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: To better understand the magnetic behavior around TC, critical behavior analysis was performed for Cu1-xNMn3+x with x = 0.1, 0.3 and 0.4. The isothermal magnetization M(H) was measured in the vicinity of TC, and Arrott plots (M2-H/M) were derived (see Supplementary Figure S2 online). The high-field isotherms of the Arrott plots were fitted with a polynomial function and then extrapolated to the H/M = 0 and M2 = 0 axes to obtain Ms and χ0−1, respectively6. By fitting Ms(T) with the relation Ms ~ (1 − T/TC)β and χ0−1(T) with the relation 1/χ0 ~ (T/TC − 1)γ, we obtained the values of β and γ, respectively. Modified Arrott plots were then obtained as M1/β versus (H/M)1/γ, which were fitted again to obtain new values of β and γ. Then, the new critical exponents were used to make modified Arrott plots again. The above procedure was continued until the critical exponents converged to stable values. The final values of Ms and χ0−1 are plotted in Figure 2(a) as a function of reduced temperature (T-TC). The obtained exponent γ decreases from ~1.63 for x = 0.1, clearly larger than the value suggested by the 3DH model (1.386) or by the 3DI model (1.24), to a value of ~1.15 for x = 0.4, which is similar to the MF magnitude of unity (1)5. Nevertheless, the β values (0.537, 0.538 and 0.488 for x = 0.1, 0.3 and 0.4, respectively) are very close to the value (0.5) predicted by the MF theory. The large γ values for x = 0.1 and 0.3 are likely unrelated to the 3DH or 3DI model because the β values do not match these models. The critical exponents can also be obtained by using a Kouvel-Fisher (KF) plot36, in which MS(dMS/dT)−1 vs. T and χ0−1(dχ0−1/dT)−1 vs. T generate straight lines with slopes 1/β and 1/γ, respectively. The KF plots for x = 0.1, 0.3 and 0.4 are displayed in Figure 2(b). The estimated values for β and γ are consistent with those derived from the modified Arrott plots shown in Figure 2(a), indicating that the results of the critical behavior analysis are reliable. |
View Article: PubMed Central - PubMed
Affiliation: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China.
No MeSH data available.