Nuclear Spin-lattice Relaxation in Metallic Ferro- and Antiferromagnets

The nuclear spin-lattice relaxation rates 1 / T I were found to be independent of temperature in the paramagnetic states of various kinds of metallic magnets. It has been ascertained from quantitative analyses that the values of 1 / Ti in the weak itenerant ferromagnets and the localized moment systems were explained by the SCR and the HBEN theories of spin fluctuations, respectively. Both theories, however, failed to reproduce the experimental results of ferromagnets in the intermediate-regime. Since the electron spin contribution to the nuclear localized-moment antiferromagnets IrzMnGa and spin-lattice relaxation rate 1 / Ti is closely related to Pd2MnAl, the invar-type intermediate-regime ferrothe imaginary part of the dynamical spin susceptibilmagnets Lu (Col-,Al,), with x = 0.125 and 0.15 and ity Im x (q, w ) , the investigation of 1 / Ti gives us the weak itinerant ferromagnets Y (C00.85A10.15)~ and valuable information to elucidate the dynamical propFeo.3Coo.7Si. We compare the data quantitatively with erties of magnetic systems. At present, we have two the two dynamical theories. (For experimental details, contrastive dynamical theories for 1 / Ti : the selfsee Refs. [5-91.) consistent renormalization (SCR) theory for weak itinerant ferromagnet taking into account of spin fluctuations only around q = 0 [I, 21, and the hyperiinebroadened exchange-narrowed (HBEN) theory for the localized moment system based on the random modulation of spin fluctuations [3]. Both theories yield qualitatively the temperature-independent 1 / Ti through the Curie-Weiss law of the magnetic susceptibility. But, since the CW law is based on the completely different mechanisms, the SCR and the localized moment theories give different order of magnitudes of 1 / Ti [2, In table I, we summarize the magnetic parameters of the present substances, where the RhodesWohlfarth (RW) ratio pc / (ps or pQ) is evaluated from the paramagnetic moment pc using the rela. 2 tion pea = pc (pc + 2) . As is well-known in the case. of weak itinerant ferromagnets as Y (Co Al), and (Fe Co) Si, the RW ratio is very large, while i t is close to 1 in Ir2MnGa and Pd2MnAl. The intermediate values of the RW ratio in Lu (Co Al), indicate an intermediate-region for the ferromagnetism [9-121, 4-91. The experimental results of NMR are listed in taIn this paper, we report on experimental reble I1 together with the probe nucleus and its gyrosults of nuclear spin-lattice relaxation in varimagnetic ratio y ~ . The 1 / TI values were found to ous kinds of metallic systems: the well-defined be independent of temperature at T >> Tc, TN for Table I. Magnetic parameters of the present systems. The values of p, and peff are in units of pB per magnetic atom. (*) Only the isolated Co is assumed to be non-magnetic. ; PC / (PS or PQ) N 1 -1 2.6 3.3 9.9 7.5 ps or PQ (PB) N 4 N 4 0.493 0.467 0.138 0.065 (*) 6 (K) -62 -85 133 132 40 24 IrzMnGa PdzMnAl LU (C00.~75A10.125)~ Lu @ o o . s ~ A ~ o . I ~ ) ~ Y (C00.85A10.15)~ Feo.aCoo..rSi Petr (PB) 4.1 4.5 2.03 2.34 2.15 1.10 (*) Tc or TN (K) 65 -