• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Magnetic properties of bilayer nano-stanenelike structure with Ruderman–Kittel–Kasuya–Yoshida coupling

    2022-08-02 02:48:36XinSuNanSiWeiJiangWeiChunGaoandFengGeZhang
    Communications in Theoretical Physics 2022年6期

    Xin Su,Nan Si,Wei Jiang,Wei-Chun Gao and Feng-Ge Zhang

    1 School of Environmental and Chemical Engineering,Shenyang University of Technology,Shenyang 110870,China

    2 School of Electric Engineering,Shenyang University of Technology,Shenyang 110870,China

    Abstract A bilayer nano-stanene-like structure with Ruderman–Kittel–Kasuya–Yoshida (RKKY)coupling described by the Ising model is proposed.The magnetic and thermodynamic properties are studied using the effective-field theory with correlations.The exchange coupling,longitudinal magnetic field,number of non-magnetic layers,and anisotropies had major influences on the magnetization,specific heat,and internal energy.Different saturation magnetizations are observed on the magnetization curve.The variation in the system blocking temperature is studied.The results provide theoretical guidance for the magnetic investigation of nanomaterials with RKKY coupling.

    Keywords:bilayer nano-stanene-like structure,mixed spin Ising model,magnetization,internal energy

    1.Introduction

    Over the past few years,the discovery of graphene has paved the way for a considerable advancement in the field of materials and condensed matter physics.Based on the studies on graphene,a large number of novel properties of twodimensional (2D) materials have been predicted and demonstrated,such as massless Dirac fermions,energy valley polarized electrons,and quantum spin Hall states [1–5].Although graphene has a series of excellent physical properties,the two chiral pairs of Dirac cones open the energy gap at the K and K′ points to a very small value and exhibit the characteristics of semimetal,which restricts the application of graphene in devices to a certain extent [6–9].To this end,studies on new two-dimensional (2D) materials and the determination of their properties have attracted considerable interest.2D materials composed of group-IV elements with a graphene-like structure and same group as carbon,such as silylene,germanene,and stanene,have attracted considerable attention owing to their new features,such as the high strength of the lattice and high electronic mobility [10–14].Among them,the 2D network stanene,composed of tin atoms,is promising because of its excellent properties.Due to its stronger spin–orbit coupling,stanene has been predicted by many theoretical physicists to have exotic physical properties that are not available in 2D materials such as graphene,silylene,and germanene,including a 2D quantum spin Hall state with a large energy gap,low-loss conductance at room temperature,topological superconductivity,quantum spin Hall state,and quantum anomalous Hall state[15–23].One of its unique features is its high carrier mobility,which allows electrons to move freely.Stanene can possess a larger band gap obtained by regulation of the external field and chemistry[24–26].The excellent properties of stanene make it a promising 2D material.

    The relevant properties of stanene have been investigated in detail by theoretical calculations and experiments.By epitaxially straining gray tin (a-Sn),Falson et al obtained superconductors with few layers of stanene,which exhibit a unique type of Ising pairing between carriers residing in bands with different orbital indices near the Γ-point.The inplane upper critical magnetic field is strongly enhanced and exhibited an upward trend at ultralow temperatures [27].Rachel et al exposed the 2D topological insulators silene,germanene,and stannane with helical edge states to charge density wave order,superconductor,out-of-plane antiferromagnetic,and in-plane antiferromagnetic fields to study the global and local manipulations at the edges to achieve the quantum spin Hall effect without edge states [28].Liao et al achieved superconductivity in a few-layer stanene grown on PbTe,while bulk α-tin is not superconductive,according to an analysis of the layer degree of freedom.Based on substrate engineering,they reported that transition from a single band to a two-band superconductor can be realized by doubling the transition temperature[29].Using low-temperature molecular beam epitaxy,Deng et al successfully grew high-quality olefins on Cu (111).An abnormal ultralight monoene is observed at the Γ point,with in-plane s–p band inversion and topological gap induced by spin–orbit coupling (~0.3 eV),which represents the most important group-IV ultralight graphene-like topology material in the experiment[30].Based on the Sn/PbI2heterostructure,Zhang et al proposed a very stable basic device with a quantum anomalous Hall effect.The experimental results showed that the quantum anomalous Hall effect can be easily realized in the tin/lead iodide heterostructure [31].Using the first-principle method based on density functional,Pamungkas et al thoroughly investigated the influences of hydrogenation and Al/P doping on the electronic structure and magnetic properties of stanene.The hydrogenation opened the band gap of stanene and converted it from nonmagnetic to ferromagnetic through the hybridization of H 1s and Sn 5p states [32].Xiong et al studied the electronic structure and magnetic properties of stanene nanoribbons.They reported that all considered armchair-type stanene nanoribbons are nonmagnetic semiconductors and that the gap is a periodic oscillation function of the band width [33].Based on Monte Carlo simulations,Fadil et al investigated the magnetic properties of a bilayer nanostanene structure with Ruderman–Kittel–Kasuya–Yoshida (RKKY)interactions.By studying the effect of RKKY interactions on the magnetic properties of the system,they discovered that,when the number of nonmagnetic layers is reduced,the blocking temperature increases under nonzero temperature conditions[34].Using the multi-orbital tight coupling model,Hattori et al systematically studied the edge states of stanene nanoribbons in the presence of Coulomb interactions and vertical electric fields.Owing to the multi-orbital effect,the resulting edge states have nonlinear energy dispersion and the stanene nanoribbons exhibit induced magnetization at the edges [35].Wu et al proposed a quantum anomalous Hall platform with a large energy gap of 0.34 eV and 0.06 eV on honeycomb lattices comprised of Sn and Ge by ab-initio band structure calculations,respectively.The results indicated that the ferromagnetic sequence is formed in a sublattice of the honeycomb structure by controlling surface functionalization instead of diluting magnetic doping [36].In our previous studies,we successfully employed the EFT to assess the magnetic characteristics of nanomaterials [37–39].

