时效工艺对PtCo合金磁性能的影响

研究了时效温度对PtCo合金磁性能的影响.磁性能测量结果显示,随着时效温度的增加合金的剩磁逐渐减小,时效温度为690 ℃时,合金的矫顽力达到最大值.第一步时效处理后,合金的有序度S随时效温度的提高而增加,长程有序度的增加说明合金有序相的晶粒尺寸也在增加,这是合金矫顽力变化的根本原因.第二步时效处理后,PtCo合金的微观组织结构不发生改变,有序相的各向异性场增大,使合金的矫顽力增大. 关键词： 时效温度 PtCo合金 磁性能 有序度     

Influence of partial rare-earth substitution for Sm in the giant intrinsic magnetic hardness compound SmCo2Ni3

The phenomenon of giant intrinsic magnetic hardness is investigated in compounds R_1−x Sm _x Co₂Ni₃ with R=Y, Pr, Gd, Tb, Er. Partial Er substitution for Sm actually increases magnetic hardness while all other substitutions decrease magnetic hardness. The strength of coercivity is thus dependent on both the sign and magnitude of the crystal field interaction. The temperature dependence of coercivity is complex in the case of Pr substitution as a result of competing effects from thermal activation and a decrease in anisotropy at low temperatures. This study has been supported by a grant from the National Science Foundation.     

Effect of ion irradiation on magnetic property of exchange coupled interfacial structures of Fe/NiO and NiO/Fe on Si substrates

The role of defects on the magnetic behaviour of exchange coupled interfacial structures of Fe/NiO and NiO/Fe on Si substrates has been studied. For introduction of defects in the structures, swift (～ 100 MeV) heavy ion irradiation has been used, which is known to cause structural and microstructural modifications. In our earlier study [Srivastava, N; Srivastava, P.C. J. Appl. Phys. 2012, 111, 123909] on similar structures, the significant magnetic behaviour (of exchange bias (EB) and coercivity) for Fe/NiO/nSi interfacial structure was observed and discussed in the realm of interfacial structural modification in the antiferromagnetic layer of the structure. The irradiated interfacial structures have been characterized from X-ray diffraction and M–H characteristics. Structural investigation has shown the formation of various silicide and oxide phases due to the irradiation-induced interfacial intermixing. A significant enhancement in EB field and coercivity has been observed for Fe/NiO/nSi interfacial structure on the irradiation (as compared to unirradiated ones). The observed enhanced EB and coercivity on the irradiation has been understood due to the creation of domain wall pinning centres across the interface as a result of ion irradiation. Moreover, the present study confirms the role of defects in the antiferromagnetic layer to cause the significant change in EB and coercivity. The observation supports the domain state model of EB in the exchange-coupled structures.     

Room-temperature ferromagnetism in pure and Mn doped SnO2 powders

We report here observation of ferromagnetism in pure and Mn doped SnO₂ powder with different Mn contents. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism (RTFM), which is identified as an intrinsic characteristic. The RTFM has been observed in the pure SnO₂ powder, which is believed to be defect induced, with a saturation magnetization of ～0.017 emu/g. The RTFM was enhanced considerably in the Mn doped samples and the magnetic properties strongly depend on doping content. A sample with 1% of Mn is ferromagnetic at room temperature with a saturation magnetization of ～0.98 emu/g, a remanent magnetization of ～27%, and a coercivity of ～270 Oe. The average magnetic moment per Mn atom decreases with increasing Mn content. Our results reveal that the large RTFM observed in Mn doped SnO₂ powder originates from a combination effect of oxygen vacancies and transition metal doping.     

Effect of microstructure on the coercivity of HDDR Nd-Fe-B permanent magnetic alloy

The effect of the grain boundary microstructure on the anisotropy and coercivity was investigated in an HDDR Nd-Fe-B permanent magnetic alloy. Considering the special microstructure of its magnetic powder grain, an anisotropic theoretical model influenced simultaneously by the structure defect at the grain boundary and the exchange coupling interaction was put forward. The variations of the structure defect factors based on the nucleation and pinning mechanism with 2r ₀/lex (where r ₀ and lex are the defect thickness and the length of exchange coupling, respectively) were calculated. The results show that the coercivity mechanism of an HDDR Nd-Fe-B permanent magnetic alloy is greatly related to its microstructure defect at the grain boundary. For a fixed lex, when 2r ₀/lex < 1.67, the coercivity is controlled by the pinning mechanism; when 2r ₀/lex > 1.67, it is determined by the nucleation mechanism. The coercivity reaches the maximum when 2r ₀/lex = 1.67. The calculation result is consistent well with the experimental result given by Morimoto et al. Supported by the National Natural Science Foundation of China (Grant No. 50671055)     

