L. Y. Lv

Anisotropy compensation and magnetostriction in TbxNd1−xFe1.9 cubic Laves alloys

Polycrystalline TbxNd1−xFe1.9 (0⩽x⩽0.8) cubic Laves phase alloys with MgCu2-type structure were prepared by high-pressure synthesis and subsequent low-temperature annealing. The crystal structure, magnetic properties, and magnetostriction have been investigated. The change of easy magnetic direction from ⟨100⟩ to ⟨111⟩ with increasing x up to 0.1 is detected by Mossbauer spectra. In accordance with Mossbauer effect study, both magnetization and magnetostriction analyses show that TbxNd1−xFe1.9 is an anisotropy compensation system and the compensation point is close to x=0.1. The present work may open an avenue in searching magnetostrictive materials with inexpensive Nd.

Large magnetic coercive field in Bi0.9La0.1Fe0.98Nb0.02O3polycrystalline compound

Single phase Bi0.9La0.1FeO3 (BLFO) and Bi0.9La0.1Fe0.98Nb0.02O3 (BLFNO) polycrystalline ceramics were prepared by conventional solid state reaction followed immediately by the quenching process. An obvious structure transition from the rhombohedral-type to the monoclinic-type with the doping of Nb was observed. The average grain size decreased from 7??m for BLFO to 500?nm for BLFNO. The magnetic ordering temperature of BLFNO decreased in comparison with the sample free of Nb. BLFNO shows a large coercive field, 1.35?T, and a large remanent magnetization, 0.23?A?m2?kg?1, at 300?K. The possible reasons for the remarkable magnetic performance of BLFNO are discussed.

Large low field magnetoresistance in ultrathin nanocrystalline magnetite Fe3O4 films at room temperature

Ultrathin (15nm) Fe3O4 nanocrystalline films with (111) spinel texture have been prepared by rapid annealing of amorphous ion oxide films. Large low field magnetoresistance (LFMR), with the values of about −6.3% at 300K and −10% at 200K under a field of 0.5T, has been observed in the films. The LFMR is mainly attributed to the boundary tunneling of high spin-polarized electrons in Fe3O4 grains of the films and nearly follows a simple relationship between MR and polarization for intergranular tunneling. The fabricating method here seems to be a good approach to prepare high quality Fe3O4 nanocrystalline films with a large LFMR at room temperature.

Electric field control of magnetic properties in CoPt/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure at room temperature

We demonstrate an obvious electric-field control of magnetic properties in CoPt/PMN-PT heterostructure at room temperature. Not only the remanent magnetization but also the coercivity exhibits an obvious response with the electric field. Without the aid of magnetic bias field, the remanent magnetization of the CoPt film shows an analogous on-off behavior with the electric field switching on and off alternatively. The magnetization reversal can be electrically controlled in this heterostructure due to the variation of coercivity caused by electric field.

Electric field control of magnetism in FePd/PMN-PT heterostructure for magnetoelectric memory devices

We report a strain-mediated magnetoelectric random access memory in FePd/PMN-PT heterostructure. Due to the strong converse magnetoelectric effect, the effective anisotropy of the FePd film is controlled by the applied electric field and used to switch the magnetization from one state to the other. Taking the advantage of the large electric-field modulation of magnetic properties, the electric-write/magnetic-read memory is obtained in such heterostructure. This magnetoelectric memory provides a promising approach to the development of a practical magnetoelectric device at room temperature.

Influence of the oxidative annealing temperature on the magnetism of (Mn, N)-codoped ZnO thin films

(Mn, N)-codoped ZnO films have been achieved by oxidative annealing of sputtered Zn2N3:Mn films at different temperatures in flowing O2 ambient. X-ray diffraction measurements and x-ray photoelectron spectroscopy studies indicate that both divalent Mn2+ and trivalent N3− ions are incorporated into ZnO lattice. Ferromagnetism with Curie temperature above 300 K was observed in the (Mn, N)-codoped ZnO films and found to be sensitive to the oxidative annealing temperature due to its strong effect on the carrier type and concentration. The strongest ferromagnetism has been found in the (Mn, N)-codoped ZnO films with the highest hole concentration in this study. The results indicate that holes are favorable for ferromagnetic ordering of doped Mn2+ ions in ZnO in agreement with the recent theoretical studies. The mechanism of ferromagnetic coupling in (Mn, N)-codoped ZnO is discussed.

