Magnetic relaxation in a three-dimensional ferromagnet with weak quenched random-exchange disorder |
| |
Authors: | S N Kaul Anita Semwal |
| |
Institution: | (1) School of Physics, University of Hyderabad, Central University P.O., 500 046 Hyderabad, India;(2) Present address: Departamento CITIMAC, Facultad de Ciencias, Universidad de Cantabria, 39005 Santander, Spain |
| |
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
and
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 τ1(T)(τ1
′(T)) and τ2(T)(τ2
′(T)) exhibit logarithmic divergence at critical temperatures
and
;
and
both increase with the external magnetic field strength,H, such that at any given field value,
. The exponent characterizing the logarithmic divergence in τ
1
′
(T) and τ
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 |
本文献已被 SpringerLink 等数据库收录! |
|