Coercivity temperature coefficient

The slightly reduced values of the room-temperature anisotropy fields when relatively small amounts of Fe in R2Fe14B are replaced by Co (see fig. 19) are not the only reason why Co substitution does not lead to improved hard magnetic properties. This is true for the temperature coefficient of the coercive force in particular. A probable reason for this is that not only JIA itself but also its temperature dependence becomes less favourable upon Co substitution. This may be inferred already from a comparison of the temperature dependences of HA in the pure ternaries Nd2Fe14B and Nd2Co17B shown in fig. 21, where it can be seen that the slope of the HA(T) curve for the latter compound around room temperature is much steeper than that of the former. In fact, the HA(T) curve in Nd2Co14B tends to approach the horizontal axis at a temperature of about 540 K, which is still far below the corresponding Curie temperature (Tc = 1007 K). The most obvious... 

Concerning the industrial application of the HDDR method, Ikegami et al. (1998) studied the thermal properties of Nd-Fe-B magnets prepared by this method. Figure 20 shows the effect of Dy additions on the temperature dependence of coercivity with optimum concentrations of Co, Ga, and Zr additives. The temperature coefficient of coercivity of anisotropic Nd2Fei4B-based magnets is typically about -0.5%/K. They also prepared samples of various coercivities, and found that the flux loss after treatment... 

Remanence (T) Br Coercivity (kAm-i) bHc I ]Hc Enei density Temperature coefficients (%K-i) rC(B,) 1 Max. operation temperature (°C) Tinax Product code... 

The temperature coefficient of irreversible polarization losses are smaller, the stronger the coercive field. Partial substitution of Nd by Dy increases coercivity and the irreversible polarization losses decreases. The polarization losses due to thermal aftereffect decrease with temperature (Rodewald 1985a, b). 

In order to compare calculated and experimentally observed phase portraits it is necessary to know very exactly all the coefficients of the describing nonlinear differential Equation 14.3. Therefore, different methods of determination of the nonlinear coefficient in the Duffing equation have been compared. In the paraelectric phase the value of the nonlinear dielectric coefficient B is determined by measuring the shift of the resonance frequency in dependence on the amplitude of the excitation ( [1], [5]). In the ferroelectric phase three different methods are used in order to determine B. Firstly, the coefficient B is calculated in the framework of the Landau theory from the coefficient of the high temperature phase (e.g. [4]). This means B = const, and B has the same values above and below the phase transition. Secondly, the shift of the resonance frequency of the resonator in the ferroelectric phase as a function of the driving field is used in order to determine the coefficient B. The amplitude of the exciting field is smaller than the coercive field and does not produce polarization reversal during the measurements of the shift of the resonance frequency. In the third method the coefficient B was determined by the values of the spontaneous polarization... 

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