The vortex matter properties of a Ba 1−x K _x Fe₂As₂ single crystal ( Tc=38.2 K) were studied, by employing both isofield and isothermal ac-susceptibility measurements, χn(f,H0)=χn′(f,H0)−iχn′′(f,H0) , in a wide range of frequencies and amplitudes of the applied ac magnetic field. The irreversibility line ( Hirr(T,θ) ), formally defined by the onset of the third harmonic, is recorded for both H∥c -axis and H∥ab -plane. It can be reproduced from the empirical equation, Hirr(T)=H0(1−T/Tc)n , with nc=nab=1.24 and μ0H0c=210 Tesla, μ0H0ab=540 Tesla. The isofield measurements of the first harmonic revealed a narrow diamagnetic peak, related to a local peak of the critical current below the irreversibility line for both H∥c -axis and H∥ab -plane. The local peak for μ0H<0.2 Tesla is transformed to a sudden drop before it completely disappears. Detailed ac-susceptibility measurements were conducted for frequencies ranging within f = 0.1–10 kHz. From these data, the pinning potential, U, is deduced both as function of temperature and dc magnetic field. These results revealed that the ac response of vortex matter exhibits three distinct dynamic behaviors. By employing a model proposed by Mikitik and Brandt (2001 Phys. Rev. B 64 184514), that is based on a Lindemann type criterion and the collective pinning theory, we reproduced the experimentally recorded vortex matter phase diagram by taking into account both thermal fluctuations and random point disorder. To this effect, we adopted a δTc pinning mechanism, cL=0.25 , D0/cL = 1.1–1.5 and a Ginzburg number Gi=10−3 .

中文翻译：

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Ba 1−x K x Fe2As2 超导体中 H ||c 轴和 H ||ab 平面的峰值效应动态交叉

a 的涡旋物质性质 1个−X 钾 _X Fe ₂ As ₂单晶（ 吨C=38.2 K) 通过采用等场和等温 ac 磁化率测量进行了研究， χn(F,H0)=χn‘(F,H0)−我χn‘‘(F,H0) ，在广泛的频率和幅度范围内应用的交流磁场。不可逆线（ HIRR(吨,θ) ), 由三次谐波的开始正式定义, 被记录为 H∥C -轴和 H∥Ab -飞机。它可以从经验方程中重现， HIRR(吨)=H0(1个−吨/吨C)n ， 和 nC=nAb=1.24 和 μ0H0C=210 特斯拉， μ0H0Ab=540 特斯拉。一次谐波的等场测量显示一个窄的抗磁峰，与不可逆线以下的临界电流局部峰有关 H∥C -轴和 H∥Ab -飞机。局部峰值为 μ0H<0.2 特斯拉在完全消失之前变成了突然下降。对范围内的频率进行了详细的交流敏感性测量F= 0.1–10 kHz。从这些数据来看，钉扎潜力，ü, 被推导为温度和直流磁场的函数。这些结果表明，涡旋物质的交流响应表现出三种不同的动态行为。通过采用 Mikitik 和 Brandt (2001物理。牧师乙64184514），即基于林德曼类型准则和集体钉扎理论，我们通过考虑热波动和随机点无序来再现实验记录的涡旋物质相图。为此，我们采用了 δ吨C 固定机制， C大号=0.25 , 丁0/C大号 = 1.1–1.5 和金兹堡数 G我=10−3个 .