V. Yu. Galkin

Magnetic behaviour in the spin-density-wave phase of ( x < 20% Mn) alloys

The magnetic susceptibilities of twelve samples in the alloy system , with x ranging from to 19.4% Mn, are measured in the temperature range , in applied fields in the range Oe, after cooling in zero field and in the measuring field. The field dependence of the magnetization M(H) is measured at T = 5 K in the range kOe. The magnetic behaviour is characteristic of a spin glass, with hysteresis of M(H) and also hysteresis between the field-cooled and zero-field-cooled states, a peak in for the zero-field-cooled state, and relaxation of M as the logarithm of time when H is changed at low temperature. Unlike a typical spin glass, however, the peak in in the zero-field-cooled state is at roughly the same temperature (between 25 and 40 K) for all concentrations, and Curie - Weiss paramagnetism is seen at higher temperatures only for Mn. The Curie constant increases by an order of magnitude between x = 11.2 and 13.5% Mn, corresponding perhaps to a change in the atomic short-range order.

Magnetic phase diagrams and impurity resonance scattering of CrFe and CrSi, and their ternary alloys with V and Mn: II. Experiment: thermal expansion and the temperature and pressure dependence of resistivity

Abstract Experiments are described and the resultant data presented for the temperature dependence of the resistivity ϱ(T) and the thermal expansion ϵ(T) of the ternary alloy systems (Cr+2.7 at% Fe)1−z(V,Mn)z, (Cr+1.5 at% Fe)1−z(V,Mn) z and (Cr+1.3 at% Si)1−z(V,Mn)z, in the range of temperature from T

Magnetic phase diagrams and impurity resonance scattering of CrFe and CrSi and their ternary alloys with V and Mn: III. Magnetic phase diagrams in the composition-temperature and the pressure-temperature planes

Abstract The magnetic phase diagrams in the composition-temperature and pressure-temperature planes of antiferromagnetic spin-density-wave (SDW) Cr1−xFex and Cr1−xSix alloys are constructed from published data, and new experimental res ults for the temperature dependence of the electrical resistivity and thermal expansion in ternary alloys are employed to study the effect of changing the Fermi level by doping with V or Mn. These systems exhibit features unique among the antiferromagnetic SDW Cr alloys, including a re-entrant commensurate SDW phase and strong first-order transitions to this phase, which show nevertheless the parallelism often seen in Cr alloys between the effects of applying pressure and reducing the electron concentration.

Magnetic behavior of spin-density-wave (Cr + 2.7% Fe)1−x(V,Mn)x alloys

Abstract The magnetic susceptibility χ of the binary alloy Cr + 2.7% Fe and of nine V-doped and seven Mn-doped ternary alloys has been measured as a function of temperature T from 5 to 300 K, and as a function of field H in the range −55 H T = 5 K. The Neel temperature T N of the V-doped alloys drops with increasing V content x , and antiferromagnetism disappears for x ≥ 2.5% V. χ ( T ) exhibits a Curie-Weiss law in both the paramagnetic and antiferromagnetic phase. In the Mn-doped alloys, for x ≥ 1.5% Mn, an additional contribution to χ ( T ) appears at lower temperatures, which is hysteretic between the field-cooled and zero-field-cooled states. The onset or pinning temperature TP p increases only slowly with increasing x , which suggests that this component of χ ( T ) corresponds to the new type of spin glass seen in binary CrMn alloys.

A new type of spin glass in spin-density-wave CrMn and CrSiMn alloys

Spin-density-wave (SDW) binary Cr1-xMnx (x<<0.1-4.6% Mn) and ternary (Cr+1.3% Si)1-xMnx (x=0.17 and 0.6% Mn) alloys are found to exhibit spin-glass behaviour, which differs however from that of a conventional spin glass in that the magnetic susceptibility chi (T) is essentially independent of temperature T between the low-temperature maximum and the Neel temperature TN, and in that the temperature of the maximum is essentially independent of the Mn concentration. Comparison of binary and ternary alloys having the same Mn content shows that the nature of the maximum in chi (T) depends on whether or not the SDW is commensurate. A model is proposed that explains the increase in chi (T) at low temperature as resulting from pinning of the phase of the SDW to the Mn moments, which are frozen below TN, causing frustration on the host Cr moments on the surfaces between the resultant SDW phase domains.

FRUSTRATION IN THE PARAMAGNETIC PHASE OF SPIN-DENSITY-WAVE CRFEV ALLOYS

The magnetic susceptibility χ(T) of the spin-density-wave (SDW) alloys (Cr+2.7% Fe)1−xVx (x=0.07, 0.29, 0.61, 0.9, 1.28, and 2.0% V) and of the paramagnetic alloys (x=5 and 10% V) measured in a field, H=100 Oe, in the temperature range, T=5–400 K, was found to exhibit hysteresis between the field-cooled and zero-field-cooled states, starting at an irreversibility limiting temperature Ti well above the Neel temperature TN in the SDW alloys, and also in the paramagnetic alloy (Cr+2.7% Fe)95V5. This behavior is attributed to the frustration of moments on the Cr atoms associated with the formation of a local-SDW phase above the bulk Neel transition.

Coexistence of spin-glass and Curie-Weiss paramagnetism in spin-density-wave CrFeMn alloys

Abstract The temperature and field dependence of the magnetic susceptibility χ ( T ) in the antiferromagnetic alloys (Cr + 2.7% Fe) 1− x Mn x and (cr + 1.5% Fe) 1− x Mn x is reported. The anomalies in χ ( T ) below about 100 K, followed at higher temperatures by a Curie-Weiss law, show that, in these ternary alloys containing magnetic Fe impurities, a spin-glass state like that reported recently for binary CrMn alloys co-exists with the Curie-Weiss paramagnetism characteristic of the spin-density-wave phase of CrFe alloys. At low concentrations, x ⩽ 0.3% Mn reduces the effective moment of the Fe impurity suppresses the spin-glass behaviour, and conversely the Mn reduces the effective moment of the Fe atom.

Re-entrant phase of the commensurate spin-density wave in (Cr + X at% Fe)1−zMnz ternary alloys

Abstract Thermal expansion data are used to construct the magnetic phase diagram for the binary alloy system, Cr 1− x Fe x , and the ternary alloy systems, (Cr + 1.5 at% Fe) 1− z Mn z and (Cr + 0.5 at% Fe) 1− z Mn z . The latter two systems are found to have a re-entrant commensurate spin-density wave phase, with the lower incommensurate-commensurate phase transition being indicated by an inflection in the curve showing the temperature dependence of the strain.

Local impurity states in SDW Cr alloys with Fe, Co and Si

Abstract The energy difference δ E between local impurity state levels in Spin-Density-Wave (SDW) alloys is determined by measuring the peaks in the residual resistivity due to resonance scattering as the Fermi level is tuned by doping with V or Mn. The occurrence of narrow peaks is predicted for the Commensurate (CSDW) phase, but in some cases they are seen also in the Incommensurate (ISDW) phase.

Ac susceptibility investigation of the Néel transition and the local moment behavior in Cr-V alloys

Abstract The ac susceptibility of Cr-0.2 at% V and Cr-0.4 at% V alloys is found to show a step-like transition at the Neel temperature ( T N ). The anomaly is much sharper than that observed in the dc susceptibility. The ac susceptibility exhibits a Curie-Weiss behavior above a certain temperature defined as T CW , which was determined to occur a few degrees above T N .