Magnetic properties of Nd(Fe1-xCox)10.5M1.5 (M=Mo and V) and their nitrides J B Fu, X Yu, Z Q Qi, W Y Yang, S Q Liu, C S Wang, H L Du, J Z Han, Y C Yang, and J B Yang Citation: AIP Advances 7, 056202 (2017); doi: 10.1063/1.4973207 View online: http://dx.doi.org/10.1063/1.4973207 View Table of Contents: http://aip.scitation.org/toc/adv/7/5 Published by the American Institute of Physics Articles you may be interested in Exchange coupling and microwave absorption in core/shell-structured hard/soft ferrite-based CoFe2O4/ NiFe2O4 nanocapsules AIP Advances 7, 056403 (2016); 10.1063/1.4972805 Thermal conductivity of ferrimagnet GdBaMn2O5.0 single crystals AIP Advances 7, 055807 (2016); 10.1063/1.4973294 Enhanced ferromagnetism in BiFeO3 powders by rapid combustion of graphite powders AIP Advances 7, 055803 (2016); 10.1063/1.4972806 Unsaturated magnetoconductance of epitaxial La0.7Sr0.3MnO3 thin films in pulsed magnetic fields up to 60 T AIP Advances 7, 056404 (2016); 10.1063/1.4972853 AIP ADVANCES 7, 056202 (2017) Magnetic properties of Nd(Fe1-x Cox )10.5 M1.5 (M=Mo and V) and their nitrides J B Fu,1 X Yu,2 Z Q Qi,2 W Y Yang,1 S Q Liu,1 C S Wang,1 H L Du,1 J Z Han,1 Y C Yang,1 and J B Yang1,3,a State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, People’s Republic of China Ganzhou Fortune Electronic Co Ltd., Jiangxi 341000, People’s Republic of China Collaborative Innovation Center of Quantum Matter, Beijing 100871, People’s Republic of China (Presented November 2016; received 23 September 2016; accepted 11 October 2016; published online 22 December 2016) In this work, alloys of Nd(Fe1-x Cox )10.5 M1.5 (M=Mo and V) were prepared via arc melting and heat treatment The nitrides of these alloys were synthesized using a gas-solid state reaction method The influence of Co substitution for Fe in NdFe10.5 Mo1.5 and NdFe10.5 V1.5 alloys and their nitrides were investigated It was found that the lattice parameters a, c, and unit cell volume V decrease with increasing Co content x for Nd(Fe1-x Cox )10.5 Mo1.5 As compared to their parent alloys, the lattice parameters and unit cells volume increase after nitrogenation, which gives rise to higher Curie temperature, magnetization and magnetocrystalline anisotropy field for nitrides A small amount of Co substitution for Fe (x≤0.3) can enhance the magnetic properties including Curie temperature, saturation magnetization and magnetocrystalline anisotropy field of the alloys and their nitrides, while higher concentration of Co (x>0.3) will deteriorates these magnetic properties, especially for the nitrides, due to the modification of the band structure by Co atom As a result, Nd(Fe1-x Cox )10.5 Mo1.5 Ny and Nd(Fe1-x Cox )10.5 V1.5 Ny with x≤0.2 become promising candidates for permanent magnet applications A coercivity of 4.6 kOe and maximum energy product BHmax of 20 MGOe were achieved for NdFe9.45 Co1.05 Mo1.5 Nx © 2016 Author(s) All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/) [http://dx.doi.org/10.1063/1.4973207] I INTRODUCTION Permanent magnets are indispensable in the modern technology They are widely used in the televisions, cellphones, computers, audio systems, automobiles and so on In the last 60 years, the intermetallic compounds composed of the rare earth and 3d elements have been mainly developed as high performance permanent magnets, such as SmCo5 , Sm2 Co17 and Nd2 Fe14 B.1–4 However, there exist problems associated with its poor temperature stability and corrosion resistance, despite the initial promise of the Nd2 Fe14 B magnet, thus it ensures that the search for better permanent magnetic materials continues unabatedly In 1990, a great progress has been made due to the discovery of the interstitial nitrogen atom effects on the magnetic properties in the R(Fe,M)12 (M=Ti, V, Mo, etc.) and Sm2 Fe17 compounds.5,6 The interstitial nitrogen atoms not only increase both Curie temperature and saturation magnetization, but also give rise to a remarkable change in the magnetocrystalline anisotropy of the host alloys As a result, the interstitially modified compounds have been found to have excellent intrinsic magnetic properties comparable to those of Nd2 Fe14 B Accordingly, R(Fe1-x Mx )12 Nx (R=Nd,Pr) emerge as potential candidates for hard magnets.8–10 Many a Author to whom correspondence should be addressed Electronic mail: jbyang@pku.edu.cn 2158-3226/2017/7(5)/056202/6 7, 056202-1 © Author(s) 2016 056202-2 Fu et al AIP Advances 7, 056202 (2017) efforts have been made