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Date: 4-3-2021
2002
Date: 18-2-2021
971
Date: 12-2-2021
1642
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Collective excitations
The comparison of magnetization data on nickel with the predictions of molecular field theory for J = 1/2 in Fig. 1 shows discrepancies both at low temperature, and in the vicinity of TC. Actually the discrepancies areworse than they appear because TC is used to determine nW, so the model is constrained to return the right Curie temperature, and the correct value of m0. Exist to determine the exchange constants directly, so it is possible to make a more telling comparison
Figure 1: Spontaneous magnetization and inverse susceptibility as a function of temperature. The molecular field predictions (grey) are compared with typical experimental data (black).
between theory and experiment, as indicated in Fig. 1. Here it is evident that ferromagnetism is considerably less stable at elevated temperature than molecular field theory would have us believe; it overestimates TC by as much as a factor of 2, depending on the dimensions and the lattice type. The spontaneous magnetization is diminished at lowtemperatures by spin-wave excitations. Near TC the critical fluctuations destroy it.
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دراسة يابانية لتقليل مخاطر أمراض المواليد منخفضي الوزن
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اكتشاف أكبر مرجان في العالم قبالة سواحل جزر سليمان
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اتحاد كليات الطب الملكية البريطانية يشيد بالمستوى العلمي لطلبة جامعة العميد وبيئتها التعليمية
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