    The aim of this study is to investigate the magnetic and thermodynamic properties of the system.The model and theory of the nano-stanene-like bilayer with the RKKY interaction are introduced in section 2.In section 3,the magnetization,magnetic susceptibility,internal energy,and specific heat are discussed.The conclusions of this paper are presented in section 4.

    2.Calculation method

    A schematic of the bilayer nano-stanene-like structure,separated by nonmagnetic layers,is shown in figure 1.The red and blue balls in layers A and B represent spin atoms,respectively.There is a ferrimagnetic exchange coupling (J)between them.The two types of magnetic atoms had spins ofσ=and spinS=.A mixed spin Ising model is developed to describe this bilayer nano-stanene-like structure.For simplicity,the exchange coupling RKKY JRKKY[40–42]between the spin atoms of layers A and B is assumed.The bilayer nano-stanene-like structure with the exchange coupling RKKY is investigated using the effective-field theory with correlations.The Hamiltonian for the bilayer nano-stanene-like structure is

    whereSizandσzjare the spin operators with possible values ofandrespectively,J (<0) is the ferrimagnetic exchange coupling,JRKKYis the RKKY exchange coupling system,D1(D2) is the anisotropy of the red (blue) spin atoms,and h is the longitudinal magnetic field.

    The JRKKYcoupling between the magnetic bilayers is defined by [34]

    According to [43,44],the coefficientais the lattice constant,while J0denotes the magnetic coupling constant.a2J0is equal to one as the unit

    Within the framework of the effective-field theory with correlations,two types of sublattice magnetization (M1and M2) can be calculated [45–47]:

    wherea1=Jη1?,a2=Jη2?,b1=JRKKYη1?,b2=JRKKYη2?and ?=??xis the differential operator and

    The total average magnetization M per magnetic atom is calculated by

    The functionsFa(x),Fb(x)andGa(x),Gb(x)can be expressed as

    whereλandφare the eigenvalues and eigenfunctions,respectively,which can be calculated using a computer program.

    The average magnetic susceptibility is

    The specific heat of the bilayer nano-stanene-like structure is

    where U is the internal energy of the bilayer nano-stanenelike structure.It can be calculated by

    where N is the number of sites.<>denotes expectation.Because the terms in equation (15) are complex,they are calculated using a computer program.

    3.Numerical results and discussion

    In this section,we discuss the magnetic and thermodynamic properties of bilayer nano-stanene-like structures.At zero temperature,we suppose that the two types of spins are arranged in opposite directions,where spin-7/2 is parallel to the longitudinal magnetic field (h),while spin-3/2 is antiparallel to the longitudinal magnetic field (h).Typical numerical results for the bilayer nano-stanene-like structure are presented in figures 2–6.The influences of the ferrimagnetic exchange coupling (J) and anisotropies (D1,D2) on the magnetic and thermodynamic properties are presented.

    The influences of the ferrimagnetic exchange coupling J on the magnetic and thermodynamic properties of the bilayer nano-stanene-like structure are shown in figures 2(a)–(f).The parameters are set to D1=-0.6,D2=-2.0,h=0.4,and N=2.The temperature dependence of the total magnetization of the system is shown in figure 2(a),which shows two different saturation magnetizations (Ms).For example,Ms=0.5 and 1.0 for J=-0.5 (-0.6) and-0.7 (-1.1,-1.5),respectively.To evaluate the variation rule of the total system average magnetization M,we study the variations of the magnetizations M1and M2of the sublattices of layers A and B of the system with the ferrimagnetic exchange coupling J,as shown in figure 2(c).With the change in the ferrimagnetic exchange coupling J,the magnetization of the sublattice also changes.The total magnetization and sublattice magnetization satisfy equation (8).For example,for J=1.1,M=(M1+M2)/2=(3.5-1.5)/2=1.The ferrimagnetic exchange coupling J mainly controls the change in the total magnetization by affecting the sublattice magnetization.According to equation (13),the susceptibility is the first derivative of the magnetization with respect to the longitudinal magnetic field.The temperature corresponding to its highest point is referred to as blocking temperature (TB).Figure 2(b) shows the curve of the system as a function of the temperature.With the increase in the ferrimagnetic exchange coupling |J|,the highest point of the susceptibility curve shifts to the hightemperature region,that is,the blocking temperature TBincreases with the ferrimagnetic exchange coupling|J|.When|J|=0.5,0.6,0.7,1.1,and 1.5,the corresponding blocking temperatures of the system are TB=0.615,1.115,2.47,5.73,and 8.405,respectively.We studied the change in the system blocking temperature,as shown in figure 2(d).The blocking temperature divides the system into ferrimagnetic and paramagnetic phases.When the temperature is higher than the blocking temperature,the system is in the paramagnetic phase(white region);otherwise,it is in the ferrimagnetic phase(yellow region).The physical origin is the competition between ordered energy and disordered energy.At lower temperature,ordered energy dominates and the system is in a ferromagnetic phase.At higher temperature,the disordered energy dominates and the system transforms into a paramagnetic phase.The system blocking temperature increases linearly with the ferrimagnetic exchange coupling |J|,which is consistent with the change in figure 2(b).The temperature dependence of the internal energy (U) for the bilayer nanostanene-like structure is shown in figure 2(e).The increase of|J| can reduce the internal energy.With the increase in temperature,the ground state will increase.After reaching a certain temperature,the system can hardly change,mainly as,at low temperatures,each sublattice is less affected by the thermal disturbance and the influence of the exchange effect J is dominant.However,with the increase in temperature,the thermal disturbance energy is dominant.The temperature corresponding to the inflection point of the internal energy curve is the blocking temperature.With the increase in ferrimagnetic exchange coupling |J|,the system blocking temperature increases,which has the same trend as in figure 2(b).The temperature dependence of the specific heat(Cv) for the bilayer nano-stanene-like structure is shown in figure 2(f).A singular phenomenon at the blocking temperature was observed in the specific heat curve.When|J|increased,the blocking temperature at the singular position shifted toward a high temperature.This agrees with the observations in figure 2(e).

