Critical magnetic properties of disordered polyerystalline Cr75Fe25 and Cr70Fe30 alloys -: art. no. 064443
Critical magnetic properties of disordered polyerystalline Cr75Fe25 and Cr70Fe30 alloys -: art. no. 064443
复制标题
DOI：
10.1103/physrevb.65.064443
复制
发表时间：
2002-02-01
影响因子：
3.7
通讯作者：
Kronmüller, H
中科院分区：
文献类型：
--
作者：
Fischer, SF;Kaul, SN;Kronmüller, H
本文首次采用体磁化和低场交流磁化率测量方法研究了无序多晶Cr 75 Fe 25和Cr 70 Fe 30合金的临界磁性。与先前的说法相反，高精度磁化强度和交流磁化率数据的详细分析表明，长程铁磁有序存在，并且在化学均匀化的合金中发生真正的铁磁到顺磁相变。化学聚类导致超顺磁性行为以上和不均匀的磁化低于居里温度，复杂的实验测定的渐近临界指数，特别是当使用高场外推法。对于化学均质化样品，有效临界指数的值为β（eff）=0.30+/-0.01，gamma（eff）=1.39 +/-0.01，delta（eff）=5.5 +/-0.1。这些数值与根据三维或二维各向同性“短程”模型得出的估计值相差很大。相反，目前确定的临界指数值表明，Cr 75 Fe 25和Cr 70 Fe 30的临界行为类似于d=2，n = 1的铁磁体，其中自旋之间的吸引长程相互作用随着距离（r）衰减，J（r）类似于tor（-）（（d+sigma）），其中sigma = 1.4。
Critical magnetic proper-ties of disordered polycrystalline Cr75Fe25 and Cr70Fe30 alloys are investigated employing bulk magnetization and, for the first time to our knowledge, low-field ac susceptibility measurements. Contrary to the earlier claims, an elaborate analysis of high-precision magnetization and ac susceptibility data reveals that long-range ferromagnetic order exists, and that a true ferromagnetic to paramagnetic phase transition takes place in the chemically homogenized alloys. Chemical clustering leads to superparamagnetic behavior above and inhomogenous magnetization below the Curie temperature, complicating the experimental determination of the asymptotic critical exponents, particularly when high-field extrapolation methods are used. The effective critical exponents possess the values beta(eff)=0.30+/-0.01, gamma(eff)=1.39 +/- 0.01, and delta(eff) =5.5 +/- 0.1 for chemically homogenized samples. These values deviate substantially from the estimates based on three- or two-dimensional isotropic "short-range" models. The presently determined values for the critical exponents instead indicate that the critical behavior of Cr75Fe25 and Cr70Fe30 is akin to that of a d=2,n = 1 ferromagnet in which the attractive long-range interactions between spins decay with distance (r) as J(r) similar tor(-) ((d+sigma)) with sigma = 1.4.