angle between the electric current and the magnetic field, (3) but depends on the magnetic field orientation with respect to the crystal axis. Magnetoresistance is expressed as M = (aH2a + bH2b + cH2c)0-3/2/H in terms of H = (Ha, Hb, Hc), the zero field resistivity 0, and parameters a, b, and c which are independent of temperature and magnetic field. We have found that b a > c. Magnetoresistance up to 40 is observed for H = 7T along the b-axis at T = 1.5K. 相似文献
17.
测定了酸性水溶液中甘氨酸、丝氨酸和天冬氨酸稀土络合物(Ln=La、Pr、Nd、Eu、Tb、Dy、Ho、Er、Tm和Yb)的13C诱导位移。对位移试剂的分析指出,三种氨基酸通过α-羧基以双齿形式配位于稀土,配位键长为0.23nm~0.25nm,天冬氨酸的γ-羧基也是配位基团。由本文与文献中已报道的各种氨基酸稀土络合物的13C诱导位移的系统分析表明,配体13C超精细偶合常数A值和结构因子G值有如下规律:(1)│A(C0)│<│A(Cα)│;A(C0)为正,A(Cα)为负;(2)│G(C0)│>│G(Cα)│;配体碳核的G均为负值。 相似文献
18.
P. C. Canfield B. K. Cho D. C. Johnston D. K. Finnemore
M. F. Hundley
《Physica C: Superconductivity and its Applications》1994,230(3-4):397-406The magnetization of single-crystal HoNi2B2C has been measured as a function of applied field (H) and temperature in order to probe the interplay between superconductivity and magnetism in this complex layered system. The normal-state magnetic susceptibility of HoNi2B2C is highly anisotropic with a Curie-Weiss-like temperature dependence for H applied perpendicular to the c-axis and with a much weaker temperature dependence for H applied parallel to the c-axis, indicating that the Ho+3 magnetic moments lie predominately in the tetragonal a−b plane below 20 K. High-field magnetization (2000 Oe), low-field magnetization (20 Oe) and zero-field specific heat all give an antiferromagnetic ordering temperature of TN=5.0 K. Remarkably, in 20 Oe applied field both superconductivity (Tc=8.0 K) and antiferromagnetism (TN=5.0 K) clearly make themselves manifest in the magnetization data. From these magnetization data a phase diagram in the H−T plane was constructed for both directions of applied field. This phase diagram shows a non-monotonic temperature dependence of Hc2 with a deep minimum at TN=5 K. The high-field magnetization data for H applied perpendicular to the c-axis also reveal a cascade of three phase transitions for T < 5 K and H < 15 000 Oe, contributing to the rich H versus T phase diagram for HoNi2B2C at low temperatures. 相似文献
19.
本文提出了予测稠苯芳杂环及其烷基链上质子化学位移的计算方法。
将稠苯芳杂环化合物用凯库勒式表示,计算式为为需考虑的苯环内的乙烯基效应。σmi,ci为各苯环的环流效应。σ1,Hc为各芳杂环的屏蔽效应,对杂环上质子它就是该单独芳杂环上相应质子的δ值,对苯环上质子要将它分解为各结构因素的效应,即:σ1,He=(1/2)d-1δx=y(或σz)+σc-c·σm,H.
σx-y与σz为杂原子或其基团的屏蔽效应,σc=c为存在于芳杂环中的乙烯基的效应,σm,Hc为芳杂环的环流效应,d为对不同质子所考虑的键数。有取代基时需考虑取代基的效应。计算环上烷基质子的公式为:δ=σp,CH3+ασc,CH3+βσt,CH3+σl,G
σl,G为稠苯芳杂环基的某级效应。 相似文献