    Figure 1.A sketch of bilayer nano-stanene-like with RKKY coupling.

    Figure 2.Thermal variations of the (a) magnetization,(b) sublattice magnetizations,(c) susceptibility,(d) internal energy,and (e) specific heat with D1=-0.6,D2=-2.0,h=0.4,N=2 and various J.

    Figure 3.Thermal variations of the (a) magnetization,(b) sublattice magnetizations,(c) susceptibility,(d) internal energy,and (e) specific heat with J=-1.5,D2=-2.0,h=0.4,N=2 and various D1.

    Figure 4.Thermal variations of the (a) magnetization,(b) sublattice magnetizations,(c) susceptibility,(d) internal energy,and (e) specific heat with J=-1.5,D1=-0.6,h=0.4,N=2 and various D2.

    Figure 5.Thermal variations of the (a) magnetization,(b) sublattice magnetizations,(c) susceptibility,(d) internal energy,and (e) specific heat with J=-1.5,D1=-0.6,D2=-2.0,N=2,and various h.

    Figure 6.Thermal variations of the (a) magnetization,(b) sublattice magnetizations,(c) susceptibility,(d) internal energy,and (e) specific heat with J=-1.0,D1=-1.4,D2=-0.6,h=0.4,and various N.

    The influences of the anisotropy D1on the magnetic and thermodynamic properties of the bilayer nano-stanene-like structure are shown in figures 3(a)–(f).The typical parameters are J=-1.5,D2=-2.0,h=0.4,and N=2.The temperature dependence of the total magnetization of the system is presented in figure 3(a),which shows two different behaviors.In the first type,the magnetization curve initially rises,drops,and finally becomes flat with the increase in temperature at D1=-1.4 and-2.2.In the other type,the magnetization curve increases with the decrease in temperature,and then becomes flat at D1=-0.6,-1.1,and-1.6.In the selected parameter range,the saturation magnetization (Ms) has three different values,Ms=0,0.5,and 1.0,when D1=-2.2,-1.6(-1.4),and-1.1 (-0.6),respectively.To better understand the variation rule of the total magnetization M of the system,figure 3(c)shows the variations of the magnetizations M1and M2of the sublattices of layers A and B of the system.With the change in D1,the magnetization of M1changes significantly,M1=1.5,2.5,and 3.5,for D1=-2.2,-1.6(-1.4),and-1.1 (-0.6),respectively.M2is constant,-1.5.The anisotropy D1mainly influences the magnetization of the A-layer sublattice.The temperature dependence of the susceptibility of the bilayer nano-stanene-like structure is shown in figure 3(b).A singular phenomenon at the blocking temperature is observed on the susceptibility curve.When|D1| increased,the blocking temperature at the singular position shifted toward a low temperature.TB=8.450,7.005,6.015,5.285,and 3.07 for |D1|=2.2,1.6,1.4,1.1,and 0.6,respectively.The anisotropy D1dependence of the blocking temperature for the bilayer nano-stanene-like structure is shown in figure 3(d).The system blocking temperature decreases linearly with the increase in anisotropy|D1|,which is consistent with the change in figure 3(b).When the temperature is higher than the blocking temperature,the system is in the paramagnetic phase(white region);otherwise,it is in the ferrimagnetic phase(yellow region).Similar results are also found in materials RKKY coupling [48].The temperature dependence of the internal energy (U) for the bilayer nano-stanene-like structure is shown in figure 3(e).The system internal energy increases with the anisotropy |D1|.However,the rate of increase gradually decreases.However,in the high-temperature region,the internal energy system almost directly increases with the increase in|D1|,because,at low temperatures,the sublattices are slightly affected by the thermal disturbance energy and the influence of D1is dominant.However,with the increase in temperature,the thermal disturbance energy is dominant.The temperature dependence of the specific heat (Cv) for the bilayer nano-stanene-like structure is shown in figure 3(f).The Cvcurves have a sharp peak at the blocking temperature for different values of D1,which corresponds to the inflection point on the U curve.The blocking temperature increases with the decrease in the anisotropy |D1|.In particular,the Cvcurves showed distinct peaks at low temperatures,because the U curve showed an abnormal temperature dependence.

