Presentation Information
[P1-53]Angular Dependence of Coercivity and Flux Loss under Tilted Field in Nd-Fe-B Sintered Magnet
*Hitoshi Yamamoto1, Hirotoshi Fukunaga2 (1. Neoji-consul (Japan), 2. Nagasaki University (Japan))
Keywords:
Nd-Fe-B magnet,coercive force,differential coercive force,demagnetization,angular dependence
In order to implement effectively Nd-Fe-B magnets for many applications such as industrial, automotive and home appliance uses, it is important to evaluate the demagnetization properties of magnets against demagnetization field Hd. In case of FA/OA and EV/HV motor applications, magnets may be often exposed under Hd, not only the direction of magnetic polarization J but also the tilted direction from J. However little papers have been reported on the demagnetization properties under the tilted demagnetization field.
The authors executed the demagnetization experiments with varying the directions and magnitude of the pulsed demagnetization field Hd, evaluating the flux loss FL on the surface of the magnet, and compared the results of FL with the measured data of the angular dependence of coercivity.
The tested Nd-Fe-B magnet is a commercially available grade N46H, of which measured magnetic properties; Br=1.34T, HcJ =1,506 kA/m. The result of flux loss FL is plotted in Fig. 1 as a function of the magnitude of Hd for θ= 0, 45, 70 and 90 degree, where θ is the angle between the direction of magnetic polarization J and the applied pulsed field Hd.
In case of θ= 0 and 45 degree, the flux was constant up to the demagnetization field Hd of 500 kA/m, and gradually decreased with increasing Hd, and finally fully demagnetized at 1,500 kA/m, which is the same value of the coercive force of the magnet. The demagnetization features of θ= 0 and 45 degree are exactly same, while the field to start to occur the demagnetization for θ= 70 and 90 degree is 800 and 1,300 kA/m respectively, which values are much higher than the values of 500 kA/m for θ= 0 and 45 degree.
To consider the flux loss FL results of Fig.1, the angular dependences of coercive force HcJ, and HcJD was measured and shown in the inset in Fig.1, where HcJD, is the derivative coercive force, which is tentatively defined as the magnetic field corresponding to the maximum of dJ/dH. As clearly seen in the inset in Fig.1, the values of HcJ, and HcJD are same at θ= 0 and 45 degree. Both values are same up to the angle of 60 degree, but over 70 degree the value of HcJ decreases rapidly, while HcJD increases gradually with increasing the tilted angle θ. The increase of HcJD for θ= 70 and 90 degree is consistent with the results of flux loss FL for θ= 70 and 90 degree in Fig.1.
It is strange that the demagnetization properties for the tilted angle θ= 0 and 45 degree is the same feature, because the demagnetization field with J direction component forθ=45 degree is much weaker than θ= 0 degree, theoretically 1/√2. Reviewing both results of Fig.1 and the inset, the demagnetization feature of Fig.1 is related with the angular dependence of the value of HcJD not the value of HcJ. The HcJD is the determined by the irreversible rotation, while HcJ reflects both irreversible and reversible rotation of the magnetic polarization J. Demagnetization of magnets is the phenomena of irreversible magnetic reversal process, therefore it is reasonable to consider that HcJD is the appropriate parameter to evaluate demagnetization properties of magnets.
The authors executed the demagnetization experiments with varying the directions and magnitude of the pulsed demagnetization field Hd, evaluating the flux loss FL on the surface of the magnet, and compared the results of FL with the measured data of the angular dependence of coercivity.
The tested Nd-Fe-B magnet is a commercially available grade N46H, of which measured magnetic properties; Br=1.34T, HcJ =1,506 kA/m. The result of flux loss FL is plotted in Fig. 1 as a function of the magnitude of Hd for θ= 0, 45, 70 and 90 degree, where θ is the angle between the direction of magnetic polarization J and the applied pulsed field Hd.
In case of θ= 0 and 45 degree, the flux was constant up to the demagnetization field Hd of 500 kA/m, and gradually decreased with increasing Hd, and finally fully demagnetized at 1,500 kA/m, which is the same value of the coercive force of the magnet. The demagnetization features of θ= 0 and 45 degree are exactly same, while the field to start to occur the demagnetization for θ= 70 and 90 degree is 800 and 1,300 kA/m respectively, which values are much higher than the values of 500 kA/m for θ= 0 and 45 degree.
To consider the flux loss FL results of Fig.1, the angular dependences of coercive force HcJ, and HcJD was measured and shown in the inset in Fig.1, where HcJD, is the derivative coercive force, which is tentatively defined as the magnetic field corresponding to the maximum of dJ/dH. As clearly seen in the inset in Fig.1, the values of HcJ, and HcJD are same at θ= 0 and 45 degree. Both values are same up to the angle of 60 degree, but over 70 degree the value of HcJ decreases rapidly, while HcJD increases gradually with increasing the tilted angle θ. The increase of HcJD for θ= 70 and 90 degree is consistent with the results of flux loss FL for θ= 70 and 90 degree in Fig.1.
It is strange that the demagnetization properties for the tilted angle θ= 0 and 45 degree is the same feature, because the demagnetization field with J direction component forθ=45 degree is much weaker than θ= 0 degree, theoretically 1/√2. Reviewing both results of Fig.1 and the inset, the demagnetization feature of Fig.1 is related with the angular dependence of the value of HcJD not the value of HcJ. The HcJD is the determined by the irreversible rotation, while HcJ reflects both irreversible and reversible rotation of the magnetic polarization J. Demagnetization of magnets is the phenomena of irreversible magnetic reversal process, therefore it is reasonable to consider that HcJD is the appropriate parameter to evaluate demagnetization properties of magnets.
