K. Kamishima

5f band metamagnetism in UCoAl: Effects of alloying and pressure

Abstract We report on the results of magnetisation and susceptibility studies of the effects induced in the 5f band metamagnet UCoAl by doping with other elements and/or by application of external pressure. In majority of aspects UCoAl shows strong similarities to the 3d band metamagnets CoS 2 , YCo 2 and LuCo 2 , which suggests an essentially same origin of field-induced phenomena in both the classes of materials. The main role of the observed alloying and pressure effects can be attributed to the involvement of the 5f-ligand hybridisation in both the U 5f-moment formation and the 5f-5f exchange interactions.

Pressure effect on spontaneous magnetization of Cr2Te3 and Cr5Te8

Abstract The pressure change of the spontaneous magnetization σ s at 4.2 K for Cr 2 Te 3 and Cr 5 Te 8 are measured by employing the subtraction magnetometer. The value of dσ s /dp for Cr 2 Te 3 is − 1.22emu/g kbar . For Cr 5 Te 8 , the pressure derivative of σ s is found to be almost zero.

Field-induced magnetic transition of Mn3GaC

Abstract Field-induced transitions were studied in Mn3GaC in magnetic fields up to 370 kOe. The antiferromagnetic (AFM)-ferromagnetic (FM) field-induced transition is of the first order. The saturation magnetization σs at 4.2 K in the FM state is 75.0 emu g−1 equivalent to 1.1 μB per Mn atom. The decreasing rate of σs is rather smaller than that of the S = 1 2 Brillouin function. In the magnetostriction measurement of Mn3GaC, an abrupt volume contraction of −0.50% was found at the AFM-FM transition temperature. The result of the forced volume magnetostriction measurement shows that σs at 4.2 K increases with pressure.

Magnetovolume effects of MnAs1−xSbx

Thermal expansion, high‐field magnetization, and susceptibility measurements have been made for MnAs0.7Sb0.3. The thermal expansion measurements show that the spontaneous magnetostriction is large and anisotropic below Tc. The spontaneous magnetostriction at 0 K is estimated to be 1.2×10−2 for a axis, −0.8×10−2 for c axis, and 1.6×10−2 for the volume. The spontaneous magnetization decreases sharply in the narrow temperature region below Tc=230 K. All the spontaneous magnetostrictions are found to be proportional to the square of spontaneous magnetization. The magnetization curves measured in a high field up to 40 T show the metamagnetic‐like transitions at temperatures above Tc, and they are almost perfectly reproduced by an equation H=A1σ+A2σ3+A3σ5, where H is the applied field and σ is the relative magnetization.

Magnetic properties of Mn3(Ga, Al)C under high magnetic field and high pressure

Abstract Mn 3 GaC is antiferromagnetic (AFM) at low temperatures and ferromagnetic (FM) above T t ( ∼ 160K). The magnetization of Mn 3 Ga 1− x Al x C with x ⩽ 0.08 has been measured under pressure ( p ) with a special interest in the p dependence of magnetic properties in this system. It is found that the pressure enhances the magnetic moment of Mn μ FM in the FM phase and changes the AFM to a new magnetic phase with spontaneous magnetization. The forced magnetostriction of Mn 3 Ga 1− x Al x C with x = 0.015 and 0.07 indicates μ FM NEW PHASE AFM .

Giant magnetovolume effect of CrTe

Abstract The pressure change of the spontaneous magnetization σ S of the itinerant electron ferromagnet CrTe has been determined in the ranges of hydrostatic pressure and temperature of 0–6.1 kbar and 4.2–70 K, respectively. The spontaneous magnetization decreases linearly with pressure at temperatures from 4.2 to 70 K. The values of d σ S /d p and d ln σ S /d p at 4.2 K are found to be −0.92 emu g −1 kbar −1 and −1.2×10 −2 kbar −1 , respectively.

5f-band metamagnetism in UCoAl

UCoAl is a 5f-band metamagnet characterized by a very low critical field Bc ≈ 0.8 T, which induces magnetization of 0.3 μB/f.u. by a distinct transition. Bc increases with increasing temperature with the rate consistent with the reduced γ-coefficient in the high-field state. Bc-values are also sensitive to stoichiometry and external pressure.

Magnetic behavior of Mn3Ga1−xAlxC under high magnetic field and high pressure

Abstract Mn3GaC is antiferromagnetic (AF) below Tt ∼ 160 K and ferromagnetic (F) above Tt. The application of pressure enhances the Mn moment in the F state and produces an intermediate state between the AF and F states. Mn3GaC shows a metamagnetic transition to the F state below Tt. From the transition fields, the electronic specific heat coefficient in the F state is estimated to be γ = 43 mJ/K2 mol, which is extremely large. The substitution of Al for Ga in Mn3GaC produces the same effect as the application of high pressure.

Effects of alloying and pressure on metamagnetism of UCoAl

Abstract Doping by other d-metals in the Co sublattice and/or application of external pressure influences strongly the magnetic properties of 5f-band metamagnet UCoAl. Already 1–2% of Ru or Fe stabilise ferromagnetism, while the doping by Ni as well as the external pressure suppress the metamagnetism. The main role of the observed alloying and pressure effects can be attributed to the involvement of the 5f-ligand hybridisation in both the U 5f-moment formation and the 5f-5f exchange interactions. In many aspects UCoAl shows strong similarities to the 3d band metamagnets CoS 2 , YCo 2 and LuCo 2 , which suggests an essentially same origin of field-induced phenomena in the both classes of materials.

Onset of ferromagnetism between the paramagnets UCoAl and URuAl

Effect of pressure and substitution of Co by Ru on magnetic properties of 5f-band metamagnet UCoAl has been studied. The onset of ferromagnetism between paramagnetic UCoAl and URuAl and strong pressure dependence of parameters of metamagnetic transition in UCoAl have been found.