Critical behavior and the universal curve for magnetocaloric effect in textured Mn5Ge3−xAlx ribbons

Mn5Ge3−xAlx ribbons with x=0,0.5, and 1 were prepared by single roller melt-spinning method. Textured structures were observed in these ribbons as a result of fast cooling, with highly ordered columnar grains perpendicular to the surface. The magnetocaloric effect and critical behavior were investigated by dc magnetization measurement. Curie temperatures decrease from 297 K to 283 K as the Al content increases, and the peak entropy changes also decrease from 4.92 J/kg K to 3.0 J/kg K under an external magnetic field change of 3 T. Critical exponents were obtained by modified Arrott plots technique, Kouvel-Fisher method, and critical isothermal analysis. Similar values of exponents of β∼0.37, γ∼1, and δ∼3.8 were obtained for all of the compositions. Moreover, rescaled entropy data for all compositions collapse into a universal curve, revealing universal behavior for the magnetocaloric effect in this series of compounds.

Structural, magnetic and magnetostrictive behavior in Nd(Fe1−xCox)1.9 compounds

The crystal structure, magnetic properties and magnetostriction of polycrystalline magnetostrictive alloys Nd(Fe1−xCox)1.9 were investigated. It was found that the single cubic Laves phase can only be obtained in the samples with x>0.4 by a traditional annealing method. In contrast, the cubic Laves phase exists over the entire composition range studied in the samples annealed under high pressure. Both the Curie temperature and saturation magnetization increase with increasing Co concentration to a maximum at x = 0.2 and then decrease with further increasing x, which could be understood in the frame of rigid band model. The spin phase diagram for Nd(Fe1−xCox)1.9 is constructed to illustrate the arrangement for the easy magnetization direction and crystal structure. The magnetostriction of Nd(Fe1−xCox)1.9 increases with increasing Co concentration and peaks at x = 0.1 and then presents an anomalous behavior when 0.2≤x≤0.6. It is suggested that the external-field-induced lattice strain should be responsible ...

The electric field manipulation of magnetization in La1−xSrxCoO3/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructures

La1−xSrxCoO3 (x = 0.18, 0.33, and 0.5) films were grown epitaxially on piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrates by pulsed laser deposition. The magnetization of these films varies with the external electric field, showing the magnetoelectric effect. With different doping content of Sr2+ ions, the change of magnetization for these films show different behaviors with increasing temperature, which can be attributed to the competition between electric-field-induced changes of spin state and double exchange interaction. This work presents an alternative mechanism to investigate the electric field control of magnetism in magnetoelectric heterostructure by tuning the spin state.

Optimization on magnetic transitions and magnetostriction in TbxDyyNdz(Fe0.9Co0.1)1.93 compounds

The structure, magnetic transitions, and magnetostriction of TbxDyyNdz(Fe0.9Co0.1)1.93 polycrystalline compounds have been investigated, with the ratio of x, y, and z spanning the line of minimum magnetic anisotropy. Anisotropy compensation with lower Tb content was realized in Tb0.253Dy0.657Nd0.09(Fe0.9Co0.1)1.93 compound. The spin configuration diagram accompanied with different crystal structures was constructed to illustrate the arrangement for the easy magnetization direction and crystal structure. An optimized effect on magnetostriction especially at the relatively low field of 1 kOe (197 ppm) was observed in Tb0.253Dy0.657Nd0.09(Fe0.9Co0.1)1.93 compound, which is about two times larger than that of the sample free of Nd (62 ppm). Meanwhile, the polycrystalline saturation magnetostriction (λs=945 ppm) of Tb0.253Dy0.657Nd0.09(Fe0.9Co0.1)1.93 is even much larger than that of the Ho-doped multicomponent single crystal compound Tb0.2Dy0.22Ho0.58Fe2 (λs=530 ppm). Low content of heavy rare earth Tb, high ...