Unusual ferromagnetic critical behavior owing to short-range antiferromagnetic correlations in antiperovskite Cu(1-x)NMn(3+x) (0.1 ≤ x ≤ 0.4).
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In addition, the paramagnetic susceptibility of all the samples deviates from the Curie-Weiss (CW) law just above T(C).This deviation is gradually smeared as x increases.The short-range antiferromagnetic ordering above T(C) revealed by our electron spin resonance measurement explains both the unusual critical behavior and the breakdown of the CW law.
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Affiliation: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China.
ABSTRACT
For ferromagnets, varying from simple metals to strongly correlated oxides,the critical behaviors near the Curie temperature (T(C)) can be grouped into several universal classes. In this paper, we report an unusual critical behavior in manganese nitrides Cu(1-x)NMn(3+x) (0.1 ≤ x ≤ 0.4). Although the critical behavior below T(C) can be well described by mean field (MF) theory, robust critical fluctuations beyond the expectations of any universal classes are observed above T(C) in x = 0.1. The critical fluctuations become weaker when x increases, and the MF-like critical behavior is finally restored at x = 0.4. In addition, the paramagnetic susceptibility of all the samples deviates from the Curie-Weiss (CW) law just above T(C). This deviation is gradually smeared as x increases. The short-range antiferromagnetic ordering above T(C) revealed by our electron spin resonance measurement explains both the unusual critical behavior and the breakdown of the CW law. No MeSH data available. Related in: MedlinePlus |
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Mentions: All the dP/dH data for the samples with x = 0.1 and 0.3 can be well fitted by a sum of two Lorentzian shape functions38, except for the data above 350 K for x = 0.1, where a single Lorentzian function fits the data well. The fitting profiles at typical temperatures are shown in Supplementary Figure S4 online. The fitted parameters, i.e., the resonant field (Hr), peak-to-peak distance (ΔHPP) and intensity ratio of each peak to the total intensity (Si/ΣS) for x = 0.1 and 0.3 are presented as a function of temperature in Figure 5(a)–(f). These parameters exhibit similar trends in both compounds. As shown in Figure 5(a) and 5(b), the two ESR peaks are well separated below TC because the Hr values are quite different. Above TC, Hr for P1 increases slightly as the temperature increases and becomes nearly independent of temperature above T#. Meanwhile, Hr for P2 increases rapidly with temperature to a peak value and then decreases upon further increasing the temperature up to T#. Above T#, Hr for P2 maintains a constant value of 3345 Oe (g ~ 2), which is attributable to PM resonance. As displayed in Figure 5(c) and (d), the ΔHPP values for both peaks show a similar dependence on temperature below TC. Above TC, ΔHPP for P1 keeps increasing with temperature, whereas ΔHPP for P2 increases initially with temperature and then dramatically decreases at T#, beyond which this parameter varies little with temperature. The Si/ΣS values for x = 0.1 and x = 0.3 are shown in Figure 5(e) and (f), respectively. Below TC, the Si/ΣS values for both peaks are comparable. Si/ΣS for P1 is stronger than that for P2 between TC and T#. When crossing T# from below, Si/ΣS for P1 jumps to a more dominant position at the expense of P2 and then decreases gradually as the temperature increases further. Eventually, the P1 peak for x = 0.1 disappears when T > 350 K (Figure 5(e)). Whereas for x = 0.3, the P1 peak still persists even at 400 K with a reduced relative intensity (Figure 5(f)). |
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Affiliation: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China.
No MeSH data available.