Ferromagnetism temperature dependence

Fig. 12. Temperature dependences of the magnetisation one curve typical for ferrimagnetic films, eg, RE-TM or garnets, the other one typical for ferromagnetic Co/Pt multilayers (39). compensation temperature = Curie temperature.

The limited magnetic measurements of very mixed -metal clusters are summarized in Table XIII. The magnetic behavior of some anti-ferromagnetic very mixed -metal carbonyl clusters (Fig. 82) has been studied by Pasynskii and eo-workers. Temperature dependences of the magnetic susceptibilities of Cr2Co(/t3-S)3(/i-SBu )(CO)2() -C3H4R)2l (R = H. Me) have been determined us-... 

The temperature dependence of the molar magnetic susceptibility (x) of an assembly of paramagnetic spins without interaction is characterized by the Curie behavior with x = C/T where C = /Vy2( 2.S (.S + l)/3k. It is a very common situation in the organometallic chemistry of radical species when the spin density is essentially localized on the metal atom. Since, in most cases, this atom is surrounded by various innocent ligands, intermolecular interactions are very weak and in most cases are reflected by a small contribution described by a Curie-Weiss behavior, with x = C/(T 0) where 0 is the Curie-Weiss temperature. A positive value for 0 reflects ferromagnetic interactions while a negative value — the most common situation — reflects an antiferromagnetic interaction. 

Fig. 6.7 Temperature dependence of the magnetic properties of hematite. Tc = Curie temperature,Tm = Morin temperature, pm = paramagnetic region, wfm = weakly ferromagnetic region afm = antiferromagnetic region. The insets show simulated Mossbauer spectra of hematite in the paramagnetic, weakly ferromagnetic and antiferromagnetic states (Murad, 1988, with permission).

Magnetic measurements of the 1 1 coordination complex of TTTA and Cu(hfac)2 3 revealed a ferromagnetic dimer with a weak interdimer antiferromagnetic interaction <2001JA3601, 2001POL1517>. Temperature dependence of the paramagnetic susceptibilities %-pT for 3 has been recorded over the range 1.8-350 K. 

Ac-susceptibility measurements on (Ga,Mn)As with x = 0.042 have been performed in alternating B from 0.1-4 mT. In the temperature dependence of susceptibility, there is a sharp peak at about 48 K at 0.1 mT, which suggests a ferromagnetic phase transition. The temperature and magnetic field dependence is rather complicated and an increase of B involves additional peaks (the number of which up to 4), which may be due to domain formation and domain wall movement (Sadowski et al. 2000). There is also a report about ac-susceptibility measurements on (Ga,Mn)As with x = 0.07, which shows that there is no difference between the field-cooled and zero-field cooled ac-susceptibilities measured with B = 10 mT (Van Esch et al. 1997). 

---