to develop promising interstitially modified compounds for hard magnets.7–19 Substitution of Fe with Co will change the magnetic properties of the R(Fe1-x Mx )12 , especially the magnetocrystalline anisotropy Studies showed that substitution of Fe by Co leads to planar anisotropy for YFe10-x Cox Mo2 20 and YFe10-x Cox V2, 21 respectively However, Xu et al.,22 and Lius et al.,23 have shown that Co will enhance the uniaxial-anisotropy in NdFe10-x Cox Mo2 and NdFe10.2-x Cox Mo1 On the other hand, in the study of nitrides, Suzuki et al.24 argued that the anisotropic field almost keeps constant with the increase of the content of Co in NdFe10-x Cox TiNx , while Kim et al.,25 believed that the uniaxial anisotropy decreases with increase of the content of Co In short, the current Co substitution effect on the 1:12 compounds is still under debate Therefore, we investigated the Co substitutional effect on the magnetic properties of NdFe10.5 Mo1.5 and NdFe10.5 V1.5 and their nitrides The structure and magnetic properties of these alloys and nitrides were investigated using XRD and magnetic measurements It was found that the a small amount of Co substitution of Fe (x≤0.3) can enhance the magnetic properties including Curie temperature, saturation magnetization and magnetocrystalline anisotropy field of the alloys and their nitrides, while higher concentration of Co (x>0.3) will deteriorates these magnetic properties, especially for the nitrides As a result, Nd(Fe1-x Cox )10.5 Mo1.5 Ny and Nd(Fe1-x Cox )10.5 V1.5 Ny with x≤0.2 become promising candidates for permanent magnet applications II EXPERIMENTAL METHODS Alloys with nominal compositions of Nd(Fe1-x Cox )10.5 Mo1.5 (x=0.0 -1.0) and Nd(Fe1-x Cox )10.5 V1.5 (x=0.0,075,0.15) were prepared by arc or vacuum induction melting 99.5% pure materials in a purified argon atmosphere Nitrides were prepared by passing purified nitrogen gas at atmospheric pressure over finely ground powder sample at 700–900 K for 2-10h, then rapidly cooling to room temperature (RT) The nitrogen content was estimated from the increased weight upon nitrogenation Anisotropic magnetic powders were prepared by a conventional milling process X-ray diffraction experiments were used to identify the phase of the samples and to determine the lattice parameters Magnetization curves parallel and perpendicular to the orientation direction and hysteresis loops with a field of up to T over a temperature range from 1.5 K to 300 K, as well as the Curie temperature over a temperature range from room temperature to 1000 K were measured by using a vibrating sample magnetometer III RESULTS AND DISCUSSION Figure plots the typical X-ray diffraction (XRD) patterns of Nd(Fe1-x Cox )10.5 Mo1.5 and their nitrides(x=0.2 and 0.4) The XRD patterns indicate that all of the alloys and nitrides have ThMn12 type structure After nitrogenation, all the diffraction peaks move to the low angle region indicating an increase of the unit cell and the nitrogen atoms enter the interstitial sites Table I lists the lattice constants a, c, unit cell volume V before and after the nitrogenation Figure shows the relationship between lattice constant and the Co content of the alloys It can be seen that with the increase of Co content, lattice constants of parent alloys are reduced and the unit cell volumes decrease This is mainly due to that Co (1.39Å) ionic radius is smaller than that of Fe (1.41 Å) The unit volume decreases with a rate of 1Å3 per Co Figure is the summary of the magnetic properties of the Nd(Fe1-x Cox )10.5 Mo1.5 alloys and their nitrides It is obvious that room temperature magnetizations of the alloys increase starting from x>0, and reaches a maximum at x=0.3, and then decrease with the increase of Co content (see Fig 3(a)) This phenomenon is similar to the feature of the Fe-Co binary alloy.26 In general, the majority band of Co atom is almost full, and the minority band of Co has some vacancies, while both the majority and minority bands of Fe atoms have vacancies The substitution of Fe by Co will first increases the magnetization of the alloys by filling more electrons into the majority 3d bands When the Co content increases further, more electrons will fill into the minority 3d band, which leads to the total magnetic moment decreases rapidly.27,28 After nitrogenation, as compared to the master alloys, the magnetization of the nitrides shows slight increases when x 0.6, the Curie temperature starts to drop which is related to the