    The influences of the anisotropy D2on the magnetic and thermodynamic properties of the bilayer nano-stanene-like structure are shown in figures 4(a)–(f).The typical parameters are J=-1.5,D1=-0.6,h=0.4,and N=2.The temperature dependence of the total average and sublattice magnetizations of the system are shown in figures 4(a)and(c).As shown in figure 4(a),the magnetization curves exhibited the same behavior types.The magnetization curve decreased with the increase in temperature T,and finally tended to a stable value of 0.078.In the selected parameter range,the saturation magnetization |Ms| is always 1.To explain the M curve,the sublattice M1(dashed) and M2(dotted) are shown in figure 4(c).With the increase in anisotropy D1,the magnetization of the system sublattice remained constant.At temperature T=0,M1=3.5,M2=-1.5.In figure 4(b),the susceptibility curve for the bilayer nano-stanene-like structure was obtained by changing D1.All curves drop rapidly at high temperatures,which indicates that the system is in the paramagnetic phase.The blocking temperature decreased when|D2|increased.This is in agreement with the M curves shown in figure 4(b).The thermal variations of the internal energy(U) of the bilayer nano-stanene-like structure are shown in figure 4(e).With the increase in D2,the internal energy of the system gradually increases.Unlike D1,the effect of D2on the internal energy of the system is always proportional.The temperature dependence of the specific heat (Cv) for the bilayer nano-stanene-like structure is shown in figure 4(f).The Cvcurves have a sharp peak at the blocking temperature for different D2values,which corresponds to the inflection point on the U curve.The blocking temperature decreased with the increase in the anisotropy |D2|.This is in agreement with figures 3(e)–(f).The maximum values corresponding to blocking temperature are found on the susceptibility curve and the specific heat curves in figures 4(b)and (f),which are in agreement with those obtained in figure 2 of [49].

    The influences of the longitudinal magnetic field h on the magnetic and thermodynamic properties of the bilayer nanostanene-like structure are shown in figures 5(a)–(f).The typical parameters are J=-1.5,D1=-0.6,D2=-2.0,N=2.The temperature dependence of the total magnetization of the system is shown in figure 5(a).At T=0,the saturation magnetization has only one value,Ms=1.When T>0,the magnetization increases with the longitudinal magnetic field h,mainly due to the competition between the thermal disturbance energy and longitudinal magnetic field energy.As the temperature T continues to increase,the magnetization curve tends to a stable value,which increases with the longitudinal magnetic field h.This shows that the magnetic properties of the system are mainly determined by the longitudinal magnetic field intensity when the temperature increases to a critical value.The magnetizations M1and M2of layer-A and layer-B sublattices are shown in figure 5(c).According to figure 5(c),the magnetization curve M2almost does not change with the change in longitudinal magnetic field h and temperature T,while the change trend of the magnetization curve M1is consistent with that of the total magnetization curve.The A-layer sublattice has a major effect on the magnetic properties of the system.In figure 5(b),the susceptibility curve for the bilayer nano-stanene-like structure was obtained by changing h.The temperature corresponding to the highest point is the blocking temperature.The blocking temperature decreases with the increase in external magnetic field h.For example,TB=7.01,6.945,6.92,6.905,6.88,6.83,6.755,and 6.635 for h=0.5,1.0,1.5,2.0,2.5,3.0,3.5,and 4.0,respectively.To study the influence of the blocking temperature on the system,the longitudinal magnetic field dependence of the blocking temperature is shown in figure 5(d).In contrast to the ferrimagnetic exchange coupling and anisotropy,there is no linear change between the blocking temperature and longitudinal magnetic field.The area of the ferrimagnetic phase(yellow area)is larger than that of the paramagnetic phase (white area),which indicates that the system is more likely to exhibit ferrimagnetism.The temperature dependence of the internal energy (U) for the bilayer nano-stanene-like structure is shown in figure 5(e).In the low-temperature region,the internal energy increases with h,while,in the high-temperature region,the internal energy does not change with the change in h,mainly because,in the intermediate temperature region,the internal energy is affected by the external field energy and thermal disturbance energy.At a smaller external field,the internal energy is more severely affected by the thermal disturbance energy and the internal energy increases faster.The temperature corresponding to the inflection point of the internal energy curve is the blocking temperature.With the increase in the longitudinal magnetic field h,the system blocking temperature decreases,which has the same trend as that in figure 5(b).The temperature dependence of the specific heat (Cv) for the bilayer nano-stanene-like structure is shown in figure 5(f).In the low-temperature region,the specific heat of the system is disturbed,which is mainly determined by the competition between the temperature and anisotropy.

    The influence of the number of nonmagnetic layers N on the magnetic and thermodynamic properties of the bilayer nano-stanene-like structure was investigated,as shown in figures 6(a)–(e).The typical parameters are J=-1.5,D1=-0.6,D2=-2.0,h=0.4.The temperature dependence of the total magnetization of the system is shown in figure 6(a).At T=0,the saturation magnetization has only one value,Ms=1.When the temperature is T>0,the magnetization decreases with the increase in N.However,the difference between one and two layers is considerably larger than that between two and ten layers.This shows that,with the increase in the number of layers,the effect on the magnetic properties of the system decreases.The magnetizations M1and M2of layer-A and layer-B sublattices are shown in figure 6(c).According to figure 6(c),the magnetization curve M2almost does not change with the change in N and temperature T,while the changing trend of the magnetization curve M1is consistent with that of the total magnetization curve.The A-layer sublattice has a major effect on the magnetic properties of the system.In figure 5(b),the susceptibility curve for the bilayer nano-stanene-like structure was obtained by changing N.The temperature corresponding to the highest point is the blocking temperature,which decreases with the increase in N.For example,TB=10.96,8.45,and 7.9 for N=1,2,and 10,respectively.The temperature dependences of the internal energy (U) and specific heat(Cv)of the bilayer nano-stanene-like structure are shown in figures 6(d),(e).The internal energy of the system increases,while the specific heat decreases with the increase in the number of layers.The disturbance of the specific heat at low temperatures is mainly caused by the competition between the temperature and anisotropy.Moreover,with the increase in the number of layers,the effect on the magnetic and thermodynamic properties of the system decreases.It is worth noting that the results obtained may be useful in helping to understand the magnetic properties of other RKKY materials,such as Ce–Al metallic glasses[48],NdRhIn5[49].