Destruction of manganite La0.825Ba0.175MnO3 ferromagnetism caused by structural disordering

The methods of neutron diffraction, X‐ray and magnetic measurements were used to study the structural and magnetic states of disordered samples of manganite La_0.825Ba_0.175MnO₃. A disordered state was attained by irradiation with fast neutrons. It was established that the ferromagnet → spin glass‐like magnetic transformation takes place at a substitution concentration of ～6%. A magnetic state diagram of structurally disordered manganite was constructed. The magnetic state transformations are explained by the effect of localization of e _g‐electrons responsible for kinetic ferromagnetic exchange. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructure and magnetic properties in arrays of ac electrodeposited FexNi1?x nanowires induced by the continuous and pulse electrodeposition

FeNi nanowires were fabricated by ac and pulse electrodeposition into the alumina template matrix. The effects of continuous ac electrodeposition as well as pulse features on the structure and magnetic properties of the nanowire arrays were studied. The microstructures and magnetic properties of the Fe _x Ni_1−x nanowires are seen to be independent of the deposition frequency and off-time between the pulses. The ac electrodeposited Ni nanowires were not formed at more than 400  Hz deposition frequency, while the Fe _x Ni_1−x nanowires, containing a small amount of Fe, formed in the all frequencies. For x less than 50% the coercivity slowly increases but over 50% Fe added to the FeNi alloy increases the coercivity with a higher rate and maximum coercivity was seen for the Fe_0.97Ni_0.03. The Fe and Fe _x Ni_1−x nanowires containing less than 30 at.% Ni was seen to have a bcc structures with (110) preferential direction while Fe _x Ni_1−x nanowires with more than 30 at.% Ni showed (110) bcc (Fe) and/or (111) bcc (FeNi) plus (111) fcc (Ni). A preferential (111) fcc structure was obtained for the Ni nanowires.     

Unusual magnetic hysteresis behavior of oxide spinel MnCo2O4

Magnetic hysteresis behavior of the oxide spinel MnCo₂O₄ has been studied at different temperatures below its T_c≈184 K. Normal hysteresis behavior is observed down to 130 K whereas below this temperature the initial magnetization curve, at higher magnetic fields, lies outside the main loop. No related anomaly is observed in the temperature variation of magnetization or coercivity. However, the anisotropy field overcomes the coercivity below 130 K. The unusual magnetic hysteresis behavior of MnCo₂O₄, at low temperatures, may be associated with irreversible domain wall movements due to the rearrangement of the valence electrons.     

Pr2Fe14(C,B)/α-(Fe,Co)型纳米晶复合磁体的结构与磁性

研究了Pr_xFe_82-x-yTi_yCo₁₀B₄C₄ (x=9—10.5;y=0, 2)纳米晶薄带的结构与磁性. 结果表明,所有薄带皆主要由2∶14∶1, 2∶17和α-(Fe, Co)三相组成. 对于y=0的合金,其内禀矫顽力随Pr含量x的增加而增加,剩磁随Pr含量x的增加而减小. 以Ti置换部分Fe (y=2),合金的磁性能得到显著提高,表现为:添加Ti后,合金的剩磁B_r基本不降低,x=10.5时合金的B_r值甚至有较明显的提高;同时添加Ti后,合金的内禀矫顽力及退磁曲线的方形度都明显改善. 当x=10.5,y=2时,合金薄带的磁性能达到最佳值为: B_r=9.6 kGs(1 Gs=10^-4 T),_iH_c =10.2 kOe(1 Oe=79.5775 A/m)和(BH)_max＝17.4 MGOe. 随着Pr含量的提高,合金中的硬磁相2 ∶14 ∶1的含量相对增加,内禀矫顽力提高;而Ti置换Fe抑制了软磁相α-(Fe, Co)在快淬和热处理过程中的优先长大,使合金中软磁相和硬磁相的晶粒尺寸及比例趋向最佳组合,交换耦合作用明显增强. 关键词： 纳米晶永磁材料 2Fe₁₄(C')" href="#">Pr₂Fe₁₄(C B) Ti添加 交换耦合     