hybridization between Co atoms and nitrogen with higher Co content.29 According to the above results, a small amount of Co substitution of Fe (x≤0.3) can enhance the magnetic properties including Curie temperature, saturation magnetization and magnetocrystalline anisotropy field of the alloys and their nitrides, while higher concentration of Co (x>0.3) will deteriorates these magnetic properties, especially for the nitrides So Nd(Fe1-x Cox )10.5 V1.5 and their nitrides with Co contents of x=0.0, 0.075 and 0.15 were synthesized Table II lists the lattice parameters and unit cell volumes of Nd(Fe1-x Cox )10.5 V1.5 before and after nitrogenation Similar to the Mo-contained compounds, the Co substitution of Fe will reduced lattice parameter and the unit cell volume, while the nitrogenation will increase the unit cell volume of the parent alloys Table III lists the magnetic properties of the Nd(Fe1-x Cox )10.5 V1.5 before and after nitrogenation As can be seen from the data, Nd(Fe9.925 Co0.075 )V1.5 Nx shows promising intrinsic magnetic properties which is suitable for the development of permanent magnets In order to improve the hard magnetic properties, the nitrides powders were further grinded to fine powders using mechanical milling with a steel ball to material weight ratio of 1:20 and time from FIG The magnetic properties of the Nd(Fe1-x Cox )10.5 Mo1.5 and their nitrides at RT 056202-5 Fu et al AIP Advances 7, 056202 (2017) TABLE II The lattice parameters and unit cell volumes of Nd(Fe1-x Cox )10.5 V1.5 before and after nitrogenation a(Å) c(Å) V(Å3 ) δV/V(%) NdFe10.5 V1.5 NdFe10.5 V1.5 Nx 8.5104 8.6070 4.7540 4.9071 344.4 363.5 5.5 Nd(Fe0.925 Co0.075 ) 10.5 V1.5 Nd(Fe0.925 Co0.075 ) 10.5 V1.5 Nx 8.5057 8.5901 4.7460 4.8771 343.4 359.8 4.7 Nd(Fe0.85 Co0.15 ) 10.5 V1.5 Nd(Fe0.85 Co0.15 ) 10.5 V1.5 Nx 8.4938 8.5705 4.7325 4.8512 341.6 356.3 4.3 TABLE III The magnetic properties of the Nd(Fe1-x Cox )10.5 V1.5 before and after nitrogenation Ms (emu/g) Ha (T) RT 1.5K Tc (K) RT NdFe10.5 V1.5 NdFe10.5 V1.5 Nx 114.0 129.0 126.7 140.6 636 869 0.4 10.8 NdFe9.6 Co0.9 V1.5 NdFe9.6 Co0.9 V1.5 Nx 125.0 138.5 136.1 150.9 670 >880 1.2 11.2 NdFe8.7 Co1.8 V1.5 NdFe8.7 Co1.8 V1.5 Nx 128.1 137.5 137.5 149.2 750 >900 1.4 11.0 to hours The best hard magnetic properties were obtained for sample NdFe9.45 Co1.05 Mo1.5 Nx Figure is the RT hysteresis loop of NdFe9.45 Co1.05 Mo1.5 Nx obtained with optimum conditions The magnetic properties are i Hc =4.6 kOe, Mr = 111 emu/g and maximum energy product BHmax = 20 MGOe In summary, the effects of Co substitution for Fe on the structural and magnetic properties of Nd(Fe1-x Cox )10.5 M1.5 (M=Mo and V) alloys and their nitrides were investigated It was found that the lattice parameter a, c, and unit cell volume V decrease with increasing Co content As compared to their parent alloys, the nitrogenation will increase the lattice parameters and unit cells volume, which gives rise to higher Curie temperature, magnetization and magnetocrystalline anisotropy field for nitrides A small amount of Co substitution of Fe (x≤0.3) can enhance the magnetic properties including Curie temperature, saturation magnetization and magnetocrystalline anisotropy field of the alloys and their nitrides, while higher concentration of Co (x>0.3) will deteriorates these magnetic FIG Hysteresis loop of NdFe9.45 Co1.05 Mo1.5 Nx at RT 056202-6 Fu et al AIP Advances 7, 056202 (2017) properties, especially for the nitrides, due to the modification of the band structure by Co atom As a result, Nd(Fe1-x Cox )10.5 Mo1.5 Ny and Nd(Fe1-x Cox )10.5 V1.5 Ny with x≤0.2 become promising candidates for permanent magnet applications A coercivity of 4.6 kOe and maximum energy product BHmax of 20 MGOe were achieved for NdFe9.45 Co1.05 Mo1.5 Nx ACKNOWLEDGMENTS This work was 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Co2.1 Mo1 .5 NdFe8.4 Co2.1 Mo1 .5 Nx NdFe6.3 Co4.2 Mo1 .5 NdFe6.3 Co4.2 Mo1 .5 Nx NdFe4.2 Co.6. 35 Mo1 .5 NdFe4.2 Co6. 35 Mo1 .5 Nx NdFe2.1 Co8.4 Mo1 .5 NdFe2.1 Co8.4 Mo1 .5 Nx NdCo10 .5 Mo1 .5 NdCo10 .5 Mo1 .5. .. before and after the nitrogenation for Nd( Fe1- x Cox )10. 5 Mo1 .5 Nd( Fe1- x Cox )10. 5 Mo1 .5 a(Å) c(Å) V( Å3 ) NdFe10 .5 Mo1 .5 NdFe10 .5 Mo1 .5 Nx NdFe9. 45 Co1. 05 Mo1 .5 NdFe9. 45 Co1. 05 Mo1 .5 Nx NdFe8.4... volumes of Nd( Fe1- x Cox )10. 5 V1 .5 before and after nitrogenation a(Å) c(Å) V( Å3 ) ? ?V/ V(%) NdFe10 .5 V1 .5 NdFe10 .5 V1 .5 Nx 8. 51 04 8.6070 4. 754 0 4.9071 344.4 363 .5 5 .5 Nd( Fe0.9 25 Co0.0 75 ) 10. 5