    4.Conclusions

    Based on the EFT,a bilayer nano-stanene-like structure described by mixed spin 7/2 and 3/2 Ising models was studied.The exchange coupling,anisotropy,external fields,and number of nonmagnetic layers regulated the magnetic and thermodynamic properties of the system.With the changes in exchange and anisotropy,the system could exhibit different magnetic configurations.The effect on the magnetic and thermodynamic properties of the system decreased with the increase in the number of non-magnetic layers.

    Acknowledgments

    This project was supported by the Nation Science Foundation of China (Grant no.51920105011) and Key R&D project of Liaoning Province of China (No.2020JH2/10300079) and LiaoNing revitalization talents program (XLYC1908034).

    久久伊人香网站| 一级毛片女人18水好多| 亚洲一区二区三区色噜噜| 日韩精品免费视频一区二区三区| 国产成人精品无人区| 欧美日韩福利视频一区二区| 免费在线观看日本一区| 一进一出抽搐gif免费好疼| 久久精品国产亚洲av香蕉五月| 制服丝袜大香蕉在线| 免费在线观看黄色视频的| xxx96com| 日本黄色视频三级网站网址| 深夜精品福利| 一区二区三区精品91| 午夜成年电影在线免费观看| 国产精品亚洲美女久久久| 国产精品久久久久久亚洲av鲁大| 久久久久久久午夜电影| x7x7x7水蜜桃| 成人永久免费在线观看视频| 在线视频色国产色| 黄频高清免费视频| 精品一区二区三区四区五区乱码| 亚洲av中文字字幕乱码综合 | 一进一出抽搐动态| 色综合婷婷激情| 麻豆成人av在线观看| 男人舔女人下体高潮全视频| 亚洲黑人精品在线| 国产aⅴ精品一区二区三区波| 免费无遮挡裸体视频| 97人妻精品一区二区三区麻豆 | 我的亚洲天堂| 老熟妇仑乱视频hdxx| 欧美黑人欧美精品刺激| 国产真实乱freesex| 精品久久久久久久久久免费视频| 久久香蕉精品热| 久久久精品欧美日韩精品| 久久性视频一级片| 脱女人内裤的视频| 日韩精品青青久久久久久| 19禁男女啪啪无遮挡网站| 久久午夜亚洲精品久久| 精品一区二区三区av网在线观看| 国产一区二区三区视频了| 亚洲激情在线av| 精品久久久久久久末码| 人人澡人人妻人| 中文亚洲av片在线观看爽| 国产免费av片在线观看野外av| 99国产精品一区二区蜜桃av| 亚洲精品国产一区二区精华液| 不卡av一区二区三区| 午夜影院日韩av| a级毛片a级免费在线| 国产极品粉嫩免费观看在线| 一级毛片女人18水好多| 国内少妇人妻偷人精品xxx网站 | 少妇被粗大的猛进出69影院| 成人手机av| xxx96com| 黄色 视频免费看| 亚洲成av片中文字幕在线观看| 成人手机av| 夜夜躁狠狠躁天天躁| 精品国产亚洲在线| 波多野结衣高清作品| 黄片大片在线免费观看| 国产激情欧美一区二区| 人人妻人人澡欧美一区二区| 男女视频在线观看网站免费 | 亚洲三区欧美一区| 十八禁网站免费在线| 制服诱惑二区| 免费观看精品视频网站| 嫩草影视91久久| 欧美性猛交黑人性爽| 国产麻豆成人av免费视频| 中文字幕久久专区| 亚洲真实伦在线观看| 听说在线观看完整版免费高清| 老司机午夜十八禁免费视频| 一本综合久久免费| 一区二区日韩欧美中文字幕| 亚洲成av人片免费观看| 亚洲av成人一区二区三| 国产又色又爽无遮挡免费看| 在线观看午夜福利视频| 亚洲精品av麻豆狂野| 色尼玛亚洲综合影院| 美国免费a级毛片| 午夜影院日韩av| 亚洲精品中文字幕一二三四区| 精品久久蜜臀av无| 国产视频一区二区在线看| 精品国产美女av久久久久小说| 丝袜美腿诱惑在线| 久久香蕉国产精品| 久久热在线av| 国产亚洲精品综合一区在线观看 | 成人欧美大片| 老熟妇仑乱视频hdxx| 久久中文看片网| 国产精品 国内视频| 18禁裸乳无遮挡免费网站照片 | 久久久国产成人精品二区| 在线观看舔阴道视频| 色在线成人网| 