Paramagnetic relaxation phenomena in nickel-lanthanum double nitrate

Abstract

Paramagnetic relaxation phenomena in single crystals of Ni 3 La 2 (NO 3 ) 12· 24H 2 O have been examined by measuring the susceptibility χ in the frequency range from 200 Hz to 1 MHz. At helium temperatures double relaxation has been observed. One of these relaxation times is found to vary over more than three decades if the magnetic field increases from 2 kOe to 6 kOe. This time becomes short ( τ ≃ 10 −7 s at H c = 6 kOe) and is hardly temperature dependent. In a magnetically diluted single crystal (7% Ni 3 La 2 (NO 3 ) 12· 24H 2 O) a complicated cross-relaxation behaviour has been observed. The Ni ions at crystallographic X sites behave as exchange coupled pairs 6 ) and these Ni-ion pairs cause the observed cross-relaxation processes. The fast relaxation in the concentrated samples is identified as cross relaxation also. Because of the large internal field values, the characteristic cross-relaxation behaviour of χ' vs . H c , as observed in the 7% sample as well as in earlier experiments 8 ), cannot be expected in the concentrated Ni 3 La 2 (NO 3 ) 12· 24H 2 O salts.