Magnetic relaxation in a three-dimensional ferromagnet with weak quenched random-exchange disorder

Kaul, S. N. ; Semwal, Anita (2003) Magnetic relaxation in a three-dimensional ferromagnet with weak quenched random-exchange disorder Pramana - Journal of Physics, 61 (6). pp. 1129-1144. ISSN 0304-4289

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Official URL: http://www.ias.ac.in/pramana/v61/p1129/fulltext.pd...

Related URL: http://dx.doi.org/10.1007/BF02704408

Abstract

Isothermal remanent magnetization decay,M r(t), and 'in-field' growth of zero-field-cooled magnetization,M ZFC(t), with time have been measured over four decades in time at temperatures ranging from 0.25T c to 1.25T c (whereT c is the Curie temperature, determined previously for the same sample from static critical phenomena measurements) for a nearly ordered intermetallic compound Ni3Al, which is an experimental realization of a three-dimensional (d = 3) ferromagnet with weak quenched random-exchange disorder. None of the functional forms ofM r(t) predicted by the existing phenomenological models of relaxation dynamics in spin systems with quenched randomness, but only the expressions MT(t) = Mo[M1 exp(-t/T1)+ (t/T2)-a] and Mzfc(t0 = Mo'(1-{M'1 exp(-t/T'1)+ (t/T'2) -a'}] closely reproduce such data in the present case. The most striking features of magnetic relaxation in the system in question are as follows: Aging effects are absent in bothM r t andM ZFC(t) at all temperatures in the temperature range covered in the present experiments. A cross-over in equilibrium dynamics from the one, characteristic of a pured = 3 ferromagnet with complete atomic ordering and prevalent at temperatures away from Tc, to that, typical of ad = 3 random-exchange ferromagnet, occurs asT ? Tc. The relaxation times t1(T)(t1 '(T)) and t2(T)(t2 '(T)) exhibit logarithmic divergence at critical temperatures TT1c(TT'1c(H)) and TT2c(TT2'c(H)); and TT'1c and TT2'c both increase with the external magnetic field strength,H, such that at any given field value, TT'1c = TT2'c. The exponent characterizing the logarithmic divergence in t 1 ' (T) and t 2 ' T possesses a field-independent value of ?16 for both relaxation times. Of all the available theoretical models, the droplet fluctuation model alone provides a qualitative explanation for some aspects of the present magnetic relaxation data Keywords Magnetic relaxation - spin dynamics - random-exchange ferromagnet - remanent magne-tization decay - time evolution of zero-field-cooled magnetization.

Item Type:Article
Source:Copyright of this article belongs to Indian Academy of Sciences.
Keywords:Magnetic Relaxation; Spin Dynamics; Random-exchange Ferromagnet; Remanent Magne-tization Decay; Time Evolution of Zero-field-cooled Magnetization
ID Code:30032
Deposited On:23 Dec 2010 03:41
Last Modified:17 May 2016 12:47

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