亚洲国产欧美一区二区综合| 免费观看精品视频网站| 精华霜和精华液先用哪个| 亚洲黑人精品在线| 99热6这里只有精品| 成人欧美大片| 亚洲成人精品中文字幕电影| 老鸭窝网址在线观看| 级片在线观看| 成人国产一区最新在线观看| 欧美激情高清一区二区三区| 伦理电影免费视频| 999久久久精品免费观看国产| 琪琪午夜伦伦电影理论片6080| 99热6这里只有精品| 欧美绝顶高潮抽搐喷水| 国产高清激情床上av| 日韩高清综合在线| 波多野结衣巨乳人妻| 国产亚洲精品第一综合不卡| 一级片免费观看大全| 欧美大码av| 久久婷婷成人综合色麻豆| 女性生殖器流出的白浆| 成人亚洲精品av一区二区| 少妇 在线观看| 99精品欧美一区二区三区四区| 无人区码免费观看不卡| 中文字幕精品免费在线观看视频| 国产私拍福利视频在线观看| 国产成人一区二区三区免费视频网站| 国产乱人伦免费视频| 亚洲,欧美精品.| 中文字幕人妻熟女乱码| 757午夜福利合集在线观看| 国产av一区二区精品久久| 嫁个100分男人电影在线观看| 中文字幕久久专区| 99re在线观看精品视频| 最近在线观看免费完整版| 国产成人精品久久二区二区免费| 久久亚洲精品不卡| bbb黄色大片| 欧美 亚洲 国产 日韩一| 两个人免费观看高清视频| 给我免费播放毛片高清在线观看| 欧美乱码精品一区二区三区| 99热只有精品国产| 老司机午夜十八禁免费视频| 亚洲人成网站在线播放欧美日韩| 国产一区二区激情短视频| 成年免费大片在线观看| 国产精品亚洲一级av第二区| 亚洲精品国产精品久久久不卡| 成年免费大片在线观看| 麻豆久久精品国产亚洲av| 露出奶头的视频| 婷婷丁香在线五月| 国产精品二区激情视频| 桃色一区二区三区在线观看| 亚洲成人免费电影在线观看| 免费观看人在逋| www.熟女人妻精品国产| 99国产极品粉嫩在线观看| 大型av网站在线播放| 九色国产91popny在线| 91字幕亚洲| 51午夜福利影视在线观看| 级片在线观看| 一级a爱片免费观看的视频| 视频在线观看一区二区三区| 精品国产国语对白av| 日韩欧美一区视频在线观看| 女警被强在线播放| 国产精品免费视频内射| 日韩欧美免费精品| 啦啦啦观看免费观看视频高清| 亚洲精品一区av在线观看| 18美女黄网站色大片免费观看| 亚洲 欧美一区二区三区| 村上凉子中文字幕在线| 亚洲人成电影免费在线| 亚洲午夜精品一区,二区,三区| 亚洲av美国av| 国产日本99.免费观看| 国产黄片美女视频| 90打野战视频偷拍视频| 91大片在线观看| 此物有八面人人有两片| 高清毛片免费观看视频网站| 国产精品乱码一区二三区的特点| 国产一区二区激情短视频| 亚洲男人的天堂狠狠| 妹子高潮喷水视频| 免费看美女性在线毛片视频| 久久 成人 亚洲| 久久精品夜夜夜夜夜久久蜜豆 | 婷婷丁香在线五月| 国产成人欧美| 国产成人精品无人区| 成人一区二区视频在线观看| 18禁国产床啪视频网站| 99久久精品国产亚洲精品| 亚洲人成网站在线播放欧美日韩| 国产成人精品无人区| 一级毛片精品| 国产精品香港三级国产av潘金莲| 非洲黑人性xxxx精品又粗又长| 精品福利观看| 90打野战视频偷拍视频| 国产高清videossex| 国产男靠女视频免费网站| 1024视频免费在线观看| 欧美日韩瑟瑟在线播放| 淫秽高清视频在线观看| 亚洲在线自拍视频| 国产又色又爽无遮挡免费看| 欧美黄色淫秽网站| 日韩精品青青久久久久久| 在线观看午夜福利视频| 欧美性长视频在线观看| 日本精品一区二区三区蜜桃| 久久久久精品国产欧美久久久| 韩国精品一区二区三区| 麻豆av在线久日| 国产熟女xx| 国产精品免费一区二区三区在线| 夜夜夜夜夜久久久久| 夜夜看夜夜爽夜夜摸| 久久久久久国产a免费观看| 亚洲国产中文字幕在线视频| 12—13女人毛片做爰片一| 两个人视频免费观看高清| 亚洲av中文字字幕乱码综合 | 精品卡一卡二卡四卡免费| 香蕉av资源在线| 国产成人欧美在线观看| 久久精品人妻少妇| 国产欧美日韩一区二区精品| 精品不卡国产一区二区三区| 亚洲七黄色美女视频| 看片在线看免费视频| 黄色女人牲交| 老司机福利观看| 此物有八面人人有两片| 国产色视频综合| 婷婷亚洲欧美| 少妇裸体淫交视频免费看高清 | 欧美绝顶高潮抽搐喷水| 久久久精品欧美日韩精品| 淫妇啪啪啪对白视频| 一区福利在线观看| 精品午夜福利视频在线观看一区| 女人高潮潮喷娇喘18禁视频| 中文字幕精品亚洲无线码一区 | 欧美黑人巨大hd| 精品卡一卡二卡四卡免费| 亚洲男人天堂网一区| 91麻豆av在线| 欧美av亚洲av综合av国产av| x7x7x7水蜜桃| 韩国精品一区二区三区| 99精品久久久久人妻精品| av免费在线观看网站| 香蕉丝袜av| 久久青草综合色| 一区二区日韩欧美中文字幕| 99热这里只有精品一区 | 人人妻人人看人人澡| 国产私拍福利视频在线观看| 国产av一区在线观看免费| 