Xenon-ion Induced Magnetic and Structural Modifications of Ferromagnetic Alloys

Thin polycrystalline films of permalloy (Ni₇₉Fe₂₁) and permendur (Co₅₀Fe₅₀) have been irradiated with Xe-ions to fluences of 10¹⁴–10¹⁶ ions/cm². Ion-induced structural and magnetic modifications have been measured by grazing angle X-ray diffraction, Rutherford backscattering and magneto-optical Kerr effect. In the case of permendur, the Xe-ion implantation first reduced the coercivity, because of stress relaxation, while higher ion fluences increased the coercivity due to pinning centers generated in the film. The ion irradiation aligned the in-plane easy axis of the magnetization along the direction of the external magnetic field during implantation. Phase shifts obtained from magnetic force microscopy confirmed these modifications. The effects of Xe-ion irradiation in permalloy films are much weaker and underline the importance of magnetostriction in the variation of the coercivity and anisotropy.     

Planar Hall effect and magnetoresistance in Ni81Fe19 and Co square shaped thin films

Ni₈₁Fe₁₉ and Co thin films have been fabricated and their transport properties have been investigated for potential applications in ultra sensitive magnetic field sensors. The Ni₈₁Fe₁₉ films exhibit an anisotropic magnetoresistance (AMR) of 2.5% with a coercivity 2.5 Oe and the Co films exhibit an AMR of 0.7% with coercivity 11 Oe. Large planar Hall effect magnetoresistance values at room temperature are reported for both cases. An unbalanced Wheatstone bridge model is proposed to describe quantitatively the observed experimental Planar Hall Effect data.     

La0.67Ca0.33MnO3薄膜中的矫顽力随膜厚与衬底的变化

系统研究了衬底为SrTiO3和LaAlO3上的La0.67Ca0.33MnO3薄膜中的矫顽力随厚度和应变的变化。结构分析表明薄膜为（001）方向织构，而且薄膜中的晶粒尺寸随着薄膜厚度的减小而减小。磁测量表明矫顽力先随着膜厚的减小而增加，在t=10-25nm附近到达一极大值。随后，矫顽力随厚度的减小而降低。还得出矫顽力的大小与测量方向有关：t≥25nm (t≤10nm)时，难磁化方向的矫顽力大于（小于）易磁化方向的矫顽力。据此，我们提出：在厚膜（t≥25nm）中，矫顽力变化由畴壁钉扎机制决定；在超薄膜（t≤10nm）中，则与磁畴的形核机制有关。根据t= 5、10、25、400nm的LCMO/STO薄膜的初始磁化曲线，以及t=5，50nm的LCMO/LAO薄膜的小磁滞回线的测量，我们对薄膜中矫顽力机制作了验证，并且还讨论了钉扎和形核机制发生的非均匀区的尺寸。     

基片对交替溅射制备的MnZn铁氧体薄膜结构和磁性的影响

使用成分分别为MnFe₂O₄和ZnFe₂O₄的靶,使用射频溅射交替沉积制备了成分不同的Mn_1-xZn_xFe₂O₄薄膜,沉积薄膜所用基片分别为单晶硅Si（100）,氧化的单晶硅SiO₂/Si（100）, ZnFe₂O₄为衬底的单晶硅ZnFe< 关键词： MnZn铁氧体 纳米晶 软磁性 磁性薄膜     

直流磁控溅射Si和玻璃衬底Fe/Co多层膜的磁性能比较

对直流磁控溅射Si和玻璃衬底［Co_t/Fe_3t］₅(t=2, 3, 4, 5nm)多层膜的磁性能进行了比较.对于t相同但衬底不同的样品,实验发现饱和磁化强度相差很小,但是矫顽力却相差很大.对矫顽力差异的理论分析表明,多层膜的粗糙度和畴壁类型是引起这种差异的主要原因. 关键词： Fe/Co多层膜 磁性能 矫顽力     

Preparation of strontium hexaferrite film by pulsed laser deposition with in situ heating and post annealing

Strontium hexaferrite (SrFe₁₂O₁₉) films have been fabricated by pulsed laser deposition on Si(1 0 0) substrate with Pt(1 1 1) underlayer through in situ and post annealing heat treatments. C-axis perpendicular oriented SrFe₁₂O₁₉ films have been confirmed by X-ray diffraction patterns for both of the in situ heated and post annealed films. The cluster-like single domain structures are recognized by magnetic force microscopy. Higher coercivity in perpendicular direction than that for the in-plane direction shows that the films have perpendicular magnetic anisotropy. High perpendicular coercivity, around 3.8 kOe, has been achieved after post annealing at 500 °C. Higher coercivity of the post annealed SrFe₁₂O₁₉ films was found to be related to nanosized grain of about 50–80 nm.     