村上凉子中文字幕在线| e午夜精品久久久久久久| 亚洲精品中文字幕在线视频| 日韩大码丰满熟妇| 国产精品99久久99久久久不卡| 成在线人永久免费视频| 男男h啪啪无遮挡| 亚洲精品色激情综合| svipshipincom国产片| 成人三级黄色视频| 女警被强在线播放| 天天躁夜夜躁狠狠躁躁| 午夜精品久久久久久毛片777| 国产精品98久久久久久宅男小说| 母亲3免费完整高清在线观看| 欧美乱码精品一区二区三区| 听说在线观看完整版免费高清| 欧美最黄视频在线播放免费| 亚洲av成人av| 精品国内亚洲2022精品成人| 长腿黑丝高跟| 啦啦啦韩国在线观看视频| 精品国产美女av久久久久小说| 人妻久久中文字幕网| 男人舔奶头视频| 别揉我奶头~嗯~啊~动态视频| 精品少妇一区二区三区视频日本电影| 一级片免费观看大全| 欧美 亚洲 国产 日韩一| 91成年电影在线观看| 成人一区二区视频在线观看| 国产黄a三级三级三级人| 日韩欧美国产在线观看| 黄色女人牲交| 法律面前人人平等表现在哪些方面| 最好的美女福利视频网| 免费在线观看成人毛片| 日韩精品青青久久久久久| 老司机在亚洲福利影院| 亚洲欧美一区二区三区黑人| 亚洲专区字幕在线| 丝袜美腿诱惑在线| 亚洲av成人一区二区三| 听说在线观看完整版免费高清| 看片在线看免费视频| 天堂√8在线中文| 国产成人av激情在线播放| 久久精品国产清高在天天线| 国产aⅴ精品一区二区三区波| 久久精品国产亚洲av香蕉五月| 特大巨黑吊av在线直播 | 国产片内射在线| 欧美绝顶高潮抽搐喷水| 欧美日韩亚洲综合一区二区三区_| 亚洲精品av麻豆狂野| 十八禁网站免费在线| 日本一本二区三区精品| 免费在线观看完整版高清| 欧美国产日韩亚洲一区| 久久精品国产清高在天天线| xxx96com| 长腿黑丝高跟| 日本一本二区三区精品| 亚洲精品美女久久久久99蜜臀| 一本精品99久久精品77| 国产一卡二卡三卡精品| 国产aⅴ精品一区二区三区波| 精品国产美女av久久久久小说| 日本三级黄在线观看| 国内揄拍国产精品人妻在线 | 欧美日本亚洲视频在线播放| 欧美中文日本在线观看视频| 国产真人三级小视频在线观看| 久久草成人影院| 亚洲国产精品999在线| xxxwww97欧美| 美女免费视频网站| 国产精品久久电影中文字幕| 国产主播在线观看一区二区| 午夜久久久久精精品| 久久精品国产亚洲av香蕉五月| 亚洲国产中文字幕在线视频| 精品国产美女av久久久久小说| 黄色丝袜av网址大全| 午夜a级毛片| 亚洲国产中文字幕在线视频| 欧美午夜高清在线| 观看免费一级毛片| 亚洲成av片中文字幕在线观看| 精品久久久久久久久久免费视频| 国产av不卡久久| 国产精品电影一区二区三区| 淫秽高清视频在线观看| 欧美乱色亚洲激情| 色播亚洲综合网| 国语自产精品视频在线第100页| av视频在线观看入口| 亚洲午夜精品一区,二区,三区| cao死你这个sao货| 一边摸一边做爽爽视频免费| 男人操女人黄网站| 成人国产一区最新在线观看| 最新在线观看一区二区三区| 美女免费视频网站| 国内久久婷婷六月综合欲色啪| 国产主播在线观看一区二区| 最近最新中文字幕大全电影3 | 亚洲avbb在线观看| 国产高清激情床上av| 丰满人妻熟妇乱又伦精品不卡| 一进一出好大好爽视频| 人妻丰满熟妇av一区二区三区| 国产精品一区二区三区四区久久 | 色综合亚洲欧美另类图片| 天堂影院成人在线观看| 亚洲精品美女久久久久99蜜臀| 啦啦啦韩国在线观看视频| 国产一区二区激情短视频| 波多野结衣巨乳人妻| 黑丝袜美女国产一区| 中文资源天堂在线| а√天堂www在线а√下载| 婷婷亚洲欧美| 在线观看免费日韩欧美大片| 免费在线观看影片大全网站| 老司机午夜十八禁免费视频| 啦啦啦免费观看视频1| 欧洲精品卡2卡3卡4卡5卡区| 1024香蕉在线观看| 一级毛片女人18水好多| 黑丝袜美女国产一区| 熟妇人妻久久中文字幕3abv| 99国产精品一区二区蜜桃av| 中文亚洲av片在线观看爽| 亚洲色图 男人天堂 中文字幕| 每晚都被弄得嗷嗷叫到高潮| 久久这里只有精品19| 午夜福利18| 久久草成人影院| 久久精品aⅴ一区二区三区四区| svipshipincom国产片| 国产精品免费一区二区三区在线| 成人欧美大片| 欧美日韩乱码在线| 一二三四在线观看免费中文在| 大香蕉久久成人网| 午夜视频精品福利| 国产视频内射| 国产主播在线观看一区二区| 夜夜躁狠狠躁天天躁| 亚洲av日韩精品久久久久久密| 国产亚洲精品一区二区www| 国产伦人伦偷精品视频| 欧美精品亚洲一区二区| 久久性视频一级片| 神马国产精品三级电影在线观看 | 日韩国内少妇激情av| 国产成人精品久久二区二区91| 一级a爱视频在线免费观看| 18禁裸乳无遮挡免费网站照片 | 一本久久中文字幕| 成人国产一区最新在线观看| 精品午夜福利视频在线观看一区| 国产精品免费一区二区三区在线| 搡老妇女老女人老熟妇| 黑人操中国人逼视频| 成人午夜高清在线视频 | 很黄的视频免费| 亚洲成人精品中文字幕电影| 丰满人妻熟妇乱又伦精品不卡| 中文字幕人妻丝袜一区二区| 热re99久久国产66热| 18禁美女被吸乳视频| 一级a爱视频在线免费观看| 两性夫妻黄色片| 亚洲av成人不卡在线观看播放网| 国产v大片淫在线免费观看| 欧美黑人精品巨大| 精品久久久久久久久久免费视频| 黑丝袜美女国产一区| 美女国产高潮福利片在线看| 男人的好看免费观看在线视频 | 欧美性猛交黑人性爽| 日韩国内少妇激情av| 免费看十八禁软件| 好男人电影高清在线观看| 免费看日本二区| 国产主播在线观看一区二区| 亚洲 欧美一区二区三区| 欧美日韩亚洲综合一区二区三区_| 午夜激情av网站| 黄片大片在线免费观看| 婷婷精品国产亚洲av在线| 久久久久国产一级毛片高清牌| 午夜免费观看网址| 午夜日韩欧美国产| 欧美zozozo另类| 午夜两性在线视频| 免费在线观看亚洲国产| 日韩欧美一区视频在线观看| 一级毛片精品| 最近最新中文字幕大全免费视频| 欧美日韩黄片免| 国产区一区二久久| 黄色女人牲交| 黄色毛片三级朝国网站| 一夜夜www| 女同久久另类99精品国产91| 日本一区二区免费在线视频| 一a级毛片在线观看| 黄色a级毛片大全视频| 露出奶头的视频| 欧美日韩精品网址| 操出白浆在线播放| 午夜a级毛片| 免费在线观看日本一区| 日本a在线网址| 国产亚洲av高清不卡| 三级毛片av免费| 久久精品夜夜夜夜夜久久蜜豆 | 欧美国产精品va在线观看不卡| 这个男人来自地球电影免费观看| 国产精品久久久久久亚洲av鲁大| 欧美国产日韩亚洲一区| videosex国产| 国产精品1区2区在线观看.| 久99久视频精品免费| 中文字幕人成人乱码亚洲影| 精品国内亚洲2022精品成人| 国产高清有码在线观看视频 | 亚洲欧美日韩无卡精品| 最新美女视频免费是黄的| 亚洲狠狠婷婷综合久久图片| 国产精品99久久99久久久不卡| 在线观看免费午夜福利视频| 午夜a级毛片| 国产精品电影一区二区三区| 久久久久久久精品吃奶| 身体一侧抽搐| 亚洲欧美精品综合久久99| 亚洲第一青青草原| 亚洲av片天天在线观看| av超薄肉色丝袜交足视频| 每晚都被弄得嗷嗷叫到高潮| 成人三级做爰电影| 亚洲av成人av| 久久久久国产精品人妻aⅴ院| 久久九九热精品免费| 女人高潮潮喷娇喘18禁视频| 久久人妻av系列| 欧美激情高清一区二区三区| 妹子高潮喷水视频| 91麻豆av在线| 国产精品九九99| 满18在线观看网站| 好看av亚洲va欧美ⅴa在| 国产成人影院久久av| 亚洲精品一区av在线观看| 中文字幕最新亚洲高清| 久久中文字幕人妻熟女| 精品国产超薄肉色丝袜足j| 久久久国产成人精品二区| 国产成年人精品一区二区| 欧美绝顶高潮抽搐喷水| 国产欧美日韩一区二区精品| av在线播放免费不卡| 国产精品野战在线观看| 亚洲五月天丁香| 亚洲 国产 在线| 成人18禁在线播放| 90打野战视频偷拍视频| 一边摸一边做爽爽视频免费| 首页视频小说图片口味搜索| 99热只有精品国产| 欧美精品啪啪一区二区三区| 男人的好看免费观看在线视频 | 满18在线观看网站| 天天躁夜夜躁狠狠躁躁| 国产高清videossex| 欧美日韩亚洲综合一区二区三区_| 精品一区二区三区视频在线观看免费| 国产v大片淫在线免费观看| 在线天堂中文资源库| 色老头精品视频在线观看| 国产麻豆成人av免费视频| 精品国产美女av久久久久小说| 搡老熟女国产l中国老女人| 久久久久九九精品影院| 村上凉子中文字幕在线| 中文字幕久久专区| 亚洲国产欧美一区二区综合| av天堂在线播放| 人人澡人人妻人| 欧美zozozo另类| 男人舔奶头视频| 久久热在线av| 大型av网站在线播放| 嫩草影视91久久| 成人18禁高潮啪啪吃奶动态图| 日本免费a在线| 午夜视频精品福利| 黄色丝袜av网址大全| 免费观看人在逋| 国产精品综合久久久久久久免费| www.熟女人妻精品国产| 免费观看人在逋| 日本免费一区二区三区高清不卡| √禁漫天堂资源中文www| 俄罗斯特黄特色一大片| 免费在线观看影片大全网站| 国产成人啪精品午夜网站| 成在线人永久免费视频| 亚洲精品国产区一区二| 亚洲国产精品久久男人天堂| 久久中文字幕人妻熟女| 99久久久亚洲精品蜜臀av| 丰满人妻熟妇乱又伦精品不卡| 中文字幕另类日韩欧美亚洲嫩草| 久久久久久人人人人人| 中文字幕最新亚洲高清| 国产高清有码在线观看视频 | 男女做爰动态图高潮gif福利片| 91九色精品人成在线观看| 欧美乱妇无乱码| 一区二区日韩欧美中文字幕| 国产成+人综合+亚洲专区| 亚洲人成电影免费在线| 91麻豆精品激情在线观看国产| 欧美乱色亚洲激情| 可以在线观看的亚洲视频| 欧美激情 高清一区二区三区| 欧美激情久久久久久爽电影| 欧美色欧美亚洲另类二区| 哪里可以看免费的av片|