Fe100－xPdx合金纳米线阵列的制备及其磁性研究

利用直流电沉积法在多孔阳极氧化铝模板中制备出了一系列Fe_100-xPd_x磁性纳米线阵列. Pd的增加使纳米线的总体磁性降低，各向异性和矫顽力也发生了较大的变化. 当Pd含量高达x=30时，纳米线仍有相当高的矫顽力(7.48 kA/m)和较明显的各向异性，但当Pd的含量增加到50%时，纳米线的易磁化方向由平行线的方向反转到垂直线的方向. 实验证明，这是由于在Fe₈₀Pd₂₀和Fe₇₀Pd₃₀中连续的磁性相在Fe₅₀Pd₅₀纳米线中变成了与非磁性相相互间隔的非连续片状结构. 片状磁性相的形状各向异性使易磁化方向转变到垂直纳米线轴的方向. 从生长动力学的角度对Fe₅₀Pd₅₀纳米线中这种片状的形成进行了解释. 关键词： 纳米线 电化学沉积 磁性     

Exchange‐coupled L10‐FePt/Fe composite patterns with perpendicular magnetization

L1₀‐FePt and exchange‐coupled L1₀‐FePt/Fe composite films are grown epitaxially on MgO(001) single crystal substrates and are subsequently large‐area patterned utilizing an electron beam lithography process with Ar⁺ ion etching. The patterning process of the continuous film system leads to a different demagnetization behavior resulting in an increase of the out‐of‐plane coercivity of the patterned samples. Due to exchange‐coupling between L1₀‐FePt and Fe the coercivity of the L1₀‐FePt/Fe composite patterns is reduced by 52% as compared to the coercivity of L1₀‐FePt patterns. From the analysis of the temperature dependence of the coercivity it follows that the dots include regions with reduced anisotropy. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ultra‐high aspect ratio Ni nanowires in single‐crystalline InP membranes as multiferroic composite

By a combination of chemical etching, atomic layer deposition (ALD) and galvanic deposition it became possible to produce Ni nanowires (NWs) with ultra‐high aspect ratio (～1000), embedded in a semi‐insulating, piezoelectric, single‐crystalline InP matrix. This Letter discusses the structural and magnetic properties of these Ni NWs. They are crystalline with a preferential growth direction of the grains in 〈111〉. For H ⊥ z , they show a very narrow hysteresis loop with a low coercivity (about 100 Oe) and a very low remanence squareness S of 0.08. So the combination of piezoelectric InP and magnetostrictive Ni forms a very promising multiferroic composite. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cu induced coercivity enhancement in the low viscosity GdCo5−xCux system

We investigate the influence of Cu substitution, on the coercivity and magnetic viscosity, in the ternary system GdCo_5−xCu_x (x=0, 0.5, 1, 1.5, 2 and 2.5) with different field sweep rates. All samples have been studied in the as cast state and crystallize in a single phase CaCu₅ structure. With Cu addition, the coercivity was 10 times enhanced for x =1.5. The behavior of the coercivity H_c against field sweep rate, dH/dt, shows that the GdCo_5−xCu_x system exhibits only a small magnetic viscosity effect, a desirable property for magnetic dynamic applications under high magnetic field.     

Study of NiCuZn ferrite powders and films prepared by sol gel method

This paper reports that a series of NiCuZn ferrite powders and films are prepared by using sol-gel method.The effects of raw material composition and the calcinate temperature on magnetic properties of them are investigated.The NiCuZn ferrite powders are prepared by the self-propagating high-temperature synthesis method and subsequently heated at 700 C～1000 C.The results show that NiCuZn ferrite powders with single spinel phase can be formed after heat-treating at 750 C.Powders obtained from Ni 0.4 Cu 0.2 Zn 0.4 Fe 1.9 O 4 gel have better magnetic properties than those from gels with other composition.After heat-treating at 900 C for 3 h,coercivity H c and saturation magnetization M s are 9.7 Oe (1 Oe=80 A/m) and 72.4 emu/g,respectively.Different from the powders,NiCuZn films produced on Si (100) from the Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 gel formed at room temperature possess high properties.When heat-treating condition is around 600 C for 6 min,samples with low H c and high M s will be obtained.The minimal H c is 16.7 Oe and M s is about 300 emu/cm 3.In comparison with the films prepared through long-time heat treating,the films prepared through short heat-treating time exhibits better